GB674965A - Fluidized-solids systems for selectively recovering tin from ores as a volatized tin-compound - Google Patents

Abstract

<PICT:0674965/III/1> A process of volatilizing tin-values in ores comprises upflowing a stream of hot scrubbing gases which yield at least 1 per cent by volume of unoxidized gaseous sulphur at solid-fluidizing velocity through a bed of finely divided ore particles maintained at a temperature which lies below the temperature at which solid particles in the bed tend to stick and thereby hamper fluidization. The bed temperature preferably lies within the range from 60 DEG C above and below the melting point of stannous sulphide (832 DEG C). In one form, sulphur-containing ore particles are fed into the upper bed 64 of a two-part reactor 11 via a conduit 42, and after treatment in the bed overflow down a conduit 35 into a lower ore-roasting bed 22, being removed therefrom by a conduit 23. Treatment gas (e.g. 83 per cent N. 7 per cent SO2, 10 per cent O2) composed of a mixture of air from pipe 25 and recycle gas is passed through the lower bed at a fluidizing velocity where the free oxygen combines with the sulphidic constituents and maintains the temperature of the bed at about 1100 DEG C. The hot gases rising from the lower bed (e.g. 83 per cent N, 3 per cent O, 14 per cent So2) then pass up through the fluidized upper bed 64, raising the temperature of the ore to 900 DEG C at which temperature being stannous sulphide in the ore is volatilized and the sulphur, formed by the decomposition of the pyrite in the ore is vaporized forming about 1 per cent of the gases in the upper bed and reacts with tin oxides in the ore to form more stannous sulphide which is also volatilized. Air passed in at 36, via a conduit 43, converts the stannous sulphide into stannic oxide and sulphur dioxide the resultant fume passing from the reactor, through a conduit 37, into a cyclone 65 where entrained ore particles are removed and into a bag filter 66 where the stannic oxide is removed. Part of the remaining gases is recycled to the retort via a pump 61. The reactor may have more than two beds, the upflowing gases from the lower bed passing through the remainder. When starting, the reactor may be first preheated by burning carbonaceous fuel and air supplied through the conduit 32 in the lower bed. The desulphurized ore removed from the lower bed, which is principally in the form of Fe3 O4, may be treated, e.g. by magnetic separation to recover the iron.