| Sulfate ion is a common anion in water,and excessive presence can cause significant harm to ecosystems and organisms.Especially acid mine wastewater containing high concentration of sulfate ions,directly discharged into the water body will cause acidification of the water body,environmental pollution,and endangering human health.The adsorption method is an important technical method for removing sulfate.The key to the adsorption method is to develop fast,effective,low-cost,simple-to-operate adsorbents.In recent years,biochar materials have received widespread attention,and appropriate anion modification methods can be used to improve their anion adsorption performance.In this study,pomelo peel was used as a raw material,and the pomelo peel biochar was modified by dipping-precipitation method and hydrothermal-precipitation method,respectively.Two modified adsorbents ZrPBC-1 and ZrPBC-2 were prepared,and their effects on sulfate were studied,and morphological structure and adsorption mechanism were analyzed.Modified pomelo peel biochar ZrPBC-1 was prepared by impregnation-precipitation method.The effects of pH,initial concentration,reaction time,and coexisting ions on sulfate adsorption were investigated.The characterization methods ofthe nitrogen adsorption-desorption curve,FE-SEM/EDS and XPS were used to analyzed the surface structure of ZrPBC-1.ZrPBC-1 was a mesoporous material with an average pore size of 4.86nm;ZrPBC-1 was loaded with Zr-OH functional groups on the surface and participates in the adsorption process of sulfate.Within the initial pH range of 2.0~12.0,ZrPBC-1 had the best adsorption capacity at pH value of 2.0.The adsorption isotherm study showed that the Langmuir adsorption isotherm model was suitable for describing the adsorption process,indicating that ZrPBC-1 adsorbedsulfate as a single-layer adsorption,and the calculated maximum adsorption capacity was 35.21 mg/g.Simulation studies showed that the adsorption process was more in line with pseudo-second-order kinetic equations.Among the coexisting ions,phosphate significantly inhibited the adsorption of sulfate,followed by fluoride,and nitrate had the least effect.In order to obtain zirconium-loaded biochar with more uniform load and good regeneration performance,based on the impregnation-precipitation method,a dispersant PEI was added and the heating conditions of the water bath were increased to obtain an improved preparation method—hydrothermal-precipitation method.The effects of PEI dosage,titration endpoint pH value,aging temperature,and PBC addition amount on the modified biochar were investigated.The effect of pH value was investigated,and the regeneration performance and stability of ZrPBC-2 were explored.The experiments showed that the ZrPBC-2 has the best adsorption capacity when 5% PEI is added,the titration end pH was 9.0,the aging at room temperature and the amount of PBC added was 1g.Testing the amount of sulfate adsorption in the pH range of 2.0~10.0,it was found that the pH value was between 2.0~3.0,and the adsorption capacity was the best.After 5 cyclesof adsorption-desorption,ZrPBC-2 was found to have good regeneration performance.In addition,the supported zirconium oxide was relatively stable,and the leaching concentration of Zr(IV)remains basically unchanged.The surface structure of ZrPBC-2 was analyzed by analyzing the changes in the concentration of hydroxide and chloride in water,as well as FE-SEM/EDS,XRD,FT-IR,and XPS.Investigated the adsorption mechanism of ZrPBC-2 on sulfate from a quantitative and qualitative perspective.The results showed that the precipitated particles on the surface of ZrPBC-2 were small and uniformly distributed,which was presumed to be an amorphous structure of hydrated zirconia.In the isothermal adsorption experiment,the change in the concentration of hydroxide and the adsorption amount of sulfateshowed a positive correlation through a linear fit,with a proportionality factor of 2.38,which was greater than the charge ratio of hydroxide and sulfate.It was possible that chloride participated in the reaction.ZrPBC-2 surface hydroxyl group(Zr-OH)decreaseed after adsorption and hydroxideincreaseed in water,so the reaction mechanism of ZrPBC-2 adsorption of sulfate can be summarized as a ligand exchange reaction,mainly hydroxide andsulfate ligand exchange,chloride may also participate in the ligand exchange process. |
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