Patent GB-759260-A (GB)
Title: Improvements in or relating to roasting sulfide ores
Inventor: LEWIS WARREN KENDALL
IPC: C22B1/10
Filed: 1952-11-18
Abstract: <PICT:0759260/III/1> Sulphur dioxide free from elemental sulphur, oxygen and sulphur trioxide are obtained from a metal sulphide ore which liberates free elemental sulphur on heating, by fluidizing the finely divided ore with an oxidizing gas in a distillation zone, the temperature and quantity of the gas being such that a portion of the sulphur in the distillation zone is oxidized to sulphur dioxide thereby generating sufficient heat to distil all the distillable remaining sulphur from the ore as elemental sulphur, withdrawing the sulphur vapour and sulphur dioxide overhead from the distillation zone and passing the solids from the distillation zone as a suspension in a second gas containing free oxygen into a roasting zone where the ore is fluidized with an oxidizing gas having an amount of oxygen insufficient to oxidize all the sulphur present and withdrawing and collecting a gas containing sulphur dioxide free from trioxide, oxygen and sulphur from a space above the fluidized bed of the first roasting zone. Preferably the sulphur vapours obtained from the distillation zone are burnt in a sulphur burning zone to produce sulphur oxides which together with excess oxygen are in part employed as the second oxidizing gas.  The solids withdrawn from the roasting zone may be passed to a second zone where, fluidized by a free oxygen containing gas, they are stripped of residual sulphur.  As shown in the Figure, ironpyrites, for example, is fed from hopper 1 to a distillation vessel 3 where it is fluidized by an oxygen containing gas entering at 6 whereby the pyrites is converted to ferrous sulphide and the sulphur and sulphur oxides formed are withdrawn through pipe 19 to a sulphur burning zone 20 to which air or oxygen is supplied by lines 18 or 21.  The solids are withdrawn from the distillation zone through a pipe 10 and passed to a first roasting zone 30 as a suspension in an oxidizing gas entering through line 15 and comprising the off gases from the sulphur burning chamber 20, the pipe 10 being of sufficient length so that any unchanged pyrites is allowed to react with ferrous oxide to produce ferrous sulphide and sulphur dioxide in the pipe 10.  On passage to the first roasting zone 30 the solids are fluidized by an oxidizing gas entering from below and the product gases leave through a heat exchanger 36.  The solids from the first roasting zone 30 are then passed through a conduit to a second roasting zone 38 supplied with air pre-heated in heat exchangers 36 and 26 (the latter recovering the heat from the sulphur burning step) through line 41 and with cold air through lines 44.  The iron oxide freed from sulphur is withdrawn at 49 and the oxygen containing gases leaving the second roasting zone 38 are passed to the first roasting zone through line 45 or through valve 47 to the distillation zone through pipe 6, or to the sulphur burning zone through line 18.  Air may be supplied to the system through lines 21, 13 and 43 and aerating jets may be provided in the pyrites feed line and in the draw-off from the distillation vessel 3.  The temperature of the distillation zone, the pipe 10, the roasting zone 30 and the second roasting zone 38 are all maintained below the sintering temperature of the solids, preferably below 1800 DEG F. Specification 710,987 is referred to.