GB858056A - Solvent extraction of sulphur - Google Patents

Abstract

A continuous process for recovering sulphur from sulphur-containing ore comprises extracting the ore crushed to a particle size of e.g. 1/4 -\ba1/2 inch with a hot solvent, preferably at a temperature above the m.p. of sulphur, withdrawing a hot sulphur solution containing suspended ore fines from the extracted ore, recovering residual solvent from the extracted ore, admixing the hot sulphur solution with water at a lower temperature so as to wet the <PICT:0858056/III/1> ore fines and cool the sulphur solution and optionally to effect partial crystallisation of the sulphur, withdrawing the wetted ore fines and added water, further cooling the remaining sulphur solution so as substantially completely to crystallise the sulphur from the solvent, separating the crystallised sulphur from the mother liquor, recovering occluded solvent from the crystallised sulphur, and recycling said mother liquor together with solvent recovered from extracted ore and crystallised sulphur to the extraction step. The ore may be partially or completely dehydrated, or extracted with a solvent at a temperature below the m.p. of sulphur to remove hydrocarbons, before the sulphur extraction. The solvent may be perchlorethylene, tetrachlorethane, or toluene. The ore may be extracted under atmospheric or superatmospheric pressure, preferably under superatmospheric pressure if moisture is present. An ore containing 30% of sulphur may be extracted with 10 times its weight of solvent. As shown sulphurcontaining ore is passed continuously by means of a screw conveyer from a hopper 11 through a steam jacketed extractor 15 which is maintained at superatmospheric pressure in countercurrent to recycled solvent entering through lines 78 and 93. The desired pressure in extractor 15 is maintained by means of a pressure relief valve 411, which allows intermittent passage of non-condensibles and water-solvent azeotropic vapour to a condenser 42 via line 41. The extracted ore is passed continuously by means of a further screw conveyer through a steam-jacketed tails dryer 30 maintained at subatmospheric pressure wherein it is mixed with ore fines and water from an insulated fines separator 53 and line 57 and is discharged to waste from hopper 39, a water-solvent azeotropic mixture passing off through line 41 to the condenser 42. Solvent containing extracted sulphur passes through line 46 and a heat insulated fines wetter 48, wherein it is mixed with recycled water at a temperature of 160-220 DEG F. admitted through line 49 from a wash tower 64, to the insulated fines separator 53. Sulphur solution at a temperature of 200 DEG F. passes through line 60 and overflow tank 61 to the wash tower 64 wherein it is cooled by contact with water flowing in through line 671, the water having been recycled from fines separator 53 via line 67 and separator 88 via line 89 and having been cooled to a temperature of 70 DEG F. by passage through heat exchangers 68 and 681. The resulting sulphur slurry passes through line 69 and overflow tank 70 to a sulphur classifier 74, from which solvent at a temperature of 70 DEG F. is recycled via line 751 to the extractor 15 after heating to a temperature of 250 DEG F. by passage through heat exchangers 68 and 76, while sulphur crystals pass through line 79 to a steam jacketed solvent still 80, internally heated by a steam coil 81, from which molten sulphur at a temperature of 300 DEG F. is recovered through line 86 and solvent and water vapours pass off through line 84 to the condenser 42. Condensed water and solvent pass to the separator, from which water is recycled to the wash tower 64 via line 89 while solvent is recycled to the extractor 15 via line 93. In a modification extracted ore from extractor 15 may be contacted with water before passing to tails dryer 30 and the water may thereafter pass to separator 53. In another modification (Fig. 5, not shown) fresh water is continuously added to the wash tower 64, the water and wetted fines are withdrawn together from separator 53, and azeotrope vapour is flashed therefrom. A portion of the water and fines may then be passed to the tails dryer 30. In another modification (Fig. 6, not shown) the water from line 67 is recycled directly to the fines wetter 48 and the wash tower 64 is replaced by a vacuum pan wherein the sulphur solution is treated with cold water. The azeotropic vapour which is thereby evolved is condensed and separated into water and solvent, the water being recycled to the vacuum pan. In another modification (Fig. 7, not shown) all or a portion of the sulphur slurry obtained from wash tower 64 is passed to a sulphur classifier from which the solvent is passed to an evaporator in which the solvent is evaporated from hydrocarbon extracted together with the sulphur from the ore, the solvent thereafter being condensed and recycled to the extractor 15.