Sulphides roasting

The principal ore of lead is galena, PbS. Although there are some galena deposits in Great Britain, much of this country s requirements must be imported. In the extraction of lead, the sulphide ore is first roasted together with quartz in a current of air ... 

The last equation explains the funetion of the limestone. An older process, in which the ore was partially roasted, the air shut off and the temperature raised so that excess sulphide reacted with the oxide produced to give lead, is now obsolete. 

The method of extraction is similar for each element involving first the roasting of the sulphide ore when the oxide is produced, for example... 

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. 

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. 

The objective in die roasting of sulphides, such as copper sulphides and zinc sulphides, is to convert these into their coiTesponding oxides by reaction with... 

The hrst successful study which clarihed the mechanism of roasting, was a study of the oxidation of pyrite, FeSa, which is not a typical industrial process because of the availability of oxide iron ores. The experiment does, however, show die main features of roasting reactions in a simplihed way which is well supported by the necessaty thermodynamic data. The Gibbs energy data for the two sulphides of iron are,... 

Lead The production of lead from lead sulphide minerals, principally galena, PbS, is considerably more complicated than the production of zinc because tire roasting of the sulphide to prepare the oxide for reduction produces PbO which is a relatively volatile oxide, and therefore the temperature of roasting is limited. The products of roasting also contain unoxidized galena as well as die oxide, some lead basic sulphate, and impurities such as zinc, iron, arsenic and antimony. 

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. 

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