Process design and validation of a new mixed eluent for leaching Cd, Cr, Pb, Cu, Ni, and Zn from heavy metal-polluted soil

Abstract

Chemical leaching, an emerging technology for treating heavy metal-polluted soils, requires a design for reasonable and new eluent and an evaluation of its efficiency on the simultaneous removal of different elements. In this study, the leaching effect and biodegradability of chelating agents were compared, and ethylenediamine disuccinic acid (EDDS) was selected to combine with ferric chloride (FeCl₃) for the design of a mixed eluent (EDDS + FeCl₃). Through batch experiments, the influences of the eluent concentration and solution pH on leaching were revealed, and leaching efficiencies of EDDS, FeCl₃, and EDDS + FeCl₃ on six heavy metals Cd, Cr, Pb, Cu, Ni, and Zn in the soil were separately analyzed. Results indicated that EDDS + FeCl₃ showed advantages over both EDDS and FeCl₃ alone, and it presented an excellent effect, especially for simultaneously leaching multiple heavy metals from the soil. The highest leaching efficiencies for Cd, Cr, Pb, Cu, Ni, and Zn reached up to 71.36%, 21.29%, 31.14%, 30.25%, 34.05%, and 4.96%, respectively. According to different soil types and target elements, the concentration, pH condition, and mass ratio of EDDS + FeCl₃ could be adjusted for soil remediation. Fourier transform infrared spectroscopy proved that the better leaching effect of EDDS + FeCl₃ was attributed to changes in the number and strength of functional groups in the solution, which enhanced the chelating ability of the mixed eluent and heavy metal ions. Therefore, chemical leaching by EDDS + FeCl₃ for the remediation of multiple heavy metal-contaminated soil is a potential feasible strategy.