Effects of Inorganic Anions on the Morphology of Sodium Oxalate Crystallized from Highly Alkaline Solutions

Abstract

The crystallization of sodium oxalate (Na2C2O4) crystals was studied in the presence of different inorganic anions of the Bayer liquor in the alumina industry, including OH–, CI–, Al(OH)4–, CO32–, and SO42–. The morphology of the obtained Na2C2O4 crystals depends on the type and concentration of anion species under similar oxalate supersaturation. The presence of divalent anions (CO32–, SO42–) has a greater influence on the morphological variability, including cyclic twins, spherulites, and double-leaf structures, through the branching growth process. The specific surface areas of Na2C2O4 crystals grown in the presence of divalent anions (CO32–, SO42–) are more than 2 times higher than those in the presence of monovalent anions (OH–, CI–, Al(OH)4–). X-ray photoelectron spectra results indicate that the inorganic anions (CI–, Al(OH)4–, CO32–, SO42–) are adsorbed onto the surface of Na2C2O4 crystals, thereby inducing internal stress (defects) of crystals and modifying the crystal morphology.