Changes in heavy metal mobility and availability in contaminated wet-land soil remediated using lignin-based...

To mitigate the serious ecological problems and risks to human health that are posed by heavy metals in the soil, it is important to enhance the efficiency of heavy metal extraction by washing contaminated soil using chemical methods. Secondary pollution of soil by chemical chelating agents has, however, brought a new threat to the environment. Here, we describe a biodegradable LBPAA (lignin based poly(acrylic acid)) composite that was designed as a chelating agent to wash soil contaminated with Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ ions. Extraction and ion transfer of heavy metal ions by the LBPAA composite improved the remediation rate of contaminated soil during water leaching. After washing five times, the LBPAA-assisted elution process reduced the amount of Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ ions in contaminated soil to 22.57%, 52.60%, 13.63% and 17.95%, respectively. These values are 2.39-fold, 5.04-fold, 5.04-fold and 1.31-fold, respectively, better than elution with deionized water. Additionally, LBPAA is able to sequester Cd²⁺ and Pb²⁺ ions from the contaminated soil and transfer them to the eluent. In summary, this work provides a safe, environmentally friendly and sustainable remediation strategy for heavy metal-contaminated soil and demonstrates a new application for lignin in the field of soil remediation.