Deep Removal Of Low-concentration Organic Heavy Metals From Water And Its Interfacial Chemical Mechanism

Heavy metals are one of the important sources of environmental water pollution,which seriously threaten the ecological environment and human health.Heavy metal pollutants in water can be divided into heavy metal ions and organic heavy metals.Among them,the organic heavy metals have low concentration and complex structure,thus the treatment is difficult.The pollution problem has not been well treated and taken seriously for a long time.Organic heavy metals can be divided into compounded heavy metals and complexed heavy metals.The compounded heavy metals have strong mobility and can be further decomposed into highly toxic heavy metal ions over time;the complexed heavy metals themselves have stable physical and chemical properties,so it is difficult to remove them.After prolonged exposure to the natural environment,highly toxic heavy metal ions will be dissociated with the characteristic of slow release.For the compounded heavy metals,improving the affinity of the material is the key to improving the adsorption efficiency,while for the complexed heavy metals,the integration of degradation and fixation is a difficult point to remove.Therefore,how to achieve a good removal effect according to the chemical properties and characteristics of different types of organic heavy metal pollutants,and to explore the specific interface removal mechanism,has important research significance and social value.This work is specifically divided into the following two parts:?1?For the combined organic heavy metals,two organoarsenic p-ASA and roxarsone?ROX?were selected as the target pollutants,and a metal organic framework?MOFs?with a zirconium core was prepared by hydrothermal method which is an amino-modified Ui O-66-D-NH₂ with defects.This material shows excellent adsorption capacity,affinity and kinetic performance for the removal of low concentration organoarsenic.When the initial concentration is 1 mg/L,the removal rate is as high as 99%.At the same time,the removal rate of low-concentration organic arsenic in simulated wastewater by Ui O-66-D-NH₂ is also as high as 99%.Mechanism studies show that Ui O-66-D-NH₂ mainly captures p-ASA and ROX through As-O-Zr coordination.Defects in the metal core provide more active sites for Zr-OH,which can promote the As-O-Zr bidentate binuclear between the material and organic arsenic coordination formation.In addition,-NH₂ on the Ui O-66-D-NH₂ ligand can form hydrogen bonds with-OH in organic arsenic,which further strengthens the secondary interaction of As-O-Zr coordination.The coordination-hydrogen bond synergistic effect greatly improves the adsorption affinity of MOF for organic arsenic.This interface regulation provides new ideas and theoretical research for the deep removal of organic heavy metal micropollutants in the water environment.?2?For the complexed organic heavy metals,select the organic chromium produced in the process of microbial removal of Cr?VI?as the target pollutant,and use the chromium glycinate simulation to synthesize nano-zero-valent iron?n ZVI?by hydrothermal method.Remove.The removal rate can reach 91%when the initial concentration is 20 mg Cr/L.Through a series of removal experiments and exploring the valence changes of n ZVI and the iron and chromium in the solution during the reaction,combined with the analysis of XPS and the shielding experiment of active oxidizing substances,infer the combined mechanism of n ZVI's adsorption-degradation-resorption of chromium glycinate.Mechanism studies have shown that n ZVI first chemically adsorbs chromium glycinate,and further degrades the organic functional groups in the chromium glycinate structure through superoxide and hydroxyl radicals generated by the reaction of n ZVI with water,releasing Cr?VI?,which is further reduced by n ZVI It becomes Cr?III?,which is finally fixed on the surface of n ZVI in the coordination mode of Fe-O-Cr.Analogous to the traditional Fenton reaction,n ZVI can achieve the degradation of complex organic chromium and the adsorption and fixation of inorganic chromium in one step.The total chromium concentration in the treated water is less than 0.4 mg/L,which has good practical application potential.In summary,this work has improved the performance of the material through material modification and interface control.It has achieved good removal of low-concentration organoarsenic and organic chromium in water,and provided a way for the deep removal of organic heavy metal micro-pollutants in the water environment in theoretical basis and new ideas.