Recovery of high-value rare earth elements from waste NdFeB by the water-soluble ammonium salt [Hbet]cl

•New leaching agent betaine hydrochloride greatly improves leaching rate and selectivity.•The best leaching results were achieved with 99.81 % Pr, 97.05 % Nd, 95.51 % Gd, 56.24 % Ce and 0.20 % Fe when the concentration of lixiviant ([Hbet]Cl) is 0.2 mol/L.•Hydrothermal pressure leaching can improve the leaching rate of rare earth elements without affecting Fe.•Leaching mechanism was analyzed, and the lattice energy U value of the ionic crystal decomposition were calculated. This paper proposes a new integrated method for recycling permanent magnet waste by betaine hydrochloride ([Hbet]Cl) solution extraction. The orthogonal experiment method was used to analyze four factors in the leaching process to explore the primary and secondary factors influencing the leaching results. The following optimum leaching conditions were obtained: leaching temperature of 200 ℃, leaching time of 8 h, lixiviant [Hbet]Cl concentration of 0.2 mol/L, and solid–liquid ratio of 1:150 g/ml. These conditions yielded the optimum leaching results of 99.81 % Pr, 97.05 % Nd, 95.51 % Gd, 56.24 % Ce and 0.20 % Fe, and almost all iron oxide remained in the residue. Compared with the results for common lixiviants, the proposed method showed a better leaching rate and selectivity, and the leaching sequence was in line with established chemical properties. The method is characterized by a high recovery rate, strong selectivity, environmental friendliness and low cost. The leaching mechanism was analyzed, and the crystal lattice energy U values of ionic crystal decomposition were calculated to explain the dissolution sequence and solubility difference of metal oxides, laying a foundation for the recovery process.