GB855544A - Improvements relating to the extraction of nickel and iron from lateritic ore - Google Patents

Abstract

In a process for extracting nickel and iron as carbonyls from a lateritic nickel-bearing ore by subjecting the ore to reduction and to subsequent treatment with CO at atmospheric pressure between 25 and 75 DEG C., the reduction is carried out between 500 DEG and 850 DEG C. in a selectively reducing atmosphere containing CO and CO2 in the volume ratio 3:2 to 1:3 and the temperature and composition of the reducing gas is so correlated that the subsequent treatment with CO yields a mixture of volatilized nickel and iron carbonyls in which the weight ratio Fe:Ni is 2:1 to 1:7. H2 and H2O may wholly or partially replace the CO and CO2, the equivalent ratio being determined from the equilibrium constant of the reversible reaction CO+H2O\sXCO2+H2. The iron oxide type ore (i.e. the high ferric oxide-low silica content final product, containing over 40% Fe, of leaching magnesia and silica from the ore by atmospheric water in a warm humid climate) should be reduced at 500-650 DEG C. so that Fe:Ni in the carbonyl mixture is not less than 1:3. Silicate type ore (i.e. the high silica and magnesia content initial product, containing less than 25% iron, from leaching) should be reduced at 650-850 DEG C. so that Fe:Ni in the carbonyl mixture is not greater than 1:1. The reduction gas may be CO, CO2, H2, and H2O mixture produced by combustion of fuels, e.g. coal, oil, natural gas, or water gas, in contact with the ore. The carbonyls are separated by liquefaction and fractionation and are heated to form the metals. The residue from the CO reaction may be leached with ammoniacal ammonium carbonate to extract cobalt and remaining nickel, which may be precipitated as sulphide. Before leaching, it is preferred to separate the finest powder fraction, e.g. less than 10m , by gas elutriation.