GB813293A - Method of subjecting ores and residues to a chloridizing roast and simultaneous sintering - Google Patents

Abstract

In the chloridized roasting of ores, ore concentrates, roasting residues, slags and like sulphidiferous materials containing iron and non-ferrous metals to form a roasted product and a sublimate containing said non-ferrous metals, said sublimate is condensed, collected and reacted with sulphuric acid at below 600 DEG C. to form non-ferrous metal sulphates and gaseous hydrogen chloride at least a part of which is recycled to the chloridized roasting process as such and/or in the form of a metal chloride. Non-ferrous metals referred to are copper, zinc, lead cobalt, nickel and titanium; specified metal chlorides are those of calcium and mag <PICT:0813293/III/1> nesium. In a preferred embodiment of the invention, illustrated by the Figure, a starting material 1 (preferably containing an unroasted or only slightly roasted ore to increase the amount of sulphuric acid obtainable in a later stage) is mixed in a mixer 3 with recycle calcium chloride solution and additional, preferably solid, calcium chloride and the mixture pelletized in granulator 4 and passed to drier 7 employing a temperature of 250 DEG C. maintained by waste gases or an oil burner. The pellets are charged to a chloridized roaster 8 into which dry air is passed through line 9, and a mixture of recycle hydrogen chloride and hot flue gases (e.g. blast furnace gas poor in hydrogen or carbon dioxide) or oil or higher hydrocarbon burner gases is passed in at 10. The solid product is withdrawn at 12 and the gases passed successively through mechanical dust separator 13 which removes iron oxide dust (which is returned to the pelletizer) and electrostatic precipitator 14 from which non-ferrous metal values are recovered and passed to the sulphating furnace. The sulphur trioxide is then absorbed in tower 26 to yield sulphuric acid which contains any sublimate not precipitated and is passed to the sulphating furnace 17. The sublimate is converted, e.g. at 550-570 DEG C., to sulphates and discharged. The non-ferrous metal values may be subsequently leached from the product and the residue remaining (comprising ferric hydroxide, calcium sulphide and slag) may be added to the raw materials used in the chloridized roasting process. The hydrogen chloride liberated is returned to the chloridizing furnace through line 21 or alternatively added to the gas (already containing hydrogen chloride) emerging from the sulphur trioxide absorber. Thereafter the hydrogen chloride is absorbed in towers 23 and the so-formed solution used to reform calcium chloride (for re-use in the initial granulating steps) by reaction with granular limestone in agitators 29. The final neutralization of the hydrochloric acid is preferably carried out with burnt or slaked lime.