Investigation and Kinetic Analysis of Rare Earth Elements Leaching: Case Study of the Weathering Crust of the Kundybay Deposit (Northern Kazakhstan)

The study investigates the process of intensifying rare earth elements (REEs) group uncovering from the Kundybay deposit (Northern Kazakhstan). Currently, there is no interest in extracting REEs because the ore lying beneath is significantly richer in both rare elements and REEs. However, this type of raw material is a potential source of REEs. The total content of all REEs in the weathering crust is 372.7 ppm; of these, 82.6% are Sc, Y, La, Ce, and Nd, which are present in the form of complex salts and native minerals. In order to find the optimal REE group leaching mode, the influence of the L/S ratio, temperature, acid concentration in the leaching solution, leaching kinetics, and the influence of adding HF and Na2S2O5 on process efficiency were studied. The optimal conditions for REE leaching are as follows: L/S-20, T = 70 °C, t = 180 min. The maximum REE extraction yields, %: Sc-70.84; Y-90.2; La-99.8; Ce-99.24; Nd-97.98. The leaching process kinetic study results show that the process is managed by two steps. The activation energy differences for Sc, Y, La, Ce, and Nd, kJ/mol: 26.19, 23.83, 29.18, 11.15, and 15.13 allow to conclude that REEs in the Kundybay deposit weathering crust are in different forms.