A novel application of H 2O 2–Fe(II) process for arsenate removal from synthetic acid mine drainage (AMD) water

Abstract

Batch experiments were carried out to investigate the influences of H 2O 2/Fe(II) molar ratio, pH, sequence of pH adjustment, initial As(V) concentration, and interfering ions on As(V) removal in H 2O 2–Fe(II) process from synthetic acid mine drainage (AMD). The optimum H 2O 2/Fe(II) molar ratio was one for arsenate removal over the pH range of 4–7. Arsenate removal at pH 3 was poor even at high Fe(II) dosage due to the high solubility of Fe(III) formed in situ. With the increase of Fe(II) dosage, arsenate removal increased progressively before a plateau was reached at pH 5 as arsenate concentration varied from 0.05 to 2.0 mg L −1. However, arsenate removal was negligible at Fe/As molar ratio <3 and then experienced a striking increase before a plateau was reached at pH 7 and arsenate concentration ≥1.0 mg L −1. The co-occurring ions exerted no significant effect on arsenate removal at pH 5. The experimental results with synthetic AMD revealed that this method is highly selective for arsenate removal and the co-occurring ions either improved arsenate removal or slightly depressed arsenate removal at pH 5–7. The extended X-ray absorption fine structure (EXAFS) derived As–Fe length, 3.27–3.30 Å, indicated that arsenate was removed by forming bidentate–binuclear complexes with FeO(OH) octahydra. The economic analysis revealed that the cost of the H 2O 2–Fe(II) process was only 17–32% of that of conventional Fe(III) coagulation process to achieve arsenate concentration below 10 μg L −1 in treated solution. The results suggested that the H 2O 2–Fe(II) process is an efficient, economical, selective and practical method for arsenate removal from AMD.