Performance And Mechanism Of Fluoride Adsorption From Water By Lanthanum-modified Pomelo Peel Biochar

As one of the global environmental problems,fluoride pollution in water has attracted considerable attention in recent years.The long-term and excessive intake of fluoride can result in dental and skeletal fluorosis.Hence,the maximum fluoride level of 1.5 mg/L has been established by the World Health Organization?WHO?for protecting human health.Several techniques have been employed to remove excessive fluoride from aqueous solution,including precipitation,membrane,ion exchange and adsorption.Among these methods,Adsorption is considered to be a promising method for fluoride removal owing to its low cost,effectiveness,simplicity of operation.In this study,an innovative lanthanum-modified pomelo peel biochar?PPBC-La?was synthesized with high efficiency,low cost and good environmental adaptability.The effects of various factors?adsorbent dosage,initial fluoride concentration,initial solution pH,co-existing anions and temperature?were investigated to determine adsorbent performance.The PPBC-La before and after adsorption were characterized by scanning electronic microscopy?SEM?,Brunauer-Emmett-Teller?BET?method,Zeta potential,Fourier transform infrared?FTIR?spectroscopy and X-ray photoelectron spectroscopy?XPS?to determine adsorption mechanism.Experimental results showed that lanthanum was successfully loaded on PPBC,which significantly increased the adsorption capacity of PPBC.The PPBC-La worked well at pH 2.4-9.6.Moreover,under acidic condition,electrostatic attraction could strengthen fluoride adsorption.The influence of other coexisting ions on fluoride adsorption was negligible except for HCO₃^-and PO₄^3-.On the contrary,humic acid?HA?could promote the fluoride adsorption.Fluoride adsorption is a spontaneous and endothermic process.Equilibrium was reached at 24 h,and the adsorption process was described well by the pseudo-second-order kinetic model.The adsorption isotherm data were fitted well by the Redlich-Peterson and Langmuir models.And the maximum adsorption capacity from Langmuir model was 21.84mg/g.At pH 5.2 and dosages of 1.0 g/L,fluoride in the actual groundwater could be reduced from 9.8 mg/L to 0.6 mg/L by the PPBC-La.The regeneration results confirmed that 70%of the initial adsorption capacity was still preserved after five regeneration cycles.Comparing with other adsorbents,the PPBC-La had more advantages.According to FTIR,XPS analysis and the anion exchange experiment,anions?NO₃^-and OH^-?exchange was the main adsorption mechanism.Moreover,the NO₃^-contributed most to the fluoride adsorption.Overall,the PPBC-La as a low-cost,simple and high efficient adsorbent for fluoride removal shows a promising application prospect.