Research on simultaneous leaching and stepwise extraction of rare earth and iron from NdFeB sludge

NdFeB waste is a precious rare earth secondary resource, and its comprehensive and efficient recovery is of great practical significance for the sustainable development and recycling of rare earth. In this paper, with neodymium iron boron oil sludge as the research object, a new process of simultaneous leaching and step-by-step extraction of rare earth and iron from neodymium iron boron oil sludge was proposed by studying its processes of low-temperature oxidation roasting, hydrochloric acid leaching, oxalic acid precipitation of rare earth, and reduction precipitation of iron. The results show that at the optimal roasting temperature and leaching conditions, the leaching rates of rare earth and iron are respectively 98.80% and 98.41%, a synchronous leaching being achieved. Under the optimal conditions of n(H₂C₂O₄): n(RE³⁺)=3:1, precipitation temperature of 60℃, and precipitation time of 30min, the precipitation efficiency of rare earth elements is 98.43%, the coprecipitation efficiency of iron is only 0.5%, the oxalate rare earth products with purity of 98.34% are obtained, and the total recovery rate of rare earth is 97.24%, realizing the selective separation of rare earth and iron. Under the optimum conditions of n(H₂C₂O₄): n(Fe)=1.5:1, n(Fe): n(Fe³⁺)=1:1, precipitation temperature of 30 ℃ and precipitation time of 30min, the iron precipitation rate is 94.28%, the ferrous oxalate products with purity of 99.22% is obtained, and the total iron recovery rate is 92.34%, realizing the comprehensive recycling. Compared with the traditional NdFeB waste recycling process, this process has the advantages of a high comprehensive utilization rate of resources, and less amount of solid waste, providing a new idea for the comprehensive utilization of rare earth secondary resources.