Removal Of Methyl Orange And Arsenic From Water By Nanometer Zinc

Azo dye methyl orange and heavy metal Arsenic are two typical environment pollutants which are severe toxic to living bodies.Azo dyes are widely used in industrial production activities.A number of dyes is lost during the dyeing process and is released in the textile effluents as industrial wastewater into the environment,owing to its complex structure,high chromaticity and poor biodegradability,the release of these colored wastewaters poses a serious threat to the environment.Therefore,the degradation of azo dyes for environmental treatment is receiving increasing attention.Arsenic is carcinogenic and has been classified as the first class of carcinogens by the International Cancer Research Center(CIRC).Methyl orange and As(?)as two typical pollutants which were chosen as targets would be removed by nanometer zero-valent zinc(nZVZ)assisted with nanometer silica gel(nSG).The influencing factors were investigated and the possible reaction mechanism was speculated.The thesis includes two parts.In the first part,the degradation of methyl orange(MO)by single nZVZ,single nSG and nZVZ assisted with nSG(nZVZ/nSG)was investigated under different conditions.And the influencing factors including the dosage of nZVZ and nSG,the initial concentration of MO,and the initial pH in the nZVZ/nSG system were studied.The results showed that the degradation of MO by nZVZ alone was slow and incomplete due to the agglomeration and rapid corrosion of nZVZ particles.However,compared with the two single systems,the degradation of MO could be markedly enhanced when nZVZ and nSG coexisted.The enhancement of MO degradation in the presence of nSG was attributed to the good dispersion and supporter role of nSG,silicic acid produced generally to prevent forming passive films of Zn(?)(hydr)oxides on the nZVZ surfaces.The optimum degradation condition was obtained.Besides,follow-up photocatalysis experiments were carried out to get the mineralization of MO.In the second part,the removal of As(?)was investigated under different conditions in a pH range of 4 to 10,and the influencing factors were also studied.The results showed that the removal of As(?)by nSG alone was negligible and the removal of As(?)by nZVZ alone was limited.However,an almost complete removal of As(?)by nZVZ in the presence of nSG could be achieved at the all tested pHs except for pH 10.And the rate of As(?)removal was enhanced with an increase of nZVZ and nSG loading to some degree.The reduce of As(?)removal under alkaline condition was attributed to the electrostatic repulsion between nZVZ and As(?).The main distribution species are Zn-O-and H2AsO3-at pH 10,respectively.