Patent GB-748490-A (GB)
Title: Improvements in and relating to the roasting of pyrites
IPC: C22B1/02
Filed: 1952-10-24
Abstract: <PICT:0748490/III/1> Material containing pyrites is roasted on a stationary or travelling grate by igniting the charge of material and blowing suctioning or otherwise forcing oxygen-containing gases such as air through the charge in an amount such that the oxygen is sufficient to convert only a part of the labile and combined sulphur to sulphur dioxide and to distil the remainder of the labile sulphur as elementary sulphur and thereafter passing the gases with the entrained sulphur to a separate combustion chamber directly associated with the grate and burning it there to sulphur dioxide with further oxygen-containing gases and subjecting the agglomerated roasted product to an additional roasting step to recover substantially all the residual sulphur.  The preferred apparatus is shown in Fig. 1 where pyrites from hopper 10 is fed to nodulizing drum 12 and from thence through hopper 13 to a travelling roasting grate 14.  The charge moving on this grate is ignited at 15 and subjected to a downwardly directed blast of air from hood 16 the gaseous products being withdrawn into a refractory lined wind-box 17 to which oxygen is supplied by line 52.  The sulphur dioxide containing gases pass through a steamboiler 19 the tubes 20 of which also pass through the refractory lined wind-box 17, and thence through a cyclone separator 28 and a precipitation apparatus 32, the gases finally being withdrawn at 33.  The grate bars are suitably water cooled by water entering at 22 and passing after leaving the grate via pipes 24 and 25 to a steam dome 21.  The roasted ore passes through a chute 34 into a crusher 35 and from thence through a hopper 38 to a further roasting device 41 of the Dwight-Lloyd type.  Air is drawn downwardly through the roasting device 41 by a fan 48 and the oxygen-containing gases thus withdrawn are fed to the hood 16 to supply oxygen for the partial combustion of the sulphur of the initial charge and partially through pipe 52 to the combustion chamber constituted by the wind-box 17.  The product from the second roasting stage is a low sulphur highly oxidized agglomerate having a high iron content suitable for blast furnace operation.  The pyrites employed may be nodulized with a calcium or magnesium chloride, iron sulphate, clay, bentonite or waste sulphite liquor binder.  Sulphides of copper, zinc, nickel, cobalt, gold and silver which may be contained in the initial pyrites may be volatilized as chlorides by adding to the charge in either of the sintering or roasting step chlorides such as calcium, magnesium, sodium or iron; alternatively the pyrites may be treated with gaseous chlorine before the first roasting step whereby the metal chlorides formed are volatilized in the subsequent roasting step, such chlorides being removed by electro-filters or by washing the effluent gases with water or water containing lime, the calcium chloride obtained being used in a fresh charge as chlorinating agent.  If desired the second roasting of the material may be effected in the same apparatus as the first roasting by placing a charge of moistened crushed roasted material on top of the ignited pyrites initial charge in the first roasting step after termination of the ignition whereby sintering is effected in two separate layers in the same apparatus.  The two layers are physically separated by a layer of crushed sulphur-free sinter of 20 to 40 mm. diameter.