Rapid uranium removal from real mining wastewaters by nucleation-induced crystallization: Effects of carbonate and magnesium on process performance and product stability

Uranium-bearing mining wastewaters often contain bicarbonate, calcium, and magnesium, which complicate rapid treatment by stabilizing aqueous uranyl complexes and altering precipitation pathways. This study evaluated nucleation-induced crystallization (NICP) as a continuous-flow process for uranium removal from three real mining wastewaters with distinct Ca/Mg compositions. Under optimized NaOH dosing, uranium removal exceeded 97.7% at a hydraulic retention time of 6 min, while continuous operation over 100 h remained stable and uranium leaching from pelletized products stayed below 5 μg·L⁻¹. In contrast, carbonate-dominated conditions suppressed uranium removal to below 22% despite effective Ca precipitation. Speciation analysis indicated that hydroxide-rich conditions shifted U(VI) toward UO₂(OH)₃⁻, which was more readily transferred to growing Ca/Mg-bearing solids, whereas carbonate-rich conditions stabilized soluble UO₂(CO₃)₃⁴⁻ and hindered solid-phase transfer. Magnesium further improved process performance and product stability by promoting uranium capture and reducing uranium release from the separated pellets. These results show that NICP is a rapid and robust treatment option for carbonate-rich uranium-bearing mining wastewaters.