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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 –, CO3 2–, and SO4 2–. 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 (CO3 2–, SO4 2–) 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 (CO3 2–, SO4 2–) 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 –, CO3 2–, SO4 2–) are adsorbed onto the surface of Na2­C2O4 crystals, thereby inducing internal stress (defects) of crystals and modifying the crystal morphology.

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