Pressure leaching

Nickel and cobalt are recovered by processes that employ both pressure leaching and precipitation steps. The raw materials for these processes can be sulfide concentrates, matte, arsenide concentrates, and precipitated sulfides. Typically, acidic conditions are used for leaching however, ammonia is also effective in leach solutions because of the tendency for soluble cobalt and nickel ammines to form under the leach conditions. 

A pressure leaching system to handle copper sulfide called the Sherritt-Cominco (SC) copper process was developed by these two Canadian firms. Pilot-plant testing was completed in 1976 (29), but commercial appHcation of this technology has not been achieved. 

The cmde oxide is pressure-leached in a steam-heated autoclave using water or circulating mother hquor. The arsenic trioxide dissolves, leaving behind a residue containing a high concentration of heavy metal impurities and sihca. The solution is vacuum-cooled and the crystallisation is controUed so that a coarse oxide is obtained which is removed by centrifuging. The mother hquor is recycled. The oxide (at least 99% purity) is dried and packaged in a closed system. 

In the most common hydrometallurgical process for zinc manufacturing, the ore is leached with sulfuric acid to extract the lead/zinc. These processes can operate at atmospheric pressure or as pressure leach circuits. Lead/zinc is recovered from solution by electrowinning, a process similar to electrolytic refining. The process most commonly used for low-grade deposits is heap leaching. Imperial smelting is also used for zinc ores. 

The metallic or semi-metallic character of many common sulfides implies the significance of electrochemical factors in the study of their oxidation, which is relevant to environmental, energy, and metallurgical issues, e.g., in connection with the direct electrochemical conversion of sulfide ores to metals, the pressure leaching of ore materials, or flotation processes. 

The example being considered under zinc ore pertains to acid pressure leaching of zinc concentrates developed by Sherritt Gordon Mines Ltd. in Canada. The basic reaction involved is... 

It will be interesting to record some of the evaluatory remarks as regards the process. There is no doubt that the direct acid pressure leach route is an attractive alternative to the conventionally followed process for zinc sulfide processing. Incentives for its adoption on a commercial scale are the reduced capital cost and production of sulfur in its most favored form, the elemental form. Nevertheless, no process is perfect and acid pressure leach process is not an exception. There are at least two aspects of the process which pose some problems. The first is the behavior of impurities, and the second is the disposal of iron. 

Iron in the feed concentrate is rejected either as unreacted pyrite mixed with elemental sulfur or as jarosites in the leach residue. The pyrite/sulfur mixtures said to be suitable for indefinite storage, but the well known environment effects caused by pyrite weathering are likely to make storage of this material a less than straightforward problem. Besides this, there are problems associated with the disposal of the leach residues from the pressure leach process. 

Chalkley, M. E. Toirac, I. L. The acid pressure leach process for nickel and cobalt laterite. Part I review of operations at Moa. Hydrometallurgy and Refining of Nickel and Cohalt, Annual Hydrometallurgy Meeting of CIM, 27th, Sudbury, Ont., Aug. 17-20, 1997, 341-353. 

Das, G. K. Acharya, S. Anand, S. Das, R. P. Acid pressure leaching of nickel-containing chromite over burden in the presence of additives. Hydrometallurgy 1995, 39, 117-128. 

Georgiou, D. Papangelakis, V. G. Sulfuric acid pressure leaching of alimonitic laterite chemistry and kinetics. Hydrometallurgy 1998, 49, 23 16. 

Papangelakis, V. G. Georgiou, D. Rubisov, D. H. Control of iron during the sulfuric acid pressure leaching of limonitic laterites. Iron Control and Disposal, Proceedings of the International Symposium on Iron Control in Hydro-metallurgy, 2nd, Ottawa, Oct. 20-23, 1996, 263-274. 

Rubisov, D. H. Papangelakis, V. G. Sulfuric acid pressure leaching of laterites—prediction of metal solubilities and speciation analysis at temperature. EPD Congress 1999, Proceedings of Sessions and Symposia held at the TMS Annual Meeting, San Diego, Feb. 28-Mar. 4, 1999, 535-546. 

Rubisov, D. H. Krowinkel, J. M. Papangelakis, V. G. Sulphuric acid pressure leaching of laterites—universal kinetics of nickel dissolution for limonites and limonitic/saprolitic blends. Hydrometallurgy 2000, 58, 1-11. 

Ozberk, E. Jankola, W. A. Vecchiarelli, M. Krysa, B. D. Commercial operations of the Sherritt zinc pressure leach process. Hydrometallurgy 1995, 39, 49-52. 

The tendency of gold(III) chlorocomplexes to adsorb on iron (hydrous) oxides that tend to form via in situ precipitation in acidic pressure leaching operations needs to be controlled to avoid undesirable metal losses. 

Comprex A process for treating sulfide ores by high-temperature pressure leaching. 

Musro [Murphy ores, CSIRO] Also written Murso. A process for beneficiating ilmenite by a combination of oxidation, reduction, and pressure leaching with hydrochloric acid. Invented in Australia in 1967 and developed jointly by Murphyores Pty and the Commonwealth Scientific and Industrial Research Organization, but not commercialized then. Further developed in 1992 by Pivot Mining NL, Queensland. 

Mackenzie, J. M. W. Virnig, M. J. Boley, B. D. Wolfe, G. A. ALTA 1998 Nickel Cobalt Pressure Leaching and Hydrometallurgy Forum, Melbourne ALTA Metallurgical Services, 1988. 

The metallic arsenic is obtained primarily from its mineral, arsenopyrite. The mineral is smelted at 650 to 700°C in the absence of air. However, the most common method of production of the metal involves reduction of arsenic trioxide, AsOs with charcoal. Arsenic trioxide is produced by oxidation of arsenic present in the lead and copper concentrates during smelting of such concentrates. The trioxide so formed, readily volatilizes and is collected in a dust flue system where further treatment and roasting can upgrade the trioxide content. The trioxide vapors are then condensed and further purified by pressure leaching and recrystallization techniques. It is then reduced with charcoal to give metallic arsenic. 

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