Removal of iron from aqueous solutions by ion exchange with Na-Y zeolite

Iron removal from aqueous solutions by batch ion exchange with a solid Na-Y zeolite has been studied. The pH of the solution was monitored continuousl y during the ion exchange process and the impact of pH on iron hydroxide pr ecipitation and zeolite structural stability is discussed. In the case of t he Fe(II)/Na-Y exchange system, the pH of the iron solutions was low enough to prevent the oxidation of Fe(II) and subsequent hydroxide deposition. Th e Al and Si contents in the solution were negligible, indicating maintenanc e of structural integrity, while scanning electron microscopic analysis did not reveal any structural breakdown. The ion exchange equilibrium isotherm , constructed at 291 +/- 2 K and a total solution positive charge concentra tion of 0.1 equiv. dm(-3), exhibited a sigmoidal shape and a maximum exchan ge of 74% of the indigenous sodium content: maximum exchange was essentiall y independent of exchange temperature. An increase in the initial Fe(II) co ncentration, in the range 0.005-0.05 mol dm(-3), lowered the removal effici ency, but the external Fe(II) was preferred to the indigenous sodium over t he entire concentration range. A maximum Fe(II) recovery of 84% from the ma ximally exchanged zeolite was achieved using 2 mol dm(-3) solutions of NaCl as regenerant while the regenerated Na-Y delivered 68% of the original Fe( II) exchange capacity. The Fe(II) recovery was lower from samples exchanged under reflux conditions, while drying the loaded zeolite at 383 K also sup pressed the degree of recovery. The treatment of Fe(III) solutions with Na- Y was not feasible due to the acidity associated with the zeolite/salt slur ries, which promotes excessive hydroxide deposition and structural disinteg ration of the zeolite.