Batch and fixed-bed assessment of sulphate removal by the weak base ion exchange resin Amberlyst A21.

Abstract

This paper investigated sulphate removal from aqueous solutions by Amberlyst A21, a polystyrene weakbase ion exchange resin. Both the pH and initial sulphate concentration were observed to stronglyaffect sorption yields, which were largest in acidic environments. Working under optimum opera-tional conditions, sulphate sorption by Amberlyst A21 was relatively fast and reached equilibrium after45 min of contact between the solid and liquid phases. Sorption kinetics could be described by eitherthe pseudo-first order (k1= 3.05 × 10−5s−1) or pseudo-second order model (k2= 1.67 × 10−4s−1), andboth the Freundlich and Langmuir models successfully fitted the equilibrium data. Sulphate uptake byAmberlyst A21 was a physisorption process ( H = −25.06 kJ mol−1) that occurred with entropy reduction(deltaS = −0.042 kJ mol−1K−1). Elution experiments showed that sulphate is easily desorbed (∼100%) fromthe resin by sodium hydroxide solutions at pH 10 or pH 12. Fixed-bed experiments assessed the effects ofthe initial sulphate concentration, bed height and flow rate on the breakthrough curves and the efficiencyof the Amberlyst A21 in the treatment of a real effluent. In all studied conditions, the maximum sulphateloading resin varied between 8 and 40 mg (SO42−) mL (resin)−1.