GB372189A - Process for the recovery of arsenic from arseniferous metallurgical intermediate products and by-products - Google Patents

Abstract

Acid solutions containing arsenic acid are treated with reducing agents, for instance with sulphur dioxide or sulphurous acid under pressure in a closed vessel having agitating means, and the arsenious acid produced allowed to precipitate, precipitation being assisted if necessary by concentration or cooling, or by addition of finely divided arsenious acid to the stirred solution. The solutions treated should preferably contain 100-120 grms. As2O5 per litre. Materials treated comprise cadmium-bearing flue dust from lead shaft furnaces, refinery slags, and waste liquors from copper sulphate processes. Solid materials are roasted if necessary to convert arsenious to arsenic acid, and then extracted with sulphuric acid, preferably so that the solution obtained contains 100-200 grms. of free H2SO4 per litre. In one example flue dust obtained from lead shaft furnaces is extracted hot with sulphuric acid, the lead sulphate sludge separated, the solution reduced with liquid sulphur dioxide under pressure, and the arsenious acid formed and precipitated removed. The strongly acid mother liquor is concentrated to deposit anhydrous cadmium sulphate, which is separated, and may then be used to leach a fresh batch of dust. In a second example a strongly acid residual liquor from a copper sulphate process containing nickel, copper, and arsenic acid is reduced with liquid sulphur dioxide, and the arsenious acid formed and precipitated removed. From the mother liquor copper is removed by electrolysis, and anhydrous nickel sulphate by concentration. In treating solutions containing a relatively small amount of arsenic, the solution is first concentrated to remove metallic salts present, and the arsenic then removed by reduction to, and precipitation as, arsenious acid.