Adsorption Of Lead And Sulfamethazine On Biochar And Its Remediation Of Soils Contaminted By Lead And Sulfamethazine

With the abuse of organic fertilizer in farm land, antibiotic pollution in soils is gradually highlighted. Combined pollution with organic pollutants and heavy metal is the most common existence form. Compared with most of remediations materials, biochar is prospective because of its potential functions, such as carbon sequestration, soil quality improvement, wide source, low cost, no secondary pollution. At present, although the biochar has be used to treat the heavy metals and organic pollutants, but the research of the heavy metal- antibiotic compound complexed pollution is scarcely reported.Two kinds of biomasses, including rape straw and excrementum bombycis, was selected to be raw materials,and was pyrolyzed at 300-700℃under limit oxygen supply condition. The physisochemical characteristics of these biochars were measured with elemental analysis, specific surface area analysis, thermogravimetric analysis, Fourier transform infrared spectroscopy 、 X-ray diffraction spectra. Pb and sulfamethazine（SMT） were choosen to be targets pollution to explore their adsorption kinetics and isotherm, and the effect of pH and Pb²⁺ in solution. In addition, red and brown soils with Pb²⁺ and sulfamethazine polluted was repaired thought adding different content biochar, and the remediation effects were evaluated by BCR and TCLP methods in different times. The results shows that:（1）The yield of biochar decreased with the increasing pyrolysis temperature, the pH value、specific surface area、C content and ash content increased. In addition, the H, O, N content and the ratios of H/C and O/C decreased, with temperature increased, but C/N increased. Biochar gradually transformed from disorder to order, from loose alkane structure into dense aromatic structure; the organic functional groups（such as-OH, C=O,-COOH） on biochar gradually weakened or even disappeared. However, the ash content increased. All the biochars have certain buffering ability.（2）The amount of SMT adsorption on different biochar followed this order: RW400>RW300>RW600>R500>700, EW300>EW400>EW600>EW700>E500, the orgamic functional groups on the biochar surface and specific surface area were the main factors influenced the amount of SMT. Additionally, in the dynamic expriments of SMT, the second order kinetics equation was fitted better（R2>0.99）, which indicated that chemical sorption occurred, the adsorption mechanism could also be related to the surface groupsand ash components; The amount of Pb adsorption on different biochar followed this order: RW600>RW400>RW500>RW300, EW600>EW500>EW300, the ash compositions on the biochar surface were the main adsorption mechanism,such as phosphates、carbonates、silicates compounds.（3） In the sorption experiment of sulfamethazine on the biochar, pH in solution could affect the surface charge of biochar and SMT forms, which affected the SMT adsorption on the biochar. Namely, when maximum adsorption for all of the biochar was optimal, the pH of the solution was a value between two pKa（pH=2.28-7.42） of SMT. Moreover, Pb²⁺ could occupy adsorption sites on biochar surface, which would affect the adsorption of SMT on the biochar.（4） The biochar could change the effective states of the Pb and sulfamethazine in soils, and reduce the environmental risk of the pollutants. When the polluted soils treated with biochar, the acid soluble metal Pb content in soil effectively reduced, which promote the acid soluble Pb to transforme into other forms, in particular. And as the biochar was added into the contaminated soil, the content of residual Pb could increase, and the metal ion Pb²⁺ was passivated and fixed. While the amount of biochar increasing and prolonging the treatment time, the passivation effect of biochar on the Pb in soils could also enhance. According to SMT, a organic pollutant, and the characteristics of the soil would influence the TCLP extract state of the pollutant, the higher pH, and the more cation exchange capacity（CEC）, the TCLP extraction organic matter is higher. And the extractable heavy metals of TCLP increased with the soil pH decreased, reduced with the extension of time.