Equilibrium and column studies of iron exchange with strong acid cation resin

•Iron exchange with strong acid cation resin has been shown to be complex.•The bottle-point method chosen for equilibrium studies was critical.•The loading of iron on the resin was dependent upon solution pH and normality.•Column trials revealed the presence of multivalent and hydrolysed iron species.•Regenerant concentration significantly impacted the iron desorption profile.

The exchange of iron species from iron(III) chloride solutions with a strong acid cation resin has been investigated in relation to a variety of water and wastewater applications. A detailed equilibrium isotherm analysis was conducted wherein models such as Langmuir–Vageler, Competitive Langmuir, Freundlich, Temkin, Dubinin–Astakhov, Sips and Brouers–Sotolongo were applied to the experimental data. An important conclusion was that both the bottle-point method chosen and solution normality used to generate the ion exchange equilibrium isotherm influenced which sorption model fitted the isotherm profiles optimally. Invariably, the calculated value for the maximum loading of iron on strong acid cation resin was substantially higher than the value of 47.1 g/kg of resin which would occur if one Fe3+ ion exchanged for three “H+” sites on the resin surface. Consequently, it was suggested that above pH 1, various iron complexes sorbed to the resin in a manner which required less than 3 sites per iron moiety. Column trials suggested that the iron loading was 86.6 g/kg of resin when 1342 mg/L Fe(III) ions in water were flowed at 31.7 BV/h. Regeneration with 5–10% HCl solutions reclaimed approximately 90% of exchange sites.