LATERITIC NICKEL MINERALIZATION AND ITS EXTRACTION TECHNIQUES-A REVIEW

Nickel plays an important role in all the developed & developing economies. It is widely used across various industries either in the form of refined nickel or in the form of alloys. Presently the sulphide minerals are the prime sources for nickel extraction in the world. However, the extensively exploited sulphide mineral reserves are depleting in alarming rate and as a result the lateritic sources are gaining importance. Lateritic ores containing up to l.8% nickel oxide have been located in the iron and chrome ore belts of Odisha. In Sukinda valley nickel mineralizes as nickeliferrous limonitic ore which occurs as an overburden to Chromite mining. This overburden contains on an average 0.5-1% Ni. Mineralogical and chemical investigations reveal that nickel is released from serpentine (nepouite) by chemical weathering and has partly been residually enriched in goethite along with supergene enrichment in goethite and Mn oxides. Apparent percentage change of elements indicates that nickel is enriched in the saprolite part of the vertical column along with iron and manganese. A specific Ni mineral phase is absent in this material with the Ni and Fe being mostly enriched in finer fractions. Distribution of Ni and Fe in various size fractions and increase of Ni with increase in Fe (goethite content) indicate that goethite is the major Ni-bearing mineral phase. The nickeliferrous overburden is not directly suitable for extraction of Nickel by pyro-metallurgical or hydrometallurgical method of extraction as the overall Ni% is less. But with simple pre-concentration i.e. by reduction in pan sintering unit followed by low intensity wet magnetic separation, the material can be made suitable for extraction.