| The Mixed Waste Biochar?MWBC?was prepared by pyrolysis technology using sludge and banana peel as raw materials.The orthogonal analysis,instrumental analysis?including surface micromorphology,infrared spectroscopy,specific surface area and pore size,Zeta potential and pH?and adsorption experiments were carried out to study the preparation,trace characteristics and adsorption of heavy metal ions(Taking Cu2+,Pb2+,Zn2+as examples)of MWBC.The adsorption effect of Cu2+,Pb2+and Zn2+as an example was studied.The adsorption kinetics and thermodynamics of MWBC on Cu2+,Pb2+and Zn2+were investigated.In addition,adsorption mechanism of MWBC was explored by combining the physical and chemical properties of MWBC.The preparation conditions of MWBC are as follows:the mass ratio of sludge to banana peel is 1:1,the pyrolysis temperature is 400?,the heating rate is 15?·min,and the final temperature residence time is 2 h.The MWBC character is as follows:?1?It has a complex lamellar and spherical structure,the surface is loose and porous and there are many mineral components;?2?it is rich in surface functional groups such as alkanes,alcoholic hydroxyl groups,aromatic functional groups,etc.?3?the specific surface area is 3.539 m2·g-11 and the average pore diameter is 31.4 nm.In addition,MWBC is mostly mesoporous and has slit pore structure;?4?Zeta potential is-43.9mV which has strong electrostatic adsorption on heavy metal ions;?5?pH 9.6,alkaline.The adsorption effects of MWBC are as follows:?1?within a certain period of time,the removal rates of Cu2+,Pb2+and Zn2+by MWBC increased with the increase of time.At 120min,the removal rates were 94.32%,79.86%,86.67%and the adsorption capacity was 37.51 mg·g-1,32.1 mg·g-11 and 34.8 mg·g-1,respectively.The adsorption behavior of MWBC on Cu2+,Pb2+and Zn2+conformed to the pseudo-second-order kinetics model;?2?with the increase of initial concentration of heavy metal ions,the removal efficiency of the three heavy metal ions decreases with the decrease of MWBC.But the adsorption capacity of Cu2+and Pb2+increases,while that of Zn2+increases first and then decreases.The adsorption behavior of MWBC on Cu2+,Pb2+and Zn2+conforms to Langmuir adsorption isotherm model.The fitting results show that the adsorption is mainly monolayer adsorption;?3?the activation energies of MWBC for Cu2+and Zn2+adsorption were 47.378 KJ·mol-11 and 61.814KJ·mol-1,respectively,both of which were greater than 40 KJ·mol-1.The fitting results indicated that the adsorption behavior of MWBC on Cu2+and Zn2+was chemical adsorption.Based on the above conclusions,the adsorption mechanism of MWBC includes the following three aspects:?1?the complexation of MWBC surface functional groups;?2?the coprecipitation of MWBC surface minerals;and?3?the electrostatic adsorption of MWBC surface negative charges. |
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