GB768297A - Improvements in roasting of sulfide ore concentrates - Google Patents

Abstract

A modification of the method of roasting iron sulphide such as pyrite or pyrrhotite in a multi-bed fluidized column by introducing roasting air into at least two vertically spaced points in a vertical column containing the sulphide, and withdrawing the roaster gases from the top of the column, as described in Specifications 660,778 and 661,560, is characterized in that the major portion by weight of the fluidized materials throughout the operation consists of coarse particles of previously roasted iron sulphide having a particle size between 6 and 35 mesh, the iron sulphide being charged to the column in finely divided form at a point below the upper surface of the uppermost fluid bed of the column, the rate of introduction of the charge being adjusted to maintain the temperature of the column at the incipient fusion temperature of the sulphide, preferably 50 to 75 DEG C. below the softening temperature of the column, whereby the roasted iron sulphide charge is withdrawn from the lower portion of the column in the form of discrete particles larger than the size of the iron sulphide particles charged, but not substantially larger than the relatively coarse particles of which the fluidized column is largely composed. The roasting air supplied to the column is preferably 5 to 20 per cent in excess of that theoretically required and may be distributed according to the above Specifications, for example such that the lowermost bed has an apparent density of 75 to 90 per cent of the unexpanded bulk density of the particles, the next uppermost bed having an apparent density of 55 to 75 per cent, and the uppermost bed has an apparent density of 40 to 60 per cent. The uppermost end of the column may be provided with an enlarged cross-section whereby loss of fines may be prevented. The temperature of the fluidized column will depend on the pyrites employed that is normally from 1040 to 1060 DEG C. The finished calcine consists predominantly of magnetite and a roaster gas containing about 14 per cent sulphur dioxide may be obtained.