Method for preparation of alkali metal selenates

The method for the preparation of alkali metal selenates comprising

• providing 4 to 6 mols hydrogen peroxide per mol of selenium in the form of a 30 to 50 weight percent hydrogen peroxide solution as a reaction medium, heating said hydrogen peroxide to a temperature of 30.degree. to 100.degree. C., adding the selenium in a powdered form at such a dosing rate such that the selenim powder floats outwardly from the point of introduction on the quiet surface of said reaction medium in a reaction zone having a peripheral wall, dissolving the selenium powder in this area of the surface of the reaction medium before reaching said peripheral wall the complete dissolution of the last selenium particles, permitting the reaction medium to undergo further reaction until evolution of gas ceases
• then after stirring adding alkali metal hydroxide or carbonate in an initial neutralization step added at a temperature of 80.degree. to 100.degree. C. until a pH of 0.5 to 5 is obtained,
• elevating the temperature of the reaction medium to 30.degree. to 100.degree. C. with the addition of 0.5 to 1 mol hydrogen peroxide per mol of selenium in the form of a 30 to 50 weight percent hydrogen peroxide solution,
• maintaining the temperature at 90.degree. to 100.degree. C. until cessation of gas evolution and
• neutralizating the selenic acid,
• and isolating the salt obtained thereby.