TABLE OF CONTENTS
Abstract ..................................................................................................................................... 3
Introduction .............................................................................................................................. 4
Classification ....................................................................................................................... 4
Formation .................................................................................................................................. 6
Views on Formation ........................................................................................................... 6
Occurrence ......................................................................................................................... 6
Features of Graphite Deposits ........................................................................................... 7
Specification of graphite for various uses ................................................................................ 8
USES OF GRAPHITE ............................................................................................................. 8
Specifications for various applications ............................................................................... 8
Graphite Resources and its Utilization ..................................................................................... 9
World Review ..................................................................................................................... 9
Graphite resources in India ..................................................................................................... 10
RESOURCES ....................................................................................................................... 10
EXPLORATION & DEVELOPMENT ..................................................................................... 10
PRODUCTION in India ....................................................................................................... 10
State/Grade Wise distribution of Graphite in India ......................................................... 11
Graphite Beneficiation Process ............................................................................................... 12
Typical Wet Grinding Circuit for high grade Graphite ...................................................... 14
Graphite beneficiation at other locations ........................................................................... 15
Panchmahal, Gujrat .......................................................................................................... 15
Minerology and chemical characterstics of the given sample ............................................... 16
Experiments ............................................................................................................................ 17
Test 1: Moisture Analysis ..................................................................................................... 17
Test 2: VM analysis .............................................................................................................. 18
Test 3: Ash Analysis ............................................................................................................. 19
Test 4: Specific Gravity ........................................................................................................ 20
Test 5: Hardgrove Grindability Index ................................................................................... 20
Test 6: Sink and Float analysis ............................................................................................. 21
Test 7: Froth Flotation ......................................................................................................... 22
Results ..................................................................................................................................... 23
Conclusion ............................................................................................................................... 25
Bibliography ............................................................................................................................ 27
ABSTRACT
The properties and occurrence of graphite around the world has been outlined. The various
types of graphite, its formation, and its major producers both locally and internationally
shave been reviewed. The major uses of graphite are pencils, lubricants, foundries,
electrodes, paints etc. They require grades of graphite ranging from 60% to 99%.
Low grade graphite samples containing 15–17 % fixed carbon from Palamu, Jharkhand, India
have been investigated for characterization and amenability to beneficiation.
The graphite is of the crystallized flaky variety, and is associated with large proportion of
quartz and some feldspar and mica as dominant gangue minerals. The properties and
liberation of graphite and their implications in beneficiation are described in this paper. The
optimum liberation size of the graphite was determined to be below 200
μm. Beneficiation studies indicated that a concentrate with around 50% fixed carbon, at a
recovery of about 80% can be easily achieved by a single stage of froth flotation in a
conventional flotation cell.
Building upon the data obtained as well established principles of mineral processing, a
method of upgrading the given sample to grade reaching 80‐90% fixed carbon or more has
been outlined.
KEYWORDS
Industrial minerals; ore mineralogy; liberation; froth flotation;
GRAPHITE
INTRODUCTION
Graphite, also known as plumbago or black lead, is a type of naturally occurring carbon. The
origin of the word “graphite” is the Greek word “graphein” which means “to write”. Indeed,
graphite has been used to write (and draw) since the dawn of history and the first pencils
were manufactured in England in the 15th century. In the 18th century, it was
demonstrated that graphite actually is an allotrope of carbon.
It consists essentially of carbon but often impure with clays, iron oxides, and other gangue
minerals. It crystallises in a hexagonal system and has a lamellar form, a grey‐ to‐black
metallic lustre and feels greasy. In addition to natural graphite, synthetic or artificial
graphite is manufactured on a large‐scale in electric furnaces, using anthracite or petroleum
coke as raw feed. The latter is known as Calcined Petroleum Coke (CPC).
Graphite is a very soft mineral and it is a specific gravity varies from 2.09 to 2.03. It is an
excellent thermal and electrical conductor. The high melting point of graphite, in absence of
oxygen, 3500°C makes it suitable for a number of refractory applications. Excellent acid
resistance and general chemical inertness make its use ideal in acid environments and other
chemical applications. Graphite fibres‐‐ drawn from organic precursors, such as rayon,
polyacrylonitrile and tar‐pitch—are used as reinforcing components in polymer composites.
Graphite is mined from open pit and underground mine operations. Open pit operations are
more economical and, thus, are preferred where the overburden is thin enough to remove.
Madagascar mines are mostly open pit type. In the Republic of Korea, Mexico, and Sri
Lanka, however, where the deposits are deep, underground mining is usually developed.
Higher purity material is obtained by further crushing, grinding, and flotation steps.
CLASSIFICATION
A useful classification of graphite depends on the mode of formation that leads to three
physically distinct common varieties: amorphous (micro‐crystalline) graphite, which has a
carbon content of 70‐85%; high crystalline graphite (lump, vein or crystalline vein), which
has a carbon content of 90‐99%; and flake graphite, which has a carbon range of 80‐98%.
Flake graphite (i.e., flat plate‐like grains from <1 mm to 2.5 cm in size) is sold in two particle
size distributions: coarse flake (‐20 to +100 mesh) and fine flake (‐100 to +325 mesh).
Crystalline graphite ranges from chip or dust to fine or amorphous lump, to coarse or
crystalline lump.
The term “flake” is self‐explanatory; flake forms occur disseminated in rock. Lump graphite
occurs in fissure‐filled veins in pegmatite dykes, also associated with chips and the rarer
needle forms. Amorphous graphite occurs in beds that were once coal, but fine‐grained,
easily ground vein graphite is also classified as amorphous.
FORMATION
VIEWS ON FORMATION
A review of literature on graphite deposits indicates that they are formed by one or more of
the processes mentioned below:
(a) METAMORPHISM—The metamorphism might have brought mineralization of graphite
by one of the following ways :
(i) metamorphism of carbonaceous layers, in which case graphite occurs in the form
of layers (Winchell 1911; Clark 1921a, and Harrington 1947);
(ii) recrystallization of organic carbon as graphite during metamorphism giving rise
to bedded deposits (Tilley 1921; and Ailing 1921);
(iii) metamorphism of sediments containing carbon impurities giving rise to
disseminated occurrences (Wadia 1943; Mukherjee 1965; and Krishna Rao et al.
1971);
(iv) Interaction of carbonaceous sediments with the gases derived from adjacent
intrusions for the graphite deposits at the contact of the intrusions (Brumell,
1908 quoted by Clark 1921a; Bastin 1912; Ailing 1918; Wilson 1920; Spence,
1920; Wadia 1943; Bose 1959; and Krishna Rao et al. 1971).
(b) DEOXIDATION—by deoxidation of CO, for the formation of veins (Winchell 1911; Clark,
1921a; Tilley, 1921; Clark, 19216; Winchell, 1921; Wadia 1943; and Mukherjee 1965) or
by release of carbon as methane from carbonate (Salotti et al. 1971; 1972) and
formation of veins.
(c) PEGMATITE DEPOSITS— the mineral occurs in acid intrusions (Clark 1921, p. 179; and
Wadia 1943, p. 16), or in meteorites and nepheline syenites.
(d) PHYSICAL MIGRATION of fine graphite flakes along grain boundaries in graphite‐bearing
rocks along a pressure gradient towards fractures during temporary release of pressure
under deep‐seated conditions and forming graphite veins (Erdosh 1970, 1972).
OCCURRENCE
Graphite occurs chiefly in those rocks that have undergone intense metamorphism and thus
it is found in older gneiss and schists, crystalline limestone, carbonaceous material in
original sandstone, shale and limestone, recrystalline in the form of graphite. It may also be
product of contact metamorphism where igneous rocks intrude carbonaceous sedimentary
rocks.
In Palamu district the main rocks associated in the graphite include various types of
metamorphosed sediments. Good amount of graphite occurs here as original constituent in
schistose rocks. At some places its close association is found with pegmatites, quartz veins
and gneissic rocks.
FEATURES OF GRAPHITE DEPOSITS
Some schistose rocks consist of essentially graphite, along with mica, quartz, and
feldspar.
The graphite‐bearing gneissic rocks are traversed by veins and stock‐works of graphite.
The veins form an intricate network in the host rock.
The host rocks in which the veins of graphite are found to contain quartz, calcite,
dolomite, diopside, wollastonite, and tremolite.
Compressed and contorted structures are displayed by the graphite lodes.
The granitic intrusions are found at or near the graphite veins indicating their close
relationship.
The graphite veins occur mostly parallel to the country rocks, but the crosscutting joints
in the latter are also occupied by graphite.
Veins of calcite are frequently found traversing the host rocks (talc‐silicate rocks) and
the graphite veins.
Graphite is not found in the acid intrusions, without the association of calciosilicate
rock.
SPECIFICATION OF GRAPHITE FOR VARIOUS USES
USES OF GRAPHITE
Graphite being versatile mineral and due to its diversified properties, it finds important
place in many crucially important industries. It is used in the manufacture of special type of
electrodes, special lubricants and also in the atomic reactors in the form of bricks of high
purity graphite. It is also used for foundry when casting iron, copper, aluminum and also
steel and magnesium under special condition.
Graphite fibers composite absorbs rather than reflects radar waves and so the use of
graphite continues to grow rapidly in the use of radar masking stealth technology and also
in making other non‐aerospace weapons. In the development of plastic engine 90% of the
components would be made of graphite fibers reinforced composites to be used in Ford's
small car to make them lighter and quieter. Although much of the graphite used in
industries is manufactured, natural graphite is indispensable for certain purpose.
SPECIFICATIONS FOR VARIOUS APPLICATIONS
Specifications for graphite for use in various industries differ considerably and sometimes
the consumers specify for the grade of graphite they use. The following table is however
indicative of the specifications, for its use in some specific industries.
Application Type C content Flake Size
Refractories Alumina graphite F Min. 85% 150 ‐ 500
μm
Crucibles AF 80 ‐ 90% +150 μm Bulk density 48 ‐ 54 g per 100 cm3 Expanded graphite F Min. 90% 200 ‐ 1700
μm
Foundry core and mould washes AF 70 ‐ 90% —75 μm Brake/clutch linings AFV Min. 98% <75 μm Bearings FV 90 ‐ 93% +150 μm Lubricants AFV 98 ‐ 99% 53 ‐ 106 μm Free from sulphides, abrasive material and
metallic contaminants. Dry cell batteries A MM. 88% 85% <75 μm No metallic impurities and S less than 0.5% Alkaline batteries AF Min. 98% 5 ‐ 75 μm No impurities such as Cu, Co, Sb and As. Recarburizing steMinn. A 98 ‐ 99% —5 μm Carbon brushes AFV 95 ‐ 99% <53 μm < 1% ash / silica. No abrasive or metallic
contaminants. Electrical FV 93 ‐ 95% +150 μm Pencils AF 95 ‐ 97% +150 μm Free of gritty impurities Packing paints FV 85 ‐ 90% <150 μm Polishes AFV 85 ‐ 90% <150 μm Drilling mud (lubricating) F 80%+ N/A About 41b per barrel of mud Explosives (control burning rate) AF 65% <150 μm Free from sulphides and acids. Low moisture
content Nuclear reactors (moderators ) F 93 ‐ 95% N/A Free from high neutron absorbing elements.
e.g. boron Boilers (scale prevention) F 50%+ N/A
GRAPHITE RESOURCES AND ITS UTILIZATION
WORLD REVIEW
World production of graphite in 2008 was estimated to be 1100000 tons, showing a
significant increase from the 1995 value of 741,000 tons. The figure is, however, about 20%
less than that of previous years. The most significant decrease in production was in China.
China continued to be the leading producer followed by India, Brazil, North Korea and
Canada. These countries accounted for almost 90% of total world production of graphite.
Country 2005 2006 2007
World 2000 2039 2100 Brazil 76 76 77 Canada 17 15 15
China 1650 1730 1800 India 126 124 116 Korea, Dem.E People's Rep. of
30 30 30
Mexico 12 12 10 Russia 14 14 14 Ukraine 10 6 NA Zimbabwe 4 7 7 Other countries 61 25 31 Source: World Mineral Production. 2003‐2007.
China leads the pack with over 800,000 ton per annum production alone. It is the largest
producer as well as the consumer of commercial graphite. The country has more than half
of the world’s top 12 producing companies. Its resources are located in Inner Mongolia,
Shandong, Shanxi and Heilongjong.
India is the world's second largest graphite producer with a production of 140,000 tonnes
per annum. Its major sources are located in Orissa. Brazil is the third largest producer with
about a third of the total world reserves. The graphite market has recently suffered slowing
of the pace due to the recent economic downturn.
Europe has decelerated graphite production primarily due to exhaustion of resources and
availability of cheap graphite from China. Africa has some serious reserves of graphite in
South Africa, Uganda, Angola, Tanzania, Ethiopia and Namibia.
GRAPHITE RESOURCES IN INDIA
RESOURCES
Graphite occurrences are reported from various states but the deposits of economic
importance are located in Andhra Pradesh, Jharkhand, Karnataka, Kerala, Orissa, Rajasthan
and Tamil Nadu.
As per the UNFC system, the total resources of graphite as on 1.4.2005 are placed at about
168.77 million tonnes, comprising 10.75 million tonnes in the reserves category and 158.02
million tonnes under remaining resources category. Resources containing +40% fixed
carbon constitute about 1.11 million tonnes and resources analyzing 10‐40% fixed carbon
21.23 million tonnes. Balance resources of 146.43 million tonnes fall under 'others',
'unclassified' and 'not known' grades. Out of total resources, Arunachal Pradesh accounts
for 43% followed by Jammu & Kashmir (37%), Jharkhand (6%), Tamil Nadu (5%) and Orissa
(3%). However, in terms of reserves, Tamil Nadu has leading share of about 37% followed by
Jharkhand (30%) and Orissa (29%)
EXPLORATION & DEVELOPMENT
GSI continued exploration for graphite in Puvandi‐Arasanur and Usilampatti area in
Sivaganga district, Tamil Nadu. In Arasanur block, presence of graphite mineralization has
been proved for a strike length of 1 km. The average width of the zone is about 12 m. and
overall average grade is 14% F.C. A resource of 0.76 million tonnes of graphite (average
grade of 13% FC) has been estimated in 2006‐07.
In the western extension of Arasanur block, a new block named Kiranur block, was
investigated and the results were found to be not encouraging. The west of the Kiranur
block, 135 m east of a mine of M/s. V. Thiruvanavukasasu, a trench (KT‐1) across graphite
gneiss exposed three bands of graphite having 1.90 m, 2.5m and 1.6m widths. In 2007‐08,
Directorate of Geology, Jharkhand, carried out exploration to determine one million
tonnes graphite resources of possible category were estimated with fixed carbon content of
5.95 to 23.47%.
PRODUCTION IN INDIA
Orissa was the leading position contributing a major share of about 44% of the total output
during 2007‐08, followed by Tamil Nadu 43% and Jharkhand by 13% (Tables ‐ 2 to 5). Mine‐
head stock at the end of the year 2007‐08 was 45 thousand tonnes as against 72 thousand
tonnes in the beginning of the year. The average daily employment of labor during 2007‐08
was 331 as against 490 in the preceding year.
STATE/GRADE WISE DISTRIBUTION OF GRAPHITE IN INDIA
Grade/State Reserves Remaining resources Total
Proved Probable Total (A) Feasibility Pre‐feasibilit
Measured
Indicated Inferred Recon Total
Total
All India:Total 5163505 1021869 4564534 10749908 12000 78386 930118 51326 5956595 16506673 134489932 158025030 168774938
By Grade
+40% FC 413639 77132 342807 833578 ‐ 37000 80 ‐ 951 238500 ‐ 276531 1110109
10%‐40% FC 4733667 937943 3943249 9614859 12000 41386 930038 8740 1596449 8952091 73897 11614601 21229460
Others 15574 6794 210952 233320 ‐ ‐ ‐ ‐ 3283001 2330151 ‐ 5613152 5846472
Unclassified ‐ ‐ 67526 67526 ‐ ‐ ‐ 2750 5882 3127538 61497720 64633890 64701416
Not known 625 ‐ ‐ 625 ‐ ‐ ‐ 39836 1070312 1858393 72918315 75886856 75887481
By States
Andhra Pradesh ‐ ‐ 1135 1135 ‐ ‐ ‐ ‐ 124758 301306 ‐ 426064 427199
Arunachal Pradesh ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ 72758257 72758257 72758257
Gujarat ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ 2520805 835000 ‐ 3355805 3355805
Jammu & Kashmir ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ 1059520 61681035 62740555 62740555
Jharkhand 442537 670448 2163106 3276091 ‐ ‐ 720000 2750 1143701 5180124 24350 7070925 10347016
Karnataka 1308 6794 188812 196914 ‐ ‐ ‐ 18200 52500 ‐ 70700 267614
Kerala 8300 17762 26062 ‐ ‐ 35600 ‐ 1148350 240418 ‐ 1424368 1450430
Madhya Pradesh ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ 1006660 ‐ 1006660 1006660
Maharashtra ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ 1160000 1160000 1160000
Orissa 1553293 336327 1217349 3106969 12000 38900 172032 8740 103281 1954721 26290 2315964 5422933
Rajasthan 47600 ‐ 165920 213520 ‐ ‐ ‐ ‐ 250000 1450034 ‐ 1700034 1913554
Tamil Nadu 3118767 ‐ 810450 3929217 ‐ 39486 2486 29136 647500 3266390 ‐ 3984998 7914215
Uttarakhand ‐ ‐ ‐ ‐ ‐ ‐ ‐ 10700 ‐ ‐ ‐ 10700 10700
GRAPHITE BENEFICIATION PROCESS
As a general rule the graphite ores are not in such a rich state, when they come from the
mine, as to admit of their being at once sent direct to the market; they contain more or less
impurities such as oxide of iron, silica, alumina and lime or are so hard that they cannot be
employed at all in their natural state. They must be enriched by some means or another so
that the worthless gangue or country rock may be got rid of, thus increasing the quantity of
carbon in the ore. The methods of enriching or refining graphite may be divided into three
general systems. 1. Hand sorting. 2. Mechanical separation. 3. Chemical refining. The
mechanical separation is again subdivided into the dry or wet method.
As to hand sorting, this is practised in a very efficient manner in the Austrian and Bavarian
mines, while no or scant attention is paid to this particular branch of ore dressing on the
North American continent. The choice of one or the other systems in the mechanical
separation or chemical refining depends entirely upon the nature of the ore to be treated
and the purposes to which the finished product is to be applied, though too often the
selection is based on chance, prejudice and limited experience.
The selection of the most profitable process and machinery for the treatment of a given
graphite ore is of great importance in a mining enterprise; but as some ores are susceptible
of successful working by more than one process—and in such cases local conditions must
determine which methods will yield the best results it is not possible to lay down exact rules
covering all cases.
Flake graphite is usually too finely disseminated for hand sorting and cobbing methods,
which are used in few countries to recover massive flake graphite. Production of graphite is
usually only possible by a combination of careful grinding and screening to recover coarse
flakes and by flotation to recover fine graphite. Flotation concentrates are sometimes
further beneficiated by tabling to remove associated gangue minerals such as quartz, mica,
hornblende, feldspar, calcite, and sulphides.
Impurities tend to float with graphite since, being soft, graphite tends to smear and coat
impurity minerals during grinding so that they behave like graphite. This is especially true
when processing finely divided ores that require extensive grinding. Size reduction is usually
accomplished by jaw, cone, or hammer mill‐type crushers; screening to recover coarse
flakes or to reject coarse hard impurities is accomplished by trommel or vibratory screens.
The recovery of intermediate and fine flake graphite is possible by roll crushing, ball, rod
milling, or jet milling, followed by additional screening, air classification, wet tabling, or
flotation. Graphite is naturally floatable and particles as coarse as 1 mm may be floated in a
slightly alkaline pH medium. Pine oil and kerosene are the standard reagents and are usually
employed together. Pine oil acts as a frother. The function of kerosene or fuel oil is as a
promoter to recover unliberated graphite middlings. Flotation is fairly fast and multiple
cleanings are necessary for recoveries of 80‐85%; recovery can be improved by regrinding
and reflotation, but careful regrinding is necessary to avoid the smearing of gangue
minerals and the production of slime graphite. Modifiers and depressants to improve
selectivity include sodium silicate, which acts as a quartz depressant and slime dispersant,
and lactic acid, C3H6O3, which is used to depress mica. Graphite may be further purified to
99% carbon by chemical treatment, chloridization, or fluoridization.
Synthetic graphite, mainly produced in the United States, is made from a mixture of
petroleum coke or anthracite filler, coal tar, or petroleum pitch binder, and various
impregnating or additive materials. The coke or anthracite, which should contain 95%
carbon and have a low sulphur content, is calcined to remove volatiles, ground, mixed with
binder and other materials, and molded to the required shape. The product, known in the
trade as “green bar” or “green stock,” is then baked at 800‐1000°C to convert the pitch
binder to coke and to solidify the shape. The resulting product is then “graphitized” by
heating in an electric furnace at 2600‐3000°C over an extended period. It is then cooled and
machined to final size specifications (e.g., the production of electrodes turned on lathes to
the desired diameter for use in steel mini‐mills).
TYPI
CAL WET GGRINDING CCIRCUIT FO
OR HIGH GRRADE GRAPPHITE
GRAPHITE BENEFICIATION AT OTHER LOCATIONS
PANCHMAHAL, GUJRAT
The ore is won by cutting trenches by manual labour and transporting it by trucks to the
beneficiating plant. The methods are very primitive and the excavation starts from surface
outcrops of graphite ore and continues along the strike and downwards. Rate of production
is slow and intermittent. Most mines sell their products without any beneficiation.
The samples had been sent to Bhabha Atomic Research Centre for beneficiation tests. They
were able to upgrade the materials from 60‐90 percent depending on the samples which
contained 10‐30% Fixed carbon. The tests carried out at Regional research Laboratory at
Bhubneshwar indicated that upgradation of ore upto 95% was economically feasible.
Sahu and Mungee (1972) have shown feasibility of upgrading ore from 25% to 55% with
around 50% recovery. Mild acid treatment before flotation reduces impurities and
repetition of flotation in identical cells further improve the grade. Multistage flotation
improves recovery by over 30%.
Most of the mineral resources in our country (excepting iron ores etc.) are low to medium
in grade which need beneficiation in some form or other to make them suitable for use in
mineral based industries. As such, these have to be upgraded to the desired specification
(within specified tolerance limits). Beneficiation of graphite includes gravity concentration
methods and also flotation. Sometimes chemical treatment like acid leaching and
chloridisation are also applied for production of high purity graphite over 99% F.C.
MINEROLOGY AND CHEMICAL CHARACTERSTICS OF THE
GIVEN SAMPLE
The sample under study was procured from near Daltonganj in Palamu District of
Jharkhand. The region has a large reserve of low grade graphite with Fixed Carbon content
ranging from 5% to 30% depending upon the source.
The given sample seemed to be of flaky type. These were present as lenticular pockets of
quartz graphite schist embedded in granite gneiss. The chief gangue minerals associated
with the sample were mostly quartz, with smaller amounts of feldspar, and shiny micas.
Upon crushing, the graphite seemed to be pretty well liberated at sizes around 400 microns.
From the data of the mineralogy, grain size, their liberation and fixed carbon content of the
samples a few important conclusions could be drawn.
1. Chemical superiority of the sample alone does not signify the real worth of the
sample but external characteristics have an important role in determining the value
of any workable deposits. Sometimes the textural characteristics play a dominant
role in this regard.
2. Flaky nature of graphite having flakes above 80 mesh finds many important uses in
industries as well as in manufacture of crucibles. It fetches higher price also.
3. Interlocking of the gangues with graphite (at very fine size) needs very fine grinding
which consumes 40‐60% of the total processing cost rendering it uneconomical.
Moreover grinding of graphite to very fine size is also extremely difficult owing to its
greasy nature.
Keeping the above points in view two ways of beneficiation of graphite may be
suggested.
(a) if the liberation of graphite is at a coarse size, gravity methods of
concentration may be effective.
(b) If the graphite grains are liberated at a finer size, perhaps flotation
techniques might work.
(c) If the graphite minerals are associated with gangue at exceptionally very fine
stage, the processing may not be economical for obvious reasons (grinding
cost will be very high).
EXPERIMENTS
Experiments on graphite bearing ore are aimed to characterize the ore, to establish the
optimum method to beneficiate the given graphite ore with maximum possible grade and
recovery. Due to unavailability of Indian standards for graphite characterization and
beneficiation procedures ASTM standards are adapted for the standardization of the
procedures.
TEST 1: MOISTURE ANALYSIS
The given sample was tested in accordance with ASTM Standards for flake graphite.
The sample was pulverized to a size of ‐75 # in a pulveriser. The testing that followed
included heating the sample in a suitable container at a temperature of about 110 °C for
duration of 16 hours. The sample was left overnight in an open air oven.
The sample was weighed in the lab using high precision electronic balances before and after
the testing to obtain the following data:
Sample Initial Weight Final Weight Difference % Moisture
Sample 1 9.9497 9.859 0.0907 0.911585274
Sample 2 9.9085 9.8033 0.1052 1.061714689
Sample 3 10.2377 10.132 0.1057 1.032458462
Total 1.001919475
The above analysis indicates that the sample is fairly dry. The traces of moisture are mostly
harmless and should pose no concern in either wet or dry processes.
TEST 2: VM ANALYSIS
The standards for measuring Volatile Matter content of graphite were not available. It
forced us to modify existing standards to suit the purpose. Since graphite can easily
withstand high temperatures, an assumption was made to heat the sample to a
temperature of 900 °C for duration of 10 minutes.
One gram of the sample we got in the last step (‐75 #, dried) was then transferred to a VM
crucible. The VM crucible was then put inside a furnace preheated to 900 °C for duration of
10 minutes. After the stipulated time, the sample was cooled and weighed in an electronic
balance. The data obtained was the following:
Sample Initial Weight Final Weight Difference % Moisture
Sample 1 1.09 1.0833 0.0067 0.614679
Sample 2 1.0023 0.994 0.0083 0.828095
Sample 3 0.9997 0.9926 0.0071 0.710213
0.7176%
The result of Volatile matter analysis indicates that there is no discernable Volatile matter in
the sample. The presence of low VM indicates that graphite can be processed and used
without much problem.
TEST 3: ASH ANALYSIS
The given sample was tested in accordance with ASTM Standards for flake graphite.
The sample was pulverized to a size of ‐75 # in a pulveriser. The procedure outlined in the
standards states that the sample should be introduced in a silica dish. The sample was put
in the silica dish so that a thin layer of sample covered the bottom of the dish (about 2
grams). The muffle furnace to be used for the process was preheated to a temperature of
500 °C. The temperature was raised to 750 °C slowly within one hour. This was followed by
another 200 °C increase in temperature in the following hour.
The sample was kept at this final temperature of 950 °C for 2‐4 hours and was periodically
disturbed by a clean iron wire to expose surfaces to air. The sample was weighed twice
during the process and it was determined that the entire carbon has been oxidized. The end
product failed to show any black particles. The sample was then placed in a desiccator for
cooling and weighed in an electronic balance. The result obtained indicated the following:
Sample Initial Weight Final Weight Difference % Ash
Sample 1 2.073 1.722 0.351 83.06802
Sample 2 2.113 1.735 0.378 82.11074
Sample 3 1.982 1.62 0.362 81.73562
82.30479
The ash percent of 82% is very high. The ash mostly contains quartz and sand particles.
Correcting for moisture and VM, the final Fixed Carbon percentage can be calculated to
around 16%. This is a difficult to wash sample and needs much processing before any viable
product can be achieved.
TEST 4: SPECIFIC GRAVITY
The given sample was tested for its specific gravity with the help of a specific gravity bottle.
The sp gravity of Kerosene was found to be 0.82.
Using this value, and the specific gravity bottle, the density of a coned and quartered ‐75#
sample was determined to be 2.56.
The specific gravity of Bromoform was determined to be 2.86
TEST 5: HARDGROVE GRINDABILITY INDEX
Hardgrove grindability index is basically defined for coal, but in the particular case it has
also been done for graphite to evaluate breaking characteristics of the graphite. Hard grove
index has been calculated as
HGI = 13 + 6.93 W
Where W is the amount of – 200 # material obtained after test
Weight of ‐200 # HGI
Sample 1 4.80 gm 46.264
Sample 2 5.43 gm 50.6229
Average Gardgrove Index = 48.45
The sample is thus very difficult to grind and the minimum amount of grinding must be
done. Otherwise, the grinding cost can make the process too expensive.
TEST 6: SINK AND FLOAT ANALYSIS
The given sample was pulverized to a size below 400 microns and then subjected to a sink
and float analysis.
PREPARATION OF DENSE MEDIA
Dense media was prepared by using Bromoform and Kerosene. The proportion of dense
media to be used was determined using mathematical equations. The exact volume of
ingredients required was thus determined. Dense media was prepared at different densities
ranging from 2.7 to 2.4 g/cc at .1 intervals.
SINK AND FLOAT TESTS
The sample was floated in the dense media prepared and the amount of sink and float in
each density class was determined.
Sp Gravity
wt% cum wt%
‐2.4 3.116348406 3.1163484062.4‐2.5 13.52310641 16.639454822.5‐2.6 47.31312558 63.952580392.6‐2.7 26.12337616 90.075956562.7 9.924043444 100
The flotation test clearly states that most of the mass is concentrated in the density range
of 2.5‐2.6 g/cc. This is primarily due to presence of dense quartz.
ASH ANALYSIS OF FRACTIONS
An ash analysis of each of these fractions was performed to better understand their
characterstics. The procedure is already outlined in Test 3.
Sp Gravity
wt% Ash %
‐2.4 3.116348406 60.6 2.4‐2.5 13.52310641 70.35 2.5‐2.6 47.31312558 77.36 2.6‐2.7 26.12337616 84.86 +2.7 9.924043444 89.77
The ash analysis confirms the earlier inference that most of the particles of ash are finely
disseminated and difficult to liberate at a size of 400 microns. A size reduction below 200
microns will be necessary to liberate the graphite properly from quartz.
TEST 7: FROTH FLOTATION
The given sample was pulverized and screened to obtain a size passing a screen of 400
microns.
CONDITIONING
The feed was prepared with a pulp density of 1.5g/cc using 496 grams of sample. Graphite is
a naturally floatable mineral and is thus easy to float.
Conditioning is performed to achieve the following:
Alkaline pH: addition of about .5g of NaOH pellets to the conditioning tank. Alkaline pH is
shown to improve flotability.
Quartz depressant: Sodium silicate selectively depresses quartz. It proves hugely beneficial
in flotation. It also acts as slime dispersant.
Conditioner: Kerosene itself is used as a conditioner. It is highly effective in graphite
flotation.
Frother: Pine oil was added to stabilize the froth long enough to remove the concentrate.
FLOTATION
The froth was collected at fixed intervals of 30seconds upto 3 times for each sample.
Floatation cell used is a Denver laboratory floatation cell have capacity of 3l, this machine
has been chosen as graphite needs more force for lifting, thus more agitation. The samples
were dried in an air oven and weighed:
Weight recovered Wt of sample wt of carbon Carbon % Yield Recovery
Tailing 323.2 1.87 0.089 2.359 0.660 0.086026162
0‐30 sec 70.03 0.67 0.3835 57.23 0.143 0.452209878
30‐60 sec 64.08 0.908 0.479 47.75 0.131 0.345216262
60‐90 sec 32.6 1.365 0.434 31.79 0.067 0.116933791
489.91
The Flotation tests indicate that a product with 60% FC can easily be prepared by a single
stage flotation.
RESULTS
By the above experiments and data collection most appropriate method for recovery of
best possible grade of graphite can be selected.
By taken into considerations of the size of the ore, and the need of the size liberation for
the process size reduction is usually accomplished by jaw, cone, or hammer mill‐type
crushers; screening to recover coarse
flakes or to reject coarse hard impurities is accomplished by trommel or vibratory screens.
The recovery of inter mediate and fine flake graphite is possible by roll crushing, ball, rod
milling, followed by additional screening, air classification.
The data collected form float and sink test and floatation test can be analyzed to check the
amenability of ore beneficiation by every process.
Sink and Float test: Float Curve
From the above float curve it has been estimate that grade greater than 31 % carbon can’t
be achieved by the gravity separation method. This practical result can be theoretically
justified as the density of graphite and other gangue matter as quartz, etc are too close.
Since 31 % carbon graphite is not used in any application, thus there is no mean is
upgrading carbon content of graphite from 16% to 31%.
Floatation is also analyzed in the same way to check its amenability. The data of floatation
time and grade recovered is plot in a following graph.
0
5
10
15
20
25
30
35
0 10 20 30 40 50 60 70 80 90 100
Carbon %
Cumm Wt %
Since it can be seen that the grade of almost 58% can be achieved at good recovery of 15 %
and grade of 51% can be achieved at recovery of 80%. Thus the process is effective in
upgradation of low grade graphite ore. This can be theoretically justified as the graphite is
naturally floatable material.
48
49
50
51
52
53
54
55
56
57
58
20 30 40 50 60 70 80 90 100
Cumm Carbon %
Floatation time
CONCLUSION
Graphite is naturally floatable and particles as coarse as 1 mm may be floated in a slightly
alkaline pH medium. Pine oil and kerosene are the standard reagents and are usually
employed together. Pine oil acts as a frother. The function of kerosene or fuel oil is as a
promoter to recover unliberated graphite middling. Flotation is fairly fast and multiple
cleanings are necessary for recoveries of 80‐85%; recovery can be improved by regrinding
and refloating, but careful regrinding is necessary to avoid the smearing of gangue minerals
and the production of slime graphite. Modifiers and depressants to improve selectivity
include sodium silicate, which acts as a quartz depressant and slime dispersant, and lactic
acid, C3H6O3, which is used to depress mica.
Graphite may be further purified to 99% carbon by chemical treatment, chloridization, or
fluoridization.
Floatation as a process can be improved by using cleaner circuits in series for better
recovery of high grade graphite.
Thus the graphite obtained have carbon content 58% , it can be used in various applications
like foundries, conductive coatings, boilers. Etc. However, after upgrading this graphite by
various methods of multicleaning flotation process and chemical methods, it can be used
for any application.
FLOWSHEET OF A TYPICAL GRAPHITE UPGRADATION CIRCUIT
BIBLIOGRAPHY
1. Graphite deposits of Devgad Baria, Panchmahal, Gujrat‐Scope for development‐ B L
Narayana
2. Industrial Minerals Laboratory Manual Flake Graphite—C J Mitchell
3. The bright side of graphite ‐‐ Alexandra Feytis, July 2010 industrial minerals
4. Graphite‐‐ Michel Dumont
5. GRAPHITE‐‐ Rustu S. Kalyoncu
6. A review on beneficiation prospect of some of the graphite deposits of Bihar P. N.
Pathak ,M. V. Ranganathan and D. M. Chakraborti