Fluoride Removal Efficiencies And Mechanism Of Schwertmannite In Acidic Solution

Fluoride has an adverse effect on both the environment and industrial production.In particular,wastewater from smelting systems containing high concentrations of fluoride is a major cause of fluoride pollution.Based on the characteristics of such wastewaters,high concentration of Fe²⁺and SO₄^2-and low p H,a targeted and integrated technology for removal fluoride using schwertmannite is proposed.In this work,the schwertmannite was prepared from the oxidation of Fe?II?by KMn O₄?Ksw?,H₂O₂?HOsw?,Na₂S₂O₈?SOsw?,Mn O₂?Msw?and Na Cl O?Clsw?,and was characterized by X-ray diffraction?XRD?,Scanning electron microscopy?SEM?,Fourier transform infrared spectroscopy?FTIR?and Laser particle sizer.The results indicated that the schwertmannite removed fluorine in solution by ion exchange.The removal efficiencies of fluoride by Ksw,HOsw,SOsw,Msw and Clsw were 92%,93%,92%,82%and 78%within 30 minutes,respectively.The p H value had a great influence on the removal efficiency,but the temperature had a little influence.In the actual wastewater,schwertmannite was prepared from Fe²⁺in wastewaters directly through pre-oxidization by oxidants,and effectively removed fluoride.Under most experimental conditions,the removal efficiency of fluoride by Ksw was always 10%higher than that by Msw.The mechanism of fluorine removal was verified by X-ray photoelectron spectroscopy?XPS?and theoretical calculations.In the course of ion exchange,appropriate 0.70 mol of OH^-and 0.30 mol of SO₄^2-were released per mole of F^-sorbed.The results showed that the higher removal efficiency of fluoride by Ksw was attributed to the higher concentration of OH^-in Ksw and the primary role of OH^-in the ion exchange.At different p H,the stability and the regeneration ability of schwertmannite was investigated.It was found that schwertmannite had the good stability at p Hrange from 4 to 9.The recycling performance was verified using H₂SO₄?p H=1.5?and Na OH?p H=12.5?.Schwertmannite was recycled through 5 adsorpted-desorpted,the adsorption capacity still kept more than 80%of the original.In consequence,Schwertmannite showed good practicability for actual industrial wastewater.