Application of polymeric aluminum salts in remediation of soil contaminated by Pb, Cd, Cu, and Zn

Soil contaminated with typical heavy metals (Pb, Cd, Cu, and Zn) was remedied by using the polymeric aluminum salt coagulants including polyaluminum chloride (PAC) and polyaluminum sulfate (PAS). The remediation efficiencies are influenced by reaction time, water amount, and dosage of remediation agent. The optimal remediation conditions are as follows: 6 h of reaction time, 1 kg/kg of water addition amount, and 0.25 kg/kg of remediation agent dosage. After PAC addition, the remediation efficiencies of diethylenetriamine-pentaacetic acid (DTPA)-extractable Pb, Cd, Cu, and Zn reach 88.3%, 85.1%, 85.4%, and 73.7%, respectively; and those for PAS are 89.7%, 88.7%, 83.5%, and 72.6%, respectively. The main remediation mechanism of the polymeric aluminum salt may contribute to the ionization and hydrolysis of PAC and PAS. H+ released from ionization of polymeric aluminum salt can cause the leaching of heavy metals, while the multinuclear complex produced from hydrolysis may result in the immobilization of heavy metals. For PAC, the immobilization of heavy metals is the main remediation process. For PAS, both leaching and immobilization are involved in the remediation process of heavy metals.