Preparation And Adsorption Properties Of Sludge Biochar/ZnO Composites

With the rapid development of industry,considerable heavy metals chromium and dyes are inevitably emitted into the effluent,and the resulting environmental pollution problem has severely threatened human health.There are many removal methods for heavy metals and dyes in water.The adsorption method,considered one of the most promising methods,has the advantages of rapidity,simplicity,low cost,and good selectivity.The development of economic,efficient,environmentally friendly,and reusable adsorbent materials is of great significance to the development of adsorption technology.The study of sludge biochar has been a hot topic in recent years.Sludge biochar not only has the advantages of low cost,easy availability,and environmental protection but also can effectively reduce the potential ecological risk of sludge by using sludge as raw material to make biochar,becoming a promising way for sludge treatment,disposal,and resource utilization in sewage treatment plants.Based on the water pollution and serious environmental risk of sludge,biochar(SBC)was prepared from the waste activated sludge and modified by ZnO to make sludge biochar/ZnO composite(SBC/ZnO).The adsorption properties and adsorption mechanism of SBC/ZnO for aqueous methylene blue(MB)and Cr(Ⅲ)were investigated.The main study results are described as follows:(1)SBC and SBC/ZnO were prepared by pyrolysis of waste activated sludge at 600℃ and precipitation method,respectively.SBC and SBC/ZnO were characterized through the elemental analyzer,BET,SEM-EDS,FT-IR and nano-particle surface potential analyzer.The results indicated that after loading ZnO,the aromaticity and stability of the biochar decreased while the polarity increased.Compared with SBC,BET specific surface area of SBC/ZnO was as significantly improved.The Zeta potential of SBC/ZnO is negative when pH is in the range of 3～12,and its surface has SiO2 and silicate groups formed by inorganic elements and oxygen functional groups such as-OH and C=O.(2)The adsorption properties and mechanism of SBC/ZnO for MB in the aqueous phase were investigated.The results revealed that compared with SBC,the adsorption properties of SBC/ZnO for MB were significantly improved.The appropriate addition amount of SBC/ZnO was 5 g/L,and the adsorption equilibrium time was 30 min.Specifically,in the initial concentration range of 10-300 mg/L,the greater the initial MB concentration,the greater the adsorption capacity,and the maximum adsorption capacity of SBC/ZnO for MB was 32.67 mg/g.The increase of the pH of the solution and NaCl concentration were conducive to the adsorption.The adsorption kinetics,isotherm and thermodynamic results showed that the adsorption of SBC/ZnO for MB was mainly monolayer adsorption,and the adsorption process was spontaneous and endothermic.The increase of temperature was beneficial to the adsorption,and the chemical adsorption was the main process.The effect of pH value on the adsorption showed that electrostatic attraction played an important role in the adsorption process.FT-IR and XPS analysis results indicated that hydrogen bonding and π-π interaction were involved in the adsorption mechanism.(3)The adsorption properties and adsorption mechanism of SBC/ZnO for Cr(Ⅲ)in the aqueous phase were explored.The the appropriate addition amount of SBC/ZnO was 4 g/L,and the adsorption equilibrium time was 4 h.The adsorption can be promoted by increasing the temperature.The optimal pH of the solution was 5.However,NaCl is not conducive to this adsorption process.Within the range of the initial concentration of Cr(Ⅲ)from 10 to 300 mg/L,the adsorption capacity of SBC/ZnO for Cr(Ⅲ)increased with the increase in Cr(Ⅲ)initial concentration,and the maximum adsorption capacity was 42.61 mg/g,suggesting that SBC/ZnO had good adsorption properties for Cr(Ⅲ).Besides,the adsorption process of SBC/ZnO for Cr(Ⅲ)can be well described by pseudo-second-order kinetics and the Langmuir isotherm model.The adsorption mechanism includes electrostatic interaction,ion exchange,and surface complexation.In summary,SBC/ZnO,which is a potential green adsorbent,has good adsorption properties for MB and Cr(Ⅲ).After the introduction of ZnO,the adsorption effect of biochar on Cr(Ⅲ)was improved more significantly.This study provides a theoretical basis for the clean utilization of municipal sludge.