indonesian mining journal vol. 16, no. 2, june 2013.pdf

8/15/2019 Indonesian Mining Journal Vol. 16, No. 2, June 2013.pdf

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Coal Geochemistry of the Unconventional Muaraenim Coalbed Reservoir ... Imam B. Sosrowidjojo

Received : 28 February 2013, rst revision : 02 April 2013, second revision : 05 June 2013, accepted : June 2013

INDONESIAN MINING JOURNAL Vol. 16, No. 2, June 2013 : 71 - 81

COAL GEOCHEMISTRY OF THE UNCONVENTIONAL

MUARAENIM COALBED RESERVOIR, SOUTH

SUMATERA BASIN: A CASE STUDY FROM THE

RAMBUTAN FIELD

GEOKIMIA RESERVOAR NON-KONVENSIONAL BATUBARA

MUARAENIM, CEKUNGAN SUMATERA SELATAN: STUDI KASUS

LAPANGAN RAMBUTAN

IMAM B. SOSROWIDJOJO

R & D Centre for Oil and Gas Technology, LEMIGAS

Jalan Ciledug Raya Kav. 109, Cipulir - Kebayoran Lama, Jakarta Selatan 12230

Ph. 021 7228614, Fax. 021 7228614

e-mail: [email protected]

ABSTRACT

Muaraenim coalbeds in Rambutan Field have typically high vitrinitic coal geochemical features that indicates

the main target for CBM development. The presence of vitrinite coals in South Sumatra Basin is indicated by

high huminite concentration (up to 83 vol.%). The coalbeds are of sub-bituminous rank (Ro


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INTRODUCTION

Coal is one of the most complex and challenging

natural materials to be analyzed. Each coal has a

unique characters, due to different plant sources

over geologic time. This diversity presents achallenge to construct a coherent picture of coal

geochemistry and the processes that inuence

chemical composition of coal (Orem and Finkel-

man, 2003).

South Sumatra Basin is very interesting, contains

some thick gassy coals at optimal depth in existing

oil elds due to having the Indonesia’s best com-

bination of resource size and quality, data control,

well services, and pipeline infrastructure. In the

basin, the coals occur in the Lahat, Talangakar

and Muaraenim Formations. The main sizablecoal seams are concentrated into two horizons

within the Muaraenim Formation.

The coal-bearing Muaraenim Formation was de-

posited during the Late Miocene-Early Pliocene.

Through detailed outcrop study, integration of

sedimentological observations and palaeonto-

logical information has led to the recognition of

a number of sub-environments within the delta

system. It has been interpreted as representing

deposition in a humid tropical regressive deltaic

system (Boyd and Peacock, 1986).

The main economically signicant coal deposits

for coalbed methane (CBM) target on the South

Sumatra Basin occur in the Muaraenim coal

(Stevens and Hadiyanto, 2004). Other important

coal deposit in the basin is in the Talangakar

coal, showing relatively thinner net thickness of

single seams. The coal thickness is often below

2 m and total net thickness is usually less than

5 m. In the two areas evaluated in this study, the

depth of the top of the coal sequence is deeper

than the typical CBM depth window (deeper than

1,500m) (Sosrowidjojo, 2006). For these reasons,the Talangakar coal prospectivity for CBM must

be rated lower than the Muaraenim coal.

Early published data on the gas storage capacity

of Indonesian coals concluded that the Southern

Sumatra coal mines are the most suitable for CBM

exploration in Indonesia (Stevens et al., 2001;

Kurnely et al., 2003; Stevens and Hadiyanto,

2004; Sosrowidjojo, 2006). Nowadays, as many

as 54 CBM working areas have been signed in

Indonesia. Some 19 working areas of them are

in the South Sumatra Basin. A map showing all

the working areas is presented in Figure 1. How-

ever, in spite of these indications showing the

existence of economical CBM resources in the

South Sumatra Basin, until recently, no systematic

drilling and exploration of these resources had

been undertaken. The purpose of this paper isto provide the coal geochemical characteristic of

Muaraenim coal in the South Sumatra Basin with

focus on the Muaraenim coalbed reservoir system

in the Rambutan Field.

GEOLOGICAL SETTINGS

The geological setting, stratigraphy and tectonic

evolution of the South Sumatra Basin have been

described by numerous authors (e.g. Adiwidjaja

and de Coster, 1973; Boyd and Peacock, 1986;Bishop, 2000; Pulunggono et al., 1992; Barber

et al., 2005; Wibowo et al., 2008; Angraini and

Yonatan, 2011). Only a brief summary is pre-

sented here.

The South Sumatra Basin is regarded as a fore-

land (back-arc) basin bounded by the Barisan

Mountains to the southwest, and the pre-Tertiary

Sunda Shelf to the northeast. The basin was

formed by east-west extension during the Late

Cretaceous to Early Tertiary. Orogenic activity

during the Late Cretaceous-Eocene divided the

basin into four sub-basins.

The structural features present in the basin are

the result of the main tectonic events: Middle-

Mesozoic orogeny, Late Cretaceous-Eocene

tectonism and Plio-Pleistocene orogeny. The rst

two events provided the basement conguration

including the formation of half grabens, horsts and

fault blocks. The last event, the Plio-Pleistocene

orogeny, resulted in the formation of the present

northwest-southeast structural features and the

depression to the northeast.

The sediments of the South Sumatra Basin

(Figure 2A) comprise an economic basement of

pre-Tertiary rocks that is overlain unconformably

by a thick Tertiary sequence. The rst Tertiary

sedimentation occurred during the Middle Eocene

and gave rise to the Lahat Formation consisting

mainly of volcanic rocks, claystone and shale

that was deposited locally in the graben areas.

The Talangakar Formation of Late Oligocene and

Early Miocene overlies the basement, where the

Lahat Formation is missing. It is a transgressive

sequence resulting from the Late Oligocene to


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gross thickness. This is the formation, which con-

tains the large brown coal or lignite resources of

the South Sumatra region which were the principal

target of Shell Coal Mining Exploration in the past.The thickness of the formation varies from 200

to over 800 m and generally decreases, together

with the percentage of coal from south (South

Palembang depression) to north (Jambi area)

across the basin, reecting a transition from delta

plain to marine dominated environments. The

formation is present throughout the Palembang

sub-basins and along the west coast of Sumatra

where the more marine facies (Eburna Marls) are

thought to be equivalent to both the Muaraenim

Coal member and the Kasai Tuff member (Stein-

hauser and van Delden, 1973).

Middle Miocene subsidence. The later sedi-

mentation during the Middle Miocene to present

produced a regressive sequence including the

Muaraenim Formation. The coal seams are foundwithin the Muaraenim Formation and were formed

during the Late Miocene and Early Pliocene. A

generalized stratigraphy of the Palembang Group

of the South Sumatra Basin is shown in Figure 2

where the coal seams of the Muaraenim Forma-

tion are shown.

The Muaraenim Formation (MEF) may be coal-

bearing over its total thickness or only partially

coal-bearing, depending on the area, with a total

coal thickness ranging between 0 and 120 m. Coal

seams typically account for 10% to 20% of MEF

Figure 1. Map showing 54 CBM working areas in some prolic coal basins in Western Indonesia, 19 of them are

in the South Sumatra Basin (modied from Sirait, 2013)


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According to Amijaya (2005), the development

of these thick coal deposits and its extremely

low content of mineral matter are explained by

the doming paleo-peat geomorphology of this

deposit. By analogy to recent conditions, these

morphological conditions limited the influx ofsuspended sediment from river water keeping any

overbank deposits thin, so that the peat could not

be enriched in mineral matter.

The andesitic intrusions in the Tanjungenim area,

South Sumatra, which represents the late stage

manifestation of post Miocene volcanic activity, is

presumed to be of Pleistocene to Early Quaternary

age, causing further uplift, faulting and folding as

well as formation of some shallow domes (Darman

and Sidi, 2000), but most importantly the local

metamorphism of the strata in the Bukit Asam coal

mine areas (Gafoer and Purbohadiwidjoyo, 1986).Moreover, Pujobroto and Hutton (2000) report the

occurrence of three main intrusive bodies near

the Bukit Asam coal mines (Air Laya and Suban).

Those are Bukit Asam dyke, Suban sill and a verti-

cal parasitic cone to the west of Air Laya Dome.

The Bukit Asam dyke is the largest intrusive body

and its outcrop forms a hill. The presence of the

andesite intrusion in the Bukit Asam area has

resulted in locally change rank of the coals (e.g.

Santoso and Daulay, 2005). These coal seams

can be classied into medium-volatile bituminous

to anthracite coals up to 5.18% Ro (Amijaya and

Littke, 2006). Coal seam with indirect contact with

the andesitic intrusion may have been coalied

by hydrothermal metamorphism (e.g. Hower and

Gayer, 2002).

METHODOLOGY

The sample preparation, canister gas desorp-

tion, canister gas composition, adsorption iso-

therm, proximate and microscopic examination

followed the procedures described elsewhere

(Sosrowidjojo, 2006). Coal particles of about 1

mm in diameter were used for preparation of

polished sections, which were embedded in a

silicone mould using epoxy resin as an embed-

ding medium. After hardening, the samples were

ground at and polished.

Five gas exploration boreholes, namely, CBM-1,

CBM-2, CBM-3, CBM-4 and CBM-5 at a spacing

of ~300 to 650 m, were drilled in the Rambutan

Field (Figure 3). The boreholes were drilled to a

maximum depth of 1,000 m and traversed ve

laterally extensive continuous coal seams and

one thick but discontinuous coal seam (hanging

seam). Coring jobs were using conventional cor-

ing equipment instead of a wireline-coring one,

and the ve continuous core-coal seams were

Figure 2. (A) Stratigraphy of the South Sumatra Basin (redrawn from van Gorsel, 1988);

(B) Stratigraphy of the Muaraenim Formation and its coal seam nomenclatures based on Shell Mijn-

bouw (Franks, 1978).


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F i g u r e 3 .

M a p o f S o u t h P a l e m b a n g S

u b - b a s i n s h o w i n g ( A ) t h e r s t C B M P

i l o t T e s t i n I n d o n e s i a . ( B ) A s e t o f v e

C B M w e l l s ( C B M - 1 t o C B M - 5 ) w e r e d r i l l e d a n d ( C )

C B M w e l l l o g t o i l l u s t r a t e P

a l e m b a n g c o a l b e d ( S e a m - 2 a n d S e a m

- 3 ) a n d P e n g a d a n g c o a l b e d r e s e r v o

i r s ( S e a m - 5 ) .


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called Seam 1 to Seam 5. Measured gas composi-

tion from wells was selected for coalbed reservoir

production only i.e. Seam 2, Seam 3 and Seam 5.

The depths and thicknesses of the selected coal-

bed reservoirs are presented in Table 1. Moreover,

the Seam 1 through the Seam 4 that is classiedas M2 has nick name as Palembang coal while

the Seam 5 (M1) is called Pengadang Coal. This

study focused on the Seam 2, the Seam 3 and the

Seam 5 only that are used pilot coalbed reservoir

development test in the Rambutan Field.

RESULTS AND DISCUSSION

a. Muaraenim Coalbed Geochemical Proper-

ties

Proximate analysis from several surfaces and

subsurface coal samples is presented on Table

2. The volatile matter of the seams are in the

range of 29.3-45.8% with maximum xed carbon

is 46.54% and described as bright and lustrous.

From those data, it can be seen that the coal in this

area is classied as lignite-sub-bituminous. Ash

contents are very low, except for one coal sample

which is relatively as high as 19.8%. The coalbed

is relatively high in volatile matter content. In short,

these factors maybe promote good cleating and

can enhance permeability.

Coalbed porosity in the Rambutan Field ranges

from 5 to 10%, and classied as high poros-

ity. High porosity means coalbed reservoir will

produce more water compare to low porosity.

Common coalbed reservoir porosity in the CBM

well testing is less than 5%, lower than any result

from the Rambutan Field. Permeability test in

the Rambutan area shows low around


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and basin hydrology. Hardly, any information is

available about the origin and the CBM compo-

sition from the South Sumatra Basin. The range

of the Muaraenim coal ranks in the Rambutan

Field, it is highly likely that biogenic gas has been

formed early in the burial history of these low rank

coals (lignite to sub-bituminous rank Ro values

0.6%). With exception to the high rank

coal for the Muaraenim coal in the surround-

ing intrusion areas (e.g. Tambang Air Laya),

thermogenic process of methane generation for

the Muaraenim coals does not seem very likely.

It might be possible that at greater depths, the

coals in the Talangakar Formation are in the

thermogenic window.

Table 2. Storage and Compositional Properties of the selected Muaraenim coalbeds from the fth CBM wells in

the Rambutan Field (representing 27 samples from all Seam 2, Seam 3 and Seam 5 only)

Reservoir Properties Values

Coalbed Reservoir (Seam) Depth

a. Top depth Seam 2 (m) 488 – 541

b. Top depth Seam 3 (m) 498 – 555

c. Top depth Seam 5 (m) 904 – 944

Coal Seam Thickness (m) 10 – 12

Gas Content (measured from canister, m3/ton) 0.43 – 5.84*

CH4 Composition (measured from canister, mol %) 71 – 98*

CH4 Composition (measured from seam/ well, mol %) 94 – 97

Storage Capacity at seam depth – as received (scf/ton) 184 – 830

Storage Capacity at seam depth – daf (scf/ton) 264 – 1,134

Langmuir Volume (scf/ton) 733 – 2,419

Langmuir Pressure (psi) 1,279 – 6,107

Vitrinite Maceral Group (%) 58.9 – 83

Moisture Content (%) 12.4 – 24.5

Volatile Matter (%) 29.1 – 53.97

Fixed Carbon 18.4 – 48.4

Ash Content (%) 5.6 – 19.8

Coal Density (g/cc) 1.3 – 1.5

CO2 Content (measured from canister, mol %)


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b. Muaraenim Coalbed Reservoir Properties

Coal sorption isotherm is used to predict the

maximum volume of gas that will be released from

a coal seam as the reservoir pressure declines

during long-term production (Mavor et al. 1990).It reects the relationship between gas storage

capacity of a given coal sample and its pressure.

When compared with measured gas contents and

reservoir pressure, the sorption isotherm data also

provides a guide as to the relative gas saturation

of the coal and the bottom-hole pressure required

to initiate signicant methane desorption (critical

desorption pressure).

The values of isotherm parameters are calculated

both in terms of absolute and gauge pressures.

The sorption isotherms of CH4 for the Muaraenimcoalbeds from the Rambutan Field were obtained

from the selected Seam 3 and Seam 5 only.

These isotherms data obtained from all the ve

CBM wells. The absolute adsorption results are

presented in Table 2 and Figure 4.

From the Figure 4, it is expected that the sorp-

tive capacity of coal is increased with increasing

depth, but it seems to decrease with increasing

depth. Although it might be noted that there is not

much of variability in terms of coal rank for these

coals, whether it is an effect of the maceral com-

position or the coal quality, can still be debated.

Also looking into the gas content measurements

and the sorptive capacity of these coals (Table 2),there is a clear bit of disconnect in understanding

the reason behind this effect. The maceral com-

position analysis of the coals from the fth CBM

wells show that the vitrinite content of the shallow

coals ranges from 74.1 to 82.2% and that of the

deepest coal seam is on an average 52.2%. Thus,

a comparison of the gas adsorption capacity with

the maceral composition shows that these prop-

erties have an important effect on the sorptive

capacity. The maceral composition also inuences

the adsorption characteristics of coal, which are

closely related to micropore development. Clark-son and Bustin (1996) found a general increase

in the total number of micropore with increasing

vitrinite content. Sosrowidjojo and Sagha (2009)

on the other hand has solely accounted for these

differences to varying ash and moisture content

of the coal samples from the CBM-1 well. One

possible explanation in this regard is that the ac-

cessible micropore volume in moist coals is much

less than in dry coals, due to either a reduction

Figure 4. Representative methane adsorption isotherms data of respective Seam 2 (green) Seam 3 (red) and

Seam 5 (black) for the CBM-1 to CBM-5 wells, respectively.


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of pore size due to water adsorption or to swell-

ing of the coals. More data points are needed to

substantiate either of the proposed reasons for the

anomaly in the sorption capacity with increasing

depth. Since little is known of Indonesia’s CBM

resources, it crucial that the coal reservoir is as-sessed properly and that means using different

techniques than what is normally used in conven-

tional plays (Moore, 2010).

Comparing the gas storage capacity (sorption

isotherm) with the actual gas yields, will give an

estimation of the gas saturation of the coal seams.

Measured gas content data from the CBM wells

have been reported in Table 2. The measured

Langmuir isotherms were conducted at reservoir

temperatures (49°-61°C). The degree of under-

saturation for each seam has been shown inFigure 6. Except for one coalbed sample from

Seam 3, all other seams have high degree of

under-saturation. Although the fth CBM wells

were drilled on the Rambutan structural high,

if the under-saturation is representative, then

there can be some serious thoughts behind the

economic viability of a CBM project in this region.

It was evident that the rig used to drill these

wells did not have wireline coring facility and the

retrieval of the coal cores once drilled, was time

intensive. Time required to retrieve these cores

was in excess of 11 hours in some cases. Thus it

is understandable that a considerable amount ofthe gas was lost in the process of retrieving the

cores and thus, the gas content measurements,

therefore, are not very representative of the actual

in-situ saturation.

CONCLUSIONS

The major findings of this evaluation for the

Rambutan pilot samples can be summarized as

follows:

- the rank of all the coalbed samples rangesbetween lignite and sub-bituminous. The

maceral composition of them is primarily

huminite, making its storage capacity and

hydrocarbon generation potential favorable

for CBM development;

- high degree of under-saturation indicative

from gas content results was not conclusive

and is too early to say whether the under-

saturation is representative. Due to high of

uncertainty on gas saturation as well as frac-

ture permeability, proper corehole campaigns

are carried out to determine these parameters

through core analysis;

- it is also recommended to further integra-

tion of properties measured in the corehole

campaign with focused on seismic andwells interpretation to allow a reduction of

uncertainty in resource estimation and help

determine potential economic viability of CBM

prospect(s) in the area.

ACKNOWLEDGMENTS

This paper is fully funded by the Government of

Indonesia. The author is indebted to the Man-

agement of Lemigas for permitting to publish

this paper and also is grateful to the Editors ofIndonesian Mining Journal, whose insightful

comments helped to improve greatly the quality

of this manuscript.

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Received : 18 February 2013, rst revision : 12 May 2013, second revision : 11 June 2013, accepted : June 2013


STUDY OF COMPRESSIONAL AND SHEAR WAVE

VELOCITY TESTS IN THE LABORATORY AND FIELD

APPLIED TO SEDIMENTARY ROCKS OF RANTAU

NANGKA DISTRICT, SOUTH KALIMANTAN

STUDI PENGUKURAN KECEPATAN RAMBAT GELOMBANG DAN

GESER DI LABORATORIUM DAN LAPANGAN PADA BATUAN

SEDIMEN DAERAH RANTAU NANGKA, KALIMANTAN SELATAN

ZULFAHMI

R & D Centre for Mineral and Coal Technology

Jalan Jenderal Sudirman 623 Bandung 40211

Ph. 022 - 6030483, Fax. 022 - 6003373

e-mail: [email protected]

ABSTRACT

Compressional (Vp) and shear (Vs) wave velocities within rocks are often investigated by testing in the laboratory

because it is easier and cheaper. However, it is more condence with investigation results derived from the eld

due to the actual situation and conditions. In the laboratory, the wave velocities are commonly measured usingultrasonic pulse velocities test. But in the eld, the velocities are commonly measured directly by several methods

such as cross-hole seismic, down-hole seismic, suspension logging, seismic reection, seismic refraction and

spectral analysis of the surface wave. In the present study of eld insitu tests, it has used down-hole seismic

method. The eld insitu test is more expensive than the laboratory test. Hence, this study would evaluate andcompare data derived from both of laboratory and eld insitu tests. Based on the measurements correlation,

it is found that regression equation for each parameter are for compressional wave veloci-

ties, for shear wave velocities, for shear modulus, for

modulus of elasticity, for bulk modulus and for

Lame constants. This equation can be applied to correct the laboratory test data in order to get close resultsbetween the laboratory and eld insitu tests.

Keywords : compressional wave, shear wave, velocities, down-hole seismic test, ultrasonic pulse velocity test

SARI

Kecepatan rambat gelombang kompresi dan geser pada batuan sering diselidiki melalui pengujian di laborato-

rium karena lebih mudah dan murah, tetapi umumnya lebih dipercaya mempelajari sifat batuan secara langsung

di lapangan karena dilakukan pada situasi dan kondisi yang sebenarnya. Di laboratorium, kecepatan rambat

gelombang biasanya diukur menggunakan kecepatan denyut ultrasonik. Sedangkan di lapangan, kecepatan

rambat tersebut biasanya diukur dengan beberapa metode seperti uji lintas lubang seismik, uji seismik lubang bor,

suspensi logging, seismik reeksi, seismik refraksi, dan analisis spektral gelombang permukaan. Pada penelitian

ini, pengukuran secara insitu di lapangan menggunakan uji sesimik lobang bor. Pengukuran secara insitu di

lapangan lebih mahal dibandingkan dengan pengujian di laboratorium. Pada penelitian ini telah dilakukan evaluasi

dan perbandingan data yang berasal dari laboratorium dan uji lapangan. Berdasarkan korelasi dari pengukuran

tersebut telah ditemukan persamaan regresi untuk masing-masing parameter, yaitu untuk cepat

rambat gelombang kompresi, untuk cepat rambat gelombang geser, untuk

modulus geser, untuk modulus elastisitas, untuk modulus


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Study of Compressional and Shear Wave Velocity Test in the Laboratory ... Zulfahmi

INTRODUCTION

Measurement of wave velocity as a dynamic prop-

erty has often been used to provide information

about rock structural properties. Magnitudes of

dynamic constants are sensitive to mineralogical

assemblages and are affected by shape, distribu-

tion and preferred crystallographic orientation of

the components. Moreover, they are affected to

an important degree by the presence of size and

orientation of defects such as pores and cracks,in such a way that also depends on the presence

of uids.

In the laboratory, wave velocity is commonly mea-

sured using a method that based on the resonant

modes of the specimens or the propagation of

elastic waves in the specimens. International

standard test to determine P and S-waves in the

laboratory using ultrasonic pulse velocity (UPV)

is found in the ASTM Standard Test Method D

2845-05. In Indonesia, the admitted standard

test is the SNI 06-2485-1991. Both standard tests

procedures are almost the same. Cylindrical rock

sample is prepared by cutting and lapping the

ends, then the length is measured. An ultrasonic

digital indicator that consists of pulse generator

unit, transmitter and receiver transducers are

used for sonic pulse velocity measurement. The

transmitter and receiver are positioned at the ends

of specimen and the pulse wave travel time is

measured. The velocity is calculated from divid-

ing the length of rock sample by wave travel time.

Both P and S-wave velocities can be measured.

In the eld, wave velocities are commonly mea-sured by several methods such as cross-hole

seismic, down-hole seismic (DHS), suspension

logging, seismic reection, seismic refraction and

spectral analysis of surface waves (SASW). In this

study, the measurement of wave velocities used

DHS test. The test requires only one borehole to

provide shear and compressional velocity wave

proles. The method uses a hammer source at

the surface to impact a wood plank and generate

shear and compressional waves. This is typically

accomplished by coupling a plank to the ground

near the borehole and then impacting the plank in

the vertical and horizontal directions. The energy

from these impacts is then received by a pair of

matching three component geophone receiv-

ers, which have been lowered down hole and

are spaced 1.5 to 3 m apart. The Standard Test

Methods for DHST is ASTM D7400 – 08.

The P and S-wave velocities are directly related

to the important geotechnical elastic constants

of poisson’s ratio, shear modulus, bulk modulus

and Young’s modulus (modulus of elasticity). Thestudy of P and S-wave propagation in the rocks

has been made to nd the poisson’s ratio, shear

and elasticity modulus, fractures and disconti-

nuities in the rock mass (Tamunobereton et al.,

2010). These parameters are used in analyzing

rock behavior under both static and dynamic

loads, where the elastic constants are input vari-

ables to the models that dene the different states

of deformations such as elastic, elasto-plastic and

failure (Rao, 2003; Zhang, 2005). The current

basic challenges do not just technical capability

but also economic feasibility of any project (Singh

and Shrivastva, 2009). P and S-wave velocities

have proved to be immensely useful in gathering

geotechnical information about the area.

The fundamental question refers to whether the

laboratory tests are precise and accurate enough

to understand the wave velocities or it should use

costly measurements in the eld to get data ac-

curately. In determining the differences from the

measurement results of wave velocities obtained

in the eld and laboratory, thus the present study

would compared both laboratory and eld mea-

surements data. Therefore, the purpose of thisstudy is to search correlation of the wave veloci-

ties (Vp and Vs) and its derivatives between eld

insitu and laboratory tests.

METHODOLOGY

The eld study area was located in Rantau Nang-

ka, Sungai Pinang District, Banjar County, South

Kalimantan. Data retrieved from geotechnical core

drilling at a depth of between 20-40 meters were

done within claystone layer. The main geologi-

ruah dan untuk konstanta Lame. Persamaan ini dapat diaplikasikan untuk meng -

koreksi hasil uji laboratorium agar dapat lebih mendekati hasil uji insitu.

Kata kunci : gelombang kompresi, gelombang geser, kecepatan, uji seismik lubang bor, uji kecepatan pulsa

ultrasonik


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84


cal formation of the area is shown in Figure 1.

The area consists of claystone, sandstone, coal,

limestone and marl overlaying semi-consolidated

pleistocenic sediments with cemented sand

(Sikumbang and Heriyanto, 1994). Field insitu

tests (DHS tests) used ve boreholes and labo-ratory tests (UPV tests) employed 50 drill cores

as shown in Figure 1. Each borehole had been

applied four times for seismic down hole tests

at 20, 24, 28 and 32 meters respectively. The

borehole was 4.5 inches in diameter with PVC

cased to ensure good transmission of the wave

energy. The hole must be cased and grouted to

prevent rock caving during the tests. The source

and receiver were placed at the depth of 20 – 40

meters within the claystone layers.

the P-wave velocity (Vp) and S-wave velocity

(Vs) can be expressed by the following equation

of Biot-Gassmann:

........................................... (eq. 1)

................................................... (eq. 2)

Where K is the bulk modulus of the rock, G is

the shear modulus of the rock and ρ is the bulk

density of rock. The equations (1) and (2) apply

to the elastic condition.

Figure 1. Location of DHS tests and geotechnical sampling

The main concept of this study is to search and

compare the velocities of wave propagation be-

tween eld insitu and laboratory tests. The former

was performed in the eld and the later was

performed at the Laboratory of Rock Mechanics,

R & D Center for Mineral and Coal Technology

(tek MIRA). Cheng and Leong, 2011 stated that

Field Insitu Tests

The DHS test is an accurate measurement

method to determine the seismic wave velocities

of the rocks. The P and S-wave velocities are di-

rectly related to the important geotechnical elastic

constants of poisson’s ratio, shear modulus, bulk


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85


modulus, and Young’s modulus (Soupios, et.al.,

2005). A fundamental assumption inherent in the

test methods is that a laterally homogeneous

medium is being characterized. In a laterally

homogeneous medium the source wave train

trajectories adhere to Snell’s law of refraction(Cheng and Leong, 2011).

Another assumption inherent in the test methods

is that the stratigraphic medium to be character-

ized can have transverse isotropy. Transverse

isotropy is a particularly simple form of anisotropy

because velocities only vary with vertical inci-

dence angle and do not with azimuth. By placing

and actuating the seismic source at offsets rotated

90° in plain view, it may be possible to evaluate

the transverse anisotropy of the medium (Vilhelm,

et.al., 2008).

The test method was to determine interval veloci-

ties from arrival times and relative arrival times of

compression either vertically or horizontally as

well as polarized shear seismic waves generated

near the surface and travel down to an array of

vertically installed seismic sensors. A preferred

method was intended to obtain data to be used

in critical projects by which the required highest

quality data were included.

Laboratory Tests

In this study, samples were tested by ultrasonic

pulse velocity (UPV). The samples were selected

at a regular interval throughout the core drill. The

specimens for testing were prepared by cutting theends of the core using a rock saw to produce at

end surfaces that satises to the ASTM standard.

After cutting process, the samples were preserved

in a vacuum sealed polyethylene bag or plastic

freezer bag to maintain insitu moisture conditions.

The UPV measurements were completed using a

low-frequency portable ultrasonic nondestructive

digital indicating tester (PUNDIT) equipped with

two 1-MHz transducers to determine the transit

time of a sound wave through the length of the

rock core.

For testing purposes, a coupling medium was

used between transducers and the rock specimen

in term of minimizing signal loss from the trans-

ducers through to the rock. The system equipped

by Fujitsu Notebook was used to record sample

dimensions as well as P and S-wave transit times

and a software was is applied to calculate the ul-

trasonic wave velocities and dynamic properties.

The P and S-wave velocities were determined

by dividing sample length over ultrasonic wave

Figure 2. Schematic of DHS test


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86


travel time throughout the sample. The velocity

was then computed using the following formula

(Chary, et al., 2006):

..................................................... (eq. 3)

.................................................... (eq. 4)

Shear modulus (G), dynamic young modulus (E),

Lame constant (l), bulk modulus (K) and dynamic

poisson ratio (u) can be represented as follows

(Rai, et al., 2011) :

..................................................... (eq. 5)

.............................................. (eq. 6)

........................................... (eq. 7)

................................... (eq. 8)

........................................ (eq. 9)

Vp is compressional wave velocity, Ls is length

of the sample, l is density, Tp is travel time ofcompressional wave and Ts is travel time of shear

wave. Results of the study by Knackstedt et al.,

(2005) claimed that the computed values of bulk

and shear modulus for the grain overlap and pore-

lining models are similar. It indicates only a small

dependence of the models on microstructure or

the distribution of the second mineral phase.

Figure 3. Schematic equipments of UPV test


This study was conducted to determine scale

effect in the measurement of the wave veloc-

ity. The scale effect has been studied by some

researchers to know geomechanics behaviors ofrocks. Thuro, et al (2001) divided the scale effect

into two components that was represented by the

shape scale, which take account the variation of

the ratio D/L (diameter/length) and the size scale

in which this ratio is constant and the size of the

specimen growth. Hence, values obtained from

the tests show that shape scale have signicant

effect in to the results, but no effect for size (Déthié

et al, 2013). Scale effect also appears in some

tests such as dynamic behaviors of rock and can

be compared by statistical approach. Compara-

tive study of compressional and shear wave ve-locities between eld insitu tests and laboratory

tests involved four separated surveys, that is at

20, 24, 28 and 32 meters depth. P and S-wave

measurements for the ve geotechnic boreholes

were made in the range of 20 - 40 meters depths.

Result of DHT is presented in Table 1 while re-

sult of laboratory test for drill core samples and

result of UPV test in the laboratory are presented

respectively in Table 2 and 3.

A correlation between compressional wave veloci-

ties from DHS (eld insitu tests) and UPV (labora-

tory tests) is shown in Figure 4. High regressioncoefcient reveals a strong correlation between

the two velocities test that enables estimating one

velocity to another. The following equation denes

this relationship:

(eq. 10)


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Table 1. Result of DHS test for compressional and shear wave velocities

NoTest I (20 m) Test II (24 m) Test III (28 m) Test IV (32 m)

Vp Vs Vp Vs Vp Vs Vp Vs

G-1 2030 1217 1970 1183 2010 863.0 2222 1218

G-2 2000 1114 2020 1255 1860 777.8 1950 964

G-3 2000 1116 2030 1255 2100 950.5 2000 1017

G-4 2061 1263 1980 1185 1990 841.4 2010 1034

G-5 2020 1176 1990 1206 2040 890.2 1886 920

G-6 2030 1178 1960 1182 2010 847.6 2010 1039

G-7 2072 1343 1970 1184 2209 1167.2 2030 1047

G-8 2051 1228 1999 1222 2051 910.5 1990 1008

G-9 2061 1236 1990 1213 2030 872.5 2051 1053

G-10 2061 1239 1980 1185 2162 1062.6 2061 1057

G-11 2350 1488 2000 1236 2050 896.2 2061 1061

G-12 2061 1268 2010 1243 2051 910.5 2094 1061

G-13 2061 1325 2100 1280 2116 978.3 2100 1070

G-14 2100 1351 1990 1219 2100 925.5 2105 1071

G-15 2200 1402 2050 1269 1793 768.4 1851 898

G-16 2300 1437 1999 1224 2105 950.9 2116 1077

G-17 2400 1531 2150 1338 1877 811.3 2127 1106

G-18 1999 1072 1960 1135 2127 983.5 2150 1158

G-19 2000 1141 1970 1184 2150 1016.3 2173 1169

G-20 2100 1356 1999 1226 2162 1063.9 1793 886

Table 2. Density of Rantau Nangka claystones, tested from drill core samples

Spec.

No.

Average

WeightDen-

sity Spec.

No.

Average

WeightDen-

sity Spec.

No.

Average

WeightDen-

sityDia-

me-

ter

Length

Dia-

me-

ter

Length

Dia-

me-

ter

Length

cm cm gr Gr/

cm3cm cm gr

Gr/

cm3cm cm gr

Gr/

cm3

L-101 4.51 10.48 358.10 2.139 L-201 4.38 8.90 286.42 2.136 L-301 5.00 11.04 434.02 2.002

L-102 4.60 11.77 410.85 2.100 L-202 4.38 11.07 362.68 2.174 L-302 5.12 10.30 433.62 2.046

L-103 5.22 10.62 373.42 2.116 L-203 4.47 10.42 320.74 1.961 L-303 5.22 11.04 447.68 1.970

L-104 4.51 10.22 362.95 2.223 L-204 4.47 9.51 320.62 2.148 L-304 6.10 13.61 761.68 1.915

L-105 4.50 9.55 310.38 2.044 L-205 4.45 11.02 312.72 1.825 L-305 5.22 12.18 598.38 1.681

L-106 5.22 10.74 348.55 2.041 L-206 4.45 10.69 320.70 1.929 L-306 5.40 11.35 499.78 1.923

L-107 4.47 10.54 329.35 1.991 L-207 5.10 11.10 474.05 2.091 L-307 5.22 10.33 407.92 1.724

L-108 4.44 10.50 367.70 2.262 L-208 5.10 10.79 456.22 2.072 L-308 4.94 10.91 427.10 2.042

L-109 4.44 10.19 353.05 2.238 L-209 5.10 11.48 481.22 2.052 L-309 4.94 11.13 445.10 2.087

L-110 4.51 10.99 377.74 2.152 L-210 5.10 9.77 400.58 2.007 L-310 5.22 10.82 482.90 2.085

L-111 4.51 11.29 396.08 2.196 L-211 5.66 11.11 570.98 2.043 L-311 5.22 11.62 504.50 2.029

L-112 4.46 11.00 385.70 2.244 L-212 5.66 11.52 586.05 2.022 L-312 4.50 9.55 310.38 2.044

L-113 4.46 10.59 378.30 2.287 L-213 5.17 11.20 494.52 2.103 L-313 5.22 10.74 348.55 2.041

L-114 4.46 10.56 358.25 2.172 L-214 5.17 11.42 502.05 2.094 L-314 4.47 10.54 329.35 1.991


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VpL is compressional wave velocity from labora-

tory tests and VpF is compressional wave velocity

from eld insitu tests.

A correlation between shear wave from DHS

(eld insitu tests) and UPV test (laboratory tests)

is established showing a power relationship as

shown in Figure 5. The high regression coef-

cient reveals a strong correlation between the

two velocities tests which enables estimation of

one velocity having another one. The following

equation denes this relationship:

.................................(eq. 11)

Table 2. Density of Rantau Nangka claystones, tested from drill core samples

Spec.

No.

Average

WeightDen-

sity Spec.

No.

Average

WeightDen-

sity Spec.

No.

Average

WeightDen-

sityDia-

me-

ter

Length

Dia-

me-

ter

Length

Dia-

me-

ter

Length

cm cm gr Gr/

cm3cm cm gr

Gr/

cm3cm cm gr

Gr/

cm3

L-115 4.47 11.63 426.82 2.299 L-215 5.02 11.02 445.82 2.044 L-315 4.44 10.50 367.70 2.262

L-116 4.47 11.44 426.08 2.138 L-216 5.10 11.15 466.02 2.044 L-316 4.44 10.19 353.05 2.238

L-117 4.48 10.20 366.15 2.277 L-217 5.10 10.26 428.56 2.045 L-317 4.51 10.99 377.74 2.152

L-118 4.48 9.68 320.00 2.097 L-218 4.97 10.05 428.02 2.093 L-318 4.51 11.29 396.08 2.196

L-119 4.43 10.10 331.20 2.126 L-219 4.97 10.72 441.08 2.121 L-319 4.98 11.48 475.22 2.052

L-120 4.43 10.95 362.20 2.146 L-220 5.50 11.16 494.92 1.867 L-320 4.98 9.77 298.56 2.007

Table 3. Result of UPV tests for compressional and shear wave velocities

Spec.

No

Vp Vs Spec. Vp Vs Spec. Vp Vs

m/sec No m/sec No m/sec

L-101 2014.99 755.19 L-201 1998.54 630.32 L-301 1085.58 243.21

L-102 1857.05 663.64 L-202 426.62 202.53 L-302 1217.58 320.18

L-103 962.37 467.61 L-203 1862.71 434.53 L-303 1621.43 348.99

L-104 990.60 482.81 L-204 1046.14 320.18 L-304 1634.06 366.12

L-105 1073.68 482.91 L-205 1127.64 350.12 L-305 1696.54 370.47

L-106 1085.58 489.44 L-206 1879.19 448.19 L-306 3172.43 590.76

L-107 1093.75 489.59 L-107 1416.76 395.09 L-307 1798.57 412.63

L-108 2210.20 823.02 L-208 1968.17 561.10 L-308 1893.99 420.73

L-109 1144.94 499.02 L-209 1696.54 396.91 L-309 3280.42 655.62

L-110 1217.58 507.18 L-210 1763.44 425.48 L-310 1912.47 426.24

L-111 1812.29 611.11 L-211 1802.34 426.24 L-311 2730.16 428.81

L-112 1224.30 518.89 L-212 1843.41 432.16 L-312 2804.72 431.89

L-113 1344.71 519.84 L-213 1873.36 444.35 L-313 2898.44 456.99

L-114 1714.33 345.38 L-214 1357.02 371.73 L-314 955.02 232.96

L-115 884.86 527.81 L-215 1756.46 420.11 L-315 2983.78 477.21

L-116 1798.57 545.17 L-216 1912.47 477.21 L-316 3027.55 489.59

L-117 884.86 371.33 L-217 1917.19 506.74 L-317 1344.74 339.03

L-118 1798.57 590.76 L-218 1929.46 531.86 L-318 3050.89 495.38

L-119 866.61 352.18 L-219 376.66 183.21 L-319 3070.96 507.18

L-120 1835.88 655.62 L-220 1969.13 586.07 L-320 1763.44 371.11


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Figure 4. Correlation between Vp from seismic DHS and Vp from UPV tests

Figure 5. Correlation between Vs from DHS and Vs from UPV tests

VsL is shear wave velocity from laboratory test and

VsF is shear wave velocity from eld insitu test.

According to equation 1, 2, 5, 7 and 8, density of

rock affects wave velocities (Vp and Vs), shear

modulus (G), Lame constants and bulk modulus.

Approximately, 60 tests results are used to deter-

mine claystone density, it is taken from drill core

at 20-40 meters in depth. Based on equation 5,

shear modulus from eld insitu tests (GF) and from

laboratory tests (GL) is shown in Figure 6.

From the correlation of GF and GL can be found

the equation as follow :

GL = 0.2739GF - 287185 ........................ (eq. 12)


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90


Using the same method to compare eld insitu

and laboratory tests for several parameters, i.e,

the Elasticity Modulus (EF and EL), Bulk Modulus

(KF and KL) and Lame Constants (lF and lL) are

shown on Figure 7, 8 and 9.

Based on its correlations, it can be obtained the

equation as follows:

EL = 0.3764EF - 1E + 06 ........................ (eq. 13)

....... (eq. 14)

........ (eq. 15)

Figure 6. Correlation between shear modulus GF and GL

Figure 7. Correlation between elasticity modulus EF and EL


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91


CONCLUSION

Compressional (Vp) and shear (Ps) wave veloci-

ties are important dynamic properties of rocks that

can be measured both at eld insitu and labora-

tory tests. The scale effect is signicant to show

whether the values decrease or increase that

are obtained from the laboratory and eld insitu

tests. Decreasing or increasing of those values is

a consequence of scale effect, which is caused

by the heterogeneity of the materials. Vp and Vs

determinations from eld insitu tests are relatively

more difcult and costly than that of laboratory

tests. The high regression coefcient (R square

more then 0.7) reveals a good correlation, which

means that the high cost of eld insitu measure-

ments can be replaced by lower cost measure-

ments in the laboratory. Direct measurement in the

eld insitu are considerably more accurate than

measurement in the laboratory. The regression

equation with high coefcient for each parameter

that have been found in this study can be used as

a corrected data of the laboratory tests results.

Figure 8 Correlation between Bulk Modulus KF and KL

Figure 9. Correlation between Lame constant lF and lL


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ACKNOWLEDGMENT

The author would like to thank Mr. Adji Subardja

and Mr. Deden Agus Ahmid - staffs of Rock and

Soil Mechanics - R&D Centre for Mineral and Coal

Technology for their help during the research,especially by providing and testing claystone

samples from Rantau Nangka district.

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Reduction of Goethitic Iron Ore Using Thermogravimetric Method, Adji Kawigraha et al.

Received : 14 October 2011, rst revision : 15 November 2012, second revision : 26 February 2013, accepted : June 2013


REDUCTION OF GOETHITIC IRON ORE USING

THERMOGRAVIMETRIC METHOD

REDUKSI BIJIH BESI GUTIT DENGAN METODE

TERMOGRAVIMETRI

ADJI KAWIGRAHA1,2, SRI HARJANTO1, JOHNY W. SOEDARSONO1 and PRAMUSANTO3

1 Department of Metallurgy and Material, Faculty of Engineering Universitas Indonesia

Jalan Salemba Raya No. 4, Jakarta

Ph. 021 330355, Fax. 021 3303432 Center of Mineral Ressources Technology

Indonesian Agency for the Assessment and Aplication of Technology

Jalan MH. Thamrin No. 8, Jakarta 10340

Ph. 021 3169091 - 3169092, Fax. 021 31690673 Department of Mining - Faculty of Engineering

Bandung Islamic University

Jalan Tamansari No. 1 Bandung

e-mail : [email protected]

ABSTRACT

Compared to main iron ore minerals, either hematite or magnetite, Indonesian goethite is relatively abundant.

However, this is not common to be used as feed material in iron making industries. Limitation in Indonesian high

quality iron ore resources, the iron making industries have to seek another iron source such as the low grade iron

ore of goethitic ore. Evaluation using thermogravimetric method was employed for analyzing behavior of goethitic

composite pellet during reduction. The data show that reduction of goethitic iron ore is started by transforming

goethite to hematite and then followed by iron reduction. The reduction was started by Fe3O4 formation at 442

°C and Fe at 910 °C. At those temperatures the composite pellet lost its weight. Identifying the FeO is hardly

difcult due to the short range of phase existence.

Keywords: goethitic iron ore, iron reduction, thermogravimetric analysis.

SARI

Laterit merupakan cadangan terbesar bijih besi yang ada di Indonesia. Jenis ini umumnya bukan merupakan

bahan baku utama dalam industri pembuatan besi namun karena keterbatasan dan semakin berkurangnya bijih

besi primer, laterit diupayakan menggantikan bijih besi tersebut sebagai bahan baku terutama melalui pem-bentukan pelet komposit. Perilaku reduksi pelet komposit yang terdiri atas laterit dan batubara dikarakterisasi

menggunakan metode termogravimetrik. Hasil menunjukkan bahwa proses reduksi pelet komposit didahului

oleh proses awahidroksilasi yang mengubah gutit menjadi hematit, diikuti oleh reduksi hematit menjadi fasa besi

lain. Reduksi dimulai pada 442 °C dengan pembentukan Fe3O4 dan Fe pada 910 °C. Proses reduksi pada pelet

komposit diikuti dengan kehilangan berat. Identikasi pembentukan FeO sulit dilakukan karena keberadaan fasaterjadi pada selang waktu yang pendek.

Kata kunci: bijih besi gutit, reduksi besi, analisis termogravimetri


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INTRODUCTION

Indonesia retains a lot of iron ore resources. How-

ever, such resources come mainly from lateritic

ore. This ore consists of goethite mineral. Based

on iron content, lateritic ore is classied as a lowgrade iron ore. This fact is contradictive with the

primary iron ores, either hematite or magnetite,

that have high grade of iron and commonly ap-

plied in iron making industries. As a result, the

lateritic ores require different process when used

for iron making.

Several researchers have studied the reduction of

lateritic iron ore (Murakami et al., 2009; Kawigraha

et al., 2013). Murakami et al. (2009) states that at

xed temperature the reduction degree of goethit-

ic iron ore is higher than that of primary iron ore.It means that the energy for goethitic reduction

is lower. Goethitic material will lose its hydroxide

components during heating (Strezov et al., 2010;

Gialanella et al., 2010)and weight in three stages

(Strezov et al., 2010) Dehydration and dehydroxy-

lation temperatures occur between 100 to 150 °C

and 260 to 425 °C respectively while decomposi-

tion temperature for clay is between 540 to 605

°C. The three stages consecutively correspond to

the loss of free water, hydroxide component and

hydroxide available in clay. Reactions involve in

second and third stages are :

2 FeOOH → Fe2O3 + H2O. (1)

Al2Si2O5(OH)4 → Al2O3 + SiO2 + 4H2O (2)

The change of Fe2O3 to Fe3O4 starts after dehy-

droxylation (Murakami et al., 2009; Kawigraha et

al., 2013). Consequently, the H2O gas is formed

at early temperature (Jozwiak et al., 2007) and

possibly there is H2 that will be generated from

H2O dissociation. The two gases may inuence

reduction process at early stage. The reaction

heats of dehydroxylation and clay decomposition

range from 38 to 230 MJ/m3 and from 2.4 to 28MJ/m3 respectively (Strezov et al., 2010).

The objective of this research is to analyze the

reduction process of composite pellet contain-

ing goethitic iron ore and coal. It also discuss as

characterization of composite pellet using ther-

mogravimetric method to determine temperature

of iron phases formation.

METHODOLOGY

Laterite ore used in this experiment is derived from

South Kalimantan that consists of goethitic iron

ore. The material shows a porous iron character

and easy to crush using a crusher and a milling

instrument. A 140-mesh powder is used for the

experiment while its reductant is subbituminous

coal that comprises 41.53 % xed carbon and

38.23 % volatile matter.

The ore is then analyzed using Rietveld method to

quantify all of major Fe phases such as FeOOH,Fe2O3 and Fe3O4. The quantication using Riet-

veld method is based on XRD difractogram.

Instrument

The main apparatus in this experiment are simul-

taneous thermal analyzer (STA) Perkin Elmer,

tube furnace which has ability to heat the compos-

ite pellet from 25 to 1000 °C, Vario gas analyzer

and XRD. The heating rate and temperature of

tube furnace can be controlled after introducing

the parameters before experiment.


Quantication of lateritic iron ore shows that the

ore consist of 70.25 % FeOOH 1.49 % Fe2O3,

1.47 % Fe3O4, and 6.78 % gangue. The powder is

then analyzed using Simultaneous Thermal Analy-

sis to elaborate its thermal properties. Chemical

analysis of the ore is shown in Table 1.

Iron ore is mixed with coal in order to analyze

their heat content by thermal analyzer. Iron oreto coal ratio in the mixture is xed to 1:3 for Fe

to C ratio. The mixture is then pelletized around

12 mm to 15 mm in diameter. A chopped pellet is

introduced into Perkin Elmer STA equipment to

observe its thermal properties during reduction

Table 1. Chemical composition of lateritic iron ore used in this experiment.

Component Fetotal FeO Fe2O3 TiO2 SiO2 Al2O3 CaO MgO Stotal SO3 Cr 2O3 Ni LOI

% 53.62 - 79.3 0.84 2.26 4.03 0.04 0.08 0.14 0.84 2.39 0.09 9.58


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release (Strezov et al., 2010). The endothermic

peak occurs at 301.9 °C. In the second region

which ranges between 370 and 640 °C, there is

only low endothermic peak and after 640 °C the

heat curve has another endothermic peak near

900 °C.

Thermogravimetic characterization of coal is rep-

resented in Figure 2. The curve can be divided

in to three regions, the rst one corresponds to

a free water release and it covers from 25 to 195

°C. The second region takes place between 195

to 350 °C and the curve is relatively stable. In the

third region the weight curve decrease quickly

which means that weight loss is erraticaly after

350 °C. Moreover the coal lost of weight continu-

ously until high temperature. During heating, the

heat curve shows that there are only four peaksof endothermic at around 100 °C, 550 °C, 750 °C

and 900 °C. The heat curve also shows an exo-

thermic peak at around 500 °C. The heat curve

diminishes quickly after 350 °C to a minimum

endothermic peak.

Differential Thermogravimetric (DTG) curve of go-

ethitic iron ore can be seen in Figure 3. The curve,

derived from thermogravimetric curve, shows

process. The experiment is accomplished from 25

to 1000 °C with the heating and nitrogen ow rates

of 10 °C/minute and 20 ml/minute respectively.

The obtained thermogravimetric curve is then

analyzed using exel program to obtain Differential

Thermogravimetric Curve.

Some pellets are also reduced in a tube furnace

using temperature of 350 , 460, 680, and 980 °C.

Furnace heating rate is 10 °C/minute until reaches

the desired temperature and then is hold for 20

minutes. The nitrogen is owed during reduction

process to carry the produced gasses during pel-

let heating. The gases are identied using gas

analyzer. The reduced pellet is then analyzed by

X-Ray Diffraction to examine its phases.

Thermogravimetric and heat curves of iron ore isshown in Figure 1. The iron loses more than 14

% of total weight from 25 to 1000 °C. It releases

gases at 301.9 °C performing ore lost around 7

% of its weight.

During heating, there are three endothermic

peaks while the heat curve itself can be divided

into three regions. The rst region is between

160 and 370 °C which Corresponds to hydroxide

Figure 1. Thermogravimetric and heat curves of goethitic iron ore.


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Figure 2. Thermogravimetric and heat curves of coal

Figure 3. Thermogravimetric and DTG curve of lateritic ore.


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that at least there are four peaks. Two peaks can

be identied easily whereas the third and fourth

peaks are low minimum peaks. The rst two peaks

correspond to dehydration and dehydroxylation

whereas the second two peaks correspond to clay

decomposition. Clay decomposition temperatureis similar to the data reported by other researcher

(Strezov et al., 2010). At 301.9 °C, the ore has a

signicant loss of weight. The loss component is

the OH available within goethite.

DTG curve of coal is shown in Figure 4. The

curve is characterized by two signicant peaks.

The rst one corresponds to hydration of free

water whereas the second one corresponds to

dissociation of carbon. The rst is at 78.8 °C and

the second is at 439.9 °C.

Thermogravimetric curve of composite goethitic

iron ore-coal is shown in Figure 5. It shows that

weight loss occurs continuously from low to high

temperatures. Signicant slope occurs at around

285 °C shows that the composite pellet loses

weight signicantly in a short time. It indicates

that the dehydroxylation of lateritic iron ore oc-

curred. There are at least 3 other slopes that

indicate the loss of composite weight. The two

peaks after 285 °C-peak can easily be identied

at 442 and 625 °C. However, the last peak can-

not easily be determined due to the limitation of

STA performance. The 825 °C-peak is not really

a peak because the DTG decreases continuously

from 700 to 1000 °C.

DTG curve analysis shows that at least there are

ve peaks. All peaks correspond to slope at ther-

mogravimetric curve. The rst and second slope

corresponds to dehydration and dehydroxylation

process. The third, fourth and fth peaks of DTG

have low loss of weight compared to the rst and

second slope. After the fourth peak the DTG curve

has a tendency to decrease.

Measurement of gases, released by composite

pellet, is shown in Figure 6. Heating the pelletwas conducted at 1 atmosphere. The identied

gases are CO, CO2 and CH4 that are responsible

for iron reduction. The Figure 6 shows that CO

has two peaks, small and high ones. They are at

630 and 920 °C. However, the CO starts to be

detected at 300 °C. CO2 has two peaks, namely

a low one at 450 °C and a high peak at 880 °C.

The ratio of two gases reach maximum before

decreases indicated the gasication of coal in

Figure 4. Thermogravimetric and DTG curve of coal.


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Figure 5. Thermogravimetric and DTG curves of composite pellet.

Figure 6. Released gas occurs during heating the composite pellet.


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the pellet completed. There are only one peak

of CH4 namely at 470 °C. The gas is released at

early temperature.

CO curve shows that iron reduction starts at above

442 °C. Around such a temperature, compositepellet loses its carbon and transforms to CH4,

CO and CO2. Reduction process may increase

with the increase of CO formation. After 700 °C,

the quantity of released CO increases with tem-

perature. At early temperature, CH4 also plays

as reductant, conrmed by DTG curve. After that,

DTG curve decreases rapidly.

XRD data conrms DTG analysis explaining that

FeOOH disappears at 350 °C (Figure 7). At such

a temperature, there are only Fe2O3 and Fe3O4.

At higher temperature (470 °C), almost all ofFe2O3 has been reduced to Fe3O4. In fact, Figure

6 shows that at 442 °C, composite pellet releases

CH4 gas. It is probably the CH4 is a reduction

agent for Fe2O3 transformation. Formation of

CH4 is supported by Figure 5 that at 442 °C, the

composite loses signicant weight.

Fe3O4 is stable at least until 680 °C due to not

enough reduction agents at this temperature. Fig-

ure 6 conrms that at that temperature CH4 and

CO present at the same time. However, CH4 will

disappear and CO will increase for a maximum

concentration.

The Fe presents when composite pellet is reduced

at 980 °C as shown in Figure 7. Fe formation

occurs due to Fe3O4 and FeO reductions by CO(Figure 6)., CO reaches maximum at around 920

°C. Reduction is followed by loss of weight con-

tinuously until temperature above 1000 °C.

CONCLUSION

Reaction of composite pellet consists of dehydra-

tion, dehydroxylation, Fe2O3, Fe3O4, FeO and Fe

formation. The reaction characterized by weight

loss at temperature below 100, 285, 442, 625, and

above 700 °C. Reduction of goethitic iron ore isstarted by Fe2O3 formation above 350 °C followed

by forming Fe3O4. The formation of FeO and Fe

occur above 680 °C.

ACKNOWLEDGEMENT

The authors are especially grateful to Center of

Mineral Technology, Agency for the Assessment

and Application of Technology (BPPT) for nancial

support through its scholarship program.

Figure 7. X-ray Diffraction of lateritic iron ore and composite pellets at 350, 470, 680, and 980 °C.


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REFERENCES

Gialanella, S., Girardi, F., Ischia, G., Leonardelli, I.,

Mattarelli, M., Montagna, M. 2010. On the goethite

to hematite phase transformation. J. Therm. Anal.

Calorim., 102, 867-873.

Jozwiak, W.K., Kaczmarek, E., Maniecki, T.P., Ignaczak,

W., Maniukiewicz, W. 2007. Reduction behaviour

of iron oxides in hydrogen and carbon monoxide

atmospheres, Applied Catalysis A : General , 326,17-27.

Kawigraha, A., Soedarsono, J.W., Harjanto, S., Pra-

musanto. 2013. Reduction of Composite Pellet

Containing Indonesia Lateritic Iron Ore as Raw

Material for Producing TWDI. Applied Mechanics

and Materials. Vol. 281, 490-495.

Murakami, T., Nishimura, T., Kasai, E. 2009. Lowering

Reduction Temperature of Iron Ore and Carbon

Composite by Using Ores with High Combined

Water Content. ISIJ International , Vol. 49, No. 11,pp. 1686-1693.

Strezov, V., Ziolkowski, A., Evans, T.J., Nelson, P. F.

2010. Assessment of evolution of loss on ignition

matter during heating of iron ores. J. Therm. Anal.

Calorim., 100, 901-907.


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A Literature Study of Beneting K-Bearing Silicate Rocks ... Agus Wahyudi and Tatang Wahyudi

Received : 18 April 2013, rst revision : 10 May 2013, second revision : 05 June 2013, accepted : June 2013


A LITERATURE STUDY OF BENEFITING K-BEARING

SILICATE ROCKS AS RAW MATERIALS FOR POTAS-

SIUM FERTILIZER

STUDI LITERATUR PEMANFAATAN BATUAN SILIKAT PEMBAWA

KALIUM SEBAGAI BAHAN PUPUK KALIUM

AGUS WAHYUDI and TATANG WAHYUDI

R & D Centre for Mineral and Coal TechnologyJalan Jenderal Sudirman 623 Bandung 40211,

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

ABSTRACT

As an agricultural country Indonesia requires NPK fertilizer up to 2.6 mil lion tons per year. However, such anumber is mostly fullled by imports, particularly potassium (K) fertilizer. Almost a 100% of K-fertilizer comes fromCanada and Russia in the form of KCl (sylvite) salt. Indonesia does not have sylvite mineral, but retains someK-bearing minerals such as K-feldspar and leucite. Both are different in characteristics from sylvite. K-feldsparand leucite are the alumino-silicate minerals. They require special treatment to process them into K-fertilizer.Several techniques can be applied to process both minerals, such as by mechano-chemistry, leaching, alkalifusion and bioleaching. Research on the utilization of K-source minerals as a raw material for K fertilizer is rela-tively rare. The opportunity to conduct such a research is widely open, as currently conducted by the Researchand Development Centre for Mineral and Coal Technology.

Keywords: feldspar, leucite, utilization, import, potassium fertilizer

SARI

Kebutuhan Indonesia terhadap pupuk NPK per tahun mencapai 2,8 juta ton namun pemenuhannya sebagian

besar masih tergantung kepada impor terutama kalium dan fosfor. Hampir 100% pupuk berbahan dasar kalium

diimpor dari Kanada dan Rusia dalam bentuk mineral silvit (KCl) sedangkan fosfor diimpor dalam bentuk batuan

fosfat dari negara-negara Timur Tengah seperti Mesir dan Jordania. Indonesia sebenarnya mempunyai potensi

agro-mineral yang cukup banyak untuk diolah menjadi pupuk. Permasalahannya adalah kualitas yang belum

memenuhi standar seperti yang disyaratkan produsen pupuk; sebagai contoh, mineral silikat berbasis kalium

seperti K-felspar dan leusit yang karakternya berbeda dengan silvit sehingga memerlukan perlakuan terlebih

dahulu agar kualitasnya memenuhi standar. Beberapa teknik dalam mengolah mineral alumino-silikat adalah

aktivasi mekanis, pelindian, peleburan dengan alkali dan bioleaching. Kajian mengenai pemanfaatan mineral

berbasis kalium untuk pupuk memang masih jarang namun kesempatan untuk melakukan hal tersebut terbuka

luas seperti yang saat ini dilakukan oleh Puslitbang Teknologi Minertal dan Batubara.

Katakunci: felspar, leusit, pemanfaatan, impor, pupuk kalium

INTRODUCTION

Along with phosphor and nitrogen, potassium isone of the essential elements as fertilizer notably

for the plant growth and reproduction. The ele-

ment also serves as a regulator since entering the60-enzyme systems within the vegetation. It helpsvegetation to endure the effects of temperatureas well as increases plant resistance to disease.

Potassium is needed, especially for carbohydrate-


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rich crops such as potatoes. Testing shows thatthe right amounts of potassium results in long andstrong growing of cotton, increasing rind endur -ance, extending rose branches, strengtheningand greening the grass, and increasing the size

and quality of fruit, grains, and vegetables (War -mada, 2004).

In 2012, the needs of NPK fertilizer in Indonesiareached 2,593,920 tons (Ministry of Agriculture,2012). Approximately 96% of Indonesian farmersuse the fertilizers to cultivate the farm, and therest (4%) applies organic fertilizer. Of the threecomponent types within such as compound fer -tilizer, phosphate and potassium are imported.Even for potassium, a 100% belongs to import,particularly from Canada and Russia. The potas-

sium import is around 435,000 tons / year or 61.6million USD (Azis, 2001). The price of KCl hasincreased 4 times since 2007 (Manning, 2010). Itreached US$1000 per ton K2O that is equivalentfor some contract during 2008. Referring to suchcondition, the use of crushed silicate rocks needsto be considered as an alternative for K-source.The rocks are occurs widely in the world and couldbe a signicant role in maintaining soil fertility forthe poorest farmers.

K-bearing silicate rocks contain most of the es-sential nutrients that plants require for growth

and development. The ground silicate rocks canbe used for fertilizer and potentially provides thenutrients to plants in various soil environments.

When used, the fertilizer yields slow releaseperformance. It continually improves soil andharvest quality. Its application to highly weathered,low fertility, acid soils has been proposed as analternative to conventional fertilization with water-

soluble fertilizers in areas where fertilizers are notavailable or in organic agriculture (van Straaten,2002). The appliance of K-bearing silicate rocksalso refers to beneting quarry by-products as oc-curred in West Australia, Queensland and Brazilas part of an alternative sustainable strategy tore-mineralize or recapitalize degraded soils (Pri-yono in www.ntb.litbang.deptan.go.id).

Based on its rock-forming minerals, the silicaterocks are divided into mac and felsic ones. Theformer is dominated by ferro-magnesian silicate

minerals that perform (mostly) dark color andcontain base cation such as Mg, Ca, micro nu-trients of Mn, Fe, Cu and Zn with less K (< 1 %K2O). The later is characterized by light mineralsthat are rich in silica (quartz and/or feldspar) butpoor in nutrient content. The K content within therocks is sufcient (4-20%). Figure 1 shows bothrock types. The choice of silicate rocks for silicatefertilizer depends on type and lack intensity of thenutrients. In this case, the silicate fertilizer of feld-spar and gneiss as K source is more appropriatethan that of basalt and dolerite. The later belongsto mac rocks.

Resources of these commodities in Indonesia arequite abundance, but those are generally in low

(a) (b)

Figure 1. Basalt as one of mac rocks that rich in micro nutrients but less in potassium (a) and a felsic rock (rhyo-lite), rich in silica (either quartz or feldspar) but poor in micro nutrients (Wahyudi et al., 2012)


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A Literature Study of Beneting K-Bearing Silicate Rocks ... Agus Wahyudi and Tatang Wahyudi

quality. This condition results in the dependencyof potassium import for this country. Figure 2shows the demand of NPK fertilizer in Indonesia.Indonesia retains abundantly K-bearing silicaterocks; however, study regarding the use of such

rocks for silicate fertilizer is very limited. Basedon data from Center for Geological Resources(Kusdarto, 2008), there is a K-mineral reserves inSitubondo regency, East Java. The mineral is leu-cite or KAlSi2O6 and amounting to 117.5 milliontonnes (inferred) and 12.5 million m3 (measured).Besides leucite, other K-mineral is feldspar thatis found almost in all parts of Indonesia, espe-cially Java and Sumatra (Mandalawanto, 1997).In addition to K- mineral resources, trachytethat spreads out in South Sulawesi is availableat district Barru, Pankep, Sinjai, Soppeng and

Bone. Their total reserve is 4.1 billion tons. Thenext source of K-mineral is biotite or (K(Mg, Fe)3AlSi3O10 (F,OH)2). The biotite occurs at Northand South Sumatras (Center for Geological Re-sources, 2009).

Naturally, mineral as the source of potassium isdivided into two groups, namely the salt and sili-cate groups as shown in Table 1. Most of fertilizerindustry still uses potassium from salt groups suchas sylvite since its K-level is already high (60%

K2O) and the solubility is good enough to easilyabsorb by plants. Unfortunately, Indonesia has noK-salt mineral similar to sylvite. The K-mineralsthat is commonly found in Indonesia is potassiumsilicate minerals but its application is still very raredue to its solubility limitation hence mineral activa-tion is required to make it gains good solubility.

METHODOLOGY

A literature survey is a main method used for this

study. The study was completed by collectingprimary and secondary data either quantitative orqualitative. The data included K-bearing silicaterock resources, its mineral charcteristics andemployed proces for processing the rocks to bepotasssium-based fertilizer. All data were thenevaluated.


Carbon (C), Hydrogen (H), oxygen (O), nitrogen(N) ,phosphorus ( P), potassium (K), calcium (Ca),

magnesium (Mg), sulfur (S), iron (Fe), manganese(Mn), zinc (Zn), copper (Cu), boron (B), nickel(Ni), molybdenum (Mo) and chlorine (Cl) are theessential micro nutrients for plant growth whilecobalt (Co), silicon (Su), and sodium (Na) servea

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