ABSTRACT: Low grade phosphate ore of Jhamarkotra that analyzes 16.5% P~2~O~5~ is upgraded to 34% P~2~O~5~ by a two stage flotation process after size reducing the ore to 90% passing through 200mesh using conventional equipment such as jaw and cone crushers followed by ball mills. Re-engineering the flotation circuit reduced the power consumption from 55 kWh per metric ton of ore treated to 50 kWh. Incorporation of roller press in the grinding circuit resulted into further reduction of power consumption to 32 kWh per metric ton of ore treated.&#xd;&#xa;&#xd;&#xa

C.L Jain

Sekhar Dmr

English

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Jhamarkotra phosphate ore processing plant 
D. M. R. Sekhar 
R. S. M. M. Ltd., Bikaner, India 
C. L. Jain 
R. S. M. M. Ltd., Udaipur, India 
ABSTRACT: Low grade phosphate ore of Jhamarkotra that analyses 16.5% P2O5 is upgraded to 
34% P2O5 by a two stage flotation process after size reducing the ore to 90% passing through 
200mesh using conventional equipment such as jaw and cone crushers followed by ball mills. 
Reengineering the flotation circuit reduced the powerconsumptionfrom55 kWh per metric ton 
of ore treated to 50 kWh. Incorporation of roller press in the grinding circuit resulted into 
further reduction of power consumption to 32 kWh per metric ton of ore treated.
 INTRODUCTION
Beneficiation   of   phosphate   ores   containing carbonate  gangue  minerals  such  as  calcite 
and dolomite is one of the toughest problems before mineral process engineers, whereas phosphate 
ores with siliceous gangue (Florida, Senegal, Matoon ores)   can be processed [1] by direct flotation 
of apatite minerals with soap collectors after desliming the ore( to remove clay,   chert etc.) 
before milling. However, laboratory/pilot stage techniques to separate apatite, carbonate 
minerals are known. These techniques [2] involve reverse flotation carrying carbonate minerals 
into the froth product using  soap  collectors  while  depressing  apatite minerals either by 
phosphoric acid or by fluosilisic acid and the phosphate concentrate is recovered as chamber 
product (tailing).
Discussing conventional crushing (e.g. jaw and cone crushers) and grinding (ball   mills   for 
example) Gaudin questions [3] “why comminuting  efficiencies  of  apparently effective 
machines should be so low”. The efficiency of grinding (Ball mill) may be 10% or still low. 
It is reported [4] that 50% of the costs incurred in base metal concentrators is on grinding. Prof.  K. 
Schonert  designed  a  size  reduction equipment (commercial machines  are  popularly known 
as roller presses or High Pressure Grinding Rolls) which is based on the principle of “crushing a 
mineral  particle  between  other  mineral  particles instead of grinding elements”. This is achieved 
by choke feeding the roller press that has two rolls of which one is fixed and the other is sliding. 
Both rolls are driven by separate motors, and comminution pressure is hydraulically applied to 
the sliding roll. These machines are highly energy efficient and are very successful in cement 
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industry. The success of these machines in mineral processing industry (hard rock) is very limited 
mainly due to the wear problems of the grinding surfaces [5].
 THE JHAMARKOTRA PROCESS  
Jhamarkotra ore is having 13 to 18% P2O5, 10-12% MgO  and 4-6%  SiO2.The  major  minerals 
are sedimentary crypto crystalline apatite, dolomite and quartz  along  with  some minor 
quantities  of oligoclase,  sillimanite  etc.  Jhamarkotra  deposit contains 40 million tons of such 
low-grade ores. The process involves size reduction of the ore lumps through crushing  and 
grinding  to 90%  passing through 74 microns followed by bulk flotation of apatite  and 
carbonate  minerals  leaving  siliceous gangue into the tailing. The bulk concentrate is taken to the 
second stage flotation where acidic pH (5.0 to 5.5) is maintained using sulphuric acid (11 to 12 kg per 
ton of ore) and phosphoric acid (6 to 7 kg per ton of ore) is used to depress apatite minerals while 
floating dolomite with oleate (1.2 kg per ton of ore). Alfa olefin sulfonate (150 to 200 grams per ton 
of ore) is used along with oleate. This process is successful with dolomite gangue while 
excessive (>6%) presence of calcite in the ore upsets the process by reducing the concentrate 
grade to below 34% P2O5. It was found [6] that  soaps of mixed fatty acids having the titre point in the 
range 22-26o C and with   an iodine value between 88-93  and having  a  total  fatty  matter 
between 60-65 are very efficient. It was proved [6] by carrying out bench scale experiments that  the 
soaps of saturated fatty acids (e.g. stearic acid) are more efficient than the soaps of unsaturated (e.g. 
oleic)  fatty  acids,  as  flotation collectors, particularly in acidic circuits. However it is required to 
prepare hot solution [7] if soap of saturated fatty is to be used.
PLANT  LAYOUT -1500 TPD
Run of mine analyzing 17.5% P2O5 in the size < 1000 mm is fed into a coarse ore bin (COB). 
The material is drawn from the COB through an apron feeder (max. capacity 345 mtph) and fed 
into a double toggle jaw crusher (1500 X 1200 mm driven by 190 kW motor). The crusher product 
(200 mm max) is taken to a buffer stock pile. The material from  the  buffer  stock  pile  is 
drawn  through  a reciprocating feeder located in a tunnel below the stockpile through a 
conveyor that feeds a double deck screen of 152.4 mm X 406.4 mm driven by 30kW motor in 
closed circuit with a short head cone crusher (1750mm, driven by 200 kW motor) of HEC. The 
secondary crusher product (60 mm max) can be either taken to stock piles where stacking and 
reclaiming arrangements are made or to the tertiary short head cone crusher (1750 mm, driven by 
200kW motor) directly, which is also in closed circuit with a double deck screen of 203.2  mm X 
508 mm, driven by 30 kW motor. The final crushed product is maximum 12.5 mm, which is fed to 
fine ore bins having a total capacity of 3000 mt. The material from the fine ore bins is fed to 
two ball mills (3.3meters dia and 4.2 meters length), each driven by a motor of 600 kW. Each mill 
can be fed at the rate of 32 to 36 metric tons per hour (mtph). The mills are rubber lined and are in 
closed circuit (Figure 1) with hydro cyclones (three D-10 cyclones in each mill operating at a time). 
The mill discharge is pumped to the cyclones through a variable speed pump (75kW). The cyclone 
overflow is classified in two sets(one each for a mill) of secondary cyclones. The secondary 
cyclone overflow goes to bulk thickeners and the underflow is taken to bulk flotation (apatite and 
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dolomite) circuit layed in two streams each stream having 6 cells of 9m3. While bulk circuit tails 
are discarded, the bulk concentrate is fed to the bulk thickeners. The bulk thickener underflow is 
drawn by horizontal pumps with variable speed motors in measured quantities at the rate of 24 to 28 
mtph dry solids basis and fed into a stream consisting of two flotation lines. The plant has two 
bulk thickeners  that feed four flotation lines at the rate of 12 mtph to 14 mtph (each line) as 
controlled by PLC. After the addition of phosphoric acid, the pH of the pulp is adjusted to 5 to 5.5 
by adding sulphuric acid. Each flotation line in the acid circuit is having 12 flotation cells of 9 m3. 
The pulp density is maintained at 1.3 before it enters the flotation circuit and soap solution is added at 
3 points in each line to float dolomite. The dolomite rougher concentrate is cleaned twice. The 
first cleaner has 3 cells of 9 m3 and the second cleaner has 3 cells of 9m3.  The phosphate 
concentrate is collected as chamber product (tail) of the rougher cells of the acid circuit. The 
concentrate is thickened and filtered to get a phosphate concentrate cake at18% ±1% moisture. 
The concentrate is air dried to get moisture content <12% and is dispatched.
 REENGINEERING
Flotation
The flotation circuits of the Jhamarkotra plant were constructed using Denver-Sala flotation 
cells (AS-9) of 9 m3 volume which were fitted with an impeller drive motor of 18.5 kW. Plant 
engineers carried out re-engineering of the flotation cells such that a single motor of 
18.5 kW drives two cells of 9 m3 each. This brought down kW/m3 from 2.05 to 1.02. At the 
same time by improving the airflow into the cells, the capacity of one line in the acid flotation 
circuit  has been increased from 14 mtph to 32 mtph. This has resulted into reduction in the 
power consumption from 55 kWh per metric ton of ore processed to 50kWh per metric ton. 
These developments raise several questions [8,9] on our current knowledge about flotation 
kinetics  and scale up of flotation circuits.
Grinding
The average Bond’s Work Index (BWI) of Jhamarkotra ore is 7 kWh per short ton. KHD 
Humboldt Wedag (Germany), tested the ore on a pilot size roller press having stud lining, 
pressing the material at 5N/mm2. After removing 125 micron size material, the coarse 
fraction is crushed to -3 mm size and BWI of this material is observed to be at 5.73 kWh 
per short ton. These tests also showed specific power consumption by the roller press to 
be 1.9 kWh per metric ton. After stabilization of the plant throughput and the process to 
give a consistent quality of phosphate concentrate at +34% P2O5, efforts were made to 
improve the grinding circuit. Roller  Press  of 120  cm  (diameter)  and 63  cm (width), 
driven   by 350   kW   motors   each manufactured  by  KHD  Humboldt Wedag)  is 
incorporated in the grinding circuit (figure 2) to work in tandem with one of the existing 
ball mills (600 kW). The roller press discharge cake is wet screened over a screen (of 3.6 
meters width and 6 meters long) having slots of 1.8 mm width and 20 mm long.
The wet screen underflow is fed to 3 cyclones of 254 mm diameter and its over flow is 
taken to secondary cyclones, while the underflow is fed to the ball mill which is operating in 
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closed circuit with 8 cyclones of 254 mm diameter. Ball mill cyclone overflow is also taken 
to the secondary cyclones. The overflow of secondary cyclones goes to the acid circuit and 
the underflow to bulk flotation. The roller press can take a feed size up to 30 mm, though it is 
presently being fed with -25 mm ore, by making necessary changes in the tertiary crusher 
set and the screen operating in closed circuit with it. The introduction of roller press in the 
grinding circuit(RPBM) has reduced the overall power consumption from 50 kWh per ton of 
ore treated to around 32 kWh, while giving, a fresh feed @ 120 mtph, and with an 
estimated recirculation load of 168 mtph.The  RPBM  circuit  became  operational  since 
27.3.2003.
CLOSING REMARKS
The Jhamarkotra process is well established to deal with low grade phosphate ores that contain 
dolomite gangue with minor quantities of silicate minerals.Separation of apatite and calcite 
is still a problem, though the presence of calcite in Jhamarkotra ore is limited to few blocks in 
the deposit. The available literature suggests a scale up factor of 2 to 2.9 for converting 
flotation time determined in bench scale experiments to residence time of industrial size 
flotation circuits whereas in actual practice [9] the scale up factor may be as high as 4.5  to 6. This 
is largely because of the difference in the rate of airflow per unit volume of the flotation cell 
and the size distribution of air bubbles in the batch flotation cell and the industrial cell. 
The least monitored parameter in an operating flotation plant is the rate of air flow, 
despite the fact that the kinetics of flotation and the capacity of a flotation cell are 
dependent on the rate of airflow per unit volume of the flotation cell. The bulk thickeners are 
removed from the reengineered (3000 TPD) flotation circuit without any adverse effect. 
The retrofitting of the roller press in the grinding circuit of the Jhamarkotra concentrator has 
drastically reduced the power consumption by 18 kWh per ton of ore treated while operating 
the plant @ 120 mtph of fresh feed. The ore forms an autogenous wear layer around the 
rolls because of   the stud   lining which prevents the wear of  the rolls.
 ACKNOWLEDGEMENTS
Thanks are due to Shri K.S. Money, former M.D., RSMML, Mr.  Rudolf Pich of KHD 
Humboldt Wedag and to Er. S.K. Madhok, formerly with M/s Hyderabad Industries Ltd., for 
their keen interest in implementing the RPBM project of retrofitting of the roller press. 
Special thanks are also due to Shri Rajat Kumar Mishra, MD, RSMML for according 
permission to publish this work. We congratulate the engineers working for Jhamarkotra 
Plant for successfully operating RPBM grinding circuit after reengineering flotation circuit to 
match the enhanced capacity. We appreciate the patience of Shri Shripal Bhandari, Shri 
Rakesh Ojha    and Shri R.P.Kumawat in preparing the manuscript. Thanks are due to M/s 
KOPPERN, M/s Krupp Polysius and KHD Humboldt Wedag of Germany for their keen 
interest in helping us (RSMML) by testing our ore and reporting the suitability of their 
machines. We are also thankful to Prof. T.C. Rao and Er. B.N. Chatterjee, the 
consultants of RSMML, who strongly advocated for RPBM circuit. Technology 
Development   Board,   Dept.   of   Science   & Technology, Govt. of India provided 
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(soft) loan (part) to RPBM project. Special thanks are due to Mr. Stephan Kirsch, Mr. Gerd 
Ehrentraut, and Mr. Goutam Basu (of KHD) for their useful suggestions that improved this 
article.
 REFERENCES
[1]  Sekhar, D.M.R., Ranga Rajan, V.S., Ramanamurthy, S.V. and Jain, V.K., Processing 
Low Grade Silica  based  Rock  Phosphate  Ore,  Fertiliser News Vol. 31, No.6, (1986).
[2] Glembotski, V.A., Klassen V.I. and Plaksin I.N., Flotation, Primary Sources, New York, 
(1972).
[3] Gaudin, A.M., Principles of Mineral Dressing, Tata Mc Graw-Hill Publishing Company 
Ltd., New Delhi, (1977).
[4] Pradip, Scientific and Technological Challenges in Mineral Processing, Mineral 
Processing and Extractive Metallurgy Review, Vol. 10, (1992). 
[5] Chris Morley, HPGR in hard rock applications, Mining Magazine, September 2003).
[6] Sekhar,  D.M.R.,  Chauhan,  Y.K.,  Soap  Flotation Plant Practice in India, Trans Indian 
Inst. of  Metals, Vol. 51, No. 4, (1998).
[7] Srinivas K., Sekhar, D.M.R., Chauhan Y.K,   Soap Flotation of Dolomite, Paper 
presented during National Seminar on Indian Mineral Processing Advances,  Organized  by 
Indian Institute  of  Mineral Engineers at Puri, 18-19 April (1996). 
[8] Sekhar,  D.M.R.    and  Rama  Shankar,  Flotation Kinetics:  An  Overview,  Process 
and    Plant  Engineering, Vol. XIX, No. 5, Annual (2001).
[9] Sekhar, D.M.R., Scale Up and Design of Flotation Circuits, Process and Plant 
Engineering, Vol. XIX, No.3, Oct.-Dec, (2001).
A version of this article is in the proceedings of International Mineral Processing 
Congress - 2006, Turkey.
 
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Figure 1. 750 tpd ball mill circuit
Figure 2. 3000 tpd roller press ball mill circuit
71 tph
71 tph
54 tph
125 tph
175 tph
32 tph
128 tph
32 tph
1)  Ore Bin
2)  Ball Mill ,  600 Kw; Bm
3)  Bm  Discharge Pump
4)  Bm, Hydrocyclones
5)  Roller Press (350+ 350) = 
700 Kw, Rp
6)  Wet Screen
7)  Rp, Hydrocyclones
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A version of this article is in the proceedings of International Mineral Processing Congress - 2006, Turkey. N a t u r e P r e c e d i n g s : d o i : .

Flotation Kinetics: An Overview,

HPGR in hard rock applications, Mining Magazine,

Primary Sources,

Principles of Mineral Dressing,

Processing Low Grade Silica based Rock Phosphate Ore,

Scale Up and Design of Flotation Circuits,

Scientific and Technological Challenges

Soap Flotation of Dolomite, Paper presented during National Seminar on Indian Mineral Processing Advances, Organized by Indian Institute of Mineral Engineers at Puri,

Soap Flotation Plant Practice in India,

Jhamarkotra phosphate ore processing plant

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Jhamarkotra phosphate ore processing plant

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