Fabrication Of Nano Iron Modified Biochar For Removal Of Hexavalent Chromium From Water

Hexavalent chromium is highly toxic and can cause cancer,skin allergies and genetic defects,which has been classified by the World Health Organization as a Class I carcinogen.Sorption is an efficient treatment for Cr???with its cost-effectiveness and simplicity.Biochar can be a cost-efficient adsorbent to treat Cr???with large surface area and abundant functional groups.By applying biochar to Cr???treatment,a win-win situation can be reached of waste biomass recycle and wastewater treatment.In this study,a unique biochar supported nano iron composite was synthesized by ferric salt soaking and slow pyrolysis.By changing the pyrolysis temperature,pyrolysis time and impregnation concentration,different types of biochar were obtained.Through characterizations,the optimum preparation conditions were 1 M FeCl₃ impregnation and450?anaerobic pyrolysis for 5 h.The XRD spectrum confirmed the iron supported on the biochar was present as magnetite.Raman and FT-IR determined that the biochar has pure carbon,less functional groups,and more sp² structure.At pH<2.5,the biochar has a positive Zeta potential and a large Cr???removal potentialThe influence of conditions parameters on the adsorption of Cr???by the biochar was investigated.When 25 mg of biochar was added to 50 m L wastewater with 50 mg/L Cr???,the adsorption capacity of biochar for Cr???decreased rapidly with pH increasing.At pH1.0,the removal rate of Cr???was 80.07%,and at pH 7.0,the removal rate was only 8.85%;The kinetic process of adsorption is very fast,25 mg of biochar was added to 250 mL of Cr???wastewater,and the pH is adjusted to 2.The reaction equilibrium state is almost reached in 5 minutes.The reaction is an endothermic reaction.The maximum adsorption capacity was 71.60 mg/g at 30?,94.85 mg/g at 40?and 110.09 mg/g at 50?.Adsorption of Cr???and total Cr both fit Sips model well.Competitive ions have limited influence on adsorption,64 times molar ratio competitive ions lead to a 20%reduction in adsorption capacity.By NaOH regenerating,the adsorption capacity maintained 70%of the maximum capacity,which demonstrates the biochar could be a recycled adsorbent.Through characterization and the density functional theory calculation,the reaction mechanism was discussed.Thecrystal face 311 of Fe₃O₄ and the sp² structure of biochar played an important role in the adsorption process.It was revealed that the d orbit of O in crystal face 311 and p orbit of O in Cr???have interaction,which leads to a more stable system and an active structure of Cr???.The active structure of Cr???is an essential preparation for Cr???reduction.