Patent GB-767230-A (GB)
Title: Improvements in the recovery of sulphur and sulphur doixide from sulphide ores
IPC: C01B17/52
Filed: 1954-09-16
Abstract: <PICT:0767230/III/1> Sulphide iron ores are roasted to produce elemental sulphur and sulphur-dioxide by passing them through a roasting zone in counter-current to and in contact with a roasting gas which consists substantially wholly of sulphur dioxide and oxygen and has a temperature of at least 450 DEG C. as it enters the roasting zone, effecting the roasting temperature between 750 and 1000 DEG C., and recovering the roasted ore.  The gas from the roasting zone is passed through a cooling zone in which the major portion of the entrained sulphur vapour is precipitated as liquid sulphur which is recovered, the temperature of the cooler being such as to leave in the gas a proportion of sulphur which, on combustion with oxygen is sufficient to cause a substantial rise in temperature of the gas to at least 450 DEG C., the gas from the cooling zone being mixed with an amount of oxygen sufficient to oxidize the residual sulphur in the gas, to convert the iron content of the ore in the roasting zone into iron oxide, and to oxidize a maximum of 20 per cent of the sulphur content of the ore.  The mixture of elemental sulphur-containing gas and oxygen is then passed through a sulphur combustion zone and returned to the roasting zone as roaster gas in a quantity sufficient to render the process self sustaining without any external heat supply.  The oxygen concentration of the roasting gas entering the roaster is preferably 5-12 per cent by volume and should be sufficient to convert the non-ferrous metals present in the ore into sulphates.  As shown in the drawing, roaster gases from a furnace 1 pass through a dust collector 7 into a heat exchanger 2 and from thence to a cooler 3.  Sulphur condenses in the latter and is withdrawn whilst the cool gases are passed in part to a sulphur dioxide recovery system 6, 8, and in part passed through pump 4 and heat exchanger 2 in indirect contact with the roaster gases, to a sulphur combustion chamber 5 where, mixed with oxygen feed, the sulphur is burnt to raise the temperature of the gases, to 500 DEG C. for example, before they return to the roaster.  The circulating gas system is maintained under a constant slight excess pressure of 1-300 mm. of mecury by means of the sulphur dioxide withdrawal system which consists of a liquid trap or seal 6 maintained full of liquid sulphur at 120 DEG C. and a gas collector 8 of conventional construction from which sulphur dioxide with a purity of over 90 per cent is recovered. According to an example iron pyrites containing minor amounts of copper, zinc and arsenic was treated with a roasting gas containing 7 per cent of oxygen entering at a temperature of 460 DEG C.  The roasted ore contained 0.1 per cent sulphide sulphur and 3.5 per cent sulphur in the form of sulphates and consisted mainly of iron oxide and soluble compounds of the non-ferrous metals.  The gas leaving the roaster at a temperature of 620 DEG C. was cooled to 450 DEG C. in the heat exchanger and then cooled to 240 DEG C. in the cooler whereby liquid sulphur was recovered. Sulphur dioxide of 95 per cent purity was withdrawn from the cooled gases; the remainder were re-cycled through the heat exchanger whereby the temperature was raised to 350 DEG ., and through the combustion zone where the addition of oxygen and subsequent combustion raised the temperature of the gases to 460 DEG C. before they returned to the roasting zone. Specification 384,464 is referred to.