Softener slag

The lead is transferred from the CDF to a series of induction-heated steel pots, a softener, and then to a continuous sulphur drossing circuit (CSD). The softener controls the antimony and arsenie at 1.2% and 0.7%, respectively. The remaining copper from the CDF is reduced to less than 0.005% in the CSD. The lead bullion is cast into 3-torme buttons for shipment to the lead refinery. The copper matte and softener slag are treated in downstream plants. 

Also included in Lead Operations are a lead allo3rs plant, a copper products plant, and an effluent treatment plant. The lead alloys plant produces arsenic-lead and antimony-lead alloys from the treatment of softener slag and silver refinery baghouse dust. The copper products plant produces copper sulphate, copper arsenate and sodium antimonate fi"om the treatment of copper matte and refinery baghouse dusts. The effluent treatment plant treats effluents from the zinc and lead operations as well as surface runoff from throughout the metallurgical operation. 

Bullion commonly contains np to two per cent arsenic. Arsenic is preferentially oxidised in the softening or Harris processes, bnt more readily than antimony. Conseqnently when softener slag is reduced to form an antimonial lead alloy, arsenic can be retained in the residual slag from where it can be extracted by leaching and precipitation as arsenic trioxide or as calcium arsenite. Alternatively it can be extracted from canstic slags from the Harris process by leaching and precipitation with lime as calcium arsenite, which can contain around 20 per cent As. 

Tellurium primarily reports to lead bullion during smelting. It follows arsenic, antimony and tin into softener slags or caustic slag formed in the Harris process. It will concentrate in the first stage Harris... 

Tin tends to follow arsenic and antimony and is removed from lead bullion in softener slags or caustic slag from the Harris process. It is the most soluble of the three metals in caustic slags and can be selectively leached with water and precipitated from the resulting solution by the addition of lime to form calcium stannate containing around 40 per cent Sn. 

The softening of a high hardness charge (3% or greater) follows the same procedure, except that after the first slag is removed, Htharge, ie, PbO, is added to hasten the reduction of the hardness to 0.5%. The bath is then blown with air to a concentration of 0.03% antimony. 

Coal deposits from east of the Mississippi River generally have acidic mineral constituents, ie, they are richer in siUca and alumina and tend to produce higher melting ash mixtures. These materials do not soften until above 1000°C and have limited problems with deposition on the inside walls of the boiler (slagging) or on the superheater tubes inside the boiler (fouling). 

Harmonic light generation, 14 678-680 Harmonic spectroscopy, 23 139 Harringtonine, 2 90 Harrison Narcotic Act, 13 683 Harris slag refining process, 16 150 Harris softening process, 14 750, 754 Hartree-Fock SCF techniques, 16 736 Harvest aids, economic aspects of,... 

The removal of small quantities of arsenic from metals and ores is a commercial problem which may be mentioned at this point. The Harris process of softening lead,6 used in several refineries, is based on the principle that such impurities as arsenic, antimony and tin may easily be oxidised and in the presence of certain alkali salts can he converted into arsenates, antimonates and stannates. Certain fluxes, such as sodium nitrate, sodium hydroxide, sodium chloride or lead oxide, are added to the molten lead, the presence of an oxidising agent and an alkali salt being essential. The alkaline slag obtained is fused 7 and... 

Slagging, fouling, and clinkering difficulties have been found to correlate not only with the composition of coal ash but also with the fusibility of the coal ash (ASTM D-1857 ISO 540) insofar as ash fusibility is related to composition. The critical temperature most commonly referenced in evaluation of the properties of coal ash is the softening temperature. 

Nonslagging coal coals whose ash softens at more than 1425°C (2600°F), requiring removal in a solid state cf. slagging coals whose ash is softened at less than 1205°C (2200°F) and can be discharged in a molten state. 

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