GB857350A - A process for the treatment of iron pyrites ores containing arsenic and lead - Google Patents

Abstract

<PICT:0857350/III/1> <PICT:0857350/III/2> Iron pyrites ores are freed from lead and arsenic by first removing at least a major portion of the labile sulphur together with some of the lead and arsenic, by distillation or partial combustion of the sulphur, and then contacting the remaining solid with a nonoxidising gas, containing either a minimum of 90% SO2, or 14-15% SO2 and 85-86% N2, at a temperature between 700 DEG C. and 1100 DEG C. to remove the remaining lead and arsenic. The solids remaining are then roasted in an oxidising atmosphere, for example in a fluidised bed in either one or two steps. The non-oxidising gas may be the effluent gas from the roasting stage. The initial heating and distillation stage, with simultaneous combustion of a part of the labile sulphur, may be carried out using a stream of an external comburent gas, which may be preheated by contacting it with the residue from the roasting stage. The removal of the lead and arsenic may be catalysed by the presence of salts or oxides of manganese, with or without salts of magnesium. There may be added to the roasting stage substances which will solubilise any copper and zinc present, for example, sulphuric acid or sodium chloride. In Fig. 1, the raw ore is fed into fluidised bed I by line A, and air is admitted through B to burn and distil the labile sulphur. The solids then pass to fluidised bed II, and are contacted with the hot roasting gases from bed III. The solids, now free of lead and arsenic, are passed to bed III, where they are roasted, employing a stream of air, and then discharged via line G. In Fig. 2 the beds I, II, III, are the same as in Fig. 1, but the material from III enters fluidised bed IV, where solubilisation of copper and zinc is effected, and air for bed I is preheated. The gases withdrawn from beds I and II, may be freed from impurities and used as a source of sulphur dioxide.