Fundamental aspects related to batch and fixed-bed sulfate sorption by the macroporous type 1 strong base ion exchange resin Purolite A500.

Abstract

Acid mine drainage is a natural process occurring when sulfide minerals such as pyrite are exposed to water and oxygen. The bacterially catalyzed oxidation of pyrite is particularly common in coal mining operations and usually results in a low-pH water polluted with toxic metals and sulfate. Although high sulfate concentrations can be reduced by gypsum precipitation, removing lower concentrations (below 1200 mg/L) remains a challenge. Therefore, this work sought to investigate the application of ion Exchange resins for sulfate sorption. The macroporous type 1 strong base IX resin Purolite A500 was selected for bath and fixed-bed sorption experiments using synthetic sulfate solutions. Equilibrium experiments showed that sulfate loading on the resin can be described by the Langmuir isotherm with a maximum uptake of 59 mg mL-resin 1. The enthalpy of sorption was determined as þ2.83 kJ mol^-1, implying an endothermic physisorption process that occurred with decreasing entropy (-15.5 J mol^-1.K^-1). Fixed-bed experiments were performed at different bed depths, flow rates, and initial sulfate concentrations. The Miura and Hashimoto model predicted a maximum bed loading of 25 e 30 g L-bed-1 and indicated that both film diffusion (3.2 x 10^-3 cm s-1 to 22.6 x 10^-3 cm s^-1) and surface diffusion (1.46 x 10^-7 cm2 s^-1 to 5.64 x 10^-7 cm2 s^-1) resistances control the sorption process. It was shown that IX resins are an alternative for the removal of sulfate from mine waters; they ensure very low residual concentrations, particularly in effluents where the sulfate concentration is below the gypsum solubility threshold.