Prepatation Of Modified Biochars And Their Adsorption Of Heavy Metal Ions

Biochar is a stable,insoluble and highly aromatized solid material prepared by pyrolysis of biomass?mainly agricultural waste?under anoxic environment at high temperature?usually<700??.It has been widely concerned by researchers at home and abroad for its simple preparation,wide source of raw materials,low cost and good adsorption performance for heavy metals in water.Increasing the selectivity of biochar to pollutants and enhancing the adsorption ability of biochar on pollutants can make biochar have better utilization value.In this paper,pine sawdust as one biomass was used as raw material to prepare biochar.In order to enhance the adsorption,the KMnO₄-modified biochars and?CH₃COO?₂Mg-modified biochar were prepared by impregnating the original biochar with KMnO₄,?CH₃COO?₂Mg solution.Ce-modified biochar was prepared by co-pyrolysis of pine sawdust with CeCl₃ at the same time.The adsorption properties of various modifiers on the original biochar and on Pb²⁺,Cd²⁺and Cu²⁺were mainly studied.The main research contents are as follows:1.Synthesis and adsorption properties of KMnO₄-modified biochars for heavy metals removal.PSC and Mg-PSC modified biochar were prepared from pine wood sawdust biomass under anaerobic condition at 500?.The effects of potassium permanganate modification on the original biochar and the adsorption of Pb²⁺,Cd²⁺and Cu²⁺in aqueous solution were studied.The results showed that:?1?After the modification of KMnO₄,manganese was uniformly distributed on the surface of the original biochar,the degree of aromatization and carbonization of Mg-PSC was increased,the structure was stable and the polarity was decreased;MnO_x exists on the surface of primordial pine biochars in amorphous form,and there are abundant functional groups on the surface of pine charcoal.?2?The adsorption capacity of KMnO₄-modified pine biochars for Pb²⁺,Cd²⁺and Cu²⁺was significantly higher than that for original pine charcoal,which indicated that potassium permanganate modification greatly improved the adsorption ability of pine biochars to Pb²⁺,Cd²⁺and Cu²⁺;?3?The adsorption of Pb²⁺,Cd²⁺and Cu²⁺by Mn-PSC accords with the Langmuir isothermal adsorption model and the quasi-second-order kinetic equation.The equilibrium adsorption capacity was 137.90 mg/g,24.69 mg/g and 28.76 mg/g.?4?The order of adsorption ability of Mn-PSC to three heavy metals is Pb²⁺>Cu²⁺>Cd²⁺.2.Synthesis and adsorption properties of?CH₃COO?₂Mg-modified biochars for heavy metals removal.Mg-PSC modified biochar was prepared from pine sawdust biomass under anaerobic condition at 500?.The effect of MgO_x on the original biochar and the adsorption of Pb²⁺,Cd²⁺and Cu²⁺in aqueous solution was studied.The results show that:?1?Pine charcoal is composed of solid particles of irregular size,but the modification of magnesium does not change its morphology,MgO_x exists on the surface of primordial pine charcoal in amorphous form.The increase of O/C value of Mg-PSC the increase of?O+N?/C molar ratio,the increase of surface polarity and the content of polar functional groups A significant increase;The specific surface area of Mg-PSC was 4 times larger than that of PSC.?2?The adsorption capacity of mg modified pine charcoal for Pb²⁺,Cd²⁺and Cu²⁺was obviously higher than that for original pine charcoal,which indicated that the adsorption capacity of mg modified pine charcoal to Pb²⁺,Cd²⁺and Cu²⁺was greatly improved.?3?The adsorption of Pb²⁺,Cd²⁺and Cu²⁺by Mg-PSC is in accordance with the Langmuir isothermal adsorption model and the quasi second-order kinetic equation.The equilibrium adsorption capacity is 8.80 mg/g,8.94mg/g and 6.12 mg/g.?4?The adsorption ability of Mg-PSC to three heavy metals was in the order of Cd²⁺>Pb²⁺>Cu²⁺.3.Synthesis and adsorption properties of CeCl₃-modified biochars for heavy metals removal.The raw material?PS?of pine sawdust was first impregnated with cerium chloride solution in the same volume.Pyrolysis of impregnated pine sawdust?Ce-PS?to form CeCl₃-modified biochars Ce-PSC;The adsorption of Cd²⁺on Ce-PSC at different temperatures was studied.The results are as follows:?1?The morphology did not change obviously because of the modification of cerium;The surface polarity decreases with the increase of the carbonization level of biochar,and the crystalline form of cerium Oxide is found on the surface.At the temperature of 25??35??45?,the isothermal adsorption of Ce-PSC pine biochars for heavy metal ion Cd²⁺in aqueous solution shows that:Langmuir equation can describe the adsorption of Cd²⁺and Ce-PSC pine biochars.The saturated adsorption capacities of Cd²⁺for Ce-PSC at three temperatures are 9.85 mg/g,10.60 mg/g and10.77 mg/g,respectively.It is proved that the adsorption behavior is endothermic reaction.The adsorption mechanism of pine charcoal for Pb²⁺,Cd²⁺and Cu²⁺heavy metal ions in this study is likely to be complexation and ion exchange.