Arsenic Removal from Groundwater Using Iron Pyrite: Influence Factors and Removal Mechanism

Iron pyrite has been reported as a kind of potential material for arsenic(As) removal from the groundwater because it exhibits a strong attraction in groundwater for both arsenite and arsenate species. In this study, batch adsorption experiments were carried out to determine the optimum conditions for As adsorption by the iron pyrite adsorbent, including the initial concentration, adsorbent dosage ratio, pH, temperature and stirring rate. Precisely characterization methods were employed to identify the mechanism of As removal. Maximum removal efficiency for As(Ⅲ) was observed 93% at pH = 7, and for As(Ⅴ) was 95% observed at pH = 5. Langmuir model resulted in the maximum adsorption capacity(qm) for As(Ⅲ) and As(Ⅴ) were 571.7 and 671.1 μg/g, respectively, as well as the experiments were found to be favorable as separation factor RL< 1. The value of “n” 2.68 and 2.47 for As(Ⅲ) and As(Ⅴ) obtained by Freundlich model(n > 1) indicates favorable adsorption. The pseudo-first and second-order kinetic models also fitted well. The addition of oxalate on the adsorbent surface plays an important role for the recycling of Fe(Ⅱ)/Fe(Ⅲ) to minimize the arsenic concentration. Specific surface area, ion exchange mechanism and structure of adsorbent confirmed that addition of oxalate could enhance the surface area of adsorbent.