Preparation And Performance Of Iron Modified Biochar And Layered Double Hydroxide As Prb Filler For Efficient Adsorption Of Vanadium(V)

With the increasing exploitation and utilization of vanadium resources,vanadium contaminated areas continue to expand,and the pollution accidents occur frequently.Therefore the remediation of vanadium contaminated groundwater has become an important demand for environment control.In this study,through an extensive screening of common adsorbents,a cheap adsorption material with large capacity for vanadium removal—modified biochar was prepared by ZnCl₂ modification and nano zero-valent iron?nZVI?loading,and a calcined Mg-Al layered double hydroxide?LDH?with excellent vanadium adsorption capacity was developed.The prepared materials were characterized by elemental analysis,thermogravimetry,scanning electron microscopy,and X-ray diffraction,and their high-efficiency adsorption performance were confirmed by permeable reactive barrier?PRB?columns experiments.Among more than 40 kinds of low-cost adsorption materials,such as commercial materials,biochars derived from different raw materials and modified biochars and ect,ZnCl₂ modified biochar?Zn-BC?was found to have a high adsorption capacity.Compared with the unmodified biochar,Zn-BC had more developed microporous and mesoporous structure,the specific surface area was increased by 4.48 times,and the saturated adsorption capacity of vanadium was 28.46 mg/g,which was 2.85 times higher than the commercial activated carbon.The main adsorption mechanisms were the surface precipitation between Zn²⁺and vanadate,and electrostatic attraction.Zn-BC was further loaded with iron-based materials,such as nZVI,?-Fe₂O₃ and Fe₃O₄?referred as Zn-BC@nZVI,Zn-BC@?-Fe₂O₃ and Zn-BC@Fe₃O₄,respectively?,and the adsorption capacities of vanadium were increased to 97.84 mg/g,74.68 mg/g and 33.53mg/g,respectively.The main adsorption mechanisms of vanadium on Zn-BC@nZVI were chemical reduction and surface precipitation.Among them,the adsorption capacity of Zn-BC@nZVI for vanadium was nearly 12 times higher than that of commercial activated carbon,and the main adsorption mechanisms were chemical reduction and surface precipitation.Zn-BC@nZVI reached high removal efficiency ?100%?for low concentration vanadium?5-50 mg/L?,therefore,it can be used as a PRB filler to treat the daily vanadium pollution in groundwater.A LDH material with high adsorption capacity has been developed to deal with vanadium pollution accidents.By comparing the adsorption performance of Ni/Al LDH,Fe/Ca LDH and Mg/Al LDH and their calcined products?Ni/Al LDO,Fe/Ca LDO and Mg/Al LDO?,it was found that Mg/Al LDO had the best vanadium removal efficiency?with the max adsorption capacity of 390 mg/g?.The main adsorption mechanisms were structural memory effect and surface adsorption.The preparation method of“organic solvent added?Synthesis of LDH by solvothermal method?preparation of Mg/Al LDH nanosheet?calcined Mg/Al LDH nanosheet”was developed,which greatly improved the adsorption performance of Mg/Al LDO.The maximum vanadium adsorption capacity of calcined Mg/Al LDH nanosheet by the addition of n-dodecanol?Mg/Al-12 LDO?was 928 mg/g.The PRB simulation column experiments with Zn-BC@nZVI and Mg/Al-12 LDO as fillers were carried out to verify their adsorption efficiencies.The results showed that Zn-BC@nZVI filled columns reached the penetration point of vanadium after 128 pore volumes?PV?running,while activated carbon could only ran 26 PV reaching the penetration point.Therefore,Zn-BC@nZVI can be used as a daily filler.Using Mg/Al-12 LDO to replace 20%?volume ratio?of Zn-BC@nZVI to fill the column,the penetration rate was 55%after 834 PV running,which could effectively prevent vanadium pollution under the accident condition.