Preparation And Application Of High-Efficiency Adsorption Treatment Composite Material For Chromium-Containing Wastewater

The continued increase in human activity caused the presence of a large amount of chromium in the environment,which has become one of the most serious pollution problems,seriously threatening the normal growth of animals,plants and human health.A long-term exposure to hexavalent chromium will increases the risk of lymphoma,leukemia and cancer of the stomach,lungs and bladder.And hexavalent chromium can be easily transferred in environmental media.Drinking water is an important exposure route to chromium,and drinking water contains large amounts of chromium in many areas around the world which is a serious threat to public health.Among the many methods for effectively removing hexavalent chromium from wastewater,adsorption has the advantages of low external energy consumption,cost-effective,simple and convenient operation,stable and high efficiency,and strong applicability.In this study,m-phenylenediamine?mPD?was combined with Fe₃O₄ and halloysite nanotubes?HNTs?to form two high-efficiency adsorbents for the removal of hexavalent chromium from wastewater.The magnetic polymer adsorbent Fe₃O₄@poly?m-phenylenediamine??Fe₃O₄@PmPD?and the halloysite nanotubes/poly?m-phenylenediamine?composite?HNTs/PmPD?was synthesized respectively by in-situ chemical polymerization using Fe₃O₄ and mPD,HNTs and mPD under the regulation of Na₂CO₃.By tuning the concentration of dopant Na₂CO₃ and apparent weight proportion for PmPD and Fe₃O₄ in the synthesis process,the effects of these factors on the adsorption capacity of Fe₃O₄@PmPD were studied.Adsorption studies show that the Fe₃O₄@PmPD prepared by the 1M Na₂CO₃ and 0.5 g Fe₃O₄ has the highest adsorption capacity.The highest adsorption capacities of Fe₃O₄@PmPD and HNTs/PmPD materials were654.39 and 855.66 mg/g,respectively,at room temperature?25°C?and pH=2.0.Then,the effects of contact time,pH of the solution,adsorbent dosage,initial hexavalent chromium concentration and temperature of the reaction system on adsorption were individually analyzed.The results show that long reaction times,low pH,more adsorbent dosage and high reaction temperatures would promote the removal of hexavalent chromium.The equilibrium adsorption data were fitted and evaluated by kinetic and thermodynamic models,and adsorption behavior is in good agreement with Langmuir and pseudo second-order equations,indicating the adsorption of Fe₃O₄@PmPD and HNTs/PmPD for Cr???are chemical adsorption.ICP–MS studies confirmes that some of the adsorbed Cr???was reduced to Cr???.The recyclability of the materials was tested by cyclic experiments.The experimental results proves that Fe₃O₄@PmPD material can be easily achieve solid-liquid separation by external magnetic field,and remained 73.18%of the initial adsorption capacity at the fifth recycle.And HNTs/PmPD shows a removal rate which higher than 90%at the third recycle.Finally,the mechanism of hexavalent chromium removal was preliminarily analyzed based on the various characterizations and the above experimental results.Amino and imine groups which abundantly present on the surface of these two materials are the main active sites for removing hexavalent chromium anions by electrostatic adsorption and reduction of the adsorbed Cr???to Cr???simultaneously.The material properties of these two adsorbents were analyzed by the above characterization and analysis methods.The actual adsorption effects of the materials were studied by adsorption experiments,kinetic and thermodynamics studies.These studies have shown that both materials have good hexavalent chromium removal capacity and recycling effect,which can effectively treat chromium-containing wastewater.