Metal sulphides roasting

Selenium and tellurium occur naturally in sulphide ores, usually as an impurity in the sulphide of a heavy metal. They are recovered from the flue dust produced when the heavy metal sulphide is roasted. 

Ores of zinc, copper, nickel and lead exist naturally in the form of sulphides. Recovery of the metal involves roasting the ore in air prior to... 

It occurs chiefly as cinnabar, the red sulphide HgS, from which it is readily extracted either by roasting (to give the metal and sulphur dioxide) or by heating with calcium oxide the metal distils off and can be purified by vacuum distillation. 

In the blast furnace reduction slag-making materials are also added together with a small amount of iron, the function of which is to reduce any sulphide which remains, to the product of the roasting operation to produce a sinter. The sinter is then reduced with coke in a vertical shaft blast furnace in which air is blown tluough tuyeres at the bottom of tire shaft. The temperature in the heartlr where metal is produced must be controlled to avoid the vaporization of any zinc oxide in the sinter. The products of tlris process are normally quite complex, and can be separated into four phases. Typical compositions of these are shown in Table 13.1. 

The production of copper from sulphide minerals is accomplished with a preliminary partial roast of die sulphides before reaction widr air in the liquid state, known as mattes, to form copper metal (conversion). The principal sources of copper are minerals such as chalcopyrite, CuFeSa and bornite CuaFeSa, and hence the conversion process must accomplish the preferential oxidation of non, in the form of FeO, before the copper metal appears. As mentioned before, tire FeO-SiOa liquid system is practically Raoultian, and so it is relatively easy to calculate the amount of iron oxidation which can be canned out to form this liquid slag as a function of the FeO/SiOa ratio before copper oxidation occurs. The liquid slag has a maximum mole fraction of FeO at the matte blowing temperatures of about 0.3, at solid silica saturation. 

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 —... 

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