The Roxarsone Removal With Molecule Oxygen Activation

Rxoarsone(4-hydroxy-3-nitrophenylarsonic)is a kind of common organoarsenic animal feed additives,which has been widely employed in livestock and poultry breeding to promote growth,improve feed efficiency,alter meat quality and control coccidial intestinal parasites.However,the majority of organoarsenic uptake by animals is excreted in manure without any structure or property change,finally making arsenic enter natural environment through a series of transference and transformation process,causing environmental pollution problems,such as water arsenic pollution,soil arsenic pollution and so on.So,it is urgent to remove organoarsenic contaminants in environment,especially in water.Up to now,treatment methods for organoarsneic pollution remedation in water were mainly adsorption by metal oxides,carbon nanotubes,metal-organic frameworks,and so on.Although these adsorbents could accomplish fair removal efficiency for organic arsenic,the adsorption capacity remained low.Compared with organoarsenic pollution remediation,there are enough treatment methods for inorganic arsenic pollution,which are highly efficient and practical.Thus,there was no doubt that the transformation of organoarsenic to inorganic arsenic laies the foundation for final arsenic removal in water.Advanced oxidation processes(AOPs),which could highly efficiently degrade some organic contaminants,even thoroughly degrade them to inorganic compounds,such as CO2 and H2O,making it attract much attention from researchers.Recently,investigations on AOPs for organoarsenic contaminants in water gradually attach people's attention.However,the developed AOPs for organoarsenic contaminants in wate suffered the defects of high-energy comsuption or H2O2 comsuption,which hindered their application in organoarsenic contaminants remedation.Thus,it was important and necessary to develop green,environmentally friendly and low-cost AOPs for organoarsenic contaminants remedation in water.In our study,we chose roxarsone as target contaminant,employed two kinds of lower valent iron inloved molecule oxygen activation treatment methods to oxidize organoarsenic contaminants to inorganic arsenic in water,and attemped to realize the immolization of generated inorganic arsenic.Meanwhile,we systematically investigated influence factors for roxarsone removal,distribution of arsenic species,reaction mechanism and possible degradation pathway.The main points in this paper are as follows:1.We employed tetrapolyphosphate(TPP)to cheate with ferrous(Fe(?)),forming Fe(?)-TPP complex for molecule oxygen activation.In this process,reactive oxygen species(ROS)was generated to remove roxarsone.The results demonstrated that the addition of TPP considerately enhance the efficiency of Fe(II)to activate molecule oxygen,which benefits the generation of ROS,promoting the degradation of roxarsone.Meanwhile,we demonstrated that hydroxyl radical(·OH)was the main ROS for the break of C-As bond in roxarsone.Furthermore,we found that roxarsone could be directly reduced to 4-hydroxy-3-aminophenylarsonic acid(HAPA)by accepting eletrons from Fe(II)-TPP complex.Besiedes,we systematically investigated the effect of reaction atmosphere,initial pH,concentration of TPP and concentration of Fe(II)that affecting the roxarsone removal in Fe(II)/TPP/Air system.Based on the results of arsenic species analysis and determination of intermediate products,we proposed a possible removal pathway for roxarsone.2.We employed solar light(Solar),iron oxides(Fe2O3)and oxalate(OX)to establish a heterogeneous photo-Fenton reaction(Solar/Fe2O3/OX)for roxarsone degradation.In Solar/Fe2O3/OX system,molecule oxygen was activated to generate ROS,such as superoxide radical(·O2-),hydrogen peroxide(H2O2)and ·OH.Among them,·OH played main role on roxarsone degradation and generation of inorganic arsenic.Meanwhile,we found that intial pH and concentration of oxalate would affect roxarsone to a greater degree.Combined with the results of arsenic species distribution and determination of intermediate products,we proposed a possible removal pathway for roxarsone.