Preparation Of Nano-zero-valent Iron Sludge-based Biochar And Its Adsorption Behavior For Sb(?) In Water

China is one of the major producers of antimony.The mining and smelting process of the antimony mine have caused large amount of antimony containing wastewater to be discharged into the environment,which has seriously threatened the ecological environment and human health.In recent years,the topic of novel modified low-cost adsorbents for the treatment of antimony in wastewater,has captured wide attention.The development of supported modified adsorbents has become a hot topic in the research area of antimony decontamination.In this study,nano-zero-valent iron sludge-based biochar?NZVI-SBC?was prepared by liquid-phase reduction method.The adsorption performance of NZVI-SBC for Sb???was optimized by changing various preparation conditions,and it's physical/chemical characterization of NZVI-SBC were carried out through various spectroscopic techniquessuch such as SEM,TEM,FTIR,BET,and XPS techniques.Then,the adsorption performance of NZVI-SBC for Sb???was studied by static adsorption experiments.In addition,the effect of O₂ and nano-zero-valent iron?NZVI?on the adsorption and oxidation of Sb???was also investigated.Finally,the adsorption behavior mechanism of Sb???on NZVI-SBC was investigated through kinetics,isotherms,and thermodynamics analysis,and the potential adsorption meachanisms was further analyzed by the FTIR and XPS techniques.The following were the conclusions in the experiment:?1?The prepared NZVI-SBC has the best adsorption performance for Sb???under the preparing conditions of 1:1 as carbon-to-iron ratio,FeSO4·7H2O as loading iron source,and300°C as calcination temperature.For sludge biochar after loading NZVI,Through SEM,FTIR analysis,it was found that it's surface has become a more loose and porous structure.At the same time,the amount of oxygen-containing functional groups has increased and obviously new oxygen-containing functional groups have appeared.The XPS scans demonstrated the presence of zero-valent iron particles.The TEM image showed that the particle diameter was substantially 30 nm,that is,the loaded particles were NZVI.The BET date showed that the specific surface area and pore volume of NZVI-SBC has significantly increased.Finally,the experimental data showed that the removal capacity of NZVI-SBC for Sb???was about 25 times than that of SBC.?2?NZVI-SBC has a strong adsorption capacity for Sb???,and the adsorption process was an endothermic process.The results showed that the adsorption of Sb???on NZVI-SBC has reached to the equilibrium within 3h,under the conditions of 298K,150r·min^-1,pH=4.8±0.2;when the dosage of adsorbent was 0.2g·L^-1,the removal rate of Sb???was up to 96.92%;the adsorption process was in accordance with the Pseudo-second-order kinetic model,which showed that the adsorption behavior was mainly chemical adsorption,and the adsorption rate was mainly controlled by liquid film diffusion;the isothermal adsorption curve both conforms to the Freundlich and Langmuir models,but the Freundlich equation can well describe the adsorption process,which indicated that the adsorption behavior was a heterogeneous adsorption;under the conditionds of 318K,NZVI-SBC has exhibited the maximum adsorption capacity of 212.76mg·g^-1 for Sb???in aqueous solution.?3?The presence of O₂ has a certain influence on the adsorption and oxidation of Sb???,and the extent of this effect was increased with the initial concentration of Sb???:anoxic environment can better promote the adsorption of Sb???and reduced the content of Sb???in aqueous solution;the important things were that,under anoxic conditions,NZVI-SBC can promote the oxidation of Sb???to convert into a less toxic Sb?V?,indicating that this material may have great potential for the remediation of Sb contamination in groundwater.Likewise,loading NZVI has also a certain influence on the adsorption and oxidation of Sb???:the adsorption and oxidation content of Sb???were increased with the increase of Fe content in aqueous solution;it was further proved that loading NZVI can promote the adsorption and oxidation of Sb???,and this phenomenon was more evident in the case of higher initial concentration of Sb???.?4?The results of FTIR and XPS analysis showed that Sb???has complexed with FeOOH on the surface of NZVI-SBC during the adsorption process,and an ion exchange reaction between Sb???and corrsion NZVI were also founded.During NZVI has been corroded,Sb???has simultaneously oxidized to Sb?V?.XPS analysis showed that some of Sb adsorbed on NZVI-SBC existed as an oxide of Sb???,and the other was bound to the surface as an oxide of Sb?V?.