Recycling and Reuse of Rare Earth Polishing Powder Waste by a Simple Gravity Settling-Acid Leaching Process

The growing market demand for glass polishing leads to the production of a significant amount of waste known as rare earth polishing powder waste (REPPW), which poses environmental risks. This study is expected to achieve the waste treatment and comprehensive utilization of rare earth resources. A simple direct and low-cost gravity settling-hydrofluoric acid (HF) leaching process is proposed to regenerate rare earth polishing powder from the glass polishing waste. Firstly, dilute and stir the waste slurry evenly before letting it stand. The next gravity settling step removes most of the large impurity particles, and the acid-leaching process restores the aggregated polishing powder particles to their original size while removing the SiO 2 impurities to obtain the regenerated polishing powder. The optimal conditions for the HF leaching process are 0.25 M, 10 min, and 25 °C. The powder regenerated reaches a rare earth content of 95.3% and can be directly used for glass polishing. Particularly, ultra-precision surface roughness is achieved and the materials removal rate reaches 119.4% of the pristine polishing powder. The regeneration mechanism of the HF leaching process is proposed. The material flow and mass balance of the products obtained during the regenerating process indicate that the recycling of 1000 kg REPPW slurry yielded approximately 658 kg regenerated polishing powder, and it provides a total economic value of 2438.7 US dollars in the regenerating process.