Study On Characteristic Of Wastewater Containing As(Ⅲ) Treatingby Iron Aode Electrocoagulation Device

This paper studies treating wastewater containing As(Ⅲ) by using self-madeelectrocoagulation device. Firstly, several factors to As(III) removal effects andadsorption kinetics are discussed; furthermore, the effect of thecoexisting anions toinhibition of As(III) exist and its mechanism are investigated; on this basis, themechanism of electroflocculation toAs(Ⅲ)’s removal is analyzed. The main researchcontentsand conclusions can be seenas follow:The influences of different parameters, such as current density,charge density,pH, initial concentration to removing As(Ⅲ) are scrutinized and the experimentalresults show that these parameters are important factors on As(Ⅲ)’s removal.What’smore, the results show that the highest removal rate reaches99.75%with thetreatment of electrocoagulation when current density value is between4.20~44.66mA/cm~2, and the effect of current density to As (Ⅲ)’s removal is stabilized when isabove17.87mA/cm~2. Compared with currentdensity,thecharge density may be morescientific to be electrocoagulation’s condition parameter. Furthermore, the higher isthe value, the better effect of removing arsenic in pH5~9. When As(Ⅲ)’ initialconcentration is within the rangeof5~20mg/L, the effect of electrocoagulation toAs(Ⅲ)’ removal declines with the increase in initial concentration of As(Ⅲ), and theminimumconcentration can be reduced to0.03mg/L.Researching about influence of coexisting anions to As(III)’s removal finds thatfluoride, phosphate and silicate ions inhibit As(Ⅲ)’s removal when the density is0mg/L to20mg/L, and the inhibition mechanism is competitive adsorption, however,the removal rate is not affected when sulfate exists. Fluoride ion plays a significantinhibitory role in As(Ⅲ)’s removal during the electroflocculation process, and thehigher the concentrationof fluoride ion,the more obvious the inhibition will be, but isdoes not affect the generation of total iron and ferrous iron in the solution.Concentration of phosphate irons and arsenic removal rate are negatively correlated,and the higher the concentration of phosphate ions, the lower the removal rate ofAs(Ⅲ). When the pH is7, silicate ions contains a small amount of silicate whichcombined with iron oxide, occupying the binding sites of As(Ⅲ) thus affecting theelectroflocculation to removal of As(Ⅲ). However, almost all silicates exist in theform of uncharged H2SiO3(>99.8%), so they can hardly absorb on the surface of theiron oxide through electrical neutralization.Therefore, silicate ions weakly inhibit the removalof As(Ⅲ).Disposing wastewater contains As(Ⅲ) by electrocoagulation conforms toPseudo-first-order model andits fittingdegree is high. Usingthe Faradaylaw andFe3+assay, the study demonstrated that Fe(s) was first reduced to Fe2+(l), and then toFe(OH)3(s) by oxy-genated and hydrolyzed in theprocess of electrocoagulation. Theanalysis of electrocoagulation’ products through XRD, FTIR indicates that ironarsenate crystal formation is not found on the precipitation sample surface; arsenicmay also exist in the dual ligandcomplex in the form of ferric hydroxide surface.TheAs-O key formstheAs-O-Fe bondwith Fe as the coordination bond.