Research On The Recovery Of Rare Earth Oxides From Rare Earth Polishing Powder Waste

With the rapid growth of the demand of the polishing industry and the improvement of the polishing accuracy of the material surface,the consumption of rare earth polishing powder and the emission of waste are also growing rapidly.Although rare earth polishing powder waste belongs to harmless solid waste,the total amount of rare earth oxide is almost the same as rare earth polishing powder.The landfill of rare earth polishing powder waste not only occupies land,but also wastes valuable rare earth resources.Therefore,this paper studies the recycling of rare earth in the waste of rare earth polishing powder,aiming to seek an efficient and safe,economic and environmental protection,simple process route,so as to realize the recycling of rare earth resources.In this paper,the rare earth polishing powder waste is used as raw material,and the rare earth elements in the rare earth polishing powder waste are recovered by two methods: sodium carbonate roasting method and reduction leaching method.The optimal recovery conditions of the sodium carbonate roasting method are: the roasting temperature is 500 °C,the roasting time is 60 min,the sodium carbonate dosage is 1.075 g/3g rare earth polishing powder waste,the amount of distilled water is 2.5m L/3g rare earth polishing powder waste,and the acidification p H is 3.The water immersion liquid-solid ratio is 10 m L/g of rare earth polishing powder waste,the water immersion temperature is 40 °C,and the water immersion time is 20 min.Finally,under optimal conditions,the content of ceria in the rare earth oxides recovered was 78.01%,and the recovery rate was 95.97%.The reduction leaching process of rare earth polishing powder waste was studied with hydrogen peroxide and thiourea as reducing agents,respectively.The optimal conditions of hydrochloric acid-hydrogen peroxide reduction leaching system were as follows: leaching temperature90 °C,leaching time 120 min,hydrochloric acid concentration 6 mol/L,hydrogen peroxide dosage 2 m L/3g rare earth polishing powder waste,and liquid-solid ratio(hydrochloric acid m L/rare earth polishing powder waste g)4.8.Under the optimal conditions,the leaching rate of cerium was 90.2%.Then the rare earth oxide was recovered by oxalic acid precipitation-oxidation roasting process: the p H of the leaching solution was adjusted to 2.0,and the dosage of oxalic acid was 1.1 times of the theoretical amount.The rare earth oxide products were obtained by washing and oxidizing the rare earth oxalate precipitation.The cerium content was 73.00%,and the recovery rate of cerium was 84.58%.The results of laser particle size analysis and scanning electron microscopy show that the recovered rare earth oxide products have uniform particles,clear edges and corners,and a rectangular appearance.The optimum conditions of hydrochloric acid-thiourea reduction leaching system are as follows: leaching temperature is 90 °C,leaching time is 60 min,hydrochloric acid concentration is 4 mol/L,thiourea dosage is 0.2 g/3g rare earth polishing powder waste,liquid-solid ratio(hydrochloric acid m L /rare earth polishing powder waste g)is 4.2.Under these conditions,the leaching rate of cerium is 99.37%.According to this process parameters,rare earth oxide was recovered by oxalic acid precipitation-oxidation roasting process.The content of cerium in the recovered product was 78.00%,and the recovery rate of cerium was 91.66%.The results of laser particle size analysis and scanning electron microscopy show that the recovered rare earth oxide products are uniform in size,and the particles are flat,with d50 of 9.073 μm.Compared with the hydrochloric acid-hydrogen peroxide system,the recovery process of hydrochloric acid-thiourea reduction leaching-oxalic acid precipitationoxidation roasting has the advantages of less acid consumption,high leaching efficiency,short reaction time and good product quality,which has great industrial application prospect.