| Heavy metal pollution in soils has not only a serious threat to the ecological system of soil and groundwater, but also harms human health because it is dormant, irreversible, and accumulative and so on. Hence, heavy metals have caused widespread concerns in the world. In recent years, due to mitigating climate change, improving soil properties and remediating polluted soil, biochar has caused wide public concern. Biochar shows excellent adsorptive capability due to its unique properties, which is expected to become one of the effective method to remedy heavy metal contaminated soils.In the paper, firstly, the batch equilibrium adsorption experiment was performed to examine the effect of different factors on the adsorption of Cu(Ⅱ) by the biochar, loess and loess with biochar, and also to discuss thoroughly the kinetic and thermodynamic adsorptive characteristics for Cu(Ⅱ). Secondly, the elution experiment was done to investigate the effect of different factors on elution of heavy metal ion from simulated contaminated soil, and to study the washing dynamic and thermodynamic characteristics of Cu(Ⅱ) from contaminated soil. Finaly, the batch equilibrium adsorption experiment was again performed to investigate adsorptive kinetics and thermodynamics of Cu(Ⅱ) on biochar and biochar with the main component of loess(Humic acid and Illite), as well as to study the effect of pH, initial concentration and temperature on adsorption of Cu(Ⅱ). The results can provide some certain theoretical basis for immobilization of heavy metals pollution in loess soil by biochar. The major findings were observed as following:(1) The equilibrium adsorption time for copper on biochar was 4 h, while the equilibrium adsorption time was 10 h on loess and the loess with biochar, respectively. Biochar addition reduced the adsorption capacity of loess for copper. The results indicated that the sorption processes of biochar, loess and loess with biochar could be well characrerized with pseudo-second-order kinetics model. The effect of pH value on the adsorption of Cu(Ⅱ) was significant. When the pH values ranged from 2.0 to 6.0, the adsorption of Cu(Ⅱ) was greater. With an increase of the initial concentration of Cu(Ⅱ), the adsorption capacity of Cu(Ⅱ) gradually increased. With 50 to 300 mg·L-1 of the initial concentration, the adsorption of Cu(Ⅱ) on loess was greater than that on biochar. When the initial concentration was 400 mg·L-1, the adsorption capacity of Cu(Ⅱ) on biochar gradually increased. At 25 ℃, the isotherm adsorption by the biochar and the biochar with loess followed the Langmuir model, but that by the loess fitted the Freundlich one. The adsorptive kinetics of Cu(Ⅱ) onto the biochar, loess and loess with biochar were spontaneous. The adsorptive capacity increased with increase of temperature from 20 ℃ to 40 ℃. The existence of inorganic salts with the certain concentrations could not obviously influence the adsorptive capacity of Cu(Ⅱ).(2) The desorptions of Cu from the loess, loess with BS600 and loess with LS600 also conformed to the pseudo-second-order kinetic model. The leaching ability(η) of Cu from solid phase improved when the initial pH values of solution were less than 3.5 in loess system and 4.0 in loess with biochar systems. The values of η in the single loess system increased and those in the loess with biochar systems did not change with temperature increasing. When the initial concentration of Cu in soil increased, the η values of Cu decreased. No obvious effect of Ca2+ on the η value was found.(3) Interactions of Cu(Ⅱ) on biochar and the mixture adsorbent of humic acid or illite were studied. Initial pH had a great impact on the adsorption of metal ion(copper). When the pH ranged from 2 to 6, the adsorption of Cu(Ⅱ) was greater. With an increase of the initial concentration of Cu(Ⅱ), the adsorption capacity of gradually increased. At 25℃, The isotherm adsorption of the biochar followed the isothermal model of Langmuir, but the biochar with humic acid or illite fitted the isothermal model of Freundlich. The adsorption kinetics of Cu(Ⅱ) from the biochar and the biochar with humic acid or illite were spontaneous, the capacity increased with increase of temperature from 20℃-40℃. |
PDF Full Text Request