Process for the extraction of arsenic from aqueous solutions containing alkali metal carbonate, sulfate and hydroxide or hydrogen carbonate and at least on metal including vanadium, uranium and molybdenum

Abstract

A process for extracting arsenic from aqueous solutions containing alkali metal carbonate, sulfate and hydroxide or hydrogen carbonate, at least one metal selected from the group consisting of vanadium, uranium and molybdenum in the form of an alkali metal salt, and inorganic and/or organic impurities, comprising the steps of caustifying the solution with lime to convert the alkali metal carbonates into hydroxides to precipitate the insoluble calcium salts formed, concentrating the solution by evaporation of the effluent liquids originating from the caustification step to obtain a precipitate substantially comprising alkali metal sulfate wherein the caustification is performed in two steps, consisting of (a) treating the solutions with an amount of lime approximately equal to but less than the stoichiometric amount necessary to convert the alkali metal carbonates into hydroxides as a first precipitate, and (b) after separating and washing the first precipitate, treating the resulting liquor with at least the stoichiometric amount of lime necessary to precipitate the arsenic in solution and the carbonate ions still present. The process is well adapted to the treatments of the liquors originating from the alkaline attack of uraniferous ore.

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