Sulfate removal mechanism by internal circulation iron-carbon micro-electrolysis

Abstract

• Internal circulation iron-carbon micro-electrolysis was used to remove sulfate. • We investigated the effects of different conditions on the sulfate removal rate. • The maximum sulfate removal efficiency was 76.6% under specific conditions. • The sulfate removal mechanism was investigated using four different techniques. Internal circulation iron-carbon micro-electrolysis (ICE) was used to treat sulfate in wastewater. The influences of the reaction time, aeration rate, pH, iron-carbon ratio, and the initial sulfate concentration on sulfate removal by ICE were investigated. The maximum sulfate removal efficiency was 76.6% under the following conditions: reaction time = 120 min, aeration rate = 0.5 m 3 /h, pH = 2, iron-carbon ratio = 1:1, and initial sulfate concentration = 500 mg/L. Scanning electron microscopy, energy-dispersive spectrometry, X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectroscopy analyses were performed to study the sulfate removal mechanism. The results showed that sulfate was mainly removed by two mechanisms: 1) sulfate may initially be reduced to SO 3 2- , and then to S 2- , which combines with H + and Fe 2+ to form H 2 S and FeS, which can be removed; 2) sulfate can be removed by flocculation and precipitation of Fe(OH) 2 and Fe(OH) 3 . Therefore, the ICE process can be used as an effective method to remove sulfate from wastewater.