Mg-Al layered double hydroxides modified by 2,4,6-trimercapto-s-triazine for effective removal heavy metals from soil

Abstract

Since 2,4,6-trimercapto-s-triazine (TMT) possesses advantages of multiple adsorption sites and strong binding ability with heavy metals, in this study, layered double hydroxides modified by TMT are prepared (LDHs-TMT) for removing Cu(II)/Pb(II) from contaminated soil. The characterization of structure indicated TMT is intercalated between LDHs layers, and affects growth of crystal structure. The data of kinetics fits pseudo-second-order and intraparticle diffusion models. The isotherms is conformed to Langmuir model, and the adsorption capacity reaches 102.8 mg/g for Cu(II) and 105.8 mg/g for Pb(II). For adsorption mechanism, when concentration of Cu(II)/Pb(II) is low, Cu(II)/Pb(II) is preferentially immobilized by interlayered TMT molecule. As concentration increases, since adsorption sites on TMT are fully occupied, Cu(II)/Pb(II) grab the hydroxy of LDHs and form hydroxide precipitation. The effects of pH, coexistence ions, column leaching and leaching experiments are conducted. The results indicate LDHs-TMT have high adsorption stability and possesses appreciable interception for heavy metal migration.