Migration Characteristics Of Adsorbed Pb(Ⅱ) On Hydrothermal Carbon Driven By Alkalinity

Lead（Pb）is one of the optimal control targets of soil heavy metal pollution in China.In the practice of remediation of soil lead pollution,it is a common method to add adsorbent to plant effective passivation of lead in soil.In recent years,the use of Hydrochar（HC）to control soil heavy metal pollution has achieved remarkable results.However,the lack of research on the structure and chemical stability of HC materials under different soil physical and chemical conditions has limited the further development of this technology.HC surface is attached with oxidized debris（HD）,similar in structure and properties to rich acid,HD can be peeled off from HC surface under alkaline conditions.At present,there are few studies on the adsorption performance of HD to HC,and even less studies on the desorption release of Pb（Ⅱ）attached to HC after the adsorption of heavy metals into the soil and groundwater environment.In-depth study on the structural composition of hydrothermal carbon,Understanding the effect of HD exfoliation on the migration mechanism of Pb（Ⅱ）adsorbed on HC surface under alkaline conditions is helpful to improve the environmental stability of HC as a heavy metal ion adsorbent.Based on the widespread distribution of alkaline soils in China,this study carried out a study on the evolution of HC structure characteristics and lead adsorption/desorption performance driven by alkalinity,in order to provide technical reference for lead-contaminated water and soil environmental treatment and remediation.The main research results include:（1）Hydrochar debris（HD）formed in the reaction of HC prepared by hydrothermal carbonization was exfoliated under alkaline conditions,indicating that HC has binary composition;The alkalinity can cause HD stripping on HC surface,and the greater the alkalinity,the more complete HD peeling.HD spalling kinetics reached equilibrium after 12 h.After the reaction of HC with 0.01 mol·L^-1,0.1 mol·L^-1,1.0mol·L^-1Na HCO₃for 24 h,the content of HD extracted from HC was 37.00 mg·L^-1,40.44 mg·L^-1,45.33 mg·L^-1,respectively.（2）Pb（Ⅱ）adsorption experiment shows that:The adsorption capacity of Pb（Ⅱ）by HC,HD and bw HC was calculated to be 55.24 mg·L^-1,342.22 mg·L^-1,and26.72mg·L^-1,respectively.（3）Sand layer was used to simulate saturated porous media.It was found that HD penetration curve was affected by background ionic strength.With the increase of ionic strength(0.001 mol·L^-1-0.1 mol·L^-1),HD recovery decreased（97.04%-50.28%）.（4）The alkalinity provided by Na OH and Na HCO₃can cause HD spalling and desorption of Pb（Ⅱ）adsorbed on the surface of HC-Pb（Ⅱ）.The amount of Pb（Ⅱ）desorption increased with the increase of basicity（0.44%-21.34%for Na OH and0.35%-20.21%for Na HCO₃）.（5）HC-Pb（Ⅱ）adsorbed Pb（Ⅱ）desorption under the basicity condition generates HD-Pb（Ⅱ）complex,whose particle size is only about 100nm,and can be stably dispersed in alkaline solution with p H>7.0 for a long time.These results indicate that adding HC in alkaline soil may increase the migration of Pb（Ⅱ）and cause potential environmental risks.