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Decationisation and dealumination of clinoptilolite tuff and ammonium exchange on acid-modified tuff

The paper presents results of investigation of exchange of the clinoptilolite tuff cations with hydrogen ions from HCl solution concentration of 0.1 mmol cm-3 and ammonium ions solutions of concentrations from 0.0071 to 2.6 mmol cm-3. Molal concentrations (x/mmol g- 1) of cations exchanged in acid solution and in ammonium ions solutions were compared with molal concentrations of cations obtained by determining of the cation-exchange capacity of clinoptilolite tuff. The obtained results show that at ammonium ion concentration lower than 0.1 mmol cm-3, with regard to exchange capacity of particular ion, best exchanged are Na+ ions, followed by Mg2+ and Ca2+ ions, while exchange of K+ ions is the poorest (Na+> Mg2+>Ca2+>K+). At ammonium concentration from 0.2 to 1 mmol cm-3 the order is Na+>Ca2+>Mg2+>K+. At concentration higher than 1 mmol cm-3 the order is Na+>Ca2+>K+>Mg2+. The results are a consequence of the uptake of hydrogen ions by zeolite samples in ammonium ions solutions concentration lower than 1 mmol cm-3 and indicate the importance of Mg2+ (besides Na+ ions) for the exchange between clinoptilolite cations and H+ ions, contrary to K+ ions whose participation in the reaction with H+ ions is the lowest. During decationisation of the clinoptilolite in acid solution, best exchanged are Na+, Mg2+, Ca2+ ions, too, while exchange of K+ ions is the poorest. Due to poor exchange of K+ and H+ ions and good exchange of Na+, Mg2+ and Ca2+ ions, it is to assume that preservation of stability of the clinoptilolite structure is caused by K+ ions present in the channel C. Clinoptilolite is dissolved in clinoptilolite A and B channels where Na+, Mg2+ and Ca2+ ions are present. On the acid-modified clinoptilolite samples, exchange of ammonium ions is poorer in comparison with natural zeolite. The longer contact time of the zeolite and acid solution, the poorer ammonium ions exchange. It can be assumed that H+ ions exchanged with zeolite cations are consumed for dissolving of aluminium in the clinoptilolite structure, therefore concentration of H+ ions as exchangeable cations decrease. In the ammonium ion solution concentration of 0.0065 mmol cm-3, from the acid-modified zeolite samples Al3+ ions are exchanged best, followed by Na+, Mg2+, Ca2+ and K+ ions. Further to the results, it is to assume that exchangeable Al3+ ions, available from clinoptilolite dissolution are best exchanged with H+ ions in acid solution.

Clinoptilolite ; Hydrogen Ions ; Ammonium ; Ion Exchange

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