Performance and mechanism of arsenic removal in waste acid by combination of CuSO4 and zero-valent iron

Abstract

Zero-valent iron (ZVI) has been extensively used to remove different contaminants in wastewater including heavy metals and arsenic compounds. This study demonstrates that a continuously accelerated ZVI corrosion driven by depositing copper on the ZVI surface to form a Fe–Cu galvanic cell system, thereby increasing the ZVI corrosion rate and arsenic removal rate. Experimental studies showed that ZVI simply coupled with CuSO4 resulted in almost complete arsenic remove in waste acid within 30 min under the experimental conditions of an iron-to-arsenic molar ratio of 6, a CuSO4 concentration of 0.5 g/L, and a reaction temperature of 35 °C. Under the optimal conditions, the concentration of arsenic in waste acid decreased from 525 mg/L to 1.04 mg/L, and the arsenic removal rate reached 99.8%. Products such as magnetite and As2O3 were characterized by X-ray diffraction analyses, while As(III), Fe(III), Fe(II), and Cu0 were detected on the surface of these corrosion products through X-ray photoelectron spectroscopy. During ZVI surface corrosion accelerated by the Fe–Cu galvanic cell system, copper plays a continuous and stable activation (overcoming iron passivation) on the ZVI surface. A large amount of fresh and reactive magnetite and hydroxyl radicals was continuously generated, and arsenic was effectively removed through various mechanisms such as adsorption and precipitation. Thus, a simple combination of ZVI and CuSO4 could remove arsenic from waste acid quickly and efficiency.