Physico-Chemical Characterisation of Lateritic Nickel Ores of Sukinda, Orissa

Abstract

The only nickel ore deposit of significance in India occurs in the chrorniferous ultramafic complex ofSukinda, Orissa. It is a lateritic nickel o re deposit with a reserve of about 150 million tonne having cut-off grade of 0.05% Ni. The processing of this ore is difficult due to ultrafine nature ofgeothite, low content of nickel in the ore (max. 1.5% Ni), complex intergrowths of goethite with quartz, talc, kaolinite and magnetite and abrupt variation of nickel content in the ores in horizontal and vertical profiles. In this study the results of detailed investigations to characterise five bulk samples collected from different sectors of Sukinda-Kansa, TISCO and OMC are discussed.The techniques used for characterisation include granulometric study, optical microscopy, X-ray diffraction, thermal analysis, scanning electron microscopic, infrared studies, electron probe microanalysis, leaching experiments and chemical analyses. This study indicates that the nickel is not present as discrete minerals but mostly associated with goethite. Kansa ore has goethite as major mineral (90%) whereas the other samples contain significant amount of free quartz along with variable amount of chromite,hematite,magnetite, talc, serpentine and kaolin. The fine grained goethite is amorphous to quasi-amorphous in nature. Mineralogy and chemistry of the samples indicate that goethite. Fe and Ni are invariably enriched in the finer size fractions. Electron probe microanalyses indicate that nodular goethire and chromite are Ni-poor (<0.2% Ni) whereas lithiophorite and magnetite contain 11% and 0.9% Ni respectively- The results of the sequential leaching studies involving oxalic, sulphuric and hydrochloric acids indicate three types of association of nickel in goethite: a part with amorphous goethite (ferrilivdrite), a part in weak/A- bonded nature and a part as lattice bound state in goethite . The laterite ore is thus proved to be of comple x in nature which creates problem for liberation of the constituent minerals based on the srnface properties. Classification down to silt size fraction increases the Ni content to about 1.0% in the material. These ores have been succes.sful/v tested on pilot plant scale for extraction of nickel metal by reduction roasting followed by arnnrotriut)r - atnmonicrcal leaching and electrowinning