Leaching of nickel laterite using fungus mediated organic acid and synthetic organic acid: a comparative study

A huge amount of overburden (nearly 8 to 10 times of the ore) containing trace amount of nickel and cobalt is generated during Chromite mining at Sukinda valley, Orissa, Chromite overburden contains around 0.4 to 0.9% Ni and 0.02–0.05% Co respectively. The setting up of nickel and cobalt processing plant based on these deposits through conventional methods such as pyrometallurgy and hydrometallurgy is not economical. The microbes and metals interaction have been studied for the exploitation in metals extraction. So an attempt has been made to extract these metals using multi metal resistant indigenous microorganisms, isolated from the Chromite overburden of Sukinda mines. A native strain of Aspergillus species was used for bioleaching. Aspergillus species are well known for their potential to produce a variety of organic acids (oxalic, citric acids etc.). The mineralogical studies indicated that there is no separate nickel bearing mineral phase in the Sukinda Chromite overburden. The mineralogy of the raw lateritic ore reveals the presence of goethite, ferrihydrites as major minerals. In the thermally activated overburden the minerals present were hematite, surimarite, quartz and traces of magnetite. Experiments were carried out with synthetic organic acids at 2.5% pulp density, 350C and 150rpm. Synthetic oxalic acid (0.1 M) leached 5% Ni and 71% Co from raw ore, whereas it leached 43% Ni and 95% Co from thermally activated ore. Citric acid (0.1 M) was not that much efficient. It leached 9% Ni and 14% Co from raw ore and 32% Ni and 45% Co from thermally activated ore. The fungal culture filtrate leached 3% Ni and 12% Co from raw ore. In case of roasted ore it leached 18% Ni and 28% Co at 2.5% pulp density, 35°C and 150rpm. Mineralogical analysis was carried out through X-ray diffraction, FTIR and transmission electron microscopy