Adsorption Of Cadmium Ions By Modified Biochar From Aqueous Solution

The heavy metal cadmium has strong biological toxicity and is easily enriched in human body through the food chain,causing great harm to human health.Biochar,as an excellent adsorption material,can effectively remove heavy metals such as cadmium,mercury,arsenic,copper,lead and chromium from wastewater due to its large specific surface area and abundant surface functional groups.In the current study,in order to improve the adsorption capacity of biochar for Cd²⁺,the biochar was modified by adjusting its pore structure,surface functional groups and ash composition.The factors that may affect the adsorption results in the adsorption process were explored,and the mechanism of heavy metals adsorbed onto biochar was discussed.This research can provide the support in theory and technology aspect for the practical application of biochar in water treatment.The main research results are as follows:（1）Modified biochar（KBC）was prepared by activating poplar sawdust biochar with KOH.Compared with unmodified biochar,KBC has a larger specific surface area,developed microporous structure,and abundant oxygen-containing functional groups on its surface.The adsorption of Cd²⁺onto KBC was in accordance with Langmuir isothermal adsorption model,and the maximum adsorption capacity was54.6952 mg/g.The results of adsorption kinetic analysis showed that the adsorption of Cd²⁺onto KBC was in accordance with the pseudo second-order kinetic model.The results revealed that the adsorption mechanisms of Cd²⁺onto BC were mainly attributed to surface complexation,electrostatic interaction and surface precipitation.（2）Amino modified biochar（BC-NH₂）was prepared by decorated amino functional groups on the surface of KBC through nitrification and nitro reduction.The surface of BC-NH₂ contained a large number of-NH₂ functional groups and metal cations that can participate in ion exchange reactions.The adsorption capacity of amino modified biochar for Cd²⁺was 91.6926 mg/g,which was about 1 time higher than that of KBC.The analysis results showed that the adsorption of Cd²⁺onto BC-NH₂ fitted the Langmuir isotherm model well,and complied with the pseudo second-order model.The complexation reaction between-NH₂ groups and Cd²⁺was the main removal mechanism for Cd²⁺adsorption by BC-NH₂.In addition,ion exchange reactions were also responsible for the adsorption of Cd²⁺onto BC-NH₂.（3）Magnetic biochar（MBC）was obtained by treating poplar sawdust with FeCl₃·6H₂O solution and then pyrolyzed.MBC was activated by KMn O₄ to obtain modified magnetic biochar（KMBC）.After modification by KMn O₄,the surface of the magnetic biochar was loaded with Mn O_x particles and became rough,the surface oxygen content and the oxygen-containing functional groups number increased.The magnetic force was stable after modification.The maximum adsorption capacity of Cd²⁺by KMBC was 53.8992 mg/g,which was about 5 times than that of MBC.The main reason for the adsorption capacity increase was the loading Mn O_x particles on the magnetic biochar surface,simultaneously,the increase of the adsorption capacity was related to the the increase of oxygen-containing functional groups.The adsorption of Cd²⁺onto KMBC was in accordance with Langmuir isothermal model and pseudo second-order model.