Preparation Of Waste Newspaper-based Biochar And Its Adsorption Properties For Copper Ions

Waste newspapers are a common waste that is rich in cellulose,hemicellulose and minerals and is a potential biochar raw material.The pllution of heavy metal on environment is more serious,and biochar is efficient on heavy metal treatment due to its unique physical and chemical properties.This paper selected waste newspapers to prepare biochar adsorbent materials at 400℃,500℃,and 600℃ under the protection of N2 atmosphere,marked as WBC-400,WBC-500,WBC-600.The adsorption performance and mechanism of Cu2+on waste newspaper-based biochar were investigated by adjusting the initial pH of the solution,the initial concentration of copper ions,the adsorption time and the adsorption temperature.The waste newspaper-based biochar before and after adsorption were characterized by conventional analysis methods such as FT-IR,XRD and BET.This article mainly draws the following conclusions:(1)The physical and chemical properties of waste newspaper-based biochar obtained from different pyrolysis temperatures were different.The specific surface area of WBC-600 was much larger than WBC-500 and WBC-400,which were 211.3 m2/g,28.7 m2/g,and 8.25 m2/g,respectively.The C content and pH of WBC-600 were higher than that of WBC-500 and WBC-400,the C content was 63.8%,62.6%,58.9%,and the pH was 10.01,9.66,8.30,respectively;at the same time,the Ca and ash content of WBC-600 were also higher than that of WBC-500 and WBC-400.The Ca content was 30.05 mg/g,22.46 mg/g,17.63 mg/g,and the ash content was 25.11%,22.93%,20.79%,respectively;the average pore size of WBC-600 was smaller than that of WBC-500 and WBC-400,which were 1.425 nm,1.614 nm,and 1.753 nm,respectively.Therefore,pyrolysis was more likely to form microporous carbon with developed pore diameter.(2)Waste newspaper-based biochar obtained from different pyrolysis temperatures also had different adsorption properties for Cu2+.The maximum adsorption capacity of WBC-600,WBC-500 and WBC-400 was 138 mg/g,115 mg/g and 107 mg/g,pH=5,respectively.(3)We simulated the kinetic model of adsorption process of three biochars.The results indicated that the adsorption process of waste newspaper-based biochar could be described by the pseudo second-order kinetic model;intraparticle diffusion equation fitted curve did not go through the origin,indicating that intragranular diffusion was not the only rate-control step,liquid film diffusion also controlled the adsorption rate,and Ki1 was significantly larger than Ki2,indicating that liquid film diffusion was the main rate-control step.(4)And the isothermal adsorption model of Langmuir and Freundlich was simulated too.Langmuir isothermal was the best model for description of the adsorption process and the R2 values of WBC-600,WBC-500 and WBC-400 were 0.9999,0.9990,0.9995,respectively.Indicating that the adsorption occurred at specific sites on the surface of biochar.(5)In addition,the thermodynamics of the adsorption process was studied.It was found that the Gibbs free energy(ΔG°)of the three biochars obtained at different temperatures were negative for the Cu2+ adsorption process,indicating that the adsorption processes were spontaneous.ΔH° and ΔS° were positive values,which indicated that the adsorption process was endothermic,and the solid-liquid surface chaos increased after adsorbing Cu2+.(6)The adsorption mechanism of biochar concluded the physical adsorption by pore size;the complexation of surface oxygen-containing functional groups include-OH,-COOH,-CO-,-O-,etc.;the precipitation of oxides,such as Cu(OH)2、Cu(OH)、CuO;the ion exchange of inorganic mineral elements on the surface of biochar,such as Ca2+、Mg2+、Si4+、Mn2+、Fe2+and Al3+etc.