Removal Of Hexavalent Chromium From Groundwater By Nano-Zerovalent Iron/Mesoporous Silica Composite Materials

The progress of people's lives and social economic development caused a series of problems about heavy metal pollution in water.Due to the considerable use of chromium in industry,in some areas occur serious chromium pollution in groundwater,which poses a great threat to human living environment and health.Nano-Zerovalent Iron?nZ??is a common environmental remediation material,which has a small size,high specific surface area and strong reduction capacity while easy to agglomerate and oxidize,thence limits the ability of nZ? to treat pollutants.In this study,mesoporous silica materials with high specific surface area and various configurations were used as nZ? carrier,and finally optimized mesoporous silica microspheres?MSM-2?and ordered mesoporous silica?SBA-15?as nZ? carrier material.Carrier materials were characterized by Scanning Electron Microscope?SEM?,Transmission Electron Microscope?TEM?,X-ray Powder Diffraction?XRD?,Brunauer-Emmett-Teller?BET?,X-ray Photoelectron Spectroscopy?XPS?,Zeta Potential,etc.The results show that nZ? and MSM-2 are connected by channels,and nZ? can immersion into the channels or attach in outer surface of SBA-15.The specific surface areas of the two composite materials are140.4 and 133.6 m²/g respectively,which greatly improves the dispersibility of nZ?.Compared with nZ?,the stability of the composite materials have also been improved.This study investigated the effects of the dosage of nZ?/mesoporous silica,reaction time,initial Cr???concentration,solution pH and coexisting ions on the removal of Cr???by composites.The results show that the removal rate of Cr???is positively correlated with the dosage of composite material and the reaction time,negatively correlated with the initial Cr???concentration and the pH of the solution.Besides,Ca²⁺,Cl^-,SO₄^2-,CO₃^2-,NO₃^-,etc coexisting ions have little effect on the chromium removal effect of the material,indicating that the composite material has good stability.When the dosage of nZ?/SBA-15 is 1 g/L,the initial concentration of Cr???is 40 mg/L,the solution pH is 4,the reaction temperature is 25?,and the shaking reaction time is 30 min,the Cr???removal rate was 1.20 mg/?g·min?.nZ?/mesoporous silica removes chromium in solution through reduction and adsorption.nZ? acts as an electron donor to reduce Cr???to Cr?III?,which is oxidized to iron?hydrogen?oxide.The product Cr?III?is adsorbed and fixed on the surface of the material,which greatly reduces the total chromium content in the solution.In addition,the chromium removal effect of the supported nZ??s-nZ??prepared with iron slag was investigated.The results show that it has a strong ability to remove Cr???in groundwater.When the dosage of s-nZ?/SBA-15 is 0.4 g/L,the initial concentration of Cr???is 10 mg/L,the reaction temperature is 25?,and the shaking reaction time is 20 min,the Cr???removal rate was 1.25 mg/?g·min?.The above research results show that the mesoporous silica carrier can improve the dispersibility and stability of nZ?,thus enhance the ability of nZ? removal pollutants.As new kind composite materials,nZ?/mesoporous silica have good application prospects to treat chromium contaminated groundwater.