Stabilization mechanism of Pb with an amino- and mercapto-polymer to assist phytoremediation

An important concern during phytoremediation of heavy metal contamination in soils is the risk of leaching of heavy metals before they can be taken up by plants. The most effective method is to use heavy metal stabilizers. However, the stabilization without selectivity will greatly inhibit the phytoremediation effect of all heavy metals. A novel polymer with amino and mercapto groups named as AMP has been prepared as a new exclusive soil stabilizer for Pb. The adsorption of AMP toward Pb belonged to a monolayer adsorption and chemical process. The adsorption capacity of Pb increased with the increase of pH and initial Pb concentration, and obeyed the Langmuir model and pseudo-second-order model, respectively. An amazing maximum adsorption capacity of 588 mg Pb g−1 was reached for AMP when initial concentration was 300 mg Pb L−1, while K2 of 0.594 g mg−1 min−1 was obtained when the initial Pb concentration was 2.0 mg L−1. The distribution coefficient of AMP to Pb in the mixture of five heavy metals was as high as 3110 mL g−1, which was at least 7-fold greater than those of other heavy metals, exhibiting high selective to Pb. AMP showed a fast, large adsorption capacity and good selectivity due to the abundance of sulfhydryl and amino functional groups in the polymer and their interaction with metal ions. The effects of AMP in soil remediation were further tested by a soil column leaching experiment and a pot experiment, and the good stabilization effect of AMP on Pb and the less effect on bioavailability of other heavy metals at recommended doses were verified. This study was expected to solve the problem of leaching risk of the target metal such as Pb in sludge during land use. It provided a new idea of exclusive stabilization to assist phytoremediation of non-target heavy metals by reducing the leaching risk of some special target metal.