Production from pyrite

TABLE 25.6 Sulfuric Acid Production from Pyrites and Other Forms (Million Tons 100% H2S04)... 

Today, a large proportion of the sulfuric acid produced in the world is what is termed fatal acid, which is manufactured to prevent substantial amounts of waste sulfur dioxide formed in metallurgical and smelting processes, such as nonferrous metal smelting and iron production from pyrites, from entering the environment (Inco Limited, 1985 Muller, 1997). 

The sulfuric acid needed to solubilize copper from chalcocite is balanced by the acid recovered from the copper electrowinning step this acid is recycled to the heaps. The overall acid requirements for the process are, therefore, dependent on the acid consumption by the gangue minerals in the ore and the acid production by pyrite oxidation. If the pyrite associated with the ore is significant and the acid consumption by the ore is low, excess sulfuric acid can be neutralized by lime. 

The last reaction cited above as shown is very effectively catalyzed by bacterial action but is very slow chemically by recycling the spent ferrous liquors and regenerating ferric iron bacterially, the amount of iron which must be derived from pyrite oxidation is limited to that needed to make up losses from the system, principally in the uranium product stream. This is important if the slow step in the overall process is the oxidation of pyrite. The situation is different in the case of bacterial leaching of copper sulfides where all the sulfide must be attacked to obtain copper with a high efficiency. A fourth reaction which may occur is the hydrolysis of ferric sulfate in solution, thus regenerating more sulfuric acid the ferrous-ferric oxidation consumes acid. 

Sulphuric acid is the largest volume chemical in the world with an annual production of about 180 mill, t/year which is used primarily for phosphate fertilizers, petroleum alkylation, copper ore leaching and in smaller quantities for a number of other purposes (pulp and paper, other acids, aluminium, titanium dioxide, plastics, synthetic fibres, dyestuffs, sulphonation etc.). The major sulphur sources for sulphuric acid production are sulphur recovered from hydrocarbon processing in the refineries and from desulphurisation of natural gas, SO2 from metallurgical smelter operations, spent alkylation acid, and to a minor extent mined elemental sulphur and pyrites. A simplified flow sheet of a modem double-absorption plant for sulphuric acid production from sulphur is shown in Fig. 1. 

The results in Table 10.8 show that the selective separation of galena from pyrite may be accomplished in alkaline medium and reducing potential. For the 1 1 mixture of galena and pyrite, the floated product assayed 76.31% Pb with a recovery of 90% at pH= 10.5 and potential -210 mV. Similar results can be achieved for the flotation separation of a mixture of galena and arsenopyrite as shown in Table 10.9. The floated product assayed 74.36% Pb with a recovery of 92% at pH = 9.5 and potential -300 mV. 

Iron oxides obtained after flame spraying of spent hydrochloric acid pickle liquor, red mud from bauxite processing, and the product of pyrites combustion are no longer of importance. They yield pigments with inferior color properties that contain considerable amounts of water-soluble salts. They can therefore only be used in low-grade applications. 

Sulfur forms analyses on the product solids are not reported here, since results of the ASTM standard procedure can be misleading in terms of Indicating which type of sulfur (pyritic, sulfate, organic) has been removed. Typically, both sulfate and pyritic sulfur are Indicated to be present in low concentrations (generally less than 0.2%) when the ASTM procedure is applied to the solid product from supercritical desulfurization of coal with alcohols. 

At the ordinary temperature this reaction is very slow, but at 200° C. it is fairly rapid. The dark deposit is microcrystalline. On carrying out the reaction in a sealed tube at 100° C. with a solution containing 1 per cent, of free sulphuric acid, marcasite is the only product. Higher temperatures and reduction of acidity favour the production of pyrites, distinct crystals being produced at 200° C. Iron pyrites is formed in neutral or alkaline solutions, as, for example, by the action of sodium polysulphide on a ferious salt. Marcasite is not produced under these conditions.1 The foregoing results are in harmony with the observation that whilst iron pyrites in nature is usually formed in deep veins from hot alkaline solutions, marcasite is produced near the surface from acid solutions.2... 

Thallium is manufactured commercially as a by-product from the roasting of pyrite ores, from sulfuric acid plants, and from the smelting of lead, zinc, and copper. The global... 

The name comes from thallos, Greek for green twig. It was discovered by William Crookes using spectroscopic analysis, who named it after the color of the spectra line. The metal was isolated by Crookes and independently by Claude-Auguste Lamy (1820-1878) in 1862. The elemental metal does not occur naturally and is extracted as a by-product from refining pyrites, lead, or zinc. In its pure form it is shiny but oxidizes quickly. It resembles lead. The element is toxic and should be handled carefully. It primary commercial use is in rodent poison and ant killer, as well as in photo cells. 

Derivation (1) By-product from the pickling of steel and many chemical operations, (2) by action of dilute sulfuric acid and iron, (3) oxidation of pyrites in air followed by leaching and treatment with scrap iron. 

Western coals tend not to contain calcite, but are enriched in calcium associated with the organic matter. Calcite in Illinois Basin coals occurs in cleat joints and in nodules within the coal seams kaolinite is also abundant along these joints. Because of these occurrences, the concentrations of calcite, kaolinite, and pyrite in cleaned coal products from this basin are much reduced compared to that of the mine-run material. 

Although the organic matter in oil shale, particularly in rich samples, produces H2S by reducing a substantial quantity of the initial pyrite to pyrrhotite, steam can potentially increase H2S production from an oil shale retort by oxidizing both iron sulfides. While investigating the steam-carbon reaction in spent oil shale (15), a noticeable amount of H2S was evolved near and below 500°C. In addition, H2S emissions from LLNL Retort Run L-2 (50% steam 50% air) were about three times higher than from LLNL Retort Run L-l (100% air) (2). These two runs used similar grades of Anvil Points shale. 

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