Study On Removal Of Hexavalent Chromium In Groundwater By Pyridyl Chelating Resin Loaded With Nano-FeCu/FeNi Bimetallic

Groundwater is a precious material resource for human beings,and it plays an irreplaceable role in people’s life and production.With the vigorous development of China’s industrial economy,a large amount of chromium-containing wastewater has been produced in industrial fields such as metallurgy,electroplating,and pigments.The chromium-containing wastewater enters the groundwater body through infiltration and other methods,which poses a great threat to the health of local residents’drinking water.In recent years,nano-zero-valent iron（NZVI）has been used by researchers to remove hexavalent chromium from the environment due to its strong reactivity and low price.However,nano-zero-valent iron has certain limitations:（1）nano-zero-valent iron particles are prone to agglomeration,resulting in a decrease in specific surface area and a decrease in reactivity;（2）nano-zero-valent iron is easily oxidized,and a dense oxide film will form on the surface.The dense oxide film formed will hinder the further contact and reaction of nano-zero-valent iron with pollutants.Aiming at the limitation of the nano-zero-valent iron itself,this paper selects a pyridyl-containing chelating resin（M4195）as a carrier to prepare a supported nano-iron-copper bimetal composite（M-Fe/Cu）and a supported nano-iron-nickel bi-metal.Metal composite materials（M-Fe/Ni）were characterized by field emission scanning electron microscopy and energy spectroscopy（SEM-EDS）,X-ray photoelectron spectroscopy（XPS）,and transmission electron microscopy（TEM）.The appearance analysis analyzed the reaction kinetics model and action mechanism of composites to remove hexavalent chromium;the effects of changes in water quality conditions such as initial hexavalent chromium concentration,p H,coexisting ions,and humic acid on the removal of hexavalent chromium from composites were also investigated.The main conclusions obtained in this paper are as follows:（1）After adding the second metals copper and nickel,the reactivity of nano-zero-valent iron to remove hexavalent chromium was significantly improved;when the copper ion concentration in the loading solution was 0.01 mol/L and the nickel ion concentration was 0.02 mol/L,The prepared M-Fe/Cu-2 and M-Fe/Ni-3materials have the highest efficiency in removing hexavalent chromium.TEM and SEM-EDX characterization show that M4195 resin is a good carrier.Nano-metal particles are dispersed uniformly on the surface of the resin.The nano-metal particle size on M-Fe/Cu-2 materials is mostly 10～20 nm.The particle size of nano-metals on M-Fe/Ni-3 materials is mostly 20～30nm.XPS characterization shows that in addition to zero-valent iron and zero-valent copper,there are also some metal oxides of iron and copper on the surface of M-Fe/Cu-2 materials;in addition to zero-valent iron and iron oxides on the surface of M-Fe/Ni-3.In addition,only Ni（II）was found and zero-valent nickel was not found.These may be due to the nano-metal particles being oxidized during the material preparation and sample detection.（2）Kinetic fitting results show that the reaction of M-Fe/Cu and M-Fe/Ni to remove hexavalent chromium conforms to a quasi-first-order kinetic model,and the addition of the second metals copper and nickel can significantly improve the reaction.Apparent rate constant;the quasi-second-order kinetic model can also fit the reaction process of hexavalent chromium removal by M-Fe/Cu and M-Fe/Ni,which illustrates the process of hexavalent chromium removal in composites Chemical adsorption,is the main way to control the adsorption rate.The intra-particle diffusion model was used to fit the process of M-Fe/Cu-2 and M-Fe/Ni-3 composites adsorbing hexavalent chromium.The results show that the process of hexavalent chromium adsorption by composites is that The process of the migration of the outer surface to the inner surface of the surface;the three adsorption line segments in the fitting figure did not pass through the origin,which indicates that the reaction process of removing hexavalent chromium by M-Fe/Cu-2 and M-Fe/Ni-3 is a complicated process In the process,the reaction rate is jointly controlled by multiple diffusion steps that occur simultaneously.（3）The mechanism of hexavalent chromium removal by the composite material is:the composite material first adsorbs Cr（Ⅵ）to the surface,and then the nano-zero-valent iron reduces the adsorbed Cr（VI）under the catalysis of the second metal to generate Cr（Ⅲ）and Fe（Ⅱ）;Fe（Ⅱ）and H₂ are formed after liquid phase contact;Fe（Ⅱ）and Cr（VI）generated by the above reaction continue to react to form Cr（Ⅲ）and Fe（Ⅲ）;after the p H value of the solution increases,Fe（Ⅲ）combines with hydroxide ions to form Cr（OH）₃,Fe（OH）₃or Fe（Ⅲ）-Cr（Ⅲ）co-precipitation.（4）Water quality conditions have a greater impact on the removal of hexavalent chromium by M-Fe/Cu-2 and M-Fe/Ni-3:as the initial concentration of hexavalent chromium increases,the initial p H of the solution increases,and The removal rate and apparent rate constant of hexavalent chromium by these composite materials are continuously decreasing;the presence of anions and humic acids such as nitrate,bicarbonate and sulfate all have an inhibitory effect on the reaction,and the inhibitory effect will vary with the concentration.The enhancement of Mg²⁺will weaken with the increase of Mg²⁺concentration;the lower concentration of Ca²⁺can play a certain promotion effect in the early stage,but when the Ca²⁺concentration is too high（up to 300 mg/L）,the promotion effect Will translate into inhibition.