Sulphide smelting

The full treatment cycle involves two stages namely, the smelting step (oxide and sulphide smelting) followed by the slag reduction step with carbonaceous materials. 

N.A. Warner, Towards Polymetallic Sulphide Smelting , Complex Sulphides. Processing of Ores. Concentrates and By-products. A.D. Zunkel et al., Eds., TMS-AIME, Warrendale, PA, U.S.A., 1985, 847-865. 

Some materials with low odour thresholds may paralyse the olfactory nerves and cause the sense of smelt to be lost within minutes (e.g. hydrogen sulphide). 

Arsenic occurs primarily in sulphide minerals associated with copper ores, and to a lesser extent with zinc, lead and gold ores. Arsenic is produced as a by-product of the smelting of these metals. Primary arsenic production has now ceased in the USA and Europe, and most arsenic is now imported from China and Mexico. The volatility of arsenic represents a significant concern, and there is at present no known natural mechanism by which arsenic is immobilized in the environment. Anthropogenic activities account for an input of some 19000 tonnes into the atmosphere, compared with 12000 tonnes from natural processes, such as volcanism and forest fires (Ayres and Ayres, 1996). 

In the classical pyrometallurgical smelting of metal sulphide concentrates most of the sulphur is driven off as sulphur dioxide. This process is becoming increasingly unacceptable from an environmental point of view. An alternative is to process the concentrates using hydrometallurgical techniques. 

A different system to that followed at Almaden and Idria, as well in principle as in manipulation, is pursued in the mercury smelting works of the duchy of Deux Pouts. In the former, the principle of the changes is the removal of the sulphur by its combustion into sulphurous and sulphuric acids, sod with this view the furnaces are constructed, so that the air is freely drawn through them at the temperature necessary to cause the expulsion of the sulphur. In the latter, the same ends aro attained—not, however, by roasting, but by the addition of bodies which take the sulphur from the valuable metal, by a process of chemical decomposition, Lime iB the body always resorted to, it being the most plentiful and cheapest but scales or grains of iron would likewise answer, and the heat causes the formation of a sulphide of calcium or of iron, and sets free the mercury which is driven off in vapor, thus —... 

It forms silver-white, rhombic crystals,7 of density 7-83, and melting point 1020° C. according to Hilpert and Dieckmann8 or 1031° C. according to Friedrich.9 It is non-magnetic. Steel-grey crystals of the arsenide of density 7-94 have been found associated with tin sulphide in the hearth of an old tin smelting furnace in Cornwall.10... 

The residue from the chloridised speiss, after extraction of soluble cobalt and nickel salts, is extracted with sodium thiosulphate, to dissolve out silver chloride, which is recovered as the sulphide and reduced to metal. The residue is dried, ground, and smelted with quartz to remove most of the iron as a slag. This slag is reworked with more ore in the blast-furnaces, as it contains silver and cobalt. The new speiss simultaneoiisly produced is treated as described above for recovering cobalt and nickel, copper, and silver. The final residue is dried, mixed with 20 per cent, of sodium nitrate and 10 per cent, of sodium carbonate, and roasted in reverberatory furnace to convert the arsenic into sodium arsenate, which is extracted with hot water. The dried residue has the following average composition ... 

Epitome of Process.—The ore is first dressed, roasted, and then smelted in blast or reverberatory furnaces to a ferruginous matte consisting essentially of sulphides of copper, nickel, and iron. This is then oxidised in a blast of air in a converter in an analogous manner to the production of steel by the basic Bessemer process. By this means practically all the iron is removed, and as much sulphur as possible without excessive loss of nickel. On an average the product contains approximately ... 

Copper deposits in Britain are said to have been known to the Phoenicians about the year 1000 b.c. In 1581 mining was being carried on at Keswick, in Cumberland, the ore being probably a sulphide. The Mines Royal Society established a works for copper-smelting at Neath, in Wales, in 1584. Various other works were started in Wales at different times, notably those erected by Lane and Pollard at Swansea in 1717. 

The silver is dissolved from the ore by an aqueous solution of a salt, and then precipitated as metal or sulphide. The cyanide process2 is the most important of the lixiviation methods, its application having been considerably extended in recent years, especially in Mexico. The ore is very finely crushed with cyanide solution in a stamp-mill, and the sludge produced submitted to agitation and aeration in contact with cyanide solution. The liquid is separated from the ore by the aid of mechanical filters, and the silver precipitated from the clear solution by addition of zinc in the form of dust or shavings. The product is smelted with nitre, and is sometimes refined by blowing air through the molten mass. 

Both neutral sulphite and bisulphite pulping liquor can be reeovered by the Tampella process (Rimpi, 1983). The residual eooking liquor is burnt in a kraft type recovery furnace and the smelt of sodium earbonate and sodium sulphide obtained as described in the seetion on kraft pulping. The dissolved smelt is carbonated with flue gas to form sodium hydrosulphide and sodium bicarbonate and the partially carbonated liquor stripped with steam in order to liberate hydrogen sulphide gas. The gas formed plus make up sulphur is then burnt to sulphur dioxide for the preparation of sulphite eooking liquor. 

The ideal of having only Na2S and Na2C03 in the smelt is not true there are nonprocess chemicals, Na2S04, Na2S203 and contaminant salts, in the green liquor. The calculated causticity and sulphidity have to adjust for the presence of these salts. 

SUD] Sudo, K., Fundamental researches on smelting of sulphide ores. XL On the equilibria in the reductions of solid nickel sulphides by hydrogen gas, Sci. Rep. Inst. Tohoku Univ. Ser. A, A4, (1952), 182-190. Cited on pages 169, 170, 277. 

Solvents are not, as a class, very odiferous materials and few can be detected at much below a 1 ppm level unlike mercaptans (which can be smelt at the low ppb level), sulphides and aldehydes. The latter are often detectable in solvents that have been recovered and recycled and make such recovered solvents unacceptable for use in household formulations. 

---