EVALUATION OF CHEMICAL ADDITIVES ON OXALATE REMOVAL RATE

Boom, E. and Clancy, T.

Oxalate removal at the Worsley refinery is based on co-precipitation of oxalate with gibbsite, re-dissolution of the sodium oxalate crystals to obtain a sodium oxalate-rich solution and re-crystallisation of sodium oxalate by addition of caustic soda solution and oxalate seed. The sodium oxalate crystals are filtered and disposed. Crystallisation of sodium oxalate is sensitive to the presence of other organic species as these impact the removal rate and morphology. These organic species originate from the bauxite and organic-based additives dosed to enhance certain processes. Eight different additives used in precipitation, hydrate classification and washing at the Worsley refinery were investigated in laboratory batch tests for their potential impact on sodium oxalate crystallisation rate and stability. It was found that none of the additives had an impact on sodium oxalate stability, but three additives had a significant impact on the crystallisation rate.