Stabilization Of Pb And Zn In Heavy Metal Contaminated Soil By Phosphate Modified Biochar

In order to explore the remediation effect of phosphate modified biochar on heavy metal contaminated soil,rice hulls were impregnated with potassium dihydrogen phosphate（KH₂PO₄）as chemical modifier and rice hulls as biomass raw material.Rice hulls were modified according to the mass ratio of KH₂PO₄ to rice hulls 0.5,1 and 2.Biochar was prepared by holding at 350,550 and 750℃for 3h.Meanwhile,unmodified biochar was prepared at the same temperature.The effects of modified biochar on the stabilization of Pb and Zn in heavy metal contaminated soil were investigated by adsorption test and soil culture test.The results show that:（1）The pH value of the unmodified biochar prepared at different temperatures ranged from 7.84 to 9.68,showing weak alkalinity,and increased with the increase of temperature.The pH of biochar modified by KH₂PO₄ decreased from 6.30 to 8.10,which also increased with the increase of temperature.At the same temperature,the pH gradually decreased with the increase of the proportion of potassium dihydrogen phosphate.The total phosphorus content of the modified biochar was relatively increased,but it did not increase with the increase of the amount of modifier.When the impregnation ratio was 1,the total phosphorus content of the modified biochar reached the highest.（2）FT-IR showed that the surface functional groups of the modified biochar increased;XRD showed that the modified biochar had more KPO₃ and K₄P₂O₇.（3）The adsorption capacity of the modified biochar to Pb and Zn in solution was significantly improved.At 550℃,when the impregnation ratio was 1,the adsorption capacities of Pb and Zn reached the maximum,which were 142.22 mg/g and 46.50 mg/g,respectively.（4）Adding modified biochar and unmodified biochar in lead-zinc contaminated soil changed the distribution of Pb and Zn in the contaminated soil,and had a good stabilizing effect on the form of Pb and Zn in B1（Acid soluble state）,which increased with the increase of the amount of biochar and decreased with the increase of the concentration of Pb and Zn in the contaminated soil.Under the same conditions,the stabilization effect of biochar modified with potassium dihydrogen phosphate on Pb and Zn in soil is greater than that of unmodified biochar.（5）When biochar was added to tailing contaminated soil,biochar could inhibit the acid production process of sulfide oxidation,and the inhibition effect of modified biochar was greater than that of unmodified biochar.The content of available Pb and Zn in soil decreased with the increase of biochar supplemental level,and the inhibition effect on the available Pb was greater than that on the available Zn,and the inhibition effect of modified biochar was greater than that of unmodified biochar.（6）The addition of biochar in AMD（acid mine drainage）contaminated soil significantly stabilizes Pb and Zn in the soil,and the stabilization of Pb is greater than that of Zn,and the stabilization of modified biochar is greater than that of unmodified biochar.The results show that the biochar modified with potassium dihydrogen phosphate is superior to unmodified biochar in the fixation of Pb and Zn in heavy metal contaminated soil and in the inhibition of heavy metal release from tailings.