Pyrrhotite, roasting

Ni is found in many ores in combination with S, As Sb, the chief sources being the minerals chalcopyrite, pyrrhotite and pentlandite. Ni ores are of two types, sulfide and oxide, the former accounting for two-thirds of the world s consumption. Sulfide ores are refined by flotation and roasting to sintered Ni oxide, and either sold as such or reduced to metal, which is cast into anodes and refined electrolytically or by the carbonyl (Mond) process. Oxide ores are treated by hydrometallurgjcal refining, eg, leaching with ammonia. Much secondary Ni is recovered from scrap (Refs 6 7) 1... 

Yagi et al. (1951) roasted pyrrhotite (iron sulfide) particles dispersed in asbestos fibers and found that the time for complete conversion was related to particle size as follows ... 

The gas composition from the fluidized bed roasters at Falconbridge was a somewhat special circumstance in that the oxygen content was quite low, approximately 1%, and the sulfur dioxide concentration approached the theoretical maximum for pyrrhotite ore roasting. The Allied reactor-regenerator system was ideally suited to this gas composition. 

These topics are discussed in detail in monographs and reviews (NAS 1975, IPCS 1991, Barceloux 1999, Mastromatteo 1986, Sunderman 1984, 2001a). Nickel constitutes less than 0.008% of the Earth s crust. The world s nickel production is obtained primarily from sulfide ores (e.g., pentlandite and nickeliferous pyrrhotite) and, to lesser extent, from oxides ores (e.g., laterite). Nickel sulfide ores, usually mined underground, are crushed and ground, concentrated by physical methods, converted to nickel subsulfide matte, and roasted to nickel oxide. The nickel oxide may be refined electrolytically to yield nickel cathodes or refined by the Mond process, which involves reduction with hydrogen, reaction with carbon monoxide to yield nickel carbonyl, and thermal decomposition to deposit pure nickel. Nickel oxide ores, usually mined in open pits, are smelted to produce ferronickel for use in stainless steel. 

When the source of the S02 Containing gases is roasting of pyrites (FeS2), pyrrhotite (approximately FesS ), or nonferrous sulfide ores, the sulfuric acid plant is simi lar to that described above (figures 11.1 and 11.3) with the foDowing differences [12,13] ... 

The Outokumpu process, which was developed in Rnland, consists of flash roasting pyrites in a nonoxidizing atmosphere in a fluidized bed. About half of the sulfur content is recovered as elemental sulfur, and the remainder is in the residue, pyrrhotite, a magnetic iron sulfide. The pyrrhotite may be roasted in an oxidizing atmosphere to recover the remaining sulfur as sulfur dioxide. 

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