Enhanced rare earth alkali cake washing and alkaline wastewater disposal via mineral phase transformation and ultrasound

Abstract

The liquid alkali decomposition method represents a relatively clean smelting process for the treatment of the mixed rare earth concentrate derived from Bayan Obo. However, the production process generates a considerable quantity of alkaline wastewater, which presents a significant obstacle to the large-scale application of this process. Accordingly, the reduction and high-value treatment of rare earth alkaline wastewater represents a pressing need and challenge. This paper presents a novel approach to the treatment of rare earth alkaline wastewater, which has the potential to revolutionize the way such wastewater is handled. The proposed method involves a series of processes, including mineral phase transformation, ultrasonic enhanced water washing, causticization treatment, and glass preparation. These processes not only reduced the volume of alkaline wastewater by over 50% compared to traditional treatment methods, but challenged the conventional wisdom surrounding the treatment of alkaline wastewater, resulted in the conversion of NaF, Na₃PO₄, and Na₂CO₃ into a mixed calcium salt, which contains CaF₂, Ca₃(PO₄)₂, and CaCO₃. And the mixed calcium salt can then employed in the preparation of high-performance glass. This process not only circumvents the deficiencies associated with the low purity and value of the final product when NaF, Na₃PO₄, and Na₂CO₃ are separated individually, but it also allows for the reuse of the generated NaOH, thereby achieving high-value utilization of the alkaline wastewater. This paper offers valuable insights into the treatment of alkaline wastewater from various rare earth minerals treated by the liquid alkali decomposition method.