Recovery of Cu(II) from aqueous solution by induced crystallization in a long-term operation

The feasibility of copper recovery by induced crystallization in a long period (174days) was investigated in a seeded fluidized bed reactor (FBR). The process was divided into 3 periods according to different influent conditions, and the period III was separated into III-a and III-b due to the adjustment of the molar ratio of CO₃^2- concentration to copper concentration ([C_T]/[Cu²⁺]). The removal efficiency could exceed 95% and the average effluent copper concentration decreased to 3.0mg/L. The mean particle size of seed grains with copper crystals coating on, raised to 0.36mm from initial 0.18mm. During period III-a, the supersaturation exceeded 2.88×10⁴, the removal efficiency decreased to 60%-80% and the particle size dropped to 0.30mm, due to the generation of fines by homogeneous crystallization and seeds breaking. And the morphology of the crystals on the seed grains changed from rod-like to spherical which lead to the particle size decreasing. In period III-b, the supersaturation was modified by adjusting the molar ratio of [C_T]/[Cu²⁺] to 1.2 from 2. The efficiency was back to 95% and the mean particle size grew to 0.36mm at the end of III-b, the crystals coating on the seeds turned back to rod-like products of good stability. This study illustrated that the copper salt crystal could keep on growing on the seed grains for over 150days, the feasibility and controllability of copper recovery by induced crystallization process in FBR were satisfactory, even under the dramatic changes in influent conditions.