Application of ultrasonic-enhanced active seed crystals in the removal of sodium oxalate from alumina refinery waste liquor.

When organic matter, especially sodium oxalate (NaCO), accumulates to a certain extent, it will seriously affect the alumina production process in the refinery and therefore urgently needs to be removed. This work attempts to illuminate the benefits of ultrasonic intensification of the crystallization process of NaCO, taking the alumina refinery waste liquor, i.e., flat plate washing liquor, as a case study. The effects of different operating parameters (seed crystal addition amount, caustic soda concentration, reaction time, ultrasonic power) on the crystallization behavior and yield are discussed, and it is found that ultrasonic can increase the NaCO removal rate to 70.4%. The addition of ultrasonic promotes the morphological evolution of NaCO and is of great significance to the optimization of the components of the precipitated NaCO. Specifically, the proportion of NaCO in the crystallized product reaches 64% with conventional conditions, while it reaches 77% with ultrasonic conditions. Therefore, ultrasonic can greatly reduce the alkali loss caused by the crystallization process of NaCO in flat plate washing liquor, which has great economic benefits.