Removal of sulphate from mine waters by electrocoagulation/rice straw activated carbon adsorption coupling in a batch system: optimization of process via response surface methodology

The removal of sulphate ions constitutes one of the main challenges in mining, metallurgical and other industries. This work evaluated sulphate removal from aqueous solutions by an electrocoagulation (EC)/raw straw activated carbon (RSAC) adsorption coupled process. The process parameters affecting sulphate removal efficiency were investigated: current density (0–100 mA/cm2), RSAC dosage (0–0.8 g/L), initial pH (4–9) and reaction time (0–40 min). A central composite design coupled with response surface methodology (RSM) was used to construct a mathematic model of EC/RSAC process that considers three key variables, namely current density, RSAC dosage and reaction time. Under optimum conditions (current density of 75 mA/cm2, dosage of 0.46 g/L and reaction time of 19.2 min), the removal efficiency of sulphate reached 95.2%. The RSM predictive value was 94.08% with a small deviation (1.12%). Thus, the fundamental data and results can provide some useful information for further studies and applications of the EC/RSAC coupled system in sulphate-containing wastewater treatment.