GB888297A - Method for removing arsenic from arsenopyrite ores - Google Patents

Abstract

<PICT:0888297/III/1> Arsenic-containing pyrites is freed from arsenic by roasting it in a fluidised bed at above 800 DEG C. in an oxygen deficient atmosphere, such that an arsenic-free calcine, containing at least 2% iron sulphide, is obtained. Volatilized sulphur and arsenic compounds together with fine solids are entrained in the flue gases, which are passed to a dust separator maintained at above the condensation temperature of the arsenic compounds and preferably above 650 DEG C. The dust-free gases so obtained are passed to a combustion chamber in which in the presence of excess oxygen, all the arsenic is converted to non volatile compounds, which are separated by scrubbing or electrostatic precipitation to give a gas stream containing arsenic free sulphur dioxide. The calcine may be subjected to a second roasting operation wherein the calcine is fully oxidised. The flue gases from which are passed to a second dust separator, the so obtained fine solids being recovered, and the dust-free gases are passed to the combustion chamber. The second roasting stage is preferably carried out at about 650 DEG C., to convert non-ferrous metals to sulphates, which may be leached out. In the Figure, the pyrites is roasted in the first stage 32, the flue gases freed from dust in 9 and burnt in 25, and the dust and calcine pass to second stage 33 via line 11. The flue gases therefrom are freed from dust in 20, the gas passed to 25, and the solids blended with the final calcine and collected in 29. Specification 721,402 is referred to.