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Trans. Indian Inst. Met. TP 1911 Vol.57, No. 6, December 2004, pp. 617-621

COBALT AND EXTRACTION FROM SIKKIM COMPLEX SULPHIDE CONCENTRATE

M.K. Ghosh, L.B. Sukla and V. N. Misra Regional Research Laboratory, Bhubaneswar-751 013 E-mail : [email protected]

(Received 16 April 2004 ; in revised form 19 July 2004)

ABSTRACT

The concentrate produced from the complex sulphide deposit of Sikkim is not suitable for usual treatment processed like due to high bismuth content. The present investigation has been carried out to study the amenability of the above concentrate towards – both chemical and bioleaching. Bioleaching of the concentrate using Thiobacillus ferrooxidans in a 2 litre bioreactor resulted in about 39% extraction of both and zinc after 168 hours of leaching under the following conditions: pulp density 10%, pH 1.5, stirring speed 500 rpm, bacterial population 108 cells/ml, temperature 35o C and air flow rate 200 cc/min For chemical leaching different routes were tried like oxidizing followed by leaching, direct sulphuric acid leaching, pressure leaching and ferric chloride leaching. Addition of lignin sulphonate as surface-active agent during sulphuric acid leaching significantly increased the recoveries of cobalt and zinc. Increasing the leaching temperature did not have significant effect on the recoveries, whereas acid concentration showed o 2 significant effect. At 140 C, 5 kg/cm oxygen partial pressure, 2.5 % (v/v) H2SO4 and 10% pulp density, 95% Co and 100% Zn could be extracted in 3 hours.

1. INTRODUCTION acid pressure leaching of sphalerite concentrate. After laboratory and pilot plant studies, a hydrometallurgical The demand for cobalt in India is about 600 tons/ process based on pressure oxidation of zinc sulphide year. Cobalt is mostly imported and partly produced concentrate was first commercially developed by from secondary sources. Essentially all of the world’s Sherritt Gordon, Fort Saskachewan, 5. cobalt production originates as a by-product of and/or whereas zinc is mainly produced from Acidophilic bacteria belonging to the genus sphalerite concentrate by Roast-Leach-Electrowin Thiobacillus have been widely used for the leaching (RLE) method1. With the development of zinc of sulphide minerals6,7. Bioleaching of metals from production in India during last two decades, about sulphide minerals is being explored using 60% demand for zinc is currently being met by bioreactors8,9. indigenous sources. From a relatively small and complex sulphide The stringent environmental restrictions imposed on deposit of about 1 million ton located in Sikkim, the sulphide smelters and need to utilize small and India, Sikkim Mining Corporation (SMC) is complex deposits stimulated the development of producing both bulk and individual concentrates of alternative methods especially hydrometallurgical copper, zinc and lead. About 1000 tons of lead routes that avoid the production of sulphur dioxide, concentrate is lying with SMC unsold/untreated due a pollutant. The conventional method for the to high bismuth content. dissolution of Ni-Co sulphides is either acid pressure The main objective of the present investigation was leaching 2 or oxidative ammonia leaching 3. For zinc to test amenability of the SMC lead concentrate sulphide concentrate various leaching agents have been towards different chemical leaching routes as well tried and reported in the literature, but the most bioleaching using. T. ferrooxidans for maximum extensively studied one is the sulphuric acid pressure cobalt and zinc extraction (with minimum ) in leaching. Forward and Veltman 4 first suggested direct the leach liquor. TRANS. INDIAN INST. MET., VOL. 57, NO. 6, DECEMBER 2004

2. EXPERIMENTAL to which 4 perpendicular rods were attached. Air was supplied from a compressor through a sparger 2.1 Concentrate fixed at the bottom. Bioleaching experiments were carried out taking 1620 ml of ferrous free 9K medium The lead concentrate used in the study was supplied and 180 ml of fully-grown inoculums. by Sikkim Mining Corporation. The chemical composition of the concentrate is given in Table 1. 3. RESULTS AND DISCUSSION The –150 Om particle size fraction was used for the investigation. 3.1 Bioleaching

2.2 Pressure Reactor Before conducting bioleaching studies in the bioreactor, shake flask experiments were carried out Pressure leaching experiments were conducted in Parr to study the influence of pulp density, pH and 2 L autoclave with titanium liner and internal parts retention time. Detailed results are reported made of titanium. Temperature was controlled elsewhere 10,11. During bioleaching in the bioreactor through a PID controller with digital read-out for following conditions were maintained: bacterial temperature, pressure and agitation speed. For each population 108 cells/ml, agitation speed 500 rpm, air run, 1000 ml aqueous solution of predetermined flow rate 200 cc/min., pH 1.5 and temperature 35oC. strength of leaching agent, 100 g concentrate and additives were charged into the vessel and the reactor Figures 1 and 2 show the metal extraction achieved closed properly. Prior to heating the autoclave, gas at 10% pulp density in the 2-litre bioreactor. After volume was purged with nitrogen three to four times 126 hours of leaching, zinc and cobalt extraction was to make the environment oxygen free during heating. found to be 34.8% and 27.3% respectively (Fig.1).

Reactor was heated to the desired temperature and The acid consumption was 137.6 g H2SO4 / ton of when the set temperature reached, oxygen was concentrate. Keeping other conditions same, leaching introduced and full agitation was placed.

2.3 Microorganism

Thiobacillus ferrooxidans used in this study was isolated from zinc tailings. The organism was grown in 9K medium and when more than 95% ferrous was oxidized, culture was harvested and preserved. The adapted culture was developed by transferring 5 ml aliquots, after 10 days from the previous set into the next set containing higher pulp density (upto 10%). % METAL EXTRACTION

2.4 Bio-reactor Fig. 1 : Extraction of cobalt and zinc in 2 litre bioreactor Batch studies of bioleaching were carried out in 2 [Time 126 hr, pH 1.5, air flow rate 200 cc/min, litre capacity bioreactor having provision for stirring agitation 500 rpm, 350 C, bacterial population 108 and aeration. Stirring was done with mechanical stirrer cells/ml]

Table 1 CHEMICAL COMPOSITION OF SIKKIM COMPLEX SULPHIDE (LEAD CONCENTRATE).

Zn Co Cu Pb Fe S Bi Ni

9.49% 0.82% 0.9% 18% 25.5% 23.1% 0.56% 0.11%

618 GHOSH, et.al., : COBALT AND ZINC EXTRACTION FROM SIKKIM COMPLEX SULPHIDE CONCENTRATE

leaching. Roasting was done at 200oC for 2 to 6 hours duration. Roasted mass was leached in 2% (v/ o v) H2SO4 at 95 C for 2 hour. But extraction of zinc and cobalt was very low - only 2% and 10% respectively

The next sets of experiments were conducted keeping in view the usual leaching agents used for base metal sulphides. The conditions of leaching and corresponding extraction values of cobalt and zinc % METAL EXTRACTION after 3 hours of leaching are given in Table 2.

Fig. 2 : Extraction of cobalt and zinc in 2 litre bioreactor From the results shown in Table 2 it is evident that [Time 168 hr, pH 1.5, air flow rate 200 cc/min, sulphuric acid pressure leaching results in better cobalt 0 8 agitation 500 rpm, 35 C, bacterial population 10 recovery. Besides good metal recoveries iron cells/ml] contamination of the leach liquor is comparatively less, which is desirable for downstream processing. time was increased in the second experiment to 168 hours and the extraction values for zinc and cobalt During leaching of sulphide materials in acidic media, were 39.4 and 38.7% respectively after 168 hours elemental sulphur forms as a by-product. Since sulphur (Fig.2). Although zinc extraction was marginal, melts at 120oC, some suitable surface-active agents cobalt extraction increased significantly with to be used if leaching is done at temperature >120o increasing time. The percentage of zinc and cobalt C in order to prevent molten sulphur from wetting obtained in bioreactor leaching is much higher than the unreacted sulphide particles. In the present that obtained with shake flasks experiments11. It is investigation lignin sulphonate was used as surface- known that and oxygen are needed active agent. for actively metabolising T. ferrooxidans, which is an autotrophic microorganism. Due to heterogeneous Figure 3 shows the leaching results at two different o o nature of the system, thorough mixing of mineral, temperatures 140 C and 155 C using 6g/l lignin 2 nutrient and microorganisms is essential. The above sulphonate, 1.5% (v/v) H2SO4 and 5 kg/cm oxygen o conditions are fulfilled in the bioreactor but not in partial pressure. At 140 C, cobalt recovery after 3 shake flask, hence bioreactor resulted in increased hour is 73% as compared to 23% without lignin recovery of metals. sulphonate (Table 2). The higher temperature enhances the initial leaching rate but final cobalt 3.2 Chemical leaching recovery is same. Zinc recovery rate increases marginally with temperature. But temperature has a Different leaching media were used in order to test pronounced effect on iron precipitation. Final the amenability of the concentrate towards leaching concentration of Fe in leach liquor at 140oC is of cobalt and zinc values. Preliminary tests were 1.1 g/l whereas at 155oC it is 0.3 g/l, which is conducted with roasting following by dilute acid beneficial from the point of view of down stream

Table 2 RESULTS OF PRELIMINARY LEACHING TESTS ON SIKKIM LEAD CONCENTRATE.

Sl. No. Conditions % Co % Zn Fe (g/l)

1HSO 1.5% (v/v), 1400C, P 5 kg/cm2 23.2 46.9 2.5 2 4 O2 2 Total NH 3.17 M, 1400C, P 5 kg/cm2 3.5 93.3 Nil 3 O2 0 3 FeCl3 0.5 M, 85 C 15.0 52.0 34.0

619 TRANS. INDIAN INST. MET., VOL. 57, NO. 6, DECEMBER 2004

as well as chemical leaching. Bioleaching of the concentrate at 10% pulp density resulted in 39% extraction of cobalt and zinc after 168 hours of leaching. Low temperature roasting followed by sulphuric acid leaching did not give significant recovery of cobalt and zinc. Sulphuric acid pressure leaching at 1400C resulted in 23% Co and 47% Zn recovery. When 6 g/l lignin sulphonate was used as surface-active agent to disperse molten sulphur from wetting the unreacted particles, both cobalt and zinc recoveries were observed to increase. Increasing the temperature from 1400C to 1550C did not improve Fig. 3 : Effect of temperature on metal extraction in presence extraction values. Increasing sulphuric acid of lignin sulphonate [Conditions: lignin sulphonate 6 concentration was beneficial for the recovery of cobalt g/l , O partial pressure 5 kg/cm2, 1.5% H SO (v/ 0 2 2 4 and zinc. With 2.5% (v/v) H2SO4, 140 C, 6 g/l v) and time 3 hour]. lignin sulphonate and 5 kg/cm2 oxygen partial pressure, 95% Co and 100 % Zn values could be leached in 3 hours.

ACKNOWLEDGEMENT

Authors are thankful to Sikkim Mining Corporation, Sikkim for providing the concentrate to carry out the present investigation.

REFERENCES

1. Monhemius A J, Topics in Non-ferrous , Burkin, A.R., Ed., Society of Chemical Industry, Oxford, 1980.

2. Canterford J H, and Dyson N F, Pressure Leaching of Mixed Cobalt-Nickel , Proc. Aust. Inst. Min. Fig. 4 : Effect of H2SO4 concentration on metal extraction in presence of lignin sulphonate. [Conditions: lignin Metall., 380, 53-57, 1981. 0 sulphonate 6 g/l, temperature 140 C, O2 partial pressure 5 kg/cm2 and time 3 hour]. 3. Forward F A, and Mackiw V N, The Ammonia Pressure Process for Leaching Nickel, Copper and Cobalt from Sherritt Gordon Concentrates, J. Metals, 7, AIME processing. Trans., 203, 457-63, 1955.

Figure 4 shows the effect of acid concentration on 4. Forward F A, and Veltman H, Direct Leaching of Zinc metal recovery at 140oC and 5 kg/ cm2 oxygen partial Sulfide Concentrates by Sherritt Gordon, J. Metals, 11, pressure. It is observed that cobalt recovery increased 836-40, 1959. from 73% (at 1.5% H2SO4) to 95% (at 2.5% H2SO4). 5. Veltman H, and Bolton G L, Direct Pressure Leaching Zinc recovery also increased from 73% to 100% of Zinc Blende with Simultaneous Production of with increase in acid concentration. Elemental Sulfur. A State-of-the-art Review, Erzmetall, 33(2) 76-83, 1980. 4. CONCLUSIONS 6 Torma A E, The Role of Thiobacillus ferrooxidans in Hydrometallurgical Processes, Adv. Biochem. Eng., 6, The lead concentrate produced from complex sulphide 1-37, 1977. of SMC was tested for amenability to bioleaching 7. Nestor D, Valdivia U, and Chaves A P, Mechanism of Bioleaching of a Refractory Mineral of Gold with

620 GHOSH, et.al., : COBALT AND ZINC EXTRACTION FROM SIKKIM COMPLEX SULPHIDE CONCENTRATE

Thiobacillus ferrooxidans, Int. J. Miner. Process., 62(1- 10. R.R.L. Report No. T/BMBT/Dec/2002, “Evaluation 4), 187-198, 2001. of Process Variables in Continuous Scale Biooxidation of Complex Sulphide Ores/Concentrates of Ambamata/ 8. Chandraprabha M N, Modak J M, Natarajan K A, and Sikkim”, submitted to Ministry of and Mines and Raichur A M, Strategies for Efficient Start-up of DST, Govt. of India, 2002. Continuous Bioreactor Processes for Refractory Gold Ores, Miner. Eng., 15, 751-53, 2002. 11. Pani C K, Patnaik L, Kar R N, Roy Chaudhury G, and Sukla, L.B., Bioleaching of Sikkim Lead Concentrate in 9. Bailey A D, and Hansford G S, Factors affecting Shake Flasks as well as in Bioreactor Using Thiobacillus Bioxidation of Sulphide Minerals at High Concentration ferrooxidans, Proc. Int. Conf. on Advances in Materials of Solids – A Review, Biotech. Bioeng., 42, 1164-74, and Materials Processing, Feb. 1-3, Kharagpur, 539- 1993. 544, 2002.

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