China Nonferrous Metallurgy

In the wet metallurgy process of rare earth elements, replacing traditional sulfonated kerosene with a new environmentally friendly diluent led to insufficient reducing capacity of the new diluent, causing Ce(Ⅲ) to oxidize into easily extractable Ce(Ⅳ). This cause excessive levels of the rare earth impurity Ce for a long time in the praseodymium-neodymium series products. Although H₂O₂ can reduce Ce (Ⅳ), there are a series of problems such as organic phase oxidation degradation, increased cost, and increased difficulty in wastewater treatment. This study proposes to replace H₂O₂ with hindered phenolic antioxidants to achieve green and efficient separation of rare earth elements by inhibiting the generation of Ce (Ⅳ) and reducing residual Ce (Ⅳ). The results showed that hindered phenols preferentially capture oxygen free radicals (HO·, ROO·) through hydroxyl hydrogen supply and steric hindrance effect, inhibit Ce (Ⅲ) oxidation, and efficiently reduce Ce (Ⅳ) in the organic phase to Ce (Ⅲ) (reduction efficiency ＞99.5%), achieving a synergistic effect of “oxidation inhibition and residual elimination”; When the amount of hindered phenol added is 1.0~2.0g/L and the temperature is 40~50℃, the generation rate of Ce (Ⅳ) decreases from 0.021g/(L·h) to 0.0023g/(L·h), and the inhibition time is greater than 120 hours. Industrial tests have shown that the Ce (Ⅳ) of organic phase has decreased from 0.05g/L to below 0.005g/L. The Ce impurity has remained stable at 200~400 ppm for a long time in praseodymium neodymium products, which meets the quality requirements of GB/T 20190—2023. Compared to H₂O₂ reduction, this technology reduces the consumption of reducing agents and avoids the risk of organic phase degradation caused by H₂O₂ decomposition. It provides technical support for the green and high-quality development of the rare earth industry and has significant industry promotion value.