Method for the removal of impurities from sodium aluminate solution

摘要

Impurities such as organic substances, i.e. sodium oxalate and inorganic impurities, i.e. sodium salts of vanadium and phosphorus or double salts containing the latter sodium salts are removed from a sodium aluminate solution in the production of alumina from bauxite according to the Bayer process by adding sodium oxalate crystals or both sodium oxalate crystals and at least one of sodium salts of vanadium and phosphorus, or double salts containing the latter sodium salts as seed to the sodium aluminate solution in the course of after the precipitation step of aluminum hydroxide to before the digestion step, thereby precipitating crystals of said impurities, separating the crystals of said impurities from the sodium aluminate solution, dissolving about 10 to 50% by weight of the amount of the newly precipitated organic substances from the separated crystals of said impurities in an aqueous unsaturated sodium oxalate solution, and recyclically using the crystals resulting from the dissolution together with the resulting solution as seed for the precipitation of the impurities in the sodium aluminate solution. The impurities can be simply and effectively removed.