Recent Research in Science and Technology 2011, 3(6): 28-33 ISSN: 2076-5061 www.scholarjournals.org www.recent-science.com 28 RRST-Microbiology Microbial Recovery of Nickel and Cobalt from Pre-treated Chromite Overburdens of Sukinda Mines using Aspergillus niger Sunil Kumar Behera * , Prangya Parimita Panda and Lala Behari Sukla Institute of Minerals & Materials Technology (CSIR), Bhubaneswar, Orissa, India -751013 Article Info Abstract Article History Aspergillus niger exhibits good potential in generating a variety of metal chelating and solubilization organic acids during cellular metabolism. In this context, the minor constituent metals like nickel and cobalt embedded in chromite overburdens (COB) of Sukinda mines have been exploited through bio-hydrometallurgical route for recovery of these metal values. XRD and EPMA analysis of COB reveals that initially nickel was intertwined in the goethite lattice while after pre-treatment (600 o C), due to phase conversion of goethite to hematite leads to exposure of nickel particles into the micro-pores and cracks developed in the matrix. Hence, becoming more susceptible to attack by the fungal bio acids and accelerates metal dissolution. At a pulp density of 2 % (w/v) of pre-treated COB maximum nickel and cobalt recovered were 33.2 % and 82.4 % respectively after 24 days in shake flasks bioleaching using A. niger. Received : 11-02-2011 Revised : 26-03-2011 Accepted : 01-04-2011 *Corresponding Author Tel : +91- 6742-581635 Fax : +91- 6742-581160 Email: skbehera2020@gmail.com ©ScholarJournals, SSR-SILAE Key Words: Aspergillus niger, Chromite overburden, Nickel, Cobalt and Oxalic acid Introduction Chromite overburdens (COB) generated at Sukinda mines, Orissa, India, are known as only nickel laterite deposits. Laterites are oxide ores widely distributed in the tropical regions. They were formed during laterization, a weathering process of ultramafic rocks which is favoured by warm climate and abundant rainfall. In India, particularly in Sukinda mines Orissa, a huge amount of overburden is generated during chromite ore mining, which having 0.5- 1.0 % nickel and 0.03- 0.04 % cobalt [1]. The existing mineral processing routes for nickel recovery from laterite are high pressure acid leaching, Caron process, ferronickel and nickel matte smelting techniques. These processes involve higher energy utilisation and operational costs [2]. In this regard an effective technology for recovery of such valuable metals from these chromite overburdens is highly desirable that can address the aforesaid challenges. Therefore bioleaching can be an alternative process for economic and environment friendly extraction of metals. With a view to extract substantial amount of metal values from chromite overburdens, pre-thermal activation of chromite overburden was carried out prior to leaching. The thermal pre-treatment of chromite overburden have significantly influence on nickel and cobalt recovery through bioleaching [3]. The thermal activation changes the mineral structure and brings the mineral phase transformation by dehydroxylation of the goethite matrix in raw chromite overburden [4, 5]. Bioleaching of oxide and silicate ores require heterotrophic microorganisms which are able to produce organic acids, mainly oxalic acid, citric acid, gluconic acid, tartaric acid, and pyruvic acid. Aspergillus and Penicillium are the most widely used important filamentous fungi for the extraction of metals from oxide ores [6, 7]. Metal leaching by heterotrophic microorganisms generally involves an indirect process through microbial production of organic acids, amino acids and other metabolites. Four mechanisms have been reported to be involved during fungal bioleaching: (i) Acidolysis (ii) Complexolysis (iii) Redoxolysis and (iv) Bioaccumulation [8]. In this present study, an attempt has been made to study the effect of thermal pre-treatment of the chromite overburden on the recovery of nickel and cobalt using fungal strain A. niger. Materials and Methods Overburden Samples Chromite overburden samples were obtained from major chrome deposits of Sukinda Mines, Orissa, India. In this overburden, nickel is associated with the goethite matrix and cobalt is associated with the manganese phase. Laterite is a highly weathered material rich in hydrated iron oxide goethite α-FeO (OH) or Fe2O3.H2O, or both but devoid of bases and primary silicates and may contain abundant quartz and kaolinite. It contains minor amount of nickel, cobalt, and chromium [9]. For the experimental purpose the raw chromite overburden (COB) samples were thermally pre-treated at 600 o C for 5 hours to convert the goethite to hematite in order to release the nickel from its goethite matrix [1, 9]. The chemical analysis of the raw and the pre-treated chromite overburdens are shown in Table 1.