Mo(VI) removal from water by aluminum electrocoagulation: Cost-effectiveness analysis, main influencing factors, and proposed mechanisms

Mo(VI) (MoO42-) removal by aluminum electrocoagulation (Al EC) with Al as anodes and cathodes was studied for the first time. At the initial Mo concentrations of 0.3 - 150 mg/L, kinetic analysis and effects of main factors (electrode connection modes, current density (CD), initial pH, and electrolytes) were examined, and potential mechanism of Mo(VI) removal were elucidated. Results showed that CD had significant impacts on anode weight loss, cathode weight loss, and total electrode weight loss (p value < 0.05). Cathode weight loss was higher than anode weight loss. XRD analysis results showed lower crystallinity of scums than that of precipitates. Boehmite was the most prevalent oxide in scums. An appropriate amount of NaCl was beneficial for enhancing the Mo(VI) removal efficiency and reducing the energy consumption of the Al EC process. Electrostatic attraction, surface complexation, hydroxyl exchange, flocculation, and coprecipitation were the main mechanisms involved in the Mo(VI) removal process by Al EC. Al EC outperformed conventional chemical coagulation in terms of Mo(VI) removal at the same dosage of Al. The Mo(VI) removal efficiencies in two real water samples (lake water and river water) reached up to 89.2% and 71.2%, respectively. This study provides novel insights into the strategies for the removal of oxoanionic metal pollutants and reduction of operating cost by Al EC technology.