Ion exchange effect on asymmetric dioxins adsorption onto FAU-type X-zeolites

• We adsorbed dioxins up to maximum size onto standard FAU-type X zeolites.
• We distinguished between dioxin adsorption into pores and onto external surfaces.
• We ensured increased pore accessibility by trivalent ion exchange.
• La3+-FAU had the same high affinity towards 1,2,3,4-TeCDD as Na+-FAU for 2,3-DCDD.

The effect of trivalent cation exchange on fully dehydrated (activated) FAU-type X-zeolites with respect to the adsorption of the sterically biggest, asymmetric dioxin-molecules (1,2,3,4 TeCDD) in iso-octane solvent was investigated. FAU 13X Na zeolites were selected due to their pore openings, close to the diameter of the 2,3-DCDD (0.74 nm) as well as their high adsorption affinity for this dioxin molecule. This zeolite also adsorbed 1,4 DCDD, but with significantly lower affinity.With the aim to eventually liberate the channel's access for the sterically biggest dioxin molecule 1,2,3,4 TeCDD, Na+ cations were replaced by trivalent cation species Y3+, Ce3+ and La3+. Symmetric dioxins were not tested in this study due to their high toxicity.Analyses performed indicate that cation exchange reaches 80% on the zeolite, while the zeolite structure is preserved during the process. La3+- FAU-type X-zeolites showed the same extreme affinity towards 1,2,3,4 TeCDD as Na+ – FAU-type X-zeolites did for 2,3-DCDD. At the same time it could be shown that both dioxins could be separated by adsorption, while 1,2,3,4 TeCDD only interacts with the external surface of Na+-FAU-type X-zeolite, not entering the zeolite pores.

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