| Chromium contaminated groundwater is an increasingly serious problem in recent years,raising concern around the world.Chromium pollution mainly comes from productivity of chromium,industrial water and gas of metallurgy,electroplating and leather.The World Health Organization(WTO)stipulates that the contents of Cr(Ⅵ)in drinking water must be less than 0.05 mg/L.Therefore,the methods of removal of Cr(Ⅵ)in the groundwater is one of the focus of current research problems.The removal of Cr(Ⅵ)in water is the most widely used or reduced precipitation method,but it is difficult to use this method to reduce the water content of some pollutants under reducing conditions.Schwertmannite is widely used in the removal of Cr(Ⅵ)in water due to the rapid reaction,low consumption and no secondary pollution in the treatment of heavy metal pollution wastewater.The synthesis of Schwertmannite has chemical and biological methods.In the present study,biosynthesis is used to treat chromium-containing wastewater with a treatment capacity of 35 ~ 55 mg / g.However,the biosynthesis process of Schwertmannite is complicated and relatively simple Chemical synthesis method is difficult to large-scale practical application.In this study,we improved chemical synthesis of schwertmannite and selected a better one for Cr(Ⅵ)adsorption,and applied to experimental study of Cr(Ⅵ)contaminated groundwater,The kinetics,thermodynamics and isotherms,meanwhile the effects of environmental factors on the schwertmannite adsorption processes were investigated.Influence,and studying the effect of groundwater environment on the repalr process,with the help of SEM-EDS,XRD,FTIR characterization methods to explore the removal mechanism of Cr(Ⅵ)in groundwater.The following conclusions can be obtained:(1)The improved Schwertmannite had a better specific surface area(12.5368 m2/g)compared to the original Schwertmannit(4.3073 m2/g),the average adsorption pore volume were 0.022 cm3/gand 0.0075 cm3/g,the average pore size of 7.1 nm and 6.93 nm,respectively.bothof them belong to the mesoporous materials,The improved Schwertmannite had more OH-and SO42-,which will be conducive to the adsorption of Cr(Ⅵ).(2)The experimental results showed that both of the minerals have strong adsorption of Cr(Ⅵ)from aqueous solution.At the pre-set initial concentrations of Cr(Ⅵ),the Schwertmannite adsorption of Cr(Ⅵ)achieved equilibrium within 24 h,and the Lagergren’s second-order model fitted the adsorption process better compared to Lagergren’s first-order model and intraparticle diffusion model.Langmiur equation fitted the adsorption isotherms better than Freundlich equation.The Cr(Ⅵ)adsorption on schwertmannite malnly involves ion exchange reaction between Cr(Ⅵ)and anions such as OH-and SO42-and surface complexation reactions.The improved Schwertmannite had a better adsorption(12.5368 m2/g)compared to the original Schwertmannit(4.3073 m2/g),the△H0 were 15.461 kJ/moland 6.368 kJ/mol,respectively,therefore the adsorption of Cr(Ⅵ)is a spontaneous and endothermic process.The △H0may caused by hydrogen bond,dipoleforce and hydrogen bond,van der WaAls forces,hydrophobic bonding force.(3)The improved Schwertmannite adsorb of Cr(Ⅵ),put in strong alkaline solution(pH = 12),Cr(Ⅵ)will be fully released after 4 h,Schwertmannite mineralization into hematite,hematite at pH = 4.5 on the adsorption of Cr(Ⅵ)better than Schwertmannite,can be resource utilization.(4)The removal of Cr(Ⅵ)from aqueous solution increased with increasing schwertmannite dosage at pH = 4.5.Acidic pH in the range of 4.5-6 favored Cr(Ⅵ)removal with schwertmannite compared to under basic conditions.Under the conditions of pH=6,maximum removal of Cr(Ⅵ).(5)The organic matter in the groundwater had a important influence on the adsorption of Cr(Ⅵ).Weak acid environment(pH = 6),organic matter had no effect on the adsorption of Cr(Ⅵ),weak alkAline environment(pH = 8),the organic matter had anegative effect on the adsorption of Cr(Ⅵ).(6)Different inorganic ionshad diverse effect on the adsorption of Cr(Ⅵ)in groundwater.Batch tests showed that the presence of HCO3-inhibited the adsorption of Cr(Ⅵ)while Cl-had no significant impact.Cationsand SO42-had a pHdependent impact on Cr(Ⅵ)removal,at pH=8,the cations would significantly inhibit the Cr(Ⅵ)sorption,while the impact could be neglected at weak acidic conditions(pH=6). |
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