Sulfides, roasting

It is good practice to keep concentrations of airborne nickel in any chemical form as low as possible and certainly below the relevant standard. Local exhaust ventilation is the preferred method, particularly for powders, but personal respirator protection may be employed where necessary. In the United States, the Occupational Safety and Health Administration (OSHA) personal exposure limit (PEL) for all forms of nickel except nickel carbonyl is 1 mg/m. The ACGIH TLVs are respectively 1 mg/m for Ni metal, insoluble compounds, and fume and dust from nickel sulfide roasting, and 0.1 mg/m for soluble nickel compounds. The ACGIH is considering whether to lower the TLVs for all forms of nickel to 0.05 mg/m, based on nonmalignant respiratory effects in experimental animals. 

Thallium is likewise recovered from flue dusts emitted during sulfide roasting for H2SO4 manufacture, and from the smelting of Zn/Pb ores. Extraction procedures are complicated because of the need to recover Cd at the same time. There are no major commercial uses for T1 metal world production in 1983 was estimated to be 5-15 tonnes p.a. and the price ranged from 60 to 80 per kg depending on purity and amount purchased. 

ElementaEmetal Soluble compounds Insoluble compounds Nickel subsulfide (includes nickel sulfide roasting and dust)... 

Roasting is a common step in recovery of metals from their ores. It consists of heating the ore. often a metal sulfide, in air to convert the sulfide to the oxide. If the metal oxide product from roasting is less stable than SOj, the free metal is obtained by sulfide roasting. This is the case for Cu S, where further heating of the mixture of Cu S and CUjO produces Cu and SO. Unfortunately, if the SOj is vented to the atmosphere, it contributes to air pollution and is one source of "acid rain" (Seetion 11.2). 

Metal sulfide roasting and smelling Sulfuric acid regeneration Metal sulfate roasting... 

The gases produced from desulfurization of lead ores contain varying concentrations of SO2 and dust, similar to gases produced during copper and zinc sulfide roasting. 

Installations processing outlet "ga ses"from iron sulfide roasting plants... 

The thermodynamics of zinc sulfide roasting have been studied by numerous investigators. The classical work on this subject is the paper by Ingraham and Kellogg [36]. Since iron tends to be present in the vast majority of naturally occurring zinc sulfide ores, the zinc-iron-oxygen-sulfur system is of considerable practical interest. This problem has been discussed extensively in Gray et al. [35] and some useful papers on this subject have been written by Kubaschewski [37] and Benner and Kenworthy [38]. Numerous kinetic studies have been made of oxidation of zinc sulfide the results of some... 

In the electrolytic processing of zinc it is desirable to convert the sulfide to a sulfate rather than to an oxide. The problem of zinc sulfate formation and the kinetic and thermodynamic criteria that would favor this process have also been extensively studied [46-51]. The study of zinc sulfide roasting in sinterbeds and in fluidized beds was investigated by Woods and Harris [51], Beveridge [52], and Kellogg [53]. 

The reader may find it somewhat disturbing that numerous, large-scale industrial processes are operating on systems for which the kinetic information is so very limited, as in the case of the roasting of copper sulfides. As a practical matter, however, the rate at which roasters may be run is controlled by heat balance considerations, i.e., the rate at which heat may be carried away from the system, rather than by the kinetics of the reaction. This may explain why the actual kinetic problems for copper sulfide roasting have not yet been resolved. 

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