Remediation Of Cd-Zn And Cd-Ni Contaminated Soils By Washing With Tartaric Acid And Other Organic Acids

An effective soil washing process was studied in order to remediate two metal-contaminated sites, one polluted by Cd、Zn(the content of Cd、Zn is respectively 2.60、214.18 mg·kg-1), and the other polluted by Cd、Ni(the content of Cd、Ni is respectively 44.74、1958.57 mg·kg-1). Refer to the BCR sequential extraction procedure, a two-step washing method using oxalic acid combined with four other acids(acetic acid, citric acid, tartaric acid, succinic acid) was evaluated, and the effect of washing with citric acid or tartaric acid alone was compared. Factors affecting removal efficiency were studied, and the cooperative effect of ultrasonic on tartaric acid washing process was investigated. In addition, the speciation distributions of Cd、Zn and Ni after washing with tartaric acid were explored. The main conclusions are:(1) The removal efficiencies of the two-step washing process using citric acid or tartaric acid(0.1 mol·L-1, for 16 h) and oxalic acid(0.2 mol·L-1, for 16 h) sequentially were higher than others mentioned.(2) With the application of tartaric acid alone(0.1 mol·L-1, for 2 h), for Cd-Zn contaminated soil, the removal of Cd、Zn was respectively 30.74%、25.59%; while for Cd-Ni contaminated soil, the removal of Cd、Ni was respectively 47.36%、6.89%. The removal efficiency of Cd washed by tartaric acid was the same as citric acid, removal efficiencies of Zn and Ni were higher than citric acid, while removal efficiency of Ca was lower than citric acid.(3) p H and concentration were the major factors affecting removal efficiencies of Cd in tartaric acid washing system; for Zn and Ni, p H and washing time were the major factors; while for Ca, concentration was the most important factor. The best combination for Cd-Zn contaminated soil was 0.1 mol·L-1 of tartaric acid with p H 2, and contact time 2 h; while for Cd-Ni contaminated soil was 0.2 mol·L-1 of tartaric acid with p H 2, and contact time 6 h.(4) The introduction of ultrasonic enhanced the removal efficiencies of Cd、Zn and Ni in tartaric acid washing system, and the removal efficiencies increased with the extension of ultrasonic duration. With the application of ultrasonic for 30 min, for Cd-Zn contaminated soil, the removal of Cd、Zn was respectively 46.19%、28.19%; while for Cd-Ni contaminated soil, the removal of Cd、Ni was respectively 46.17%、10.66%.(5) Results of BCR sequential extraction procedure showed that, Cd、Zn and Ni washed by Tartaric acid mainly came from acid extractable、reducible、and oxidizable fraction.