Kinetics and Impact Factors for Nanoscale Zinc Adsorption of Arsenite from Water

As(Ⅲ) is a highly toxic, mobile, and predominant arsenic species in anoxic groundwater.The removal of arsenic in contaminated water by using nanoscale iron particles has received extensive attention. The reduction potential and storage of Zn is lower and easier than that of Fe. Therefore, Zn is considered to be the best choice for the reduction of chlorinated organic compounds. To our knowledge, there is little research on the reduction of arsenic with nanoscale zinc in water. The objectives of this study were to investigate kinetics and impact factors by batch experiments. Pseudo-first-order, second-order kinetics and the intraparticle diffusion model were applied to simulate the sorption process. The sorption process was best fitted by the pseudo-second-order kinetic with reaction rate constants (k2) of 0.18 g/(mg·min). The adsorption capacity of nanoscale zinc for As(Ⅲ) was 0.47 mg/g. Chemical adsorption is the main mechanism of As(Ⅲ) removal by nanoscale zinc. The shaking time for optimum removal of As(Ⅲ) has been noted as 120 min for nanoscale zinc. The adsorbent dose for nanoscale zinc is 2.5 g/L. Maximum removal of As(Ⅲ) was observed in the pH range of 2-7. Over 99.5% As(Ⅲ) and As(Ⅴ) were removed within 120 min in an initial concentration of 0.565 g/L. These results suggest that nanoscale zinc particles can be used for treating As-affected groundwater that contains substantial As(Ⅲ) without preoxidation of As(Ⅲ) to As(Ⅴ). In comparison with traditional methods, the removal of As(Ⅲ) by nanoscale zinc is simple, inexpensive and has a high efficiency for application in water treatment facilities.