Softening of coal seam gas associated water with aluminium exchanged resins

Abstract

This study concerned aluminium exchanged strong acid cation resin for the removal of alkaline earth ions from simulated coal seam gas (coal bed methane) associated water samples which comprised of significant bicarbonate concentrations. The hypothesis was that use of aluminium exchanged resins for water softening would require only one regenerant stage, thus avoiding health and safety issues associated with strong acids and alkali on a coal seam gas water treatment site. Equilibrium exchange tests revealed that the selectivity of the aluminium exchanged resin was in the order Ba>Sr>Ca>Mg, albeit the exchange was unfavourable unless a stoichiometric excess of bicarbonate ions was present in solution. Equilibrium studies of multi-component solutions of alkaline earth ions indicated that at low loadings the alkaline earth ions co-sorbed on the resin surface, but the more preferred ion displaced ions of lesser affinity as monolayer exchange was approached. The presence of sodium ions not only reduced alkaline earth ion loading when in concentrations relevant to coal seam gas associated water application but also appeared to be incorporated into flocs in the form of salts. Column studies revealed significant loading of alkaline earth ions (0.787eq/kg resin) but regeneration with AlCl3 (aq) did not recover all these species (0.67eq/kg resin). Partial restriction of the flow was noted during column tests due to floc formation. A subsequent loading/regeneration cycle resulted in further diminishment in alkaline earth ion uptake and an inability to achieve low effluent concentrations of alkaline earth ions.