A method for recovery of selenium from a selenium or its compounds-enriched solution

摘要

Selenium dioxide is produced from water containing free or combined selenium by introducing the water in atomized form into a gas comprising free oxygen, e.g. air or oxygen, in the presence of a metal oxide oxidation catalyst, preferably cupric oxide, ferric oxide, or nickel oxide, at a temperature of 500 DEG -700 DEG C. The oxide may be deposited on a carrier, e.g. silica or diatomaceous earth. The water containing the free or combined selenium may be obtained by contacting the reaction gas from a process for the production of, for example, acrolein or acrylonitrile from propylene, in the presence of selenium, with water at pH 7-9 and a temperature not exceeding 50 DEG C., and the selenium dioxide produced may also be used in such a process.ALSO:Acrylonitrile is prepared by contacting a propylene-air mixture at 310 DEG C. with metallic selenium which vaporizes, and a mixture of the resulting selenium-containing gas and ammonia is fed firstly over copper oxide at 400 DEG C. and secondly over molybdenum oxide. The product gas containing acrylonitrile is scrubbed with water which dissolves all selenium and compounds thereof present, and the solution so obtained is atomized into a gas comprising free oxygen in the presence of a metal oxide oxidation catalyst at a temperature of 500-700 DEG C. All selenium and compounds thereof present are converted to selenium dioxide which is used subsequently instead of selenium in the process for producing acrylonitrile.