Effect of humic acid-loaded biochar on the adsorption performance of Mn2+in soil leachate from mining area
Humic acid modified biochar(CSB-HA)was prepared using corn stover-based biochar(CSB)loaded with hum-ic acid for the adsorption of Mn2+from the soil leachate in the mining area and its adsorption characteristics were ana-lyzed.With the help of SEM,BET,XRD,XPS and FT-IR,the prepared samples were characterized and analyzed.The res-ults show that the specific surface area of CSB-HA is 7.911 m2/g,which is 1.98 times that of CSB,and the pores are mostly mesoporous.The excellent pore structure provides a large number of adsorption sites and promotes the contact with pollutants,so that the adsorption performance is enhanced.The surface of CSB-HA is enriched with the oxygen-contain-ing functional groups such as C=O,O=C—O and—COOH,and the oxygen atoms in the functional groups can be com-plexed and coordinated with heavy metal ions to form a stable ligand bond,thus removing Mn2+.The maximum adsorp-tion of Mn2+by CSB-HA is 21.493 mg/g,and the quasi-primary kinetic model,quasi-secondary kinetic model,Langmuir isotherm and Temkin isotherm can fit the adsorption process well,and the Temkin constant b＜1 kJ/mol can prove that the adsorption process Physical adsorption exists.The quasi-secondary kinetic model and Langmuir isotherm fit the adsorp-tion process better and closer to the actual detection value,so the adsorption process is a single molecule layer adsorption,which is subject to the joint action of physical adsorption and chemical adsorption,and the chemical adsorption is domin-ant.Therefore,the type and mass fraction of oxygen-containing functional groups have an important effect on the adsorp-tion of Mn2+by CSB-HA.The diffusion process was analyzed by the liquid-film diffusion model and the intra-particle dif-fusion model.The fitted line of the liquid-film diffusion model has a small intercept with the longitudinal axis,so the pro-cess is not a velocity-controlled phase.The intra-particle diffusion model can be fitted into a membrane diffusion stage(0-60 min)and an intra-particle diffusion stage(60-240 min),the latter adsorption rate is significantly lower(kid1=1.159＞kid2=0.287),and the fitted lines do not pass through the origin,so that the intra-particle diffusion stage is the key stage of the adsorption process for controlling the rate.In the thermodynamic simulations,the separation coefficients RL are in the range of 0.4-0.6,ΔH=15.41 kJ/mol＞0,and ΔG is negative and decreases with increasing temperature,indic-ating that the adsorption process is reversible and spontaneous heat absorption,and the adsorption reaction can be facilit-ated by warming up.ΔS=49.90 J/(mol·K)＞0,which proves that the solid-liquid interface stoichiometry increases during the adsorption process.The simulated adsorption experiments on leaching solution show that CSB-HA has a good adsorp-tion effect on Mn2+and a regulating effect on the pH of leaching solution.
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