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Acid decomposition reactions on compounds and minerals in the Fe-Ni-Sulphide system Jibiki, Kyosuke

Abstract

A recent awareness of sulphur dioxide air pollution encourages the sulphide treating metallurgical plants to recover SO₂ from exhaust gases. Although manufacture of sulphuric acid is probably the most economical way of recovering SO₂, the limited market for acid and the difficulties involved in handling it could make elemental sulphur a more desirable end-product. Hydrometallurgical oxidative treatment of sulphide ores has commonly been considered and practiced to be an option for the direct recovery of sulphur as elemental sulphur. Acid decomposition of sulphides has also been considered to be an alternative way to recover sulphur as elemental form via H₂S. In this study, the acid decomposition of natural and synthesized pyrrhotites was investigated kinetically choosing temperature and the compositions of the various phases as independent parameters. Comparison of the acid decomposition reaction rates was made for various compositions of synthesized sulphides in the Fe-Ni-S system. These results indicated that virtually quantitative separation of pentiandite from pyrrhotite can be achieved. The results obtained in above studies were not directly applicable to nickel concentrates due to interference by the products of air oxidation of pyrrhotite during milling and flotation. Methods of overcoming the inhibiting effect of air oxidation in the dissolution of pyrrhotite were separately studied. Reduction of the nickel concentrate by hydrogen at 500~800°C prior to leaching was found to be a suitable way to activate the pyrrhotite in the nickel concentrate. It was found that by appropriate control of reduction and leaching conditions a satisfactory separation of pyrrhotite and pentlandite in the nickel concentrate was obtained and the acid decomposition of the pentlandite was also achieved. A conceptual flowsheet is proposed for the treatment of pyrrhotite and nickel concentrates in a hydrometallurgical plant. Firstly, the pyrrhotite and secondly, the pentlandite are leached for iron rejection and nickel recovery, leaving a residue that constitutes a copper concentrate. Sulphur is recovered as elemental sulphur via H₂S.

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