Study On Adsorption And Stabilization Of Heavy Metal From Modified Cow

Dairy manure biochar is a pyrogenic black carbon prepared at low temperature(≤ 700°C) and under oxygen-free conditions. In general, it is characterized by a high porosity and surface area, strong ability of adsorption for it has large quantities of oxygen-containing groups and mineral composition. In order to increase its sorption and stabilization ability for heavy metals, alkali activation method was applied to improve its sorption and stabilization effect.First of all, dairy manure was used as precursor substance to prepare dairy manure biochar(BC300). GBC was made from activation of BC300 by strong alkali. Biochar was characterized by physical and chemical properties, element analysis, chemical titration of surface groups. The results showed that modification increased the p H of biochar from 9.75 to 9.98, and its surface area increased about 2.76 times from 9.40 m2/g to 25.94 m2/g. Acidic oxygen containing functional groups increased from 0.63 mmol/g to 0.70 mmol/g, and basic oxygen containing functional groups increased from 2.60 mmol/g to 2.93 mmol/g.Secondly, the Pb(Ⅱ) and Cd(Ⅱ) sorption kinetics and isotherms by BC300 and GBC were studied respectively. The results revealed that modification process increased the sorption ability of BC300: sorption capacity of Pb(Ⅱ) increased from 50.41 mg/g to 192.22 mg/g by BC300 and GBC, of Cd(Ⅱ) increased from 23.63 mg/g to 40.74 mg/g respectively. The adsorption equilibrium could accomplish within 4 hours. In addition, the competitive adsorption was investigated between Pb(Ⅱ) and Cd(Ⅱ) at different p H, it turned out that Pb(Ⅱ) has a higher adsorption affinity for BC300 and GBC. Increasing the p H of heavy metal solutions increased sorption capacity of BC300 and GBC.Then BC300 and GBC were used as soil amendment to immobilize heavy metal in soil. The physical and chemical properties of soil p H, cation exchange capacity, Olsen-P, organic matter were analyzed. Results indicated that BC300 and GBC could increase soil p H, cation exchange capacity and Olsen-P, also the improve effects were better when biochar applying amount increased. While the organic matter content was decreased. The toxicity characteristic leaching procedure and BCR sequential extraction procedure were applied to detect the changes of heavy metals after the soil was disposed with BC300 and GBC. It was turned out that applying biochar can apparently reduce the concentrations of TCLP extract heavy metals, the effects were Pb(37.5%) > Cu(37.1%) > Zn(20.6%) > Cd(18.5%) for 5% BC300 process, and Cu(65.5%) > Pb(65%) > Cd(55.1%) > Zn(54.2%) for 5% GBC process. The forms of heavy metals in the biochar-amended soils changed from acid soluble to reducible, oxidizable and residual fractions. In conclusion, the GBC’s heavy metal stabilization effect was better than that of BC300.