The leaching of nickeliferous laterite with ferric chloride
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TRODUCTION
THE majority of the world’s known and anticipated reserves of nickel ores are lateritic deposits. Nickeliferous limonites,[1,2,3] which constitute one of three zones of a typical laterite deposit, are also future sources of cobalt, chromium, and iron. Laterites are near-surface deposits of oxidized material formed by extreme weathering (or ‘‘laterization’’) of parent ultramafic rock. As a result of escalating mining costs, depleting sulfide reserves, and an increasing world demand for nickel, laterites appear to be promising, because they are abundant and relatively inexpensive to mine. Several processes have been described for the selective recovery of nickel and cobalt with dilute acids,[4,5,6,7] as well as for the selective conversion of nickelous and cobaltous oxides with gaseous hydrogen chloride,[8] followed by selective reduction with carbon monoxide/carbon dioxide mixtures. Heertjes and Van Nes[9] have described a method for increasing the ratio of the amounts of nickel and cobalt with respect to iron. Roorda and Queneau[10] proposed a process based on the pyrometallurgical selective reduction of nickeliferous limonites, followed by aqueous chlorination in seawater. The processes currently in commercial operation include pressure acid leaching, matte smelting, the production of ferrous nickel by electric or blast furnace, and the selective reduction roast followed by ammoniacal leach. All of the leaching procedures previously described have certain unit processes in common, such as a pretreatment stage, usually reduction roasting, and/or high-temperature pressure leaching. As a result of escalating energy costs, it is prudent to bypass the expensive pretreatment reductionroast stage; however, proposed processes for the direct extraction of nickel and cobalt by mineral acid[11] have been unsatisfactory because of a lack of selectivity in metal dissolution and severe corrosive conditions. Mineralogically, the predominant mineral species present in nickeliferous laterites is goethite (a-FeO(OH), HFeO2, or Fe2O3,H2O) with NORMAN D.H. MUNROE, Assistant Professor, is with the Mechanical Engineering Department, Florida International University, Miami, FL 33199. Manuscript submitted July 2, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS B
varying amounts of nickeliferous phyllosilicates of the montmorillonite and serpentine types which contain less than a tenth of the total nickel. The solubilization of goethite by acids of equal normality greater than 1N has been found by various workers[12,13,14] to increase in rate in the following order: perchloric acid , sulfuric acid , hydrochloric acid. Azuma and Kametan[15] have correlated the absolute rates of the leaching of goethite in different acids with the complexation constants of the respective anions for ferric ions. Recently, Tzeferis[16,17] and Tzeferis and Agatzini-Leonardou[18] described the leaching of low-grade laterite ore using fungi and biologically produced acid metabolites, and organic acids. The bioleaching of lateritic nickel ore using a he
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