Chester, R.T., He, C., Kildea, J.D.

The presence of sodium oxalate in Bayer liquor presents a number of challenges to alumina refinery operators. In many plants, reducing or eliminating the detrimental effects of solid sodium oxalate crystals on process operations requires significant effort and resources. As a result, management of the precipitation of sodium oxalate from solution is integral to efficient operation.

A key to the appropriate management of oxalate is to control where and how it precipitates within the process. Ideally, sodium oxalate precipitation should be prevented in those parts of the process where it is undesirable and enhanced in those areas where solid oxalate is wanted. Control of the crystal form (or morphology) of the oxalate is also critical. Crystal Growth Modifiers (or CGMs) are known to affect oxalate precipitation in various ways, while other chemical additives such as oxalate stabilizers and morphology modifying agents can be readily applied to enhance the control of oxalate.

Recent development of a new range of morphology modifiers (the ORT product range) has enabled more effective production of oxalate in the ball form, instead of the needle-like crystals that typically precipitate. The development and use of these new ORT additives is presented, together with how these products can be used within different operational strategies to enhance management and control of sodium oxalate in the Bayer process.