Effects of enzyme-induced carbonate precipitation (EICP) with different urease sources on the zinc remediation

Enzyme-induced carbonate precipitation (EICP) has been studied in the remediation of heavy metals in recent years. This study aims to investigate the impact of EICP with jack bean urease (JU) and sword bean urease (SU) on the Zn²⁺ remediation. The results show that relatively high concentration of organic molecules in SU can protect urease from deactivation and absorb Zn²⁺. For the treatment subject to 1 mmol/L of Zn²⁺ without calcium chloride added, the final NH₄⁺ conversion efficiency and Zn²⁺ immobilization percentage for the SU group are 95 % and 95.1 % higher than those for JU group, respectively. For the treatment with calcium chloride added, SU group can produce enough CO₃^2-, contributing to over 99 % formation of CaCO₃. The CaCO₃ can decrease Zn²⁺ concentration through the physical absorption. The highest Zn²⁺ immobilization percentage (98.9 %) can be achieved using SU with 0.5 mol/L calcium chloride. The XRD, FTIR and SEM-EDS analysis also show that CaCO₃, ZnCO₃, and Zn(OH)₂ can be generated, and the organic molecules in SU and CaCO₃ can adsorb Zn²⁺. SU is recommended as the catalyzer to immobilize Zn²⁺. The mechanism of Zn²⁺ immobilization can be understood as bio-mineralization to form ZnCO₃ and Zn(OH)₂, as well as adsorption by organic molecules in SU and CaCO₃.