Synergistic effect and removal mechanism of trichloroethylene (TCE) by nano scale zero-valent iron (nZVI) supported on biological calcium carbonate (CaCO3)

Microbial induced calcium carbonate precipitation (MICP) is a green and environmentally friendly technology. Herein, porous biological CaCO3 was prepared by MICP technology and then used as the carrier material for nZVI to prepare CaCO3@nZVI composite. Afterwards, the various properties of the CaCO3@nZVI composite were methodically characterized. Subsequently, the adsorption kinetic equation and adsorption isotherm model of TCE were carefully investigated, and the CaCO3@nZVI composite dosage, initial pH, temperature, aging time and the number of cycles on the TCE removal efficiency were examined. Finally, the degradation mechanism of TCE by CaCO3@nZVI composite was revealed. The results showed that nZVI particles were successfully supported on the biological CaCO3 surface, and the specific surface area of the CaCO3@nZVI composite was 52.641 m2/g, which was much higher than that of bare nZVI (8.757 m2/g). The adsorption kinetics of CaCO3@nZVI composite for TCE removal was conformed to the pseudo-second-order kinetic equation, and Freundlich model was more appropriate as the adsorption isotherm model. The optimal conditions for the TCE removal were obtained to be 0.24 g/L CaCO3@nZVI composite dosage, 25 ℃, and initial pH of 7.0, respectively. Furthermore, the CaCO3@nZVI composite exhibited good stability and reusability. The main degradation products of TCE by CaCO3@nZVI composite were acetylene, ethylene, and ethane, and the synergistic effects of adsorption and degradation were the main mechanisms of TCE removal. Generally, this paper provides experimental support for the selection of nZVI carrier materials, which is useful for promoting the development and advancement of green repair materials.