Harmless Treatment Of Hexavalent Chromium Ions In Soil

With the rapid development of China's industry and agriculture,heavy metal ion pollution in the soil is becoming more and more serious,and chromium is a very important environmental pollutant.Due to the different forms of chromium,the degree of environmental pollution is also different,the adsorption and reduction behavior of chromium in soil has become a matter of great concern.In this paper,the adsorption and adsorption mechanism of lignin resin and activated carbon composite adsorbent on Cr(VI)in soil were studied.The process conditions were optimized,and the adsorption performance analysis and characterization analysis were carried out to achieve the purpose of harmless treatment of Cr(VI)in the soil and repairing chromium contaminated soil.Lignin-based weakly acidic resin(LBR)was used as adsorbent to study the adsorption effect of Cr(VI)in soil by adding LBR.The conditions of LBR preparation were optimized by single factor experiments and orthogonal experiment.The repair process of Cr(VI)in soil by LBR was investigated by reaction time,pH,adsorbent dosage and temperature.It is concluded that the Langmuir adsorption isotherm model is more suitable for describing the adsorption process.The adsorption process of Cr(VI)in soil by LBR is an endothermic process,and it is mainly chemical adsorption.In the process of adsorbing Cr(VI)in soil by LBR,the pseudo-secondary kinetics is more suitable.According to the characterization analysis,the surface of LBR material contains a large number of acidic oxygen-containing functional groups,such as hydroxyl,ester,carboxyl,etc.The unique chemical structure can effectively reduce Cr(VI)in soil to form Cr(III),and the generated Cr(III)undergo complexation to form a stable structure.The maximum adsorption capacity of Cr(VI)in soil by LBR can reach 3.95 mg/g,and the removal rate can reach 91.9%.In addition,commercial activated carbon and glucose were used as raw materials to synthesize activated carbon composite adsorbent by hydrothermal synthesis method,and its adsorption effect on Cr(VI)in soil was investigated.In order to increase the oxygen-containing functional groups on the surface of activated carbon,the specific surface area,pore diameter,pore volume and adsorption site of activated carbon.The adsorption process of Cr(VI)in soil by activated carbon composites was investigated by factors such as reaction time,pH,adsorbent dosage and temperature.It is found that the Freundlich adsorption isotherm model can well fit the isothermal adsorption data.The adsorption process of Cr(VI)in the soil by activated carbon composites is a spontaneous process,mainly based on chemical adsorption,and the pseudo second-order kinetics can be more a good description.Through characterization analysis,complex chemical changes occurred in the process of hydrothermal treatment of activated carbon and glucose.The number of oxygen-containing functional groups on the surface of activated carbon composites increased significantly,such as hydroxyl,aldehyde,and ester groups were generated,mainly C-OH,which was beneficial to the adsorption of Cr(VI)in soil.The maximum adsorption capacity of Cr(VI)in the soil by activated carbon composites can reach 3.54 mg/g and the removal rate can reach 74.8%,under the same conditions,the removal rate of Cr(VI)in soil was increased by 16.2%compared with activated carbon raw materials.The results show that the lignin-based resin material and the activated carbon composite material can effectively adsorb Cr(VI)and reduce the concentration of Cr(VI)in the soil to achieve the Cr(VI)in the soil.Therefore,the use of two adsorbents for the repair of chromium contaminated soil has a good application prospect.