Preparation Of Microwave Biochar And Its Adsorption Behavior And Mechanism For Copper,Lead And Cadmium

In recent years,with the expansion of mining,heavy metal smelting and processing,and the scale of chemical companies,the problem of excessive heavy metal content in water bodies caused by the discharge of heavy metal wastewater has become increasingly serious.Biochar is a porous carbonaceous material produced by pyrolysis of biomass in an oxygen-limited environment.The wide source of biochar materials,green economy,and unique structure and properties have great potential for the adsorption and removal of heavy metals in the environment.The experiment used wheat straw biomass and hydrogen peroxide?H₂O₂?to pretreat wheat straw biomass to prepare WM microwave biochar?WM100,WM200,WM300,WM400,WM500,WM600?and HPWM microwave biochar?HPWM100,HPWM200,HPWM300,HPWM400,HPWM500,HPWM600?,and use the prepared microwave biochar to explore the adsorption performance and mechanism of Cd²⁺,Pb²⁺and Cu²⁺.The physical and chemical properties of biochar were analyzed by scanning electron microscopy,Fourier infrared spectrometer,pore size and specific surface area analyzer,thermogravimetric analyzer,X-ray diffractometer and Beohm titration.The effects of preparation power,metal ions(Na⁺,K⁺,Ca²⁺)and pH on biochar adsorption were investigated.The adsorption kinetics and isothermal adsorption characteristics of microwave biochar to Pb²⁺,Cd²⁺and Cu²⁺were studied.The results showed that:?1?The higher the power for preparing WM biochar,the larger the specific surface area and the most approximate diameter of the biochar,the more developed the pore structure,and the lower the yield.The specific surface area and optimal diameter of HPWM biochar are higher than those of WM biochar prepared under the same conditions,and the yield is lower than that of WM biochar.As the preparation power increases,the pore volume of HPWM biochar?0.0018⁰.1309 cm³/g?is slightly higher than that of WM biochar?0.0015⁰.0741cm³/g?,and increases with the increase of power.?2?The total amount of acidic functional groups of biochar decreases with the increase of preparation power.HPWM biochar not only has oxygen-containing functional groups such as carboxyl group,carbonyl group and ether bond of WM carbon,but also has more obvious carboxylate functional group peaks.The thermal stability of HPWM biochar is lower than that of WM biochar;WM biochar and HPWM biochar have dispersion peaks caused by cellulose 002 crystal plane at about 18³0°and sharp inorganic salts after 25°and 40°Diffraction peaks.?3?The adsorption kinetics data of several biochars for heavy metals are more in line with the pseudo second-order kinetic equation?q_t=K ₂ q_e² t/?1+K₂ q_e t??,and the isothermal test data are in line with the Langmuir isothermal model?q_e=bq ⁰C_e/?1+bC_e??;?Pb:137.36mg/g,Cd:52.92mg/g,Cu:30.29mg/g?,the optimal adsorption capacity of HPWM biochar for heavy metals is?Pb:68.17mg/g,Cd:198.82mg/g,Cu:67.80mg/g?;?4?The pH value has a greater influence on the adsorption of heavy metals by the two types of microwave biochar.The optimal pH values for Cu²⁺,Cd²⁺and Pb²⁺are 5,6 and 6respectively.The complex precipitation of heavy metal ions is not conducive to adsorption;Na⁺,K⁺and Ca²⁺are not conducive to the adsorption of three heavy metal ions by biochar.?5?The mechanism of microwave biochar adsorption of Pb²⁺,Cd²⁺and Cu²⁺mainly includes electrostatic attraction,surface complexation,precipitation and cation exchange.Complexation and precipitation are greatly affected by the type and number of functional groups on the surface of the biochar.Electrostatic attraction and cation exchange are greatly affected by background ions and H⁺in the solution.The desorption test results show that WM400,WM500 and WM600 biochar have good adsorption performance for heavy metal ions,and the desorption rate is above 50%.