Sulphide ores, roasting

The contemporary commercial reactors used for sulphide ore roasting, Ficher-Tropsch synthesis and acrylonitrile manufacture were routinely operated in the bubbling and turbulent fluidization regimes [56, 112]. 

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 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. 

Smaller quantities of sulphur are obtained in the preliminary roasting of certain sulphide ores where the desulphurised mass is required for... 

Zinc sulphide ore For fluid bed roasting of 4 x 30 mesh pellets... 

There is a large class of industrially important heterogeneous reactions in which a gas or a liquid is brought into contact with a solid and reacts with the solid transforming it into a product. Among the most important are the reduction of iron oxide to metallic iron in a blast furnace the combustion of coal particles in a pulverised fuel boiler and the incineration of solid wastes. These examples also happen to be some of the most complex chemically. Further simple examples are the roasting of sulphide ores such as zinc blende ... 

Spherical particles of a sulphide ore 2 mm in diameter are roasted in an air stream at a steady temperature. Periodically small samples of the ore are Femoved, crushed and analysed with the following results ... 

Particles of a sulphide ore are to be roasted in a fluidised bed using excess air the particles may be assumed spherical and uniform in size. Laboratory experiments indicate that the oxidation proceeds by the unreacted core mechanism with the reaction rate proportional to the core area, the time for complete reaction of a single particle being 16 min at the temperature at which the bed will operate. The particles will be fed and withdrawn continuously from the bed at a steady rate of 6 tonnes of product per hour (1.67 kg/s). The solids hold-up in the bed at any time is 10 tonnes. 

For many elements, a sulphide is the commonest natural source. It is usually most convenient to roast this in air to yield the oxide, which is then reduced. In some cases, the elemental substance can be obtained more directly by converting part of the sulphide ore to oxide, then heating the mixture of sulphide and oxide in the absence of air, e.g. ... 

When the ores contain iron, it is impossible to separate the ferrous sulphate and cupric sulphate by crystallization. If the mixed sulphides are roasted at a suitable temperature, the ferrous sulphate formed is converted into oxide. Another method of separation depends on heating a solution of the two sulphates under pressure at 180° C., the ferrous salt crystallizing out.7 For agricultural purposes the removal of the iron is unnecessary. 

Other obsolete methods include the Augustin process, in which the sulphide ore was roasted with salt, and the silver chloride dissolved in hot brine the Patera process, in which the brine was replaced by a solution of sodium thiosulphate and the Kiso process, in which calcium thiosulphate was employed. In the Russell process the ordinary extraction with thiosulphate was followed by treatment with sodium copper thiosulphate, or extra solution, the object being to extract any metallic silver and undecomposed sulphide present. 

Selenium (9 x % of the earth s crust) occurs in small quantities in sulphide ores, particularly FeS2. It is extracted from the flue dusts produced in the roasting of sulphide ores and from the lead chamber mud formed in sulphuric acid manufacture, as a solution in aqueous KCN. It is precipitated from the filtered solution by the addition of HCl. 

Crude vermiculite ore produces the basic material used in the manufacture of fire protection and industrial insulation products. The process equipment consists of three rotary furnaces for heating and reaction. Torftech Ltd. (UK) replaced these with a single toroidal fluidized bed (Torbed) furnace of 1-m diameter with a capacity of 2 ton/hr. This led to a reduction in overall energy consumption and in vermiculite wastage and maintenance costs. The new process resulted in a payback period of 16 months. Now 11 plants are operational in Europe with this Torbed technology. This technique is also commercialized to produce silica from rice husk and roasting of sulphide ores, etc. 

Apphcations of the Torbed include ore roasting (a typical unit 4m high X 3m ameter ng te o sulphide ore), and drying (e.g. chicken litter), where... 

Sulphide ores. Some sulphide ores are roasted in air to convert them... 

Falconbridge process A selective leaching process used to extract copper and nickel from a sulphide ore containing nickel, copper, and other precious metals that has been roasted to remove the sulphur known as matte. The nickel is removed using hydrochloric acid and recovered as nickel chloride crystals. The residue is then leached with sulphuric... 

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 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,... 

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