jurnal bumi

INDONESIAN MININGJOURNAL

Volume 8 Number 03, October 2005

ISSN 0854-9931

zSignificance of Type and Rank of Selected Kutai Coals with Respect to Their Utilisation Characteristics Binarko Santoso and Bukin Daulay

zPetrography of Raw Coal and Its UBC ProductBukin Daulay

zLeachability of Metals From Coal Ash Using Batch System ExtractionRetno Damayanti, Rahayu DH and Selinawati TD

zSilver Extraction From Tailing Resulted From Gold Ore Cyanidation, PongkorHadi Purnomo, Lili Tahli and Nuryadi Saleh

zDesign and Engineering of Artesian Well Development Equipment Using Air Lift MethodsHendro Supangkat, Eko Pujianto and Sidiq Suwondo

zNote for Contributor

Resinite (dark grey) infilling cell lumensin distinct layers with telovitrinite (grey).

INININININDODODODODONNNNNESIESIESIESIESIAAAAAN N N N N MMMMMININGININGININGININGININGJOURNAL

ISSN 0854-9931Volume 8 Number 03, October 2005

Significance of Type and Rank of Selected Kutai Coals with Respectto Their Utilisation CharacteristicsBinarko Santoso and Bukin Daulay

Petrography of Raw Coal and Its UBC ProductBukin Daulay

Leachability of Metals From Coal Ash Using Batch System ExtractionRetno Damayanti, Rahayu DH and Selinawati TD

Silver Extraction From Tailing Resulted From Gold Ore Cyanidation, PongkorHadi Purnomo, Lili Tahli and Nuryadi Saleh

Design and Engineering of Artesian Well Development EquipmentUsing Air Lift MethodsHendro Supangkat, Eko Pujianto and Sidiq Suwondo

Note for Contributor

1 – 12

13 – 19

20 – 24

40 - 47

48

25 – 39

INDONESIAN MINING JOURNALJl. Jend. Sudirman 623 Bandung 40211, Indonesia,

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Dr. BUKIN DAULAY, Dr. PRAMUSANTO and Dr. SITI ROCHANI

EditorsTATANG WAHYUDI, SRI HANDAYANI, RETNO DAMAYANTI

NINING SUDINI NINGRUM, DARSA PERMANA, ZULFAHMIMAMAN SURACHMAN and TENDI RUSTENDI

Business and Administration StaffSUMARTONO, UUN BISRI, YUSI NURIANA and BACHTIAR

IMJ is published three times a year by R & D Centre for Mineral and Coal TechnologyISSN 0854-9931, STT No : 2205/SK/Ditjen PPG/1996

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From the EditorFrom the EditorFrom the EditorFrom the EditorFrom the EditorDear readers,

Coal is one of the world’s energy sources since long time ago. Unfortunately, we are awarerecently, the coal will be a prima donna as a main energy source in the future, even as fuel energy.It is probably late to be aware or it is our culture when the oil fuel is huge, the coal is nevertouched. Nowadays, the coal is being exploited in all parts of Kalimantan, Sumatera, Jawa andSulawesi, due to scarcity of the oil fuel. Our conscience of coal benefit in our lives and our nationaleconomy has convinced us to commit how to utilise coal in terms of technology, economy andenvironment.

In order to colour this journal, we are providing papers of coal issues. Binarko Santoso andBukin Daulay indicate an accuracy matter of type and rank of the Kutai coal for its use characteris-tics. A petrographical assessment for raw coal its UBC product is presented by Bukin Daulay. Fromthe environmental aspects, Retno Damayanti et al. try to assess a leachability aspect from metalresulted from coal ash using extraction system. By recognising this aspect, we can anticipate it’s abad probability of its ecology, particularly for groundwater and surface water.

Besides providing the coal issues, we are also presenting silver extraction and artesian well. Thesilver extraction from waste due to a cyanidation process of gold ore from Pongkor is written byHadi Purnomo et al. Whereas issue of design and engineering for artesian well development equip-ment is assessed by Hendro Supangkat et al.

Assessment of the coal benefits as a scientific treasure in this journal is probably like a paddy ofhuge imported paddy. However, we expect that all papers can give a contribution of utilising coalin Indonesia optimally.

The Editor .

1Significance of Type and Rank of Selected Kutai Coals ... Binarko Santoso and Bukin Daulay

SIGNIFICANCE OF TYPE AND RANKOF SELECTED KUTAI COALS WITH RESPECTTO THEIR UTILISATION CHARACTERISTICS

BINARKO SANTOSO AND BUKIN DAULAYR & D Centre for Mineral and Coal TechnologyJalan Jenderal Sudirman 623 Bandung 40211

Ph. 022-6030483, fax. 022-6003373, E-mail: [email protected]

ABSTRACT

Type and rank characteristics of the Tertiary Kutai coals in East Kalimantan express their geologicalsetting and utilisation. Type and rank variation in the coals were assessed by petrographic examina-tion of thirty samples. The coals are dominated by vitrinite, common liptinite and rare inertinite andmineral matter. Vitrinite macerals are dominated by detrovitrinite and telovitrinite. Cutinite and resiniteare the dominant liptinite macerals in the coals. The inertinite macerals include semifusinite,inertodetrinite and sclerotinite. Clay and pyrite are the dominant mineral matter in the coals. The typedifferences largely reflect climatic influence and differences in peat conditions. Rank of the coals, ingeneral, depends largely on the geological age. Reflectance measurements on the coals indicate thatthere is a substantial difference in rank between Palaeogene and Neogene coals. The Palaeogenecoals are sub-bituminous to high volatile bituminous rank (Rvmax of 0.57% to 0.67%), whereas theNeogene coals are sub-bituminous rank (Rvmax of 0.40% to 0.57%). The change in vitrinite reflec-tance from Palaeogene to Neogene coals is due to the thicker cover/overburden on the high rankcoals. The coal characteristics (most of which are related to rank and type) are important in combus-tion, namely: specific energy, grindability, swelling behaviour and ash properties. Specific energyincreases with increases in vitrinite reflectance. The coals are generally suited to use for energysource of direct combustion, although high moisture contents present significant problems with someof the low rank coals.

1. INTRODUCTION

Petrographic characteristics of coal can specifi-cally be considered in terms of two essentiallyindependent concepts, namely coal rank and coaltype. Coal rank can be defined as the relative po-sition of coal in the series of peat to anthracite(degree of coalification). The rank of coal is mea-sured by vitrinite reflectance. The vitrinite reflec-tance increases as the rank of coal increases.Coal type is related to the type of plant material inthe peat and the extent of its biochemical andchemical alteration. It is a response to the first(biochemical) stage of coalification (Cook, 1982).Coal petrology contributes to an understanding ofthe nature and aids in determining its utilisationpotential. The Kutai coals have been chosen for

this study due to its potential reserve of 2.4 billiontons (Adhi et al., 2004) that can be used to supplythe energy demand in the surrounding areas. TheIndonesian Government is aware that the coalshave an important role in the regional/national en-ergy development, particularly in the utilisation fordirect combustion of steam generation and indus-trial processes. To use the coals as effectively aspossible, studies on coal petrography are desir-able. Petrographic methods are generally the mostsuited for determining the genetic characteristicsof coal, largely because they lead to expressionsof the variations in coal properties. The coal char-acteristics are identified and related to rank andtype that are important in combustion process.

This study is aimed at obtaining an understanding

2 INDONESIAN MINING JOURNAL Vol. 8 No. 03, October 2005 : 1 - 12

of the aspects as follows:

– To determine type and rank characteristics ofthe coals by making maceral analyses andreflectance measurements.

– To establish the broad patterns of variation ofrank and type.

– To examine the implications of the petro-graphic data with respect to the utilisation ofthe coals.

2. METHODS

Thirty coal samples studied were obtained fromTertiary coalfields of the Kutai Basin in EastKalimantan based on the procedure of the Stan-dards Association of Australia (1964). All sampleswere examined in the laboratory of coal petrogra-phy, Research and Development Centre for Min-eral and Coal Technology, Bandung. They wereexamined in reflected white light and reflected ul-traviolet light excitation. Maceral analyses weredetermined in oil immersion in reflected planepolarised light at a magnification of x500. Theliptinite group of macerals was studied using ul-traviolet light excitation at a magnification of x500.An orthoplan microscope fitted with a Leitz Vario-Orthomat camera was used for all photography.

Reflectance measurements were carried out us-ing a Leitz Ortholux microscope fitted with a LeitzMPV 1 microphotometer. The microphotometerwas calibrated against synthetic garnet standardsof 0.917% and 1.726% reflectance and a syntheticspinel of 0.413% reflectance.

Normal point count techniques were applied formaceral analysis. Approximately 500 points werecounted for each maceral analysis (StandardsAssociation of Australia, 1986). After completionof the analysis, maceral group or mineral was ex-pressed as a percentage of the total points re-corded. Each point could be examined in reflectedwhite light and fluorescence mode.

Reflectance measurements were made on vitrinite,because it undergoes changes consistently withrank (Standards Association of Australia, 1981).Vitrinite shows some inherent variability in reflec-tance according to type. It is the most abundantmaceral in most coals and occurs as relativelylarge particles, thereby enabling easy measure-ment. The Standards recommend taking 100 mea-surements to obtain a precise mean value. The

result of the measurements is called the meanmaximum vitrinite reflectance (Rvmax).

3. GEOLOGY

The Kutai Basin is the largest (165,000 km2) andthe deepest (12,000-14,000 metres) Tertiary sedi-mentary basin in Indonesia (Darman and Sidi,2000). The basin is defined to the north by theMangkalihat High, to the south by the Adang Fault,to the west by the Kuching High and to the eastby the Makassar Strait (Figures 1 and 2). TheTertiary stratigraphic succession within the basinbegan with the deposition of Palaeocene sedi-ments in the inner basin. The basin was subdi-vided during the Late Palaeocene-Middle Eoceneto Oligocene, because of basement rifting, andbecame the site of deposition of the MangkupaShale in a marginal to open marine environment.Some coarser siliciclastics, the Beriun Sands, arelocally associated with the shale sequence, indi-cating an interruption of basin subsidence by up-lift. The basin subsided rapidly after the deposi-tion of the Beriun sands, mostly through themechanism of basin sagging, resulting in the depo-sition of marine shales of the Atan Formation andcarbonates of the Kedango Formation (Satyanaand Biantoro, 1996). Subsequent tectonic eventsuplifted parts of the basin margin by the Late Oli-gocene. The uplift was associated with the depo-sition of the Sembulu Volcanics in the easternbasin.

The second stratigraphic phase was contempora-neous with basin uplift and inversion started in EarlyMiocene. During the time, a vast series of alluvialand deltaic deposits were deposited in the basin.They consist of deltaic sediments of the Pamaluan,Pulubalang, Balikpapan and Kampungbaru Forma-tions, prograding eastwards, which range in agefrom the Early Miocene to Pleistocene times (Fig-ure 3). Deltaic deposition continues to the presentday as the basin continuously subsides and ex-tends eastwards into offshore Kutai Basin. Atpresent, the structural style of the basin is domi-nated by a series of north-northeast to south-south-west trending folds that are parallel to the coastall ine, and are known as the SamarindaAnticlinorium-Mahakam Fold Belt (Figure 2).These fold belts are characterised by tight, asym-metric anticlines, separated by broad synclines,containing Miocene siliciclastics. These featuresdominate the eastern basin and are also identifi-able offshore. The deformation is increasingly more


Figure 1. Simplified geological map of Kutai Basin, East Kalimantan (Darman and Sidi, 2000)

Figure 2. Kutai Basin cross section (Darman and Sidi, 2000)

Makas

sar S

trait


complex in the onshore direction. The westernbasin has been uplifted and a minimum of 1,500m to 3,500 m of sediments has been removed bya mechanism of inversion (Wain and Berod, 1989;Courteney and Wiman, 1991). Not much is knownabout the structure of the western basin, althoughlarge structures are evident, a similarity in struc-tural trend and style is not apparent from the data(Ott, 1987). In this region, the tectonics may in-

volve the basement. Tectonic reversal in terms oforigin and its strain response is not as obvious asin the Barito Basin.

Prograding deltaic sediments have contributed tothe mechanism of structural inversion, by a mecha-nism of diapirism or growth faulting. These mecha-nisms are very different from those, which affectedthe Barito Basin. The origin of folds and faults in

EPOCH FORMATION LITHOLOGY THICKNESS(M)

QU

ATE R

NA

RY

PLE

ISTO

CEN

E

ALLUVIUMSANDSSILTSCLAYS

-

PLI

OC

EN

E

KAMPUNGBARU

SANDSONESSILTSTONESCLAYSTONESMUDSTONECOALS

SANDSONESCOALSLIMESTONESBALIKPAPAN

MID

DL E

TO

LAT

E M

IOC

ENE

EA

RLY

MIO

CEN

E

PULUBALANGMUDSTONESLIMESTONESSANDSTONES

SANDSTONESPAMALUANOLIGOCENE

TER

TIA

RY

900

3000

2750

-

Figure 3. Tertiary stratigraphy of Kutai Basin (Addison et al., 1982)


the Kutai Basin remains unresolved (Rose andHartono, 1978; Ott, 1987).

Palaeogene coal measures are present at thesoutheastern part of the Kutai Basin that isrecognised as the Pasir Sub-basin. Resting onpre-Tertiary ultramafic rocks and mudstone or con-glomerate, three coal seams are recognised in thissub-basin (Samuel and Muchsin, 1975). Neogenecoal measures are also present in the Kutai Ba-sin. The principal coal-bearing strata in this basinare the Early Miocene Pamaluan and PulubalangFormations and the Miocene to PlioceneBalikpapan and Kampungbaru Formations. In thewest and south of Samarinda, the PulubalangFormation consists of a series of limestone lenses,calcareous mudstones and thin sandstones, whichare essentially marine. The overlying LowerBalikpapan Formation comprises a series of coalmeasures, which are indicative of a deltaic envi-ronment (Samuel and Muchsin, 1975; Siregar andSunaryo, 1980). The Upper Balikpapan Formationcontains a greater proportion of sandstone, thedeltaic sequence becoming more strongly influ-enced by fluvial processes.

4. TYPE AND RANK

In order to determine type and rank, maceral analy-ses and vitrinite reflectance measurement wererespectively carried out for the Tertiary Kutai coals.

4.1 Type

The Kutai coals comprise mostly vitrinite andliptinite with minor inertinite (Table 1 and Photos1 and 2). The vitrinite and inertinite contents slightlydecrease from Neogene to Palaeogene coals.Otherwise, the liptinite and mineral matter con-tents increase slightly from Neogene to Palaeogenecoals. The liptinites of the Palaeogene coals showyellow to orange fluorescence, whereas the Neo-gene coals having yellow to orange fluorescence.Cutinite is dominant in both Palaeogene and Neo-gene coals.

Palaeogene

Vitrinite is the dominant maceral of Palaeogenecoals in East Kalimantan. Its content ranges from80% to 88% with an average of 84%. Liptinite con-stitutes from 5% to 13% with an average of 10%.The liptinite shows yellow to orange fluorescence.Inertinite is rare, containing less than 5%. Mineral

matter comprising clay and pyrite is common withsome samples containing more than 5%.

Telovitrinite is formed as thin isolated bands inthicker layers with a detrovitrinite matrix.Gelovitrinite that mainly consists of corpovitriniteand porigelinite is scattered throughout the coals.It is mostly associated with cutinite.

Liptinite of the Palaeogene coals is dominated bycutinite, resinite and sporinite. Cutinite having weakyellow to orange fluorescence constitutes up to6% and is present as thin cuticle. Resinite consti-tutes up to 3% and commonly occurs as rodletsand infilling cell lumens in the coals. It has yellowto orange fluorescence. Like cutinite, sporinite alsoconstitutes up to 3% in the coals. The sporinitetypically occurs evenly disseminated throughoutthe coals. It fluoresces yellow to orange.

Sclerotinite and inertodetrinite are the dominantinertinite maceral, whilst semifusinite is onlypresent in a minute amount in the coals.Sclerotinite including single and twin-celledteleutospores constitutes a trace to 2%. It is mostlydisseminated throughout the coals. However, somelocal concentrations take place. Inertodetrinitecontent ranges from a trace to 2% and is evenlydisseminated throughout the coals. Semifusiniteusually forms thin layers or lenses isolated in adetrovitrinite matrix. It constitutes mostly tracesexcept for one sample containing 1%.

Mineral matter consisting of clay and pyrite is sig-nificantly common in Palaeogene coals. Its con-tent varies from 1% to 11%. It mostly forms aspods disseminated throughout the coals and insome cases infilling cell lumens.

The liptinite and inertinite contents of thePalaeogene coals are systematically related tothe vitrinite content. The liptinite and inertinite con-tents decrease with increases in the vitrinite con-tent. The liptinite content is not related to theinertinite content.

Neogene

According to the petrographic studies on the coalsamples, it reveals that all the samples have ahigh vitrinite content, common liptinite and traceinertinite. Mineral matter that is mainly clay andpyrite are present.

Vitrinite of the Neogene coals ranges from 75% to


Tabl

e 1.

Mac

eral

com

posi

tion

of K

utai

coa

ls

Sam

Age

Mac

eral

ple

Vitr

inite

(%

)In

ertin

ite (%

)Li

ptin

ite (

%)

MM

No.

Pal

aeog

ene

Neo

gene

TVD

VG

VSF

Fus

Scl

Iner

tR

esC

utSu

bSp

oLi

pt(%

)

123

586

--

1tr

25

tr2

11

236

4011

--

-tr

13

11

tr6

327

4612

1-

trtr

24

tr1

14

4Pa

sir

3438

9tr

-1

-1

2tr

2tr

115

2150

9tr

-2

23

62

11

36

2748

9tr

-1

12

42

31

27

4431

8tr

-2

13

51

21

28

4234

8tr

-1

13

41

31

2

9Lo

a D

uri

2547

151

-tr

13

33

1-

110

2550

122

-1

23

31

-tr

tr11

3936

73

-1

23

51

trtr

112

4629

81

tr1

-3

71

--

113

4137

122

tr-

-2

2tr

--

114

6323

5tr

-tr

tr2

1tr

-tr

115

7312

61

-tr

-3

1-

--

116

4629

81

trtr

12

71

-1

217

4038

6tr

-1

13

31

trtr

118

3144

151

-tr

12

31

--

119

4341

111

-tr

1tr

1tr

tr-

120

2640

98

12

51

41

-tr

121

4836

103

--

1tr

1tr

--

tr22

2658

8tr

-tr

11

31

tr-

1

23S

amar

inda

4929

101

-tr

23

31

tr-

124

5330

61

-tr

11

1-

11

1

25Lo

a K

ulu

3645

72

1-

22

11

trtr

226

4537

92

tr1

21

1tr

-tr

127

1653

94

11

32

31

tr1

128

2947

71

-tr

13

81

trtr

229

3043

9-

--

-6

41

-1

230

3147

82

-1

23

3tr

1-

1

Not

e:TV

: te

lovi

trini

te,

DV

: de

trovi

trini

te,

GV

: ge

lovi

trini

te ;

SF

: se

mifu

sini

te,

Fus

: fu

sini

te,

Scl

: s

cler

otin

ite,

Iner

t :

iner

tinite

Res

: r

esin

ite,

Cut

: c

utin

ite,

Sub

: s

uber

inite

, S

po :

spo

rinite

, Li

pt :

lipt

odet

rinite

; M

M :

min

eral

mat

ter,

tr :

trace


95% with an average of 86%. Vitrinite mostly takesplace as thick layers with a detrovitrinite matrixinterbedded with thin bands of telovitrinite. Thickmassive telovitrinite, in some cases, is presentwith the detrovitrinite-dominated coal. Gelovitrinitecomprising corpovitrinite and porigelinite occursas small discrete masses throughout the coals.Liptinite of the Neogene coals varies between 1%and 12% with an average of 8%. The liptinitemaceral is dominated by cutinite, resinite andsuberinite. Sporinite and liptodetrinite are rare.Cutinite consisting of thick and thin wall cuticlesconstitutes up to 8%. It has strong yellow to or-ange fluorescence. Resinite content varies be-tween a trace and 6% with an average of 2%. Itmostly occurs as discrete small bodies through-out the coals. Some resinite infilling cell lumensoccurs as distinct layers. It fluoresces greenishyellow to yellow. Suberinite that has weak yellowfluorescence constitutes a trace to 3% and ismostly associated with corpovitrinite.

Inertinite is rare in the Neogene coals, with asample containing 8%. Semifusinite is the domi-nant inertinite maceral. It mostly takes place asthin layers or lenses isolated in detrovitrinite ma-trix. In some cases, the semifusinite occurs asthin to thick layers interbedded with thin bands oftelovitrinite. Inertodetrinite containing up to 5% isdisseminated throughout the coals. Sclerotiniteincluding single, twin-celled teleutospores andsclerotia constitutes a trace to 2%. It is usuallyscattered throughout the coals. Fusinite is trace

in some samples.

Mineral matter that consists mainly of clay andpyrite constitutes a trace to 2% in the coals. It iscommonly associated with detrovitrinite.

The liptinite and inertinite contents of the Neogenecoals are systematically related to vitrinite con-tent. Liptinite and inertinite contents decrease withincreases in vitrinite content. The liptinite contentis not related to inertinite content.

4.2 Rank

Vitrinite reflectance was carried out on the KutaiPalaeogene and Neogene coals. Rank of thecoals, in general, depends largely on the geologi-cal age. Reflectance measurements on the coalsindicate that there is a substantial difference inrank between Palaeogene and Neogene coals(Table 2). The Palaeogene coals are sub-bitumi-nous to high volatile bituminous rank (Rvmax of0.57% to 0.67%), whereas the Neogene coals aresub-bituminous rank (Rvmax of 0.40% to 0.57%).The change in vitrinite reflectance from Palaeogeneto Neogene coals is due to the thicker cover/over-burden on the high rank coals.

Proximate analysis of the Kutai coals reported byBemmelen (1970), Hardjono and Syarifuddin (1983)and Roeslan (1984) illustrates that with increas-ing age, the specific energy becomes higher andthe total moisture decreases (Table 3).

Photo 1. Detrovitrinite (grey), inertinite(white) and pyrite (bright white).Rvmax: 0.47%, field width: 0.34mm, reflected white light

Photo 2. Resinite (dark grey) infilling celllumens in distinct layers withtelovitrinite (grey). Rvmax: 0.46%,field width: 0.28 mm, reflectedwhite light


5. CHARACTERISTICS OF UTILISATION

Utilisation of the Kutai coals for the domestic pur-poses can be divided into two broad categories:

– as a fuel, for steam raising, lime brick andcement processing.

– as a feedstock for chemical industry or as araw material for coking.

In order to use the coals as effectively as pos-sible, studies on coal petrography are desirable.Petrographic methods are generally the mostsuited for determining the genetic characteristicsof coal, largely because they lead to expressionsof the variations in coal properties.

With regard to utilisation of the coals as a rawmaterial for combustion, liptinite macerals are

Table 2. Rank of Kutai coals

Sample Age Vitrinite Reflectance Rank

Number Palaeogene Neogene (Rvmax %) (Australian Standard)

1 Pasir 0.63 High volatile bituminous2 0.64 High volatile bituminous3 0.67 High volatile bituminous4 0.62 High volatile bituminous5 0.57 Sub-bituminous6 0.61 High volatile bituminous7 0.62 High volatile bituminous8 0.62 High volatile bituminous

9 Loa Duri 0.47 Sub-bituminous10 0.46 Sub-bituminous11 0.41 Sub-bituminous12 0.45 Sub-bituminous13 0.45 Sub-bituminous14 0.42 Sub-bituminous15 0.4 Sub-bituminous16 0.46 Sub-bituminous17 0.43 Sub-bituminous18 0.45 Sub-bituminous19 0.46 Sub-bituminous20 0.46 Sub-bituminous21 0.46 Sub-bituminous22 0.44 Sub-bituminous

23 Samarinda 0.45 Sub-bituminous24 0.47 Sub-bituminous

25 Loa Kulu 0.47 Sub-bituminous26 0.47 Sub-bituminous27 0.43 Sub-bituminous28 0.41 Sub-bituminous29 0.48 Sub-bituminous30 0.57 Sub-bituminous

Table 3. Relationship between vitrinite reflectance and proximate analysis of Kutai coals

Age Specific Energy Total Moisture Rvmax(kcal/kg) (%) (%)

Neogene 5,000-6,000 20-Aug 0.40-0.57Palaeogene 6,400-7,000 7-Mar 0.57-0.67


important. In combustion and coking processes,liptinites are the main precursors of tar. Sporeswere designated as tar and gas producers andbands of coal rich in liptinite produce significantamounts of tar (Krevelen, 1961 and Stach, 1968).Stach (1968) found that the yield of tar from sporesand cuticles in general varies between 20% and40% by weight, but resins, waxes and carbohy-drates form as much as 80% to 90%. The yield oftar increases with the proportion of hydrogen. Incontrast to liptinite, the inertinite maceral group issubhydrous and richer in carbon. Inertinites showlittle or no fluidity during coking processes (Nandiet al, 1977).

Direct combustion of coal currently accounts forthe largest consumption in Indonesia and will prob-ably continue to do so for many years in the fu-ture. This is caused by subsidy of fuel price thatis gradually reduced by the government to followthe international price. The primary use of thisenergy source is for steam generation. This en-ergy is used directly and indirectly in industrialprocesses and by utilities for electric power gen-eration.

Mackowsky (1982) identified four coal character-istics (most of which are related to rank and type)that are important in combustion: specific energy,grindability, swelling behaviour and ash properties.Quality-related variables for the Kutai coals aresummarised in Table 4. Specific energy increaseswith increases in vitrinite reflectance, up to ap-proximately 0.37%.

Coal used for pulverised fuel combustion is groundto a particle size mainly below 65 microns (Ceelyand Daman, 1981). Due to the energy required forthis grinding, grindability of a coal is a significantcharacteristic. Hardgrove Grindability Index (HGI)is related to rank and type (Neavel, 1981). TheHGI of the Kutai coals increases with increases inrank to about 0.37% vitrinite reflectance. Higher

HGI values indicate that less energy is requiredfor grinding than for lower HGI values. HGI valuesof the coals increase with increases in mineralmatter content. Higher inertinite and liptinite con-centrations of the coals cause high volatile coalsto be tougher (lower HGI value, Neavel, 1981). Thecoals that consist of mostly of brighter lithotypesare easy to grind and commonly accumulate inthe finer fractions. The Palaeogene liptinite-richcoals (generally tougher than the Neogene liptinite-poor coals) are difficult to grind and are commonlyconcentrated in coarser sizes.

For the Kutai coals, an increase in explosive ten-dencies of dust was correlated with increases inthe sum of liptinite, vitrinite and pyrite (Neavel,1981). He also noted that the tendency for spon-taneous combustion in storage piles could occurwith coals rich in fusinite and pyrite. Some of thecoals containing less than 1% fusinite but havepyrite contents (up to 11%) tend to be prone tospontaneous combustion.

Combustion properties of coal in furnaces are alsorelated to volatile matter yield and swelling char-acteristics. Volatile matter yield is principally rankrelated, for instance, it decreases with increasesin vitrinite reflectance in the coals. Liptinite due toits high yield of volatile matter expands explosivelyand then quickly burns. Swelling characteristics,which can affect combustion properties in furnace,have been reported to be independent of rank(Neavel, 1981).

Shibaoka (1969) in a series of experiments usinga microscope with an attached heating stageshowed that the order of ignition for the maceralgroups was liptinite-vitrinite-inertinite. Among in-dividual macerals, resinite was found to be espe-cially reactive. At the other extreme, fusinite inthe early stages of heating changed very little,except to become more fractured. Eventually asheating progressed, the fusinite was consumed,

Table 4. Quality of Kutai coals

AGEMACERAL+MINERAL (%) Rvmax PROXIMATE ANALYSIS

ASH S

V I L MM (%) SP.EN VM (%) MOIS HGI FSIKcal/kg (%)

(%) (%)

Neogene 75-95 9-Jan 15-Feb 2-Jan 0.30-0.57 5,000-6,000 31.0-48.1 8.0-26.7 1.1-11.0 2.8 48.3 1Palaeogene 76-94 6-Jan 19-Mar 6-Jan 0.53-0.67 6,400-7,000 33.7-38.1 8.0-20.0 1.2-5.2 0.1-1.9 57.8 2

Note: V: vitrinite, I: inertinite, L: liptinite, MM: mineral matter SP.EN: specific energy, VM: volatile matter, MOIS:moisture,S: sulphur ;HGI: hardgrove grindability index, FSI: free swelling index


but at a slower rate than the other macerals. Thestudies show the concept of reactive and inertapplies to the performance of macerals duringcombustion as well as in carbonisation or gasifi-cation. The Kutai coals generally contain less than6% inert macerals. Combustion system for thecoals can therefore operate with normal combus-tion temperatures that is 1,400ºC.

Ash content of the Kutai coals ranges between1.1% and 11.0%. The ash properties are relatedto mineral matter composition (Reid, 1981). Min-eral matter affects heating values of the coals;variations in type of mineral matter affect ash fu-sion properties. Ash disposal is important withregard to the development of ash deposits andcorrosion.

Sulphur is a major contributor to external corro-sion. Sulphur content of the Kutai coals containsup to 2.8%.

Nandi et al. (1977) found that fly ash in their ex-periments consisted of unreacted particles offusinite, semifusinite, mineral matter and oxidisedvitrinite. Fly ash can commercially be used in themanufacture of concrete products, cement, light-weight aggregates, soil stabilisation products,asphalt paving mixes and ceramic products (Reid,1981). The Kutai coals can be used for cementmanufacture and also for lightweight aggregates,asphalt paving mixes, concrete, soil stabilisationand ceramic products.

Moisture level of coal should also be consideredwhen they are used for combustion. High mois-ture level promotes low heating values. The Kutaicoals contain less than 30% total moisture. Thetotal moisture content of the coals decreases withincreases of vitrinite reflectance.

In summary, the Kutai coals are in general suitedfor direct combustion, although high moisture con-tents and spontaneous combustion will presentproblems with some of the lower rank coals. Themajor utilisation will be for electricity generation.Use of the coals in other industries will be mostlyrelated to the expansion of domestic cement pro-duction. The combustion process in influenced bycoal rank and type. Vitrinite reflectance is the bestmethod for measuring lateral and vertical variationsof rank. Vitrinite-rich coals are suited for prepara-tion in combustion, because the coals are easyto grind through to the finer fractions. The vitrinite-rich coals are generally tougher than the inertinite-

rich coals.

6. CLOSING MARKS

Type differences between the Neogene andPalaeogene coals in the Kutai Basin reflect theinfluence of peat environment and climate. Verti-cal and lateral rank variation characteristics re-sulted from contrasting burial andpalaeotemperature histories. Both type and rankcharacteristics of the coals influence the utilisation.

Vitrinite is the dominant maceral in the coals con-sisting mostly of detrovitrinite and telovitrinite andminor gelovitrinite. Liptinite is common in the coalsand its content is typically in the range of 2% to13%. Cutinite is the dominant liptinite maceral inthe coals, although resinite is dominant in someoccurrences. Sporinite and suberinite are commonand liptodetrinite is rare in the coals. Some of thecoals, typically the Palaeogene coals, containmore than 4% inertinite (mostly semifusinite andsclerotinite). Mineral matter consisting mainly ofclay and pyrite is common in the coals rangingfrom a trace to 11%. High proportions of vitrinite inthe coals indicate that the original plant materialconsisted essentially of woody plant tissue andthe peatification occurred under relatively wet re-ducing conditions.

The Kutai Neogene coals are typically much lowerin rank than the Palaeogene coals. The Neogenecoals have vitrinite reflectances in the range of0.40% to 0.57%, whereas the Palaeogene coalsvarying from 0.57% to 0.67%. The vitrinite reflec-tance of the coals shows significant increases withdepth.

The Kutai coals are generally suited to use fordirect combustion. The major utilisation potentialis for power generation. The absence of fibroustelovitrinite in the coals suggests that grindabilitycharacteristics should generally be favourable. Therank of the coals is sufficiently low for spontane-ous combustion to be a significant problem. Mois-ture contents of the coals are moderate to high,giving moderate to low specific energy.

REFERENCES

Addison, R., Haryoko, S. and Land, D.H., 1982.The East Kalimantan coal project, report onthe coal geology of the Badak Syncline. Re-


port No. S.D.M. 004. Directorate of MineralResources, Bandung (unpublished).

Adhi, R.N. et al., 2004. National resources andreserves of mineral, coal and geothermal. Spe-cial Publication, 103. Directorate of MineralResources Inventory, Bandung.

Bemmelen, R.W.van, 1970. The geology of Indo-nesia, vol.II, economic geology. MartinusNijhoff, The Hague.

Ceely, F.J. and Daman, E.L., 1981. Combustionprocess technology. In: Elliot, M.A. (editor),Chemistry of coal utilisation. John Wiley andSons Inc., New York.

Cook, A.C., 1982. The origin and petrology of or-ganic matter in coals, oil shales and petro-leum source rocks. The University ofWollongong. Wollongong.

Courteney, S. and Wiman, S.K., 1991. Indone-sian oil and gas fields atlas, volume 5,Kalimantan. Indonesian Petroleum Associa-tion. Jakarta.

Darman, H. and Sidi, F.H., 2000. An outline of thegeology of Indonesia. Indonesian Associationof Geologists, Jakarta.

Hardjono and Syarifuddin, I.I., 1983. Explanatorynotes on coal resources map of Indonesia. Spe-cial Publication of Directorate of Mineral Re-sources (unpublished). Bandung.

Krevelen, D.W.van, 1961. Coal. Elsevier,Amsterdam.

Mackowsky, M.Th., 1982. The application of coalpetrography in technical processes. In: Stach,E. et al., Stach’s textbook of coal petrology.Berlin-Stuttgart.

Nandi, B.N., Brown, T.D. and Lee, J.K., 1977. In-ert coal macerals in combustion. Fuel, 56.

Neavel, R.C., 1981. Origin, petrography and clas-sification of coal. In: Elliot, M.A. (editor), Chem-istry of coal utilisation. John Wiley and SonsInc., New York.

Ott, H.L., 1987. The Kutai Basin-a unique struc-ture history, Indonesian Petroleum Associa-tion. Proceedings of 16th annual convention

and hydrocarbon exploration, Australian Pe-troleum Exploration Association Journal 33/1.

Reid, W.T., 1981. Coal ash-its effect on combus-tion system. In: Elliot, M.A. (editor), Chemis-try of coal utilisation. John Wiley and SonsInc., New York.

Roeslan, K., 1984. The coal resources of Indone-sia and Southeast Asia. Paper presented toAGID-ILP Workshop, 7th AGC, Sydney.

Rose, R. and Hartono, P., 1978. Geological evo-lution of the Tertiary Kutai-Melawi Basin,Kalimantan, Indonesia. Proceedings of 7th

annual convention. Jakarta.

Samuel, L. and Muchsin, S., 1975. Stratigraphyand sedimentation in the Kutai Basin,Kalimantan. Proceedings of Indonesia Petro-leum Association, 4thAnnual Convention,Jakarta.

Satyana, A.H. and Biantoro, E., 1996. Seismicstratigraphy of Eocene Beriun Sands of westBungalun, east Kalimantan, Indonesia: a con-tribution to the Palaeogene stratigraphicknowledge of the Kutai Basin. In: IntemericaAbstracts with programs, volume 25, no. 7.

Shibaoka, M., 1969. An investigation of the com-bustion processes of single coal particles.Fuel, 42.

Siregar, M.S. and Sunaryo, R., 1980. Depositionalenvironment and hydrocarbon prospects,Tanjung Formation, Barito Basin, Kalimantan.Proceedings of Indonesia Petroleum Associa-tion, 9thAnnual Convention, Jakarta.

Stach, E., 1968. Basic principles of coal petrol-ogy: macerals, microlithotypes and some ef-fects of coalification. In: Murchison, D.G. andWestoll, T.S. (editors), Coal and coal bear-ing-bearing strata. Oliver and Boyd, Edinburgh.

Standards Association of Australia, 1964. Aus-tralian standard code of recommended prac-tice for taking samples from coal seams insitu, AS CK 5. Australia.

Standards Association of Australia, 1981. Micro-scopical determination of the reflectance ofcoal macerals. AS 2486.


Standards Association of Australia, 1986. Coalmaceral analysis. AS 2856.

Wain, T. and Berod, B., 1989. The tectonic frame-

work and palaeogeographic evolution of theUpper Kutai Basin. Indonesian PetroleumAssociation. Proceedings of 18th annual con-vention. Jakarta.

13Petrography of Raw Coal and its UBC Product ... Bukin Daulay

PETROGRAPHY OF RAW COALAND ITS UBC PRODUCT

BUKIN DAULAYR & D Centre for Mineral and Coal TechnologyJalan Jenderal Sudirman 623 Bandung 40211

Ph. 022-6030483, fax. 022-6003373, E-mail: [email protected]

ABSTRACT

Petrographic study of coal is based on the morphology, colour, size of the constituents, reflectanceand anisotropy of the macerals in reflected white light and autofluorescence of the constituents underblue-ultraviolet radiation. This research intends to determine if the Upgraded Brown Coal (UBC) prod-uct of Kutai coal can be distinguished petrographically from the raw coal, both air dried and oven dried.The UBC sample used in the study is resulted from the Palimanan (Cirebon) UBC pilot plant. The UBCprocess is a technology to upgrade low rank coal by reducing moisture content. It is based largely onthe slurry dewatering procedure. There is no significant textural differences of maceral in three samples(raw coal air dried, raw coal oven dried and UBC product), but the vitrinite reflectance mean is higherin the raw coal oven dried and UBC product compared with the raw coal air dried. The vitrinite reflec-tance value of 0.60% in UBC product is markedly above the main range, but omitting this value doesnot affect the mean. The value of 0.60% was obtained within a grain that also gave a value of 0.43%and it appears that the rise of vitrinite reflectance is not completely uniform within grains. Although thevitrinite reflectance differences found are small but it is significant especially if assessed in terms ofthe standard deviations found. It should be remembered, however, that the vitrinite reflectance valuesobtained for low rank coals such as these are strongly affected by the atmospheric conditions. Someholes are present in UBC product sample, may be a result of degassing vesicle formed during theprocess.

Keywords: Petrography, UBC, Maceral, Vitrinite Reflectance

1. INTRODUCTION

The petrographic characteristics of coal can beconsidered in terms of two essentially indepen-dent concepts, i.e. coal type and coal rank. Coaltype refers to the nature of the organic matter foundin the coal and coal rank refers to the stage ofcoalification that has been reached by the organicmatter. In more specific, the petrography of coalis based largely on the concepts of maceral andmicrolithotype. Maceral is an elementary micro-scopic constituent of coal that can be recognizedby its shape, morphology, reflectance and fluo-rescence. An assemblage of macerals with mini-mum width of 50 microns is called microlithotype.Therefore, the petrography of coal encompassesmany properties of organic matter including reflec-tance, bireflectance, morphology, relief and size

of the macerals, and autofluo-rescence of themacerals when viewed in blue-ultraviolet radiation.

Upgrading technologies of low rank coals can beconsideration a solution for clean coal technology,since this effort is subjected to reduce the mois-ture contents and automatically increase the calo-rific value in coal. Various upgrading process hasbeen developed since 1920s, among them are thesuperheated and pressurized steam drying, hotand supercritical water drying and hydrothermal-mechanical compression drying processes(Suwono, A. and Hamdani, 1999; Mahidin et.al.,2002). However, UBC is considered to be one ofthe relatively simple and mild due to low tempera-ture and pressure process and no chemical reac-tion occurs during the process (Shigehisa et. al,2000; Komatsu et.al., 2004).


Miocene low rank coal from Kutai area of EastKalimantan has been tested at UBC pilot plant inPalimanan, Cirebon Indonesia. The pilot plant of 5tons/day capacities is operated under 150-160ºCtemperature and 0.20-0.35 MPa pressure. Basedon the process performance tests, it has beenconfirmed that the Kutai coal can be upgraded tohigh calorific value coal through reducing inherentmoisture content and performances of the mainequipment including crushing, slurry dewatering,coal oil separation, rotary steam tube dryer andbriquetting were very good and stable. The mainaim of the present study is examine the effect ofUBC process to petrographic characteristics.

2. METHODOLOGY

2.1 Sample Preparation

Samples examination in this study were collectedfrom Palimanan UBC Pilot Plant, both of them wereraw coal and UBC product of Kutai coal. A portionof the raw coal was stabilized by heating in anoven to 110oC prior to mounting. The raw coal wasalso mounted untreated. The UBC product has afine top size and appears to have a bimodal sizedistribution with unusually high proportion of ultra-fine coal.

The three blocks (raw coal air dried, raw coal ovendried and the UBC product) of Kutai coal weremounted and polished following normal petro-graphic methods. Each sample was placed in aplastic mould and stirred into a mixture epoxy resinand hardener before being placed in a vacuum ovento remove all bubbles. Each block was cut per-pendicular to any gravitational settling of the grains.The surface was then ground flat and polishedsuccessively in three steps on carborundum pa-pers ranging from 400, 600 and 1200 grit. In orderto get the required level of polish for petrographicanalysis, additional fine polishing steps were car-ried out in water slurry on selvyt cloth-coveredmechanical laps using f irst ly chromiumsesquioxide (Cr2O3) and finally magnesium oxide(MgO) polishing powder.

2.2 Microscopic Examination

The samples were examined in reflected white lightand blue-ultraviolet radiation. The microscope ex-amination method used in this research involves

coal type determination by maceral analysis andrank determination by measuring vitrinite reflec-tance. The type and abundance of liptinite wasdetermined by employing fluorescence mode mi-croscopy. The examination of polished blocks wasconducted under controlled temperature and hu-midity conditions using ortholux microscope andphotomicroscopy.

2.2.1 Maceral Analysis

The maceral analysis procedure followed the Aus-tralian Standard for coal maceral analysis, AS 2856(Standard Association of Australia, 1986). Analy-sis were carried out in reflected white light andfluorescence mode using x32 and x50 oil-immer-sion objectives and x10 oculars giving a total mag-nification of approximately x400 to x500. At least500 data points were counted giving approximately90% coverage of the block. Liptinite was distin-guished from other macerals using fluorescencemode, though some vitrinite and minerals also hadweak fluorescence. The volumetric abundance ofvarious maceral groups, individual macerals andmineral matter were converted to percentage ofthe total points recorded.

2.2.2 Reflectance Measurement

Reflectance measurements were made on vitrinitebecause vitrinite undergoes changes consistentlywith rank, shows some inherent variability in re-flectance according to type, the most abundantmaceral in most coals and occurs as relativelylarge particles to make easy measurement. Theprocedure of reflectance measurement followed theAustralian Standard AS 2468 (Standard Associa-tion of Australia, 1989). Calibration of the equip-ment was conducted before measuring vitrinitereflectance in order to check linearity of the equip-ment. Reflectance measurements were made us-ing an oil immersion objective lens of nominalmagnification 60 times. The stage of the micro-scope was rotated to obtain the first maximumreading and then rotated through approximately180ºC to obtain the second maximum reading.Each pair of readings was summed and the meancalculated to give mean maximum vitrinite reflec-tance in oil immersion. Readings were rejected ifthe pair of readings obtained was not within 5%relative of each other. At least twenty five reflec-tance readings were taken to obtain the meanmaximum reflectance.


3. RESULT AND DISCUSSION

3.1 Maceral Variations

The three Kutai coal samples have relatively thesame proportion of maceral composition. Vitrinitein the samples was generally 82.6%, followed byinertinite 9.2% and liptinite 7.1%. Mineral mattercontent, mainly silica and clay minerals is only1.1% in the samples. Vitrinite mostly occurs astelovitrinite (predominantly textinite texto-ulminite,eu-ulminite and lesser telocoll inite) anddetrovitrinite (attrinite, densinite and desmocollinite)with gelovitrinite a minor component. Under re-flected white light, vitrinite shows grey – dark greycolour. Inertinite, is generally associated withvitrinite comprises predominantly semifusinite (oc-curs as layers, lenses or isolated fragments),sclerotinite (consisting of unilocular and bilocularteleutospores and sclerotia) and inertodetrinite.Inertinite shows white colour under reflected whitelight.

Liptinite comprises predominantly resinite (occursas discrete bodies, layers and lenses), suberinite(commonly occurs in association with corpogelinite),liptodetrinite and cutinite with minor sporinite. Theliptinite maceral has greenish yellow to orange fluo-rescence. Bitumen, oil cut and exsudatinitie thatinfills irregular cavities of different size and shapeare present in the sample. In some that the, celllumen of semifusinite and sclerotinite are filled witheither bitumen or weak fluorescence mineral mat-ter. However strong oil cut fluorescence thatpresent in UBC product is probably from materialused during the process.

The maceral composition of the Kutai samples isrelatively equal to maceral composition of mostIndonesian Miocene coals (Daulay, 1994) althoughinertinite content lies towards the high end of thenormal range. This high local concentration ofinertinite in the samples reflects to the changes inthe regional environment as also reported byDaulay (1994) for some Miocene Mahakam coals.

Small amounts of weathered coal are present inraw coals both air dried and oven dried. This typeof coal is not found in the UBC product. Stronggreenish yellow fluorescence of oil cut andexsudatinite are present in raw coal, both air driedand even dried. The oil cut and exsudatinite arealso present in the UBC product no significant dif-ference of fluorescence colour. This is assumedto indicate that there is no chemical degradation

and no loss of volatile hydrocarbons during theUBC process that is needed to change fluores-cence properties.

Photographs of the raw coal air dried, raw coaloven dried and UBC product are shown in the Plates1 to 6. Weathered coal grains (Plates 1 and 2) ofraw coal both air dried and even dried were notfound in the UBC product, but this is probably achance occurrence due to sampling. Vitrinite richcoal associates with liptinite (mostly resinite).Layers of suberinite are present in the samples,mostly associated with telovitrinite. In some casesthe layers of suberinite are have different morphol-ogy and different fluorescence characteristics.

Inertinite is unusually abundant (Plates 3 to 4) andthe abundance of inertinite indicates a Neogeneorigin. Most of the inertinite is fungal in origin al-though small amounts of inertodetrinite that areprobably higher plant in origin are also present.Where is lower inertinite content present, the re-duction in moisture for the bulk coal may beslightly more marked than for this suite of testcoals.

A small number of circular voids were found in theUBC product (Plate 5) and these may have formedduring evolution of moisture in the steam phase.Plate 6 also shows small voids that could havedeveloped during processing although these couldalso be primary structures within the original coal.For comparison, pores (voids) that occurred dur-ing the thermally affected coals can be seen inPlate 7 (less strongly thermally affected coal) andPlates 8 (the most strongly thermally affected coal).The two different heat affected coals are derivedfrom Bukit Asam semi anthracite coal (Daulay,1985).

From the above explanation it can be concludedthat there is no significant difference in maceralcomposition between raw coal (air dried and ovendried) and UBC product. However, there is a slighttextural difference can be distinguished in the UBCproduct. Some of the vitrinite layer show slightcompact (dense) compare with raw coal. Underreflected white light, some vitrinite and inertiniteshow more bright colour that of raw coal (both airdried and oven dried). In addition some holes orvoids can be observed in the UBC product sample,although they are not present frequently. This voidmay results of processing rather that a primarystructure within the coal. This is indicated that theUBC process is very mild that operated under low


temperature and pressure conditions. There is nochemical reaction occurs during the process,therefore no internal coal texture and structurechanges. Changes in textural or morphologicalproperties of the coal macerals can be only re-lated with increases in coal rank and depth of burial,although vitrinite (particularly telovitrinite) texturesare sensitive to increasing temperature and pres-sure. Textural properties of coal maceral could bechange if the temperature is above 400ºC. Smithapplied changes in textural properties of vitriniteto correlate the increase in coal rank with depth ofburial. He reported that in the Tertiary sequencesof the Gippsland Basin (Australia), vitrinite of ap-proximately 1250 metres depth with 0.30% vitrinitereflectance showed remnants of cell lumens. Withincreased depth into 1740 metres. He recognizedalmost all cell lumens of vitrinite had completelygelified with 0.45% vitrinite reflectance.

3.2 Vitrinite Reflectances

Vitrinite reflectance of the raw coal air dried is0.38% (0.29 – 0.44%) with 0.039 standard devia-tion. Raw coal oven dried shows a rise vitrinitereflectance results to a mean value of 0.43% (0.32– 0.51%) with 0.038 standard deviation. The UBCproduct has the highest vitrinite reflectance with amean value of 0.45% (0.35 – 0.60%) with 0.053standard deviation. It can be seen in the range ofreadings, the UBC product contains some fieldswith vitrinite reflectance above 0.50% and one fieldwas 0.60%. The grains where these higher valueswere obtained also contained vitrinite withreflectances near the mean value of 0.45%. Ex-clusion of the field with a vitrinite reflectance of0.60% did not alter the mean value in the seconddecimal place. The same trend is also indicatedby specific energy which increase from raw coalair dried (5048 kcal/kg, adb) through UBC product(6310 kcal/kg, adb).

Although the differences in the means are rela-tively small especially between the UBC productand the oven dried sample, they are significantwhen considered in terms of the standard errorsof the mean vitrinite reflectance values. It appearsthat the processing has a similar effect to dryingat a temperature of between 120oC and 150oC.Examination of the reflectance modes shows someadditional differences. The vitrinite reflectance his-tograms (Figures 1, 2 and 3) show some bimodal-ity in the distributions. In addition to the changesin the mean vitrinite reflectance, the histograms

show alterations in the location of the modes asshown in the Table 1.

As can be seen in the standard deviation is higherfor the UBC product compared to raw coal, bothair dried and oven dried Figures 1, 2 and 3. It meansthat there is a slight influence of the temperatureduring the process to the reflectivity of the maceral,although the effect is less compared to the heataffected coal as shown in Plates 7 with R vmax of0.89% and Plate 8 with vmax of 2.28%. The ex-tend of mean vitrinite reflectance increase dependsprimarily on temperature and pressure or distanceof coal seam from the intruded igneous rocks.

4. CONCLUSIONS

Three samples of Kutai coal (raw coal air dried,raw coal oven dried and UBC product) have beenanalyzed petrographically, both maceral analysisand vitrinite reflectance measurement. Product ofUBC is processed under low temperature (150-160ºC) and pressure (0.20-0.35 MPa) at PalimananUBC pilot plant. The UBC product has a slightlyhigher vitrinite reflectance than raw coal. The dif-ferences are small but are consistent. The rangesand standard deviations for the UBC coals are alsohigher than for the raw coals. The differences mightbe higher if the raw coals had not been dried priorto being mounted.

The raw coals are relatively mature in texturalterms, with some texto-ulminite but mainly eu-ulminite. It is possible that some increased de-gree of textural maturity has resulted from the UBCprocess but this is difficult to quantify, althoughsome voids (hole) can be identified in UBC prod-uct that could be resulted during the process .

REFERENCES

Daulay, B., 1985. Petrology of Some Indonesianand Australian Tertiary Coals. MSc Thesis,Wollongong University, Wollongong, Austra-lia, 265 p. (unpubl.).

Daulay, B., 1994. Tertiary Coal Belt in EasternKalimantan, Indonesia: The Influence of CoalQuality on Coal Utilization. PhD Thesis,Wollongong University, Wollongong, Austra-lia, 326 p. (unpubl.).


Plate 1. Raw coal air dried. Grain ofweathered coal showing fracturepattern due to weathering.Reflected white light mode, fieldwidth 0.22 mm, Rvmax 0.43%

Plate 2. As for Plate 1 but in fluorescence-mode. Grain of weathered coalshowing fracture pattern due toweathering. Resinite (R) associ-ates with vitrinite

Plate 3. Raw coal oven dried, suberinitesectioned close to bedding. Theinertinite in the lower part of thefield is probably derived fromfungal tissues. Reflected whitelight mode, field width 0.22 mm,Rvmax 0.43%

Plate 4. As for Plate 3 but in fluorescence-mode. The suberinite showsstrong fluorescence. Theinertinite is non-fluorescing butthe associated lumens containingresinite or bitumen

Plate 5. UBC Product, telovitrinite. In thelower left of the field the circularhole appears to represent adegassing vesicle formed duringprocessing. Reflected white lightmode, field width 0.22 mm,Rvmax 0.45%

Plate 6. UBC product, telovitrinite. Thesmall voids may be a result ofprocessing rather than a primarystructure within the coal. Re-flected white light mode, fieldwidth 0.22 mm, Rvmax 0.45%


Plate 7. Vitrinite thermally affected coal.Bukit Asam. Reflected white lightmode, field width 0.28 mm,Rvmax 0.89%

Plate 8. Pores in Vitrinite thermallyaffected coal. Bukit Asam, Re-flected white light mode, fieldwidth 0.22 mm, Rvmax 2.28%

Figure 1. Vitrinite reflectance histogram forraw coal air dried

Figure 3. Vitrinite reflectance histogram forUBC product

Figure 2. Vitrinite reflectance histogram forraw coal oven dried

0.20 0.24 0.28 0.32 0.36 0.40 0.440.480

- Telovitrinite - Detrovitrinite

1

2

3

4

5

6

8

7

0.520.56Vitrinite Reflectance, %

NO

OF

FIELD


0.20 0.24 0.28 0.32 0.36 0.40 0.44 0.480

1

2

3

4

5

Vitrinite Reflectance, %

NO

OF

FIELD

0.20 0.24 0.28 0.32 0.36 0.40 0.44 0.480


1

2

7

3

4

5

6

7

0.52 0.56 0.60 0.64Vitrinite Reflectance, %

NO

OF

FIELDS

Table 1. Distribution of vitrinite readings

Low HighSample Reflecting Reflecting

Mode Mode

Raw coal 0.39% 0.43%Oven dried coal 0.45% 0.41%Processed coal 0.42% 0.48%


Komatsu, N., Sugita, S. Deguchi, T., Shigehisa,T. and Makino, E., 2004. Development of Up-graded Brown Coal Process. Paper presentedon the 5th International Conference and Exhi-bition on CoalTech 2004, Kuala Lumpur, Ma-laysia, 9 p.

Shigehisa, T., Deguchi, T., Shimasaki, K. andMakino, E., 2000. Development of UBC Pro-cess. Paper presented on the InternationalConference on Fluid and Thermal Energy Con-version, Jakarta, Indonesia, 8 p.

Smith, G.C., 1981. Tertiary and Upper Cretaceouscoal and coal measure sediments in the Bassand Gippsland Basins. Ph Thesis, WollongongUniversity, Wollongong, Australia, 331 p.(unpubl.).

Standard Association of Australia, 1986. Austra-

lian Standard AS 2856: Coal Maceral Analy-sis. Standard Association of Australia,Sydney, 24 p.

Standard Association of Australia, 1989. Austra-lian Standard AS 2486: Microscopy Determi-nation of the Reflectance of Coal Maceral. Stan-dard Association of Australia, Sydney, 22 p.

Suwono, A. and Hamdani, 1999. Upgrading theIndonesian’s Low Rank Coal by SuperheatedSteam Drying with Tar Coating Process andits Application for Preparation of CWM. CoalPreparation, Vol. 21, pp. 149-159.

Mahidin, H. Usui, Singo Ishikawa and Hamdani,2002. The Evaluation of Spontaneous Com-bustion Characteristics and Properties of Rawand Upgraded Indonesian Low rank Coals. CoalPreparation, Vol. 22, pp. 81-91.


LEACHABILITY OF METALS FROM COALASH USING BATCH SYSTEM EXTRACTION

RETNO DAMAYANTI1), RAHAYU DH. 2) AND SELINAWATI TD.3)1,3) R & D Centre for Mineral and Coal Technology

Jalan Jenderal Sudirman 623 Bandung 40211Ph. 022-6030483, fax. 022-6003373

2) Directorate of Mineral Resources InventoryJalan Soekarno Hatta No. 444, Bandung 40254

Ph. 022-5202698, fax. 022-505809

ABSTRACT

Coal ash, a by-product is produced by coal burning activities. Coal combustion by product has beenutilized for concrete, cement mixture and etc. The conducted experiment covered minerals analysisand single extraction tests to evaluate trace elements that might be leached out. Result shows thatcoal ash consists of various concentrations of trace elements and heavy metals. Those metals leachedin most solvent used. The most leachable metals are Fe, Mn, Pb, Cr, Cd and Ag. Such heavy metals(Pb, Cr and Ag) from coal ash show high mobility in most pH condition (acid, base and neutral pH).This also happens in redox vicinity. Compare to Fe, Mn and Cd mobilities on the bottom ash, thosefrom fly ash is lower.

1. INTRODUCTION

Normally by product of coal combustion refers tosolid residue that comes from coal fired powerplants. In the power plant the coal was ground,pulverized, and then burnt within combustion cham-ber to heat the boiler. Inorganic pollutant, knownas coal ash, may remain in the combustion cham-ber or carry away in the flue gas stream, whilecoarse particles or known as bottom ash and boilerslag will stay on the bottom of the combustionchamber. Finest particles, called as fly ash, stillremain in the suspension of the flue gas stream.To prevent fly ash enters to the air or before com-ing out from the stack, the ash must be capturedby electrostatic precipitator or an other scrubbingsystem like cyclone. Power plant completed byflue gas desulfurization unit will produce a by-prod-uct that is called FGD materials (Anonymous, 2000).

The composition of coal combustion by productsis determined by either coal type or boiler/com-bustion chamber condition. Generally, the maincomponents of inorganic pollutants included fly ash(35%), FGD materials (23%), bottom ash (16%)

and boiler slag (3%). Of the four materials, fly ashis the most usable materials (33%). The main in-organic within coal phases are clay, carbonate,sulfide and quartz (Anonymous, 2000). In coal ash,those will be formed in many compounds of min-erals depend on temperature, ambient conditionand the cooling rate of ash forming processes.

Metals leachability experiment was conducted inthe laboratory using batch system. The solutionsused in the extraction procedure were taken un-der such a pH condition. The conditions are basedon condition of dilute acid, dilute basic and neu-tral solutions (Sandhu et.al., 1993 and Swaine, 1990).The observation of metals leachability based onpH effects and redox characteristics of the solu-tion extraction.

The study of leachability was undertaken to evalu-ate and compare metals leaching characteriza-tion coming from coal ash utilization. This shouldbe taken into account because the utility of coalash was made in several activities. Chemical char-acterizations of coal ash and water chemistry ofthe ash basin water were analyzed to examine

21Leachability of Metals From Coal Ash Using Batch ......... Retno Damayanti, et al.

the metals release from the disposal area.

2. LEACHABILITY OF TRACEELEMENTS

Trace elements in coal ash can be leached out tothe environment under physical and chemical in-fluence. Components in coal ash that chemicallypredicted as active agents are clay minerals, or-ganic materials, carbonate materials and oxidesof iron and manganese (Swaine, 1990). Parts of themmay absorb cations from solution and release suchan equivalent one into them.

The purpose of trace metals leaching test fromcoal ash is to evaluate such metals leachability inthe acid, basic and neutral conditions. Single ex-traction or batch extraction system was appliedin this study. In general, information on the totalconcentration of trace metals within coal ash isonly for monitoring trace metals condition but thosedo not yet give such information for predictingmetals toxicity and its bioavailability.

Trace metals accumulated in coal ash happenthrough many mechanisms that can be known bycontinuous extraction using various solutions.

3. MATERIALS AND RESEARCHMETHODS

Materials

1. Fly ash from electrostatic precipitator2. Bottom ash

Reagents

1. HNO3 pH of 32. NaOH pH of 83. NH2OH.HCl 0.04 M4. H2O2 30%5. Aquadest

Apparatus

1. Shaking machine2. pH meter3. AAS Flame Emission Varian Techtron AA-54. AAS Hydride generation5. ICP-AES Jobyn Yvon

Methods

Study of trace metals leachability in some solu-tion is based on data from previous study. Thedata cover coal ash chemical analysis and toxic-ity tests. The experiment is conducted in batchextraction system that uses acid and basic solu-tions and aquadest as well. The experiment con-dition is designed as close as natural leachingcondition.

Shaking of mixture samples for 3 hours in 100 mlof various extraction solution will obtain metalscontaining filtrates. Effects of solution pH on themobilization of trace metals are studied usingaquadest, HNO3 pH 3, NaOH pH 8. The trace metalconcentrations are determined by either AAS orICP.

4. PROCEDURE

Metals extraction using single or batch ex-traction system

About 5 grams of fly ash and bottom ash samplesis extracted at room temperature with 100 ml ofaquadest and then shaker for 3 hours. Same treat-ments are applied using HNO3 pH 3, NaOH pH 8,NH2OH.HCl 0.04 M and H2O2 1M. Trace metalsare determined by ICP-AES in Geochemistry Labo-ratory of the Directorate of Mineral Resources.

5. RESULTS AND DISCUSSION

Metals concentration in coal ash samples is shownin Table 1 that illustrates main iron (Fe) and man-ganese (Mn) in their oxide forms. The analyseswere conducted using Perkin Elmer Atomic Ab-sorption Spectrophotometer. Mercury analyzer isused to analyze trace mercury.

Elemental analyses of filtrate were analyzed us-ing ICP-AES and AAS. Explanations of the pHeffects of solution are as follows:

1. AquadestThe aquadest pH used in this experiment was7.91. Most metals such as lead (Pb), chro-mium (Cr) and silver (Ag) were leached outfrom coal ash. The extracted metals from flyash were about 2 – 8%. Other metals were


leached out in small quantity. Seven metalswere leached out from the bottom ash includ-ing lead (Pb), cobalt (Co), nickel (Ni), copper(Cu), cadmium (Cd), chromium (Cr) and silver(Ag). The percentage of metals extracted inneutral solution was around 1 – 7%. Stovebottom ash showed mostly the same charac-teristics with bottom ash from power plant butthe extracted metals from stove bottom ashwere higher (1 – 9%) than those from powerplant bottom ash. Compare to fly ash, metalsfrom bottom ash were leached out more. Thosemetals especially Cd, Ag and Cr must be takeninto account due to its ease leachability inneutral conditions.

2. HNO3Metals were leached out variously than thosein fly ash sample. Fly ash sample showed thatsilver leached more than others (Cd, Cr andPb). Metals leachability in fly ash is around 2– 9.5%. In power plant bottom ash sample,most metals are leached out. Cadmium hashighest leachability in acid conditions followedby silver (Ag), nickel (Ni), lead (Pb), chromium(Cr), cobalt (Co), manganese (Mn) and zinc(Zn). Leaching percentage of those metals areabout 2 – 11%. Again, metals in stove bottomash has the same characteristics with powerplant bottom ash but their leachability werelower.

3. NaOHCadmium (Cd), silver (Ag), chromium (Cr) and

cobalt (Co) showed high extractions when theash was leached by NaOH at pH 8 (about 5 –9.5 %). Lead (Pb) and manganese (Mn) wereleached around 2% and other metals in smallamounts (ppb). In basic condition, cadmium(Cd), chromium (Cr) and silver (Ag) from flyash were much more leached out than lead(Pb). But in both bottom ash samples, mostmetals were leached out above 2% exceptcopper (Cu) and zinc (Zn). Manganese (Mn)in stove bottom ash leached quiet high (above2%).

Base on the experiment facts, metals in coal ashsamples show different mobility in different extrac-tion solution. Generally, cadmium (Cd), chromium(Cr) and silver (Ag) in coal ash show high leach-able characteristics (Figure 1). In the extreme ex-traction solution like nitric acid and sodium hy-droxide, some metals (iron, manganese, zinc andcopper) in fly ash are more difficult to leach out. Inthe basic condition metals leachability is higherthan in acid condition.

6. CONCLUSION

1. Metals leachability in acid condition is lowerthan in basic condition.

2. The leaching test using various solutionsshowed that in general, lead (Pb), chromium(Cr) and silver (Ag) had high mobility.

3. Compare to metals mobilities in the bottomash, some metals in fly ash like iron, manga-

Table 1. Metals concentration in coal ash

No. Composition SatuanSamples

FA BA O

1. Fe % 3.51 2.7 1.42. Mn ppm 1018 561 49.13. Pb ppm 86.8 40.6 89.54. Cu ppm 98.7 34.9 152.15. Zn ppm 510 184 1356. Ni ppm 201 65.4 2317. Cr ppm 236 262 2448. Co ppm 133 40 81.99. Cd ppm 3.9 2.1 3.5

10. V ppm 421 136 10411. Ag ppm 4.9 6.4 7.612. Hg ppb 791 647 1511

Note:FA : Fly ash from electrostatic precipitatorBA : Bottom ashO : Bottom ash from stove

23Leachability of Metals From Coal Ash Using Batch ......... Retno Damayanti, et al.

Power Plants Fly Ash

0

2

4

6

8

10

H2O H2O2 NaOH HNO3

Extractants

% M

etal

s Ex

trac

ted

Fe Mn Pb Cu ZnCd Cr Co Ni Ag

Power Plant Bottom Ash

0

2

4

6

8

10

12

H2O H2O2 NaOH HNO3

Extractants

% M

etal

s Ex

trac

ted


Stove Bottom Ash

0

2

4

6

8

10

H2O H2O2 NaOH HNO3

Extractants

% M

etal

s Ex

trac

ted


Figure 1. Metals leachability from coal ash samples in various solution


nese, zinc and copper (Fe, Mn, Zn and Cd)have lower mobilities.

7. SUGGESTION

Detailed research on batch and continuous ex-traction systems must be carried out to figure outmechanism of natural leaching condition of theash. Tests on other various extraction solutionsmust also be carried out due to high possibilitiesleaching characteristics that may be happened.

8. ACKNOWLEDGEMENT

The authors are grateful to Djuarsih, supervisor ofMineral Chemistry Laboratory in CMTRDC andTubi Sudaryanto, environmental staff at PaitonPower Plant for analysis assisstance and helpfuldiscussion. Thanks also to staffs of Geochemis-try Laboratory at Directorate of Mineral ResourcesInventory for their technical assistance during re-search periods.

REFERENCES

1. Coal Combustion By-Products, The Fly AshResource Center, http://www.geocities.com.

2. Evangelou, V.P., J.K. Neathely, 1995. Bitu-minous Fly Ash Release Potential Modelingand Remediation of Arsenic, Boron and HeavyMetals, Univ. of Kentucky.

3. Fleming, L.N., Abinteh, H.N., Inyang, H.I.,1996. Leachant pH Effects on the Leachabil-ity of Metals from Fly Ash, J. of Soil Contami-nation, 5(1): 1996, p. 1-7.

4. Sandhu, S.S., Mills, G.L., Sajwan, K.S., 1993.Leachability of Ni, Cd, Cr and As from CoalAsh Impoundments of Different Ages on theSavannah River Site, Lewis Publishers.

5. Swaine, D.J., 1990. Trace Elements in Coal,Butterworths.

6. Utility Ash Pond Treatment, Graver WaterSystems. Inc., 1996.

25Silver Extraction From Tailing Resulted ...... Hadi Purnomo, Lili Tahli and Nuryadi Saleh

SILVER EXTRACTION FROM TAILING RESULTEDFROM GOLD ORE CYANIDATION, PONGKOR

HADI PURNOMO, LILI TAHLI AND NURYADI SALEHR & D Centre for Mineral and Coal Technology

Jalan Jenderal Sudirman No. 623, Bandung 40211, IndonesiaPh. 022-6030483, fax. 022-6003373

ABSTRACT

Cyanidation process applied at Gold and Silver Processing Business Unit, Pongkor, results incyanidation slurry in the form of tailing containing valuable metals of gold and silver. Based on analy-ses results of Sample-1 and Sample-2, the tailing has grade of gold of 1.67 g/t and 1.46 g/t and silverof 35.11 g/t and 34.71 g/t. Gold and silver ore contained in the tailing has grain size of > 200 mesh inthe amount of 62.22% in Sample-1 and 63.31% in Sample-2. Considering the fact, the tailing has agood prospect to be treated for gold and silver extraction. The tailing resulted in this cyanidationprocess reaches the amount of about 1.000 ton/day. The method applied in this process is combina-tion of gravity concentration and cyanidation. Gravity concentration is purposed to obtain concentratewith grade of gold >10 g/t, whereas cyanidation is aimed at dissolving gold and silver from gravityconcentrate followed by recovery method such as electrowinning to recover gold and silver. Finalconcentrate, as raw material of cyanidation process, has grade of 15.24 g/t Au and 257.44 g/t Ag withgold and silver recovery of 40% and 43% respectively and ratio of concentration was 25.16%. After-wards, the concentrate was ground up to 90% of 200 mesh followed by cyanidation process. Cyanidationprocess of the concentrate has not yielded optimal results. This condition was indicated by very lowsolubility of gold and silver, about 75%.

1. INTRODUCTION

Cyanidation process conducted at Gold and Sil-ver Processing Business Unit, PT. Aneka Tambangproduce tailing with high content of gold and sil-ver, in the ranges of 1.46-1.67 g/t of gold and 34.71-35.11 g/t of silver respectively. Grain fraction ofthese metals in the tailing in the size of >200 meshis more than 60%. In this fact, concentration pro-cess is considered as a suitable process for thistailing to increase gold and silver grade beforeconducting cyanidation process.

Gravity concentration test on this cyanidation tail-ing was done using various concentrator equip-ments such as jig, Knelson concentrator, andshaking table. This process was carried outthrough rougher and cleaner stages to recoverconcentrate with high content of gold and silver.

Gravity concentration is a process to separate

valuable mineral and metal from its associatedminerals based on the distinction of specific grav-ity in a fluid. The successful of this process mostlydepends on the type of equipment used which itsselection closely relates to particle size.

Many advantages can be obtained in applicationof gravity concentration of gold processing as fol-lows :

– The equipments used in the process is rela-tively simple therefore its operational and in-vestment cost is also lower;

– No chemicals is needed so the process isfriendly to the environment;

– Can be applied to concentrate coarse graingold which can’t be done in flotation process.Some gravity equipments are even can beused for fine grain gold processing.

26 INDONESIA MINING JOURNAL Vol. 8 No. 03, October 2005 : 25 - 39

2. THEORETICAL BACKGROUND

2.1 Equipment Selection for GravityConcentration

Type of equipment used in concentration gravitycan be classified based on its separation mecha-nism and the media used in the process. Table2.1 shows characteristics of gravity concentrationequipments including feed size, water requirement,and capacity.

Based on its separation mechanism, gravity con-centration can be divided into six groups, i.e.:stratification concentration, flowing film concen-tration, shaking concentration, centrifugal concen-tration, hindered settler concentration, and air dryconcentration.

Sratification is a mechanism of grain layer forma-tion composed of minerals based on the distinc-tion of specific gravity and grain size as a result ofseparation forces in fluid media. Coarse and finegrain heavy mineral as well as coarse grain lightmineral will be stratified at the lowest layer. Theclose range of feed size, therefore, is supportingits separation process and the coarse light min-eral is not stratified. Jig is designed by taking ad-vantage of the stratification mechanism.

Stratification process may be conducted in a flow-ing film of which separation forces are found de-pend on its flowing design. The equipments usethis mechanism consist of sluice box, reichertcone, pinched sluice, strake and spiral, includingshaking table, orbital and crossbelt. Separation isresulted from toggle movement.

Centrifugal mechanism is also used in mineralseparation process. In this case, feed is put inspinning bowl and light mineral will be trapped inoverflow and out from mouth of bowl. Whereas,heavy mineral is trapped in wall of bowl completedwith ribs or riffles. Spinning bowl, Knelson con-centrator, and Falcon concentrator are centrifugalconcentrators.

Figure 2.1 shows the relationship of size range offeed particle to the type of gravity concentrationequipment used in the process. Jigging, flowingfilm concentrator (sluice box, riechert cone,pinched sluice and spiral) need coarser feed thanthat used in shaking and centrifugal concentra-tors (shaking table, bartles-mozley and crossbelt).

Jigging is generally applied in early process ofconcentration (rougher) followed by shaking incleaning stage.

Table 2.1 Characteristics of equipments for gravity concentration (Laplante,2004)

Type 4 MachineOperating size Water

Capacity 6range (mm) requirement 5

Stratification Jigs-Conventional 0.10 → 100 high mediumJigs-Circular 0.05 → 100 high highJigs-Centrifugal 0.02 → 2.0 high medium

Flowing Film Sluice Box 0.15 → 10.0 high mediumReichert Cone 0.05 → 1.5 low highPinched Sluice 0.05 → 1.5 low mediumStrake 0.15 → 2.0 high lowSpiral 0.03 → 2.0 medium medium

Shaking Shaking Table 0.02 → 2.0 medium mediumOrbital 0.01 → 0.07 high lowCrossbelt 0.01 → 0.03 high low

Centrifugal Spinning Bowls 0.01 → 1.7 very high high

Hindered Settler Density Separator 0.07 → 0.60 medium high

Air Dry Pneumatic Jig 0.15 → 25 none mediumAir Table 0.25 → 6 none low

3) Spiller,2000; Generalized; specific machine operating on site-specific materials may or may not perform thesecharacteristics

4) Kelly and Spottiswood, 19825) Relative6) Relative per unit; multiple units always equal to high capacity


2.2 Cyanidation

Cyanidation is a process of gold-silver extractionby dissolving the gold-silver ore using cyanidesolvent reagent. In this case, cyanide sodium(NaCN) is generally used as solvent reagent, butcyanide potassium (KCN) is also may be used.Cyanidation process is based on the capability ofcyanide ions to form complex compounds havinghigh stability with gold and silver. Nevertheless,several minerals can disturb cyanidation processdue to its reaction to cyanide (cynicides).

Ion reactions (known as Elsener Equity) that hasbeen conventionally admitted as a method in goldleaching using cyanide are as follows :

4 Au + 8 CN- + O2 + H2O 4 Au(CN)-2 +OH- .............................................................. (1)

In spite of that, the recent research on the mecha-nism of gold dissolving indicates that reaction isrun in two stages (Adamson, 1972). Most of golddissolving is done through reaction as follows:

2 Au + 4 CN- + O2 + 2 H2O -à 2 Au(CN)-2 +H2O2 + OH- .................................................. (2)

The rest is dissolved through reaction (1)

The rate of gold dissolving depending upon NaCNconcentration and solution basicity, optimum pHis generally 10.3 (Dorey et.al., 1988). Practically,cyanidation process is often associated with otherprocesses such as amalgamation, flotation andgravity concentration with the aim at recoveringgold in maximal quantity. Selection of theses pro-cesses primarily depends on mineralogical char-acteristics of gold ore.

Many factors mostly influence efficiency of goldand silver dissolving process in cyanide solventsuch as cyanide solution strength, solution pH,agitation and aeration strength, and ore charac-teristic.

Results of experiment indicated that in a cyanideleaching circuit 1 pound cyanide per ton of solu-tion (0.05% NaCN) was able to reach maximumstrength of solvent (Denver, 1978). The use of weaksolution in cyanide leaching is caused by the de-creasing effect of cyanide consumer minerals inlow concentration in line with the decrease of toxiccyanide steam formation in hot condition.

The more increase of cyanide concentrationstrength will accelerate gold and silver dissolvingup to a certain concentration and then the rate ofdissolving does not increase anymore. Lower con-

Figure 2.1 Relationship between particle size and type of gravity concentrator (Laplante, 2004)


centration of cyanide is needed in gold ore solu-tion with small content of silver, whereas the orewith high content of silver requires higher concen-tration of cyanide. Practically, if the ore contain-ing gold and silver, cyanide solution used shouldbe able to dissolve both metals.

Gold and silver leaching process in cyanide solu-tion should be conducted in basic condition, be-cause NaCN is hydrolyzed easily in acidic condi-tion (low pH) as reactions below:

NaCN - Na+ + CN- ............................................. (3)H+ + CN- HCN ....................................... (4)

The above reactions show that if solution pH islow, ion H+ concentration is high which will bindCN- ion and form HCN that can evaporate easily.The loss of free cyanide results in the decrease ofcyanide solubility while toxicity of HCN is danger-ous for human life.

To set up solution pH, many type of base and saltlike NaOH, Na2CO3 and CaO may be used. CaOin form of lime is mostly utilized. Besides its lowprice, it has other advantages as follows:

– to avoid loss of cyanide;– to settle fine grains contained in suspension

in thickening process;– to neutralize acidic compounds in ore.

Gold and silver leaching can be done well in cer-tain pH, therefore, it is important to control cya-nide solution pH periodically. Utilization of lime asregulator reagent of pH should be observed be-cause Ca2+ ion will hamper solubility of gold andsilver at pH more than 11 due to the reaction be-low:

Ca(OH)2 + H2O2 CaO2 + 2 H2O................ (5)

In this reaction, CaO2 may be settled at metalsurface and hamper the direct contact betweengold-silver and cyanide. To get optimal condition,lime is usually added at early stages of the pro-cess (ore grinding). In term of pH and cyanidesolution strength controlling, sampling of solutionwas conducted systematically and regularly.

Mixture agitation in leaching process was requiredto avoid sedimentation of ore grains and to makeeven distribution of grain in slurry so thatcyanidation process could be done efficiently.Besides, reaction in gold leaching process needs

free oxygen because it has more advantage thanoxidant or pure oxygen. In a stronger aeration,carbon dioxide in solution will increase. Carbondioxide can decrease the content of free cyanidein solution. The most important thing in gold andsilver leaching is the comparison between thegrades of free NaCN and O2 in solution.

3. RESEARCH METHODOLOGY

The first stage that has to be conducted in de-signing gravity concentration is characterizationof gold ore.

3.1 The aim of Characterization

Feed characterization in gold ore processing isaimed at obtaining particle distribution and spe-cific gravity mineralogically and physically. Char-acterization is closely related to selection of grav-ity concentration equipment. Mineralogical studywill describe the following matters:

– Type and composition of valuable mineralsincluding its specific gravity;

– Type and composition of associated mineralsincluding its specific gravity;

– Range of grain size of valuable and associ-ated minerals;

– Liberation degree that indicates associatedcondition of gold with its gangue minerals;

– Form and its association property (lock or in-terlock).

Tables 3.1 and 3.2 show the results of sieve analy-ses and distribution of sample taken from tailingpond. These tables indicate gold contents of 1.46g/t and 1.67 g/t whereas silver contents are 34.71g/t and 35.11 g/t respectively. Grain size of >200mesh is 63.31% that led to unrepresentative sam-pling and cyanidation process could not be donein optimal condition. In this case, about 66.68%of gold was distributed at the size of grain.

3.2 Results of Mineralogical Analyses

Results of mineralogical analyses of samplestaken from tailing pond is showed in Figures 3.1and 3.2. These figures show that native gold hasvery fine size about 10 um, 16 um and 30 um,


which was dominated by included grains in limo-nite and pyrite (52% of total observed grains). Goldgrain sizes comprise 30 um. 35 um, 20.5x10 um(in limonite) and grain sizes of 10x25 um, 15 um,10.8x16 um and 8 um were included in pyrite. Inaddition, grain sizes of 10x50 um, 6x8 um, 6x12um, and 28 um were associated with pyrite.

3.3 Stages of Experiment

Stages of experiment can be seen in Figure 3.3.At early stage of the process (rougher concentra-tion), Humphrey Spiral or Knelson Concentratorwas used and concentrate resulted in this stagewas refined using shaking table (cleaner stage).Before conducting cyanidation, this concentratewas previously ground up to 200 mesh size of grain.

4. RESULTS AND DISCUSSION

4.1 Concentration using Humphrey Spiral

Considering the more part of grain distribution isin the size of > 200 mesh (about 53.31%), theequipments used in this stage were Humphreyspiral and Knelson concentrator. A big capacity

concentrator was required to process tailing inpond which was able to result in representativesamples with finer grain size distribution. Prior toconcentration stage, wet sieving of tailing was doneto remove -200 mesh size.

Re-calculation results of sieved tailing sample isshown in Table 4.1. As Humphrey spiral feed, tail-ing pond containing 1.54 g/t Au and 34.64 g/t Ag.Concentration process was conducted usingHumphrey spiral and its results is shown in Table4.2. The concentrate resulted in this process hasgrade of 4.09 g/t Au and 29.83 g/t Ag with Aurecovery of 80.55% and Ag recovery of 26.11%.Gold and silver contained in tailing yielded byHumphrey spiral were 0.43 g/t and 36.73 g/t re-spectively. Ratio of concentration was 3.3.

4.2 Concentration using KnelsonConcentrator

To seek for optimal condition, concentration pro-cess by using Knelson concentrator has also beenconducted and its results are shown in Table 4.3.Optimal grade and recovery of gold and silver wasachieved at condition K-1 with Au and Ag grade of3.85 g/t and 60 g/t and gold and silver recovery of

Table 3.2 Sieve analyses and distribution of gold and silver from tailing pond (Sample-2)

Berat Kadar (gr/ton)Fraksi

(gr) (%) Au Ag

60 74,5 4,8 2,4 4540 341,7 22,02 1,68 38,240 310,2 19,99 1,53 3460 239,2 15,41 1,68 38,6

125 343,3 22,12 1,71 30,3-325 243,1 15,66 1,53 32,5

Total 1552 100 1,67 35,11

Table 3.1 Sieve analyses and distribution of gold and silver from tailing pond (Sample-1)

Fraction Weight % % % Grade (g/t) %, Distribution % Cum(gr) Weight Cum Cummesh Retained Retained Retained Passing Au Ag Au Ag Au Ag

60 230 5,15 5,15 94,85 2,21 39,3 7,79 5,83 7,79 5,8340 877 19,64 24,79 75,21 1,36 32,72 18,28 18,51 26,07 24,3440 842 18,85 43,64 56,36 1,28 34,91 16,52 18,96 42,58 43,360 878,5 19,67 63,31 36,69 1,79 35,09 24,1 19,88 66,68 63,1970 722 16,17 79,48 20,52 1,53 36,14 16,93 16,83 83,61 80,0255 238 5,33 84,81 15,19 1,7 39,65 6,2 6,09 89,81 86,1

-325 678,5 15,19 100 0.00 0,98 31,75 10,19 13,9 100 100

Total 4466 100 1,46 34,71 100 100


Figure 3.1 Mineralogy of gold particle (14μμμμμm, 22 um, and 50 μμμμμm) takenfrom tailing pond

A. Gold particle 14 µm as pyrite inclusion

B. Gold particle 22 µm liberated

C. Gold particle 50 µm as limonite inclusion

A. Gold particle 5 µm as pyrite inclusion

B. Gold particle 12 µm as limonite inclusion

Figure 3.2 Mineralogy of gold particle (5 μμμμμmand 12 μμμμμm) taken from tailingpond

87.23% and 64.58% respectively.

Performance of Humphrey spiral and Knelson con-centrator did not show a significant difference, bothin grade and recovery of gold and silver. Grade ofgold and silver has not met minimum requirementfor cyanidation process, as a consequence thegrade should be improved through cleaner stageusing shaking table.

4.3 Cleaning-Scavenging Stage

This stage was conducted using a series of shak-ing table. Due to high content of gold and silver intailing yielded by shaking table, the tailing has tobe scavenged. The concentrate resulted from thisstage of the process was re-circulated to cleaningstage.

Experiment results of cleaning and scavengingstage is shown in Figure 4.1. As raw material forcyanidation process, final concentrate has Au and

Ag content of 15.24 g/t and 257.44 g/t respec-tively with gold and silver recovery amounted to40% and 43%.

4.4 Performance of CyanidationExperiment

Performance of cyanidation process is shown inTable 4.4. Condition of the process was 30% solidpercentage and pH 10.5. Cyanidation was done inbottle roller with open edge to pass the air as oxi-dant into experiment system.

Cyanidation concentration was kept at constant


Figure 3.3 Diagram of experiment

Table 4.2 Material balance of Humphrey spiral to sample from tailing pond

Feed Concentrate Tailing

Wt(%) 100 30,33 69,67Au (g/t) 1,54 4,09 0,43Ag (g/t) 34,64 29,83 36,73REC. Au (%) 80,55REC. Ag (%) 26,11RoC 3,3

Table 4.1 Sieve analyses and distribution of sieved gold and silver from tailing pond

Fraction Weight % % % Grade (g/t) %, Distribution % Cum(gr) Weight Cum Cummesh Retained Retained Retained Passing Au Ag Au Ag Au Ag

60 230 8,13 8,13 91,87 2,21 39,3 11,68 9,23 11,68 9,2340 877 31,02 39,15 60,85 1,36 32,72 27,41 29,29 39,09 38,5240 842 29,78 68,93 31,07 1,28 34,91 24,77 30,01 63,86 68,5360 878,5 31,07 100 0 1,79 35,09 36,14 31,47 100 100

Total 2827,5 100 1,54 34,64 100 100


Figure 4.1 Material balance in cleaning-scavenging stage

Table 4.3 Material balance of Knelson concentrator to sample from tailing pond

KodeFeed Conc. Tail. Grade Conc.(g/t) Recovery (%)

RoC(%) (%) (%) Au Ag Au Ag

K1 100,00 37,785 62,21 3,85 60,0 87,23 64,58 2,65K2 100,00 21,744 78,26 4,65 52,5 60,63 32,52 4,60K3 100,00 1,960 98,04 13,65 185,0 16,04 10,33 51,02K4 100,00 2,015 97,99 16,56 185,4 20,00 10,64 49,64K5 100,00 2,023 97,98 13,79 187,0 16,73 10,78 49,42

RoC ratio of concentration


condition whereas free cyanide concentration wasdefined using titration method using nitrate silverand rhodanine as indicator, in which 1 ml nitratesilver solution equivalent to 0.01% of free cyanide.

At early experiment cyanide has normal strength,

about 0.1-0.3% NaCN (1.000-3.000 ppm), as it isgenerally used at Gold and Silver Processing Busi-ness Unit, Pongkor. Table 4.4 shows that at nor-mal strength dissolved gold is 74.10% and silverabout 65.98%. The increasing concentration ofcyanide as shown in Table 4.5 was resulted in the

Figure 4.2 Cyanide influence on gold and silver % extraction

Table 4.4 Performance of cyanidation experiment at strength of 0.15% NaCN

LEACH TEST Concentrate of shaking tableDESCRIPTION Standard leachingDATEGRIND p80% passing 200 meshCONDITION 0,15% NaCNWT%SOLID 25Grade concentrate Au 15,24 g/t

Ag 257,44 g/tPbNO3 addition 2 kg/tpH natural 8,68

initial 11,70final 11,45

Sample code Weight or Concentration Recovery, %

pHNaCN,Volume (g) (ppm)

Konsentrat Au Ag Au Ag grammeja goyang 30.91

Waktu (jam)

0 100 0 0 0 0 8.68 0.151 100 0.15 5.23 3.18 6.57 11.70 0.002 100 0.23 10.26 4.88 12.89 11.80 0.084 100 0.56 15.98 11.89 20.07 11.78 0.076 100 0.89 26.66 18.90 33.49 11.75 0.008 100 1.23 3026 26.11 38.02 11.71 0.0612 100 1.78 35.64 37.79 44.65 11.67 0.0924 100 2.15 41.56 45.65 52.21 11.62 0.0048 100 3.49 52.50 74.10 65.98 11.45

Total 0.36


increase of gold and silver solubility up to 75%.

To increase gold and silver solubility up to >90%,cyanide concentration was increased significantlyin variations of 1%, 1.5% and 2% as it is con-ducted in cyanidation industry using concentrateraw material (intensive cyanidation). Condition ofsignificant increase of cyanide concentration isshown in Figure 4.2. It can be seen that extremelycyanide concentration increase did not increasegold and silver solubility significantly. In this case,gold and silver solubility was about 75-76%.

Stationary solubility of gold and silver is possiblybecause of interlocking condition of gold and sil-ver grains by quartz gangue mineral. Mineralogi-cal analysis of residue resulted from cyanidationprocess is very necessary to find out refractori-ness properties of tailing.

4.5 Economic Aspect of Tailing PondTreatment Technology

Ratio of concentration throughout the process was25.16. It means that to obtain 1 ton of concentratewith gold and silver content of 15.24 g/t and 257.44g/t respectively, about 25.16 ton of tailing feed isrequired for a plant with capacity of 1,000 ton perday.

In a recovery process consisting of cyanidation,electrowinning, and smelting will be resulted in 401g of gold (with assumption of gold extraction per-centage at cyanidation is 75%, electrowinning ef-ficiency is 93% and smelting is 95%) and 6,779 gof silver (with assumption of gold extraction per-centage at cyanidation is 75%, electrowinning ef-

ficiency is 93% and smelting is 95%).

4.6 Proposed Diagram of Tailing PondTreatment

In application it is better to use Knelson concen-trator at rougher stage to anticipate varied headgrade and dominant distribution of finer size of goldparticle. This is a simpler process as can be seenin Figure 4.6. The concentrate yielded by Knelsonconcentrator is re-circulated using Wiffley table.Its tailing is returned to tailing pond.

Cleaning stage is done using two Wiffley tables.Tailing resulted from first shaking table is improvedby using second shaking table which is called asscavenging stage. This stage is aimed at recover-ing gold associated in tailing yielded by first shak-ing table.

The concentrate from second shaking table is re-circulated to the similar shaking table to avoid theloss of gold. The tailing from the second shakingtable is removed to tailing pond.

The minimum graded concentrate yielded from thefirst shaking table is ground using ball mill to get80% of 200 mesh grain size for cyanidation pro-cess. Grinding in a closed system is done usingcyclones, underflow product is circulated to ballmill whereas overflow is used as cyanidation feed.

5. CONCLUSIONS

Based on the above description, some conclusionsare as follows:

Figure 4.3 The effect of cyanide concentration on gold and silver extraction percentage


Figure 4.4 Performance of cyanidation at 0.25% NaCN strength

LEACH TEST Konsentrat meja goyangDESCRIPTION Standard leachingDATEGRIND p90% lolos 200 meshCONDITION 0,25% NaCNWT%SOLID 25Grade concentrate Au 15,24 g/t




Sample Code Weight or Konsentrasi Perolehan, %

pHvolume(g) (ppm) NaCN

Konsentrat Au Ag Au Aggram

meja goyang 30.91

Waktu (jam) 0

0 121.4 0 0 0 0 8.54 0.301 121.4 0.19 3.09 4.14 3.99 11.56 0.002 121.4 0.28 5.71 6.11 7.37 11.59 0.074 121.4 0.56 11.62 12.21 15.00 11.76 0.006 121.4 0.89 17.43 19.41 22.51 11.74 0.108 121.4 1.24 23.72 31.35 30.63 11.70 0.04

12 121.4 1.75 33.55 38.17 43.32 11.69 0.0524 121.4 2.83 49.39 61.73 63.78 11.61 0.0048 121.4 3.47 57.03 75.68 73.64 11.57

Total 0.56


Sample code Weight or Concentration Recovery, %

pH

NaCN,volume (g) (ppm)

Konsentrat Au Ag Au Aggram

meja goyang 31.22

Waktu (jam)

0 104.51 0 0 0 0 8.75 0.311 104.51 0.54 10.91 11.86 14.19 11.65 02 104.51 0.87 17.15 19.11 22.3 11.68 0.14 104.51 0.96 18.82 21.09 24.47 11.67 06 104.51 1.23 24.71 27.02 32.13 11.71 0.128 104.51 1.56 30.89 34.27 40.17 11.7 0.03

12 104.51 2.13 37.68 46.79 49 11.65 0.1324 104.51 2.95 52.73 64.8 68.57 11.61 048 104.51 3.44 57.29 75.56 74.49 11.68

Total 0.69


LEACH TEST Konsentrat meja goyangDESCRIPTION Standard leachingDATEGRIND p90% lolos 200 meshCONDITION 0,3% NaCNWT%SOLID 25Grade concentrate Au 15,24 g/t



Figure 4.5 Performance of cyanidation at 0.3% NaCN strength


TAILING WILFLEY TABLE

TAILING KNELSON

KNELSON CONCENTRATOR

KONSENTRAT AKHIR

WILFLEY TABLE

CYCLOPACK

KONSENTRAT KNELSON

BALL MILL

-200 MESH

TAILING POND

TAILING POND

-200 MESH

WILFLEY TABLE KONSENTRAT SCAVENGING

SIANIDASI

Figure 4.6 Diagram of tailing treatment from tailing pond


– The grain of gold in tailing pond was domi-nantly included in pyrite limonite with very finesize (10-30 um), very small amount of the grainwas liberated;

– Concentration test of sample taken from tail-ing pond by using Humphrey spiral resulted inconcentrate (30.33% w/w) with the grade ofAu and Ag of 4.09 g/t and 29.83 g/t and Auand Ag recovery of 80.55% and 26.11% re-spectively. Meanwhile, the tailing yielded byHumphrey spiral has Au and Ag content of0.43 g/t and 36.73 g/t. Ratio of concentrationwas 3.3;

– Concentration test of sample taken from tail-ing pond by using Knelson concentrator at lowback water pressure resulted in concentrate(37.39% w/w) with the grade of 3.85 g/t Auand 60.0 g/t Ag and Au and Ag recovery of87.23% and 64.58% respectively. Ratio ofconcentration was 2.65;

– As a consequence of the increase of backwater pressure at Knelson concentrator, thegrade of gold and silver has also increased,and its recovery tend to decrease. The gradeof gold and silver increased to 16.56 g/t and185.4 g/t respectively, whereas gold recoverydecreased to 20.00% and silver recovery to10.64%;

– Cyanidation process with standard strength,1.000-3.000 ppm NaCN, showed gold and sil-ver recovery of about 75%;

– The increase of cyanide concentration up to 1– 2% did not result in significant increase ofgold and silver solubility.

REFERENCES

PT. Aneka Tambang Unit Geomoin, Cikotok, 2000.Operasional Proses Pengolahan Bijih EmasPasir Gombong, Unit Geomoin – CikotokAneka Tambang.

Adamson, R.J., 1972. The chemistry of the ex-traction of gold from its ores, in Gold metal-lurgy in South Africa, Cape and TransvaalPrinters,Cap Town, South Africa.

Chamberlain, P.G. & Pojar, M.G., 1981. ‘The Sta-tus of Gold and SilverLeaching Operatins in

The United States, in Gold and Silver Leach-ing, Recovery And Economics’, Editor W.J.Schlitt, W.C. Larson, & J.B. Hiskey, Procs.From the 110th AIME Meeting, Illinois, Febru-ary 22-26.

Denver Equipment, Mineral Processing Flowsheet,Denver Equipment, Denver.

Dorey, R., Van Zyl, D. & Kiel, J., 1988. Overviewof Heap Leaching Technology, in Introductionto Evaluation, Design and Operation of Pre-cious metal Heap Leaching Projects, EditorVan Zyl, Hutchison, & Kiel, Society of MiningEngineers, Colorado, pp. 3-22.

Hiskey, J.B., 1984. ‘Gold and Silver Extraction:The Application of Heap Leaching Cyanidation’,field notes, Arizona Bureau of Geology andMineral Technology, Tucson, vol. 15, no.4,winter, pp.1-5.

Laplante, A.R., 2004. A Standardized Test to De-termine Gravity Recoverable Gold, <http://www.Knelson.com>.

Laplante, A.R., Liming H. & Harris, B.G., 2004.The Upgrading of Primary Gold Gravity Con-centrate, <http://www. knelson.com>.

Laplante, A.R., Spiller, D.E., 2004. Bench Scaleand Pilot Plant Testwork for Gravit y Concentra-tion Circuit Design, <http://www.Knelson.com>.

Laplante, A.R., Woodcock, F., & Noaparast, M.,2004. Predicting Gravity Separation GoldRecoveries.<http://www.Knelson. com>.

Mc. Quiston ,Jr., F.W., & Shoemaker, R.S., 1980.Gold and Silver Cyanidation Plant PracticeMonograph, vol. I, The American Institute ofMining, Metallurgical, and Petroleum Engi-neers, New York.

Mc. Quiston ,Jr., F.W., & Shoemaker, R.S., 1980.Gold and Silver Cyanidation Plant Practice,vol. II, Society of Mining Engineers of Ameri-can Institute of Mining, Metallurgical, and Pe-troleum Engineers, New York.

Mineral Processing Flowsheet,Denver Equipment,Denver, Colorado.

Murr, L.E., 1979. ‘Observations of Solution Trans-port, permeability, and leaching reactions in


large, controlled, copper-bearing waste bod-ies’, Hydromet, vol.5, pp. 67,93.

Murr, L.E., 1980. ‘Theory and Practice of CopperSulphide Leaching in Dumps and Insitu’, Min-eral Science Engineering, vol.12, no.3, pp.121-129.

Pizarro, R., McBeth, J.D.,& Potter, G.M., 1974.‘Heap Leaching Practice at the Carlin GoldMining Co,Nev.’, Solution Mining Symposium,American Institute Mineral, Metallurgy, and Pe-troleum Engineers, New York, pp. 253-267.

Thorstad, L.E., 1987. ‘How Leaching Changed theWest, World Investment News’, A Pacific Re-gency, Vancouver, B.C., February, pp. 31, 33.

Von Michaelis, H., 1985. ‘Role of Cyanide in Goldand Silver Recovery, in Cyanide and the Envi-ronment’, Editor Dirk van Zyl, GeotechnicalEngineer Program, Colorado State University,Fort Collins, vol. 1, pp. 51-64.

Yusuf, R., 1984. ‘Liquid Flow Characteristics inHeap and Dump Leaching’, M.Sc. Thesis,University of New South Wales.


DESIGN AND ENGINEERING OF ARTESIANWELL DEVELOPMENT EQUIPMENT

USING AIR LIFT METHODS

HENDRO SUPANGKAT, EKO PUJIANTO AND SIDIQ SUWONDOR & D Centre for Mineral and Coal Technology

Jalan Jenderal Sudirman No. 623 Bandung 40211, IndonesiaPh. 022-6030483, fax. 022-6003373

ABSTRACT

Artesian wells will need certain maintenance to keep the water debit production stable from time totime. This procedure needs special equipment to clean the well. In this experiment, the equipmentthat comprises compressor of 7 bars pressure specification combined with ventury was tried to beused for well development. The ventury is designed in 10 types with different diameter and reductionangle. The result showed that ventury with diameter of 3 inches gives the best result, whereas reduc-tion angle has no impact on producing water debit.

1. INTRODUCTION

The main problem of artesian wells of 100 – 200 mdepth is the decrease of its capacity, especiallyin water quality and the debit. This problem maybe caused by fine particles lining inside the pipe.Therefore, it needs continuous maintenance. Oneof the maintenance methods is called air lift usingsubmersible pump. However this method has highrisk that can cause pump broken down. Sand lock-ing or friction mainly causes the pump damage.

Air lift equipment is comprise of compressor withpressure of 10 – 20 bar. However, It is difficult tofind compressor with that specification in the mar-ket, mostly only 7 bars can be found. In this re-search was tried to utilize compressor of 7 barspressure to clean artesian well with depth of 100 –200 m and water level of 55 to minus 100 m belowsurface level.

2. METHODOLOGY

First step of the experiment is to create 10 venturieswith various sizes. Second step is applied it inartesian well by recording water debit and the waterlift height difference from the edge of artesian well.The experiment is highly dependent on compres-

sor ability to lift the water and its capacity.

3. BASIC THEORY

Theoretically, factors that influence air lift equip-ment are as follows :

a. atmospheric pressure of compressor of 7 barequal to 7 x 10.336 m = 72.35 m water col-umn height. Where 1atm = 76 cm Hg; Den-sity of mercury (Hg) = 13.6

b. According to Atlas Copco, ratio of venturydepth and total head has to be over 0.3 (Fig-ure 1).

Based on those two factors above, the air lift meth-ods application will succeed if the ratio of blownpipe length below surface with the total of pipelength reaching 60%. This ratio will be decreasingaccording to water surface level. The minimumpermitted ratio is 30%. Compressor capacity se-lection for air lifting can be calculated using em-pirical formula, where ¾ cfm (0.024 m3/minute)air is demanded for every 3.82 l/minute of water.

For instance, for typical pressure height in welledge with depth of 90 – 122 m, will need compres-

41Design and Engineering of Artesian Well ... Hendro Supangkat, Eko Pujianto and Sidiq Suwondo

sor of 125 psi (862 kPa). Pressure of 43 psi (296kPa) is usually needs for every 30.5 m depth ofblown pipe below surface to obtain best air lifting.

Theoretically, water lifting from the well can be cal-culated. For water surface of 60 m depth andventury depth of 30 m, the maximum lifting is100m. It means that there is the excess of liftheight from maximum well edge about 10 m.

Empirical formula of Atlas Copco (1978)

h 3 — = —— H 10

Where,

Water surface of experimental well = - 60 mh = ventury depth from water surfaceH = ventury depth from total head

Theoretically, the water can be lifted to well edgewith condition of :

If minimum ventury depth h = 25.715 m or 25.71m.

25.71 3———— = ——— H 10

H = 257,1/3

It means that no water lifting because in that pointthe water pressure is equal to compressor pres-sure. Hence the ideal ventury location for 7 barscompressor capacity and water surface of – 60 mis in depth of 85.71 m < H < 132.35 m. Theoreticalratio between depth of ventury and maximum total

lifting is as shown in Table 1.

4. DESIGN AND ENGINEERING

The equipment used for artesian well cleaningshould have high pumping (debit) capacity to suckdirt that clog the screen or aquifer around thescreen. In obtaining sufficient suction velocity, highcapacity compressor of 600 cfm is necessary tobe used. As mentioned previously, that type ofcompressor is rarely found in the market, hencein this experiment compressor of 7 bars is used.

Factors that are influence air lift ability are amongothers :

– compressor pressure– compressor capacity– ventury capacity, and– compressor position under water.

In this experiment, vetury component was madeusing steel pipe in certain diameter and length andconnected upright with smaller diameter pipe andjoined with compressor using high pressures hose.The ventury tube is connected with pipe in up di-rection. In the operation, the ventury should beplaced underwater. The sketch of pre-designed anddesigned ventury is as in Figure 2.

Ventury operation is based on air blow in certain

Table 1. Theoretical ratio between depth ofventury and maximum total lifting

No. Ventury Total lift Lifting differencesdepth from well edge

1. 30 m 100 m 10 m2. 40 m 133,33 m 33,33 m3. 50 m 166,67 m 56,67 m4. 60 m 200 m 80 m5. 70 m 233,33 m 103,33 m6. 72.35 m no lifting hydrostatic

equilibrium

Figure 1. “Air Lift” methods configuration


pressure and high velocity through blown pipe,hence the air pressure moved will be smaller thanwater pressure, hence water well can be lifted up.

The water debit will be influence by the balance ofair pressure from the compressor with water col-umn pressure inside the well and how deep is theventury placed underwater.

5. EXPERIMENTAL PROCEDURE

Well development is conducted after gravel liningstage. It is done with the aim to clean inside pipewall, aquifer invasion zone, and liberated gravelfrom fine particles hence aquifer pore can be widelyopened and the water can flow freely to the well. Ifcleaning stage is conducted on the right way itwill result in efficient maximum type capacity(Fletcher 1986).

(a) Original

Figure 2. Venturi design

(b) Modified

The advantages of development stage are as fol-lows:

– Reducing/eliminating aquifer clogging in borehole wall and the edge of invasion zone as aside effect of drilling and eliminating sandbridge effect

– Increasing aquifer porosity and permeabilityaround the well

– Maximizing well type capacity and efficiency– Reducing pumping operational cost as a re-

sult of the decrease of pressure height lossesin well intake zone (interval of screening)

Methods of cleaning are comprise of :

– Overpumping– Backwashing– Jetting– Airlifting, and


– Surging or swab.

Sink the equipment to the well until the venturyposition is on underwater. Pumping process iscarried out since the ventury is placed 1 m belowthe water surface. Up to 86 m below surface, thewater is beginning to flow to the surface. At first,the water flow volume is less than air, but after theventury is placed in deeper place the air is de-creasing. Water debit monitoring is carried out upto 131 m depth until reaching hydrostatic equilib-rium condition (no more pumping action). The ex-periment is conducted for 10 types of ventury.

The first stage of well developing process eitherair lift or surging is flowing air to the well graduallyfrom weak to strong pressure. If the well is clogged,direct strong air pressure application will damagethe screen. When water became relatively clear,it is save to increase air pressure and continue to

clean the entire screen by moving the ventury upand down.

Surging process is generally carried out about 0.5

– 1 minute, and then pressure hose was con-nected to the ventury that can cause lifting. Thiscycle is repeated many times by moving theventury up and down until sand content on wateris less than 5 mg/l. This process is started fromthe upper screen down to the deepest one closeto the well base.

Generally fine particles that clog borehole wall,aquifer invasion zone, and gravel lining pore is claymaterial. As known, clay has strong cohesion char-acteristic hence thus it tends to stick to each other.Hence, for well development polyphosphate solu-tion (Sodium Acid Pyrophosphate-SAPP, TetraSodium Pyrophosphate-TSPP, and Sodium Tri-

Figure 3. Field work

Compressor

Tripod

Water tank

Water meter

Pipe φ 1 inch

Well's wall

Groundwater level

Ventury

Blow hose

Foot Valve


polyphosphate-STPP) is necessary to dissolveclay. For every cubic of water need 17 – 20 kg ofpolyphosphate. It needs 12 – 24 hours to reacheffective dissolving time. Before polyphosphate so-lution is pumped to the well, it should be dissolvebeforehand with warm water in a container becauseit is hardly to dissolve on water. Sodium hypochlo-rite should be added to the well to control bacte-rial growth inside the well as a result ofpolyphosphate solution. For every cubic of waterwill need 2- 2.5 kg of sodium hypochlorite to reach3 – 15% concentration.

6. RESULT OF THE EXPERIMENT

There is no pumping action available until depth of85 m for ventury no 1 and 2 (diameter of 2 inches).The water is started to flow when the ventury is in87 m depth, and stop at the hydrostatical equilib-rium of 131 m depth.

Same condition was happened for ventury no 3and 4 (diameter of 2 inches), the water was startedto flow at depth of 87 m, and stop at thehydrostatical equilibrium of 131 m depth. The dif-ference between venturi no 1 & 2 with ventury no 3& 4 was in angle.

Venturies no 5,6 and 7 have diameter of 3 inches.The water flowed at depth of 87 m, and stop at thehydrostatical equilibrium of 131 m depth.

Venturies no 8, 9 and 10 have diameter of 4 inches.The series of equipment was not able to be sinkto the well because of trouble inside the well. Themaximum dept that could be reach by theseventuries were only 89.5 m, and no continuouspumping debit. Water was mixed with air from thecompressor.

From the data can be concluded that the deeperventury placed the more water debit we can get.For example for ventury no 2, at depth of 87 m thewater debit is 2.20 liter and at depth of 93 m thewater debit became 2.40 liter. Similarly for venturyno8, at depth of 85.5 m water debit is 1.90 l/minuteand at dept of 89.5 the debit is increasing to 3.75l/minute.

From Figures 4 to 13 can be visualize that thecurve of water debit and ventury depth are almostsimilar. This is almost fit to the theory that watercould be obtain between 85.71 m < H < 132.35 m.The slightly bias is might caused by the compres-sor capacity. It might be not exact 7 bars pres-sure, and also lowering water surface during theexperiment.

Figure 4. Ventury type 1 depth vs water debit



7. CONCLUSION

The ventury can be designed in various type andsizes, and fit to the vessel pipe of the well. It canbe seen from Figure 4 to 13 that the best venturyis type with 3 inches diameter with pumping debitof 23.3 l/minute. There is no influence of reductionangle.

The equipment designed can be of various func-tions either as lifter or surging equipment in welldevelopment. We only have to move blown pipefrom ventury connector to the return pipe.

In the experiment can be proved that the ventury

can be used in well development up to 150 m depth(according to hydrostatics law is 131 m). It isproved that 7 bars compressor with capacity of175 cm can be use to develop the well up to 150m depth.

REFERENCES

Atlas Copco 1978. Manual, Stockholm, Sweden,pp. 114-5.

Fletcher, G.D., 1986. Groundwater and wells,Johnson Division, St. paul, Minnesota, pp.497-528.

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