Chemistry of inorganic compounds – Selenium or tellurium or compound thereof
Patent
1984-08-22
1986-08-12
Doll, John
Chemistry of inorganic compounds
Selenium or tellurium or compound thereof
C01B 1900
Patent
active
046055444
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to a method for preparing selenium salts, particularly alkali metal selenate, from metallic selenium; and to the products produced.
The object of the invention is to provide a possibility of rationally producing alkali metal selenate, these salts being essential salts for the administration of selenium to human beings and animals as trace elements.
2. Background Art
It is known to administer sodium selenite, Na.sub.2 SeO.sub.3, as a trace substance to human beings and to animals, selenium constituting an important trace substance for both human beings and animals. In this respect, selenite is administered either indirectly, in animal fodder or in foodstuffs, or directly, in the form of a spray which is administered orally.
It is known that in the case of human beings, such illnesses as multiple sclerosis (MS), cardiovascular illnesses, and certain forms of cancer can be related to a selenium deficiency. It is also known that selenium deficiency in animals can lead to, among other things, muscular dystrophy and reduced fertility.
It is also known that selenium can be administered through plants which are eaten by animals, the selenium being incorporated in the fertilizers used, in plant top-dressing substances, or in the seed. When concerning the amount of selenium absorbed by plants, selenate is more effect than selenite. Consequently, the administration of selenium through the fertilizers used constitutes a simple and rational method, especially in the case of large herds of grazing animals, when compared with administering selenium orally in the form of selenite.
The large herds of animals which roam and graze free in many countries throughout the world, have greatly increased the need of supplying selenate either through the fertilizers used or in the form of selenate prills.
It is known to produce sodium selenate electrolytically, starting from a solution of sodium selenite.
It is also known to produce selenic acid H.sub.2 SeO.sub.4 by oxidizing selenious acid H.sub.2 SeO.sub.3 with hydrogen peroxide. The resultant selenic acid, however, contains 2-3% selenious acid. The selenic acid can then be reacted with sodium carbonate, to form sodium selenate, although the selenate becomes contaminated with elementary selenium. When selenic acid is reacted with sodium hydroxide, the end product is contaminated with sodium selenite.
EP-A1 No. 0 020 826 describes a method for separating and recovering metals, including selenium, from anode slime by leaching, solvent extraction, precipitation and reduction, whereby the anode slime is primarily leached with nitric acid, separating the selenium with liquid-liquid to denitration and chlorination extraction, reducing the selenium by sulphur dioxide.
Gmelin Handbook of Inorganic Chemistry, supplement, vol. B 1, system nr 10, 1981, pages 227 and 297 describes the reaction of selenious acid with alkali hydroxides in aqueous solutions to form selenites; as well as the formation of the selenate ion by oxidizing SeO.sub.3.sup.2- with O.sub.2, O.sub.3 or H.sub.2 O.sub.2. However, any reaction in basic environment is not disclosed, and oxidation of SeO.sub.3.sup.2- in acidic environment follows the route and drawbacks indicated above.
Consequently there is a need for a method which enables high-quality selenate to be manufactured in a simple and rational manner, especially selenate having alkali metal cations.
DESCRIPTION OF THE INVENTION
It has now surprisingly been found possible to produce selenates in a simple and rational manner by means of the present invention, which is characterized by dissolving metallic selenium in nitric acid to form selenious acid; reacting the selenious acid with an alkali metal hydroxide, alkali metal carbonate and/or some other metal oxide/hydroxide to form an alkali metal selenite; oxidizing the selenite in a basic environment with an oxidant in the form of hydrogen peroxide to form a selenate, which is then spray-dried.
Further, characterizing features of the invention are set fo
REFERENCES:
The Condensed Chemical Dictionary, 8th edition, Van Nostrand Reinhold Company, New York, 1960.
Gremlin Handbook of Inorganic Chemistry, 8th Edition, 1981, pp. 227 and 297.
Bjornberg Arne
Martensson Ulf S.
Paulsson Karin M.
Boliden Aktiebolag
Doll John
Leeds Jackson
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