Biochar Loaded Nano Zero-valent Iron For Selenium And Chromium Removal

With the development of society,the situation of heavy mental pollution of the water becomes more and more serious.Research and development of new materials and new technologies heavy metal pollution treatment are of great significance for the harmless treatment of heavy metal wastewater.In this paper the cornstalk-secondary product of crop impregnated with Fe³⁺was used as the row material,then the nano zero-valent iron supported on biochar was synthesized by high temperature pyrolysis,and the removal performance of chromium and selenium from wastewater was also evaluated,used to treat containing.The nano zero-valent iron supported on biochar was charactered by XRD,TEM,and BET.The XRD analysis showed the typical zero-valent iron characteristic diffraction peaks are found at 2?of 44.8°,65.2°,and 82.5°respectively.From the TEM image,it can be seen that the nano zero valent iron are dispersed homogeneously in biochar,and the nano zero-valent iron is about 50 nm in size.The BET analysis showed the specific surface areas of the two materials of BC-nZVI1.5-800 and BC-nZVI3-800 are 497.685 m²·g^-1,438.906 m²·g^-1,and the most probable pore sizes are all about 2 nm.The effect of pH value,air,Fe²⁺and coexisting anions on removal capacity of chromium???,selenium???and selenium???from water by nano zero-valent iron supported on biochar.The kinetics,and isotherm of removal chromium???,selenium???and selenium???from water by nano zero-valent iron supported on biochar were also studied.Experimental results show,the removal capacity reaches the maximum at the pH of 4.0,With pH rises,the removal capacity decreases,the reason is that under high pH conditions the surface passivation of nano-zero-valent iron is facilitated.The kinetic data are better fitted to the pseudo second-order kinetic model,with the kinetic constants of Cr???,Se???and Se???are 0.62 g·?mg·min?^-1,0.0016 g·?mg·min?^-1,and 0.0002 g·?mg·min?^-1 respectively.The thermodynamic data were better fitted into the Langmuir model and the balance adsorption capacities of Cr???,Se???and Se???on nano zero iron supported on biochar via Langmuir isotherm model were 45.5 mg·g^-1,35.1 mg·g^-1 and 108.4 mg·g^-1 at 35?.The effect of the coexisting anions on the removal capacity increases in the order of HA<Cl^-<NO₃^-<SO₄^2-.HA,Cl^-and SO₄^2-mainly act by competing the active sites of the surface of nano-zero-valent iron,but NO₃^-acts as a competitive redox anion,which can be reduced by nano-zero-valent iron.The role of Fe²⁺in the removal process was verified by experiments.Fe²⁺can increase the conductivity of the zero-valent iron surface oxide layer and increase the electron transfer rate in the nano-zero-valent iron corrosion products.The solid after adsorption was characterized by XPS.The biochar-loaded nano zero valent iron can reduce Cr???,Se???to Se???,Cr???respectively.For Se???removal,Se???is first adsorbed on the surface of nano zero-valent iron supported on biochar,then some of the Se???is reduced to Se?0?.