Adsorption And Removal Of Complexed Cr(Ⅲ) In Water By Magnesium Hydroxide And Its Compsites

In recent years,heavy metal pollution had frequently affected the ecological environment and people’s health.Therefore,dealing with heavy metal pollution in water has always been a major problem facing worldwide.Heavy metal（Cr（Ⅲ））is one of the important potential pollutants,mainly come from the main and reclamation stages in the tanning process.There is a large number of organic and inorganic ligands with high coordination capability involved in the tanning process,which forms a stable complex with the Cr（Ⅲ）.Due to these stable complexes Cr（Ⅲ）treatment from the water is a bit difficult process.The main aim of this study to overcome the problem of wastewater with Cr（Ⅲ）complex.To deal with this problem a novel environment-friendly nanomaterial magnesium hydroxide is developed with larger specific surface area,more active sites,and high adsorption capacity.It has been verified that this adsorbent has the ability to remove the heavy metals from the wastewater and neutralized acidic wastewater.However,there is little research on the removal of complexed trivalent chromium Cr（Ⅲ）by nanomaterial magnesium hydroxide.In this work,nanomaterial magnesium hydroxide,composite magnetic magnesium hydroxide（Fe₃O₄@Mg（OH）₂）and multiphase Magnetic composite（Fe₃O₄@C@Mg（OH）₂）adsorbents were synthesized in the laboratory and than complexed trivalent chromium（Cr（Ⅲ）-EDTA）is adsorbed under the alkaline environment.The effect of different concentration,pH,coexisting cations on the adsorption was investigated.The adsorbed materials were desorbed and recycled.The adsorption mechanism of adsorption was preliminarily investigated by Fourier infrared spectroscopy（FT-IR）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,Scanning electron microscopy（SEM）,thermogravimetry（TGA）,Specific surface area（BET）and other characterization results.Mainly get the following conclusions:（1）Removal of complexed trivalent chromium Cr（Ⅲ）-EDTA by nanomaterial magnesium hydroxide:In this experiment,nanomaterial magnesium hydroxide was successfully synthesized by solid phase grinding method,and the nanometer magnesium hydroxide was characterized by XRD,SEM,BET,and XPS.The results showed that the nanometer magnesium hydroxide had a diameter of about 80 nm and a specific surface area of 103.23 m²/g.Under alkaline conditions,nanometer magnesium hydroxide had a good adsorption effect on the complexed chromium which is difficult to precipitate in water.The maximum adsorption capacity is 178.65 mg/g.The adsorption isotherm of Cr（Ⅲ）-EDTA could be fitted by Freundlich isotherm equation.It is kinetic data could be fitted by pseudo-second-order equation.High concentration of cations Na⁺,K⁺,Ca²⁺had little effect on the removal of the complexed trivalent chromium Cr（Ⅲ）-EDTA in magnesium hydroxide.（2）Removal of complexed trivalent chromium Cr（Ⅲ）-EDTA in water by composite magnetic magnesium hydroxide（Fe₃O₄@Mg（OH）₂）:In this experiment,Fe₃O₄@Mg（OH）₂ was synthesized by hydrothermal method and used to adsorb Cr（Ⅲ）-EDTA in water.It was characterized by XRD,FTIR,BET,SEM,TGA,and XPS were used to characterize the structure and surface properties of the material.The results show that Mg（OH）₂ has been successfully loaded onto Fe₃O₄.The surface has good adsorption capacity for complex Cr（Ⅲ）-EDTA in water.The maximum adsorption capacity is 15.52mg/g.The adsorption isotherm conforms to the Langmuir isotherm,and the adsorption kinetics can be fitted by quasi-secondary kinetics.As the pH increases,the amount of adsorption decreases,and high concentrations of cations in the water promote the adsorption.After three adsorption and desorption experiments on the material,the complexed trivalent chromium Cr（Ⅲ）-EDTA still has good adsorption capacity,which proves that the adsorbent can be recycled.（3）Removal of complexed trivalent chromium Cr（Ⅲ）-EDTA in water by multiphase magnetic composites（Fe₃O₄@C@Mg（OH）₂）:In this experiment,the carbon-coated iron（Fe₃O₄@C）was hydrothermally synthesized by a two-step method,and then magnesium hydroxide was loaded onto the surface of the carbon-coated iron by hydrothermal method（Fe₃O₄@C@Mg（OH）₂）.The characterization of the method showed that magnesium hydroxide was supported on the surface of carbon-coated iron.The specific surface area of Fe₃O₄@C@Mg（OH）₂ was 46.05m²/g.It was easy to separate under the application of a magnetic field.The maximum adsorption capacity of trivalent chromium Cr（Ⅲ）-EDTA was reached up to 24.25 mg/g,the adsorption isotherm conforms to the Freundlich adsorption isotherm,and the kinetic equation was well fit the pseudo-second-order kinetic equation.The adsorption is not affected by the pH change in solution,and the adsorption process is not inhibited in the presence of a high concentration of cations,which proves that the adsorbent is suitable for a high salt and high complexing agent environment.