A novel nucleation-induced crystallization process towards simultaneous removal of hardness and organics

The co-existence characteristics of saline and organics in industrial effluents complicates their removal by conventional methods. In this study, a novel nucleation-induced crystallization process (NICP) is proposed for the simultaneous removal of organics and hardness ions, and the subsequent densification of the final product. The pre-dosed seed provides reaction sites for the lattice ions, thus inducing the Ca²⁺/Mg²⁺ ions to adhere to the seed surface in the form of CaCO₃ and Mg(OH)₂ by adjusting the pH value. Moreover, organics attach to the seed surface through the coprecipitation and surface complexation in the crystal growth process. Aromatic and carboxyl groups can be considered as reaction sites for organics removal. Hydraulic regulation can accelerate the mass transfer of crystal growth, thus increasing the size of the nucleating pellet. Due to the presence of organics on the growth site of the Ca/Mg crystals, the nucleation pellet surface contains large amounts of functional groups, which enhances the surface complexation with organics. Furthermore, the removal efficiency is improved by the multi-stage NICP, e.g., the removal rates of total hardness and chemical oxygen demand (COD) can achieve 65.63 % and 42.95 % via the 3rd-stage NICP, respectively.