Removal of strontium from liquid waste using a hydraulic pellet co-precipitation microfiltration (HPC-MF) process

Abstract

Hydraulic pellet co-precipitation microfiltration (HPC-MF) process was developed for the treatment of radioactive wastewater. Strontium was removed by forming compact crystal particles when sodium carbonate, ferric chloride and calcium carbonate were used as the precipitating agent, flocculating agent and seed crystal, respectively. When the seed crystal concentration was 0.340g·L−1, the mean and highest decontamination factors (DFs) were 842 and 1000, respectively. The concentration factor (CF) was greater than 2650. The hybrid process eliminated difficulties associated with the mechanical equipment, radiation protection and precipitate concentration; besides, it achieved efficient and stable strontium removal. Furthermore, the strontium removal mechanism was fully revealed. The transfer of Sr2+ to the solid phase was primarily completed in the hydraulic reactor. The microfiltration process was essential to not only ensure stable separation efficiency but also further improve DF. Sr2+ was transferred from the liquid phase into the solid phase by being incorporated into the calcium carbonate crystalline lattice, which formed a strontianite solid solution that was removed by subsequent solid–liquid separation. The strontium concentration exhibited an exponential decrease. A higher seed crystal concentration resulted in faster precipitation kinetics, a shorter equilibrium time and a lower effluent strontium concentration.