Arsenate removal from water by Ti electrocoagulation: Main influencing factors, response surface optimization, and potential mechanisms

This paper detailedly investigated the efficacy and mechanism of As(V) removal by Ti electrocoagulation (Ti EC) using batch test. The Box-Behnken design method with 3 factor 3 level was used to optimize main process parameters (electrode distance, current density, and initial pH). The obtained optimal parameters for the maximum arsenic removal at 30 min were as follows: electrode distance of 9.2 mm, current density of 15.5 A/m2, and initial pH of 6.5. Initial pH had a significant impact on the arsenic removal (P < 0.01). The quadratic polynomial mathematical model was developed. Flocs characterization (TEM, XRD, XPS, FTIR, and zeta potential) combined with adsorption test were conducted for the mechanism analyses. Results showed that the flocs generated by Ti EC (rutile TiO2 as main crystalline phase) were nano-aggregates and had high reactivity. The As(V) removal mechanisms by Ti EC mainly involved flocculation, flotation, surface complexation, hydroxyl exchange, and coprecipitation. The As(V) removal efficiency of Ti EC was also investigated using real water samples (0.2 mg As/L) collected from the local lake and river waters. The corresponding As(V) removal efficiencies was up to 99.0 % and 99.2 %, respectively, within 30 min and at a CD value of 25 A/m2. This study shows that Ti EC has many advantages such as green safety, low cost, and high efficiency, thereby it is a potential water treatment technology for As(V) removal.