Lime-enhanced reduction of sulfide concentrates: A thermodynamic discussion
- PDF / 1,805,483 Bytes
- 12 Pages / 603.28 x 783.28 pts Page_size
- 54 Downloads / 208 Views
I.
INTRODUCTION
MANYnonferrous
metals such as copper, nickel, lead, zinc, cadmium, molybdenum, and mercury are produced from sulfide minerals. Normally, the pyrometallurgical route involves selective oxidation during which the conrained sulfur is emitted as sulfur dioxide. The containment of this off-gas is a major problem in sulfide smelters, particularly copper smelters. The conventional copper extraction process of reverberatory smelting followed by converting has been criticized as being inefficient, uneconomical, batchwise in character and, above all, a major contributor to atmospheric pollution. Recently-developed processes based on flash smelting, electric smelting, or continuous smelting principles are generally less polluting, but are still not efficient in totally controlling the level of sulfur dioxide pollution. In addition to this, conventional smelting also inherits other problems such as complex flowsheets, capital intensive technology, high energy consumption, and generally is not suitable for small scale operations. Further, the increasing depletion of high grade ores and scattered small-scale ore deposits, the high cost of energy, the increasingly high emphasis on energy conservation and environmental preservation, and socio-economic factors have increased the effort to develop alternative processes for the extraction of metals from sulfide minerals. One such process which has gained considerable interest in recent years is the direct reduction of sulfides with a reductant, e.g., hydrogen, carbon monoxide, or carbon in the presence of a desulfurizer, such as lime. This paper examines the thermodynamic aspects of these lime-enhanced reduction reactions for various metal sulfide concentrates.
II.
THERMODYNAMIC CONSIDERATIONS
The discussion in this paper is restricted to the limeenhanced reduction of chalcopyrite (CuFeS2), chalcocite (Cu2S), and pyrrhotite (FeS) with carbon monoxide (CO), hydrogen (H2), and carbon, although a similar approach may be used for other sulfide minerals. A. R. UDUPA, Postdoctoral Fellow, K. A. SMITH, Assistant Professor, and J. J. MOORE, Professor and Associate Director, are with the Mineral Resources Research Center, University of Minnesota, 56 East River Road, Minneapolis, MN 55455. Manuscript submitted July 16, 1985.
METALLURGICALTRANSACTIONS B
A. Free Energy and Enthalpy
The direct reduction of sulfide minerals with a reductant alone as represented by reactions MS + H2 = M + H2S
[A]
MS + CO = M + COS
[B]
MS + 0.5C = M + 0.5CS2
[C]
thermodynamically unfavorable due to the low equilibrium constants which can be seen in Tables I, II, and HI for chalcopyrite, chalcocite, and pyrrhotite. These low equilibrium constants impose severe limitations on the reduction process. In order to make the reactions thermodynamically more feasible, the product gases such as H2S, COS, or CS2, which will be at concentrations of only a few parts per million (ppm), must be removed from the reaction site. This causes the partial pressures of these product gases to drop to a very
Data Loading...
