Synthesis Of Iron-loaded Biochar By Co-pyrolysis Method And Its Adsorption Performance And Mechanism Of Antimony From Aqueous Solution

A large amount of antimony-containing sewage is produced by the operation of mining,beneficiation,and smelting,which causes environmental pollution.The iron-based materials have been widely applied for antimony(Sb)removal.However,its nanoparticles are prone to agglomeration to form large-scale particles,leading to a significant decrease in excellent abilities even lost.Biochar could promote carbon sequestration and mitigate greenhouse gas emissions and have a porous structure,which makes it ideal for loading and dispersing iron particles.Herein,to remove antimonite(Sb(Ⅲ))and antimonate(Sb(Ⅴ))from the aqueous solution,the iron-loaded biochar was fabricated by the co-pyrolysis method using cottonwood sawdust as the biomass.The effect of the species of metal salt and co-pyrolysis temperature on their physicochemical properties and adsorption performance was systematically investigated.Firstly,the physicochemical characteristics of FeCh-based iron-loaded biochar synthesized under different temperature conditions were characterized,and it was found that the co-pyrolysis temperature significantly affected their pore structure and iron-loaded amount.The iron-loaded biochar prepared at 800℃ had a more developed porous structure and higher Fe-loaded amount,with a specific surface area(316.65 m2·g-1)and Fe loading(4.49 mmol·g-1)were 4.96 times and nearly 2 times higher than those at 500℃,respectively.Also,Fe0 and Fe3O4 was formed and loaded under 500℃ and 800℃,respectively.The adsorption experiments revealed that the co-pyrolysis temperature affected the adsorption capacities of FeCl3-based iron-loaded biochar for Sb with different valence states,where the composites prepared at 800℃ was easy to adsorb Sb(Ⅲ),while the composites prepared at 500℃ was easier to adsorb Sb(V).The effect of co-pyrolysis temperature on the physicochemical properties and the adsorption performance of Sb(Ⅲ/Ⅴ)on K2FeO4-based iron-loaded biochar was then investigated.It was found that K2FeO4-based iron-loaded biochar had a larger specific surface area of 515.49 m2·g-1 and 5.48 times larger at 800℃ than that of 500℃.The iron phases on the surface of K2FeO4-based biochar at different temperature conditions were the same as those of FeCl3-based iron-loaded biochar.The comparison revealed that K2FeO4 possessed stronger performance to form the porous structure than FeCl3 and could increase the Fe-loaded amount to 6.44 mmol·g-1,which leaded to a significant increase in the adsorption of Sb(Ⅲ)and Sb(Ⅴ)to 144.48 and 45.29 mg·g-1.The iron-loaded biochar could oxidize the highly toxic Sb(Ⅲ)to the less toxic Sb(V),and the oxidation mechanism was determined by the iron-loaded phase,in which Fe3O4 could act as the electron acceptor to directly oxide,while Fe0 could passivate and catalytically oxide.To enhance the adsorption capacitiy of FeCl3-based iron-loaded biochar for Sb(Ⅲ/Ⅴ),MnCl2-FeCl3-based iron-loaded biochar was fabricated at different temperatures.It was found that the more developed porous structure was produced under the addition of MnCl2,with a 7-fold increase in specific surface area at 500℃and a 3.75-fold increase in average pore size at 800℃ compared with FeCl3-based iron-loaded biochar.MnCl2 co-pyrolysis at 800℃ prevented Fe3O4 from being reduced and shaped its grain into the morphology of nanosheets.Adsorption experiments showed that MnCl2 greatly improved the adsorption capacity of Sb(Ⅲ/Ⅴ)by adjusting the pore structure and iron phase,and the adsorption capacity could reach 157.83/57.32 mg·g-1,which was larger than that of K2FeO4-based ironloaded biochar prepared at 800℃.The common anions and cations and dissolved organic matter in antimony-containing sewage had little effect on the adsorption performance of MnCl2-FeCl3-based iron-loaded biochar.The results of the present thesis could provide theoretical and technical guidance for the efficient treatment of antimony-containing sewage.