| Soil heavy metal pollution has become one of the most serious environmental problems of global concerns. Accumulation of heavy metal in soil not only destroy the microbial community in soil; restrain the growth of crop, but also pose risks and hazards to human health through:direct ingestion; food chain and drinking of contaminated ground water. In situ immobilization of heavy metal is one of the promising technologies. It is based on the reduction of metal bioavailability and mobility. The application of soil amendments can react with heavy metal physically and chemically such as adsorption, complexation, precipitation, and then change the combined form of heavy metal in soil. In this study, we extracted a novel environmental friendly soil amendment from the peat soil to remedimate the contaminated soild. The adsorption character in soil solution and the effects of humin addition in soil waere studied. The main experiments and conclusions are as follows:Humin was extracted from peat soil to study how its adsorption isotherms and kinetic characteristics might help mitigate heavy metal pollution from Cd(Ⅱ), Pb(Ⅱ) and Cu(Ⅱ). We also studied the influence of the soil solution’s pH, ionic strength, and soluble organic matter concentration on humin’s adsorption properties, and compared humin’s ability to deactivate heavy metals in both real soil and simulated soil solutions. Study results show that: 1) Humin contains massive oxygen-containing functional groups.2) Its adsorption capacities for Pb(Ⅱ) is greater than that of Cu(Ⅱ), which is greater than that of Cd(Ⅱ). Pb(Ⅱ) adsorption conforms to the Freundlich model, while Cd(Ⅱ) and Cu(Ⅱ) adsorption follow the Langmuir model.3) The adsorption kinetics of humin with respect to heavy metals align with second-order kinetics equations.4) As pH rises, heavy metal adsorption by humin increases rapidly.5) Electrolyte ions and tartaric acids in solution both inhibit humin’s adsorption of heavy metals.6) Humin’s ability to inactivate heavy metals is better in real field soil solutions than in simulated soil solutions.The effects of humin addition on the mobility and bioavailability of Pb and Zn in soil were studied through a batch soil column incubation experiment. The results showed that the treatments with humin could significantly reduce the leaching concentration of Cu and Zn. Compared with the control, the treatments with 2% humin could reduce the leaching concentration of Cu and Zn by 45.16% and 56.97% respectively after five days incubation. The leaching concentration of heave metal became stable after ten days incubation. Three kinds of fertilization, urea, ammonium sulfate and potassium dihydrogen phosphate, could enhance the passivation effects of humin on Pb. The leaching concentration of Pb decreased 29.86%,23.71% and 28.69% respectively. However, there was no significant impact on Cu. The treatments with 2% humin could reduce the exchangeable fraction of Cu and Pb from 15.68%,15.79% to 0.48%,1.22%, while the proportion of organic fraction increased from 5.35%,10.93% to 13.24%,27.32% respectively after 30 days incubation.Based on the former research results, sulfhydryl humin was gained by humin modification in the presence of thioglycolic acid and acetic anhydride. The chemical structure of modified humin was studied by Fourier Infrared Absorb Spectrum(FTIR) and Thermograimetric Analyzer. The batch adsorption experiment was carried to study the adsorption thermodynamics of sulfhydryl humin on heavy metal cadmium in solution. The effect of sulfhydryl humin and normal humin addition on remedying contaminated soil was comparied through soil fostering experiment. The results showed thatthere are a number of carboxyl group on the surface of humin. Compared with humin, there is a peak on 2578cm-1 in the modified humin fourier infrared abosorb spectrum which indicates the existing of sulfhydryl group. The adsorption of Cd on sulfhydryl humin follows Langmuir model in different temperature. The adsorption capacity of sulfhydryl humin reaches 8.9091mg·g-1 in 298K, which is higher than humin (6.5335 mg·g-1), indicating the increasing of adsorption ability by sulfhydryl modification. Thermodynamic parameters indicated that the adsorption is spontaneous, endothermic accompanied by increase in entropy.The treatment with 2.5% sulfhydryl humin addition increase the remedying effect of Cd, Pb and Cu by 44%,65% and 50% respectively after ten days incubation.Compared with the treatment of humin addition, the impact of cadium increase significiantly by 12%. However there is no significiant impact on lead and copper.The results highlighted the potential of modified humin amendment to reduce the mobility and bioavailability of heavy metal in contaminated soil. |
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