GB802037A - Improvements in the chloridising roasting of raw materials containing iron and non-ferrous metals - Google Patents

Abstract

In the chloridizing roasting of ferrous raw materials to convert the non-ferrous components to leachable compounds while leaving the iron in the insoluble oxide form, the roasting is carried out in a fluidized bed in the presence of alkali metals salts, under conditions such that the temperature of the bed is between 550 DEG and 650 DEG C., preferably 610 DEG to 630 DEG C., the roaster gas contains between 0.1 per cent and 10 per cent by volume, preferably 0.3 to 2.5 per cent, of sulphur oxides and between 0.1 per cent and 10 per cent by volume, preferably 1 per cent to 5 per cent of chlorine and hydrogen chloride, and that a portion of the fluidized bed, not exceeding 25 per cent by weight, preferably 15 to 20 per cent, is present in the fused state due to the union of alkalimetal salts with non-ferrous metal salts. As alkali-metal salts there can be added to the initial materials a total of 6 to 15 per cent by weight of sodium chloride, sodium sulphate, or potassium chloride, either singly or together in the form of double salts. The amount of the bed which is in the fused state is determined by withdrawing a sample from the bed and comparing the conductivity of a portion of this sample at 300 DEG C. with another portion of the sample at the temperature of the fluidized bed by a Wheatstone bridge method, from which the proportion which is fused may be deduced. The temperature of the bed may be adjusted by the addition of a carbonaceous fuel to the solid, or by adding steam to the roaster gas. The roaster gas composition may be adjusted by limiting the supply of oxygen or by adding sulphur dioxide, chlorine, or hydrogen chloride. Specification 668,119, [Group XX], and 696,003 are referred to.