China Nonferrous Metallurgy

Domestic plants producing alumina by Bayer process, the decomposition process mostly adopts large flat bottom mechanical stirring decomposition tank. The wall of the decomposition tank is easy to scab, and the scab grows fast. The traditional cleaning method will cause the organic matter in the scar to re-enter the system, which can not reduce the harm to the production. The results show that the main component of the scab is Al(OH)₃, followed by sodium carbonate, sodium oxalate and other organic carbon (TOC), therefore, the method of washing causticization was determined to remove the organic matter in the scab. The results of laboratory test and industrial test showed that the removal rates of Na₂C₂O₄、Na₂CO₃and TOC were 97.32%, 93.99% and 73.45% respectively when excessive lime milk was added, and the total carbon content in the scab of decomposition tank after washing was 0.013%. After ten months of industrial application, the contents of organic carbon and oxalate in the system decreased significantly.