Phase equilibria in the metal-sulfur-oxygen system and selective reduction of metal oxides and sulfides: Part I. The car
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I.
INTRODUCTION
PYRITE-BASED minerals such as chalcopyrite (CuFeS2) are one of the primary sources of copper, whereas nickel and cobalt occur both as oxides and sulfides. In general, copper is a more abundant metal than either nickel or cobalt. The association of various metallic species in minerals is determined by their chemical similarities. For example, the chemical dissemination of nickel and the less abundant cobalt in copper-iron-sulfide and arsenopyrite is likely due to the comparative ionic sizes of the base metals, leading to an easier substitution of the metallic ions in the mineral crystal lattice. In lateritic and limonitic mineral lattices, on the other hand, iron ions are partially replaced by nickel and cobalt ions; consequently, a complex multicomponent solid-solution mineral sulfide phase is formed. In nickeliferous silicates, notably in serpentine Mg6Si40~o(OH)s, the magnesium ions are partially replaced by nickel, cobalt, and iron. This is because the ionic radius of Mg 2§ (0.065 nm) is comparable with the ionic radii of bivalent transition metal ions, e.g., Ni 2§ (0.072 nm), Fe 2§ (0.076 nm), and Co 2+ (0.074 nm). Laterites are also an important source for metals such as chromium, and hence their reduction behavior
ANIMESH JHA, Reader, formerly with the Department of Materials Technology, Brunel University, Uxbridge UB8 3PH, United Kingdom, is with the School of Materials, University of Leeds, Leeds LS2 9JT, United Kingdom. SANCHUAN TANG, Research Assistant, is with the Changsha Research Institute of Mining and Metallurgy, Changsha, People's Republic of China. ANDREAS CHRYSANTHOU, Lecturer, is with the Department of Materials, University of Surrey, Surrey GU2 5XH, United Kingdom. Manuscript submitted February 7, 1995. METALLURGICAL AND MATERIALSTRANSACTIONS B
makes an interesting investigation for alloy powder production via the reduction of laterites and limonites. The present investigation of the phase equilibria in the M(metal)-S(sulfur)-O(oxygen) system is divided into two parts. Part I examines the carbothermic reduction of oxide and sulfide minerals in the presence of CaSO~ for achieving preferential separation of the constituent metallic species. The phase equilibria for a selective reduction of a complex sulfide matte in the presence of lime as a sulfur exchange medium are also discussed. In part II, the results obtained from the direct reduction of laterites and their major constituent transition-metal oxides are reported. Nickel, chromium, and cobalt are metals of strategic importance. Their combined concentrations in any deposit rarely exceed a few percent. The total concentration of nickel and cobalt in the richest deposits can be as high as 5 to 6 wt pct; while the leanest deposits may contain as low as 0.8 wt pct. The presence of chromium often makes the metal extraction process economically more attractive when the deposits are particularly lean in cobalt. Chromium is not associated with the pentlandite mineral from Kalgoorlie, Western Australia, investigated in this article.
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