ES348303A1 - Process of purification of iron oxide - Google Patents

Abstract

Iron oxide containing as impurities elements which form volatile halides is purified by contacting it with at least one gaseous hydrohalic acid at a temperature sufficiently high for said elements to be converted into halides and volatilized whilst the iron oxide remains substantially unconverted, and in the presence of water vapour, the amount of gaseous hydrohalic acid used being at least stoichiometric with respect to said elements, removing said halides by entraining them in a carrier gas, and recovering the concentrated iron oxide. The acid is preferably HCl, the reaction temperature 500-800 C., and the iron oxide may be preheated before being contacted with the acid gas in a fluidized bed. The HCl gas may be provided as such or introduced in a carrier gas, which may be water vapour, in which case this is achieved by volatilizing azeotropic (20% by weight) HCl solution, or may be produced in situ by dissociation of a suitable compound such as NH 4 Cl, with is supplied as an atomized solution, a sublimed vapour, or mixed with the iron oxide. In Fig. 2, pyrites ashes containing as impurities Zn, Pb, Cu and As, are fed via hopper 1 into bed 2, fluidized by the passage of smoke gases from combustion chamber 3 wherein natural gas from 4 is burned in air from 5, and 20% (azeotropic) HCl solution is injected in at 6, heated in exchanger 7, and reacts with the impurities in the bed 2. Dust is removed from the exhaust gas in cyclones 9 and 10, and the vapours of the chlorides of the metallic impurities pass into tower 12 where they are scrubbed with water, and tapped off as an aqueous solution at 15. Iron oxide containing substantially none of the above-mentioned impurities is drawn off at 8. Other apparatuses for performing embodiments of the invention are described.