Chemistry of inorganic compounds – Sulfur or compound thereof – Elemental sulfur
Patent
1991-04-04
1995-04-04
Straub, Gary P.
Chemistry of inorganic compounds
Sulfur or compound thereof
Elemental sulfur
423 99, 4235781, C01B 1702
Patent
active
054035716
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the removal of mercury and possibly other metal contaminants from elemental sulphur contaminated with such metal impurities.
Sulphuric acid is frequently used in food processing, animal feed production and fertilizer manufacture, and it is clearly necessary that sulphuric acid used for this purpose should not contain undesirably high levels of toxic elements such as mercury. Elemental sulphur is commonly used in the manufacture of sulphuric acid on a commercial scale, and thus it is necessary that such elemental sulphur should be relatively free from such contamination. For example, if sulphuric acid is to contain less than 1 gram/tonne (g/t) mercury, which is a requirement now specified for the purposes mentioned above, then elemental sulphur utilized in the production of sulphuric acid must contain less than 3 g/t mercury. Commercially produced elemental sulphur of volcanic origin, or resulting as a by-product of metallurgical operations, for example, zinc pressure leaching, has been found to contain up to about 50 g/t mercury. It is therefore necessary to reduce the mercury content in such elemental sulphur before it can be used in the production of sulphuric acid which is substantially mercury free.
Tests have shown that the mercury is present in solid solution with the elemental sulphur, probably as mercuric sulphide (HgS) in the form of cinnabar (alpha-HgS) or metacinnabar (beta-HgS). No commercially successful way of reducing the mercury content of such commercially produced elemental sulphur to the low level required is known.
It is therefore an object of the invention to provide a process for removing mercury and possibly other metal impurities from elemental sulphur contaminated therewith.
The present invention is based on the discovery that mercury contaminants and possibly other metal contaminants can be removed from elemental sulphur contaminated therewith by mixing the contaminated elemental sulphur in a molten state with an aqueous sulphide solution or an aqueous solution of sufficiently high pH which reacts with elemental sulphur and forms a sulphide solution to cause extraction of mercury and possibly other metal contaminants from the elemental sulphur into the aqueous sulphide solution. The aqueous sulphide solution containing mercury and possibly other metal contaminants is then separated from the molten elemental sulphur to provide an elemental sulphur product substantially free from such mercury and other metal contaminants.
It was previously known that mercuric sulphide is soluble in sodium sulphide solutions and in sodium hydrosulphide solution, especially at high pH, see U.S. Pat. No. 3,213,006 (Crain et al) issued Oct. 19, 1965. and two Papers by Efremova et al, namely Efremova, E. P.; Kuznetsov, V. A.; and Shubnikov, A. V.; "Solubility and Crystallization of Cinnabar under Hydrothermal Conditions", Proc. Int. Symp. Hydrotherm. React., 1982, 317-331 and Efremova, E. P.; Kuznetsov, V. A.; and Shikina, N. D.; "Solubility of Cinnabar (Alpha-HgS) in Hydrosulphide Solutions at High Temperature", Geokhimiya, 1982, 1, 56-63. However, the Crain et al patent is merely concerned with an electrolytic cell process with provision for mercury recovery, and the Efremova et al Papers are merely reports of academic research with respect to "Solubility and Crystallization of Cinnabar under Hydrothermal Conditions" and "Solubility of Cinnabar (Alpha-HgS) in Hydrosulphide Solutions at High Temperature". A method for separating mercuric sulphide from elemental sulphur using alkali solution has also been reported, see Japanese Patent, Kokai No. 52(1977)-61, 196 (Yamamoto and Kamio), but this method involves suspension, rather than dissolution, of mercuric sulphide in the aqueous alkali phase, and the concentration of mercury in the sulphur recovered by this method is in the range of 30 to 220 g/t, far in excess of the quantity acceptable if the sulphur is to be used for sulphuric acid manufacture. None of this prior art is concerned with the problem dealt with in the present ap
REFERENCES:
patent: 3954451 (1976-05-01), Kinoshita
Chalkley Michael E
Collins Michael J.
Makwana Manher M.
Masters Ian M.
Sherritt Gordon Limited
Straub Gary P.
Vanoy Timothy C.
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