High-efficiency removal of As(iii) from groundwater using siderite as the iron source in the electrocoagulation process.

Abstract

Electrocoagulation technology, due to its simplicity and ease of operation, is often considered for treating arsenic-contaminated groundwater. However, challenges such as anode wear have hindered its development and application. This study aims to develop a siderite-filled anode electrocoagulation system for efficient removal of As(iii) and investigate its effectiveness. The impact of operational parameters on the removal rate of As(iii) was analyzed through single-factor tests, and the stability and superiority of the device were evaluated. The response surface methodology was employed to analyze the interactions between various factors and determine the optimal operational parameters by integrating data from these tests. Under conditions where the removal rate of As reached 99.3 ± 0.37%, with an initial concentration of As(iii) at 400 μg L-1, current intensity at 30 mA, initial solution pH value at 7, and Na2SO4 concentration at 10 mM. The flocculant used was subjected to characterization analysis to examine its structure, morphology, and elemental composition under these optimal operational parameters. The oxidation pathway for As(iii) within this system relies on integrated results from direct electrolysis as well as ˙O2 -, ˙OH, and Fe(iv) mediated oxidation processes. The elimination of arsenic encompasses two fundamental mechanisms: firstly, the direct adsorption of As(iii) by highly adsorbent flocculants like γ-FeOOH and magnetite (Fe3O4); secondly, the oxidation of As(iii) into As(v), followed by its reaction with siderite or other compounds to generate a dual coordination complex or iron arsenate, thus expediting its eradication. The anodic electrocoagulation system employing siderite as a filler exhibits remarkable efficiency and cost-effectiveness, while ensuring exceptional stability, thereby providing robust theoretical underpinnings for the application of electrocoagulation technology in arsenic removal.