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The structural features and the thermal behavior of natural, Na-, Ca-, K-, Mg-, and Cd-exchanged clinoptilolite from the Beli Plast deposit (Bulgaria) were studied. Purified clinoptilolite sample was preliminary prepared and ion-exchanged at 100 °C for six days. DSC-TG analyses were performed for all studied forms. The effects in the DSC curves show differences with temperature due to release of weakly bound H2O molecules and strongly bound ones. The endotherm minima temperatures were between 78 and 115 °C decreasing in the sequence K- < Na- < Natural- < Ca- ≤ Mg- < Cd-clinoptilolite. The hydrate complexes around the exchanged cations also influenced the DSC curves. The cation-coordinating H2O molecules and the non-coordinating ones were determined by XRD structural refinement for all exchanged samples. The H2O molecules of the cation–hydrate complexes are released at higher temperatures than weakly bound ones and affected the DSC curves differently. The structural adjustments made by the Rietveld method, as well as the applied EDS analyzes for the chemical composition of the samples, allowed us to correlate these data to the thermal characteristics of the studied clinoptilolite samples. [ABSTRACT FROM AUTHOR]

Cadmium exchange on clinoptilolite is performed and structurally studied for different durations of the ion exchange process (2 h, 24 h, 72 h, 168 h, 12 days, 22 days) at room temperature and 90 °C. The distribution of Cd2+ ions in all samples is elucidated after exchange on clinoptilolite using powder XRD data processed by Rietveld structural software. Clinoptilolite is not selective for cadmium cations, but at 90 °C the exchange is ~2.5 cations per unit cell. At RT it reaches ~1.25 cations per unit cell being twice as low. The obtained maximum exchanged sample for 22 days 90 °C was structurally refined in order to find the cadmium positions in the clinoptilolite voids. The structural refinements of the occupations of the incoming and outgoing cations give an idea of how the intracrystalline diffusion is processed. A good correlation between results obtained by structural refinement of the Cd-exchanged samples and the data of the EDS measurements was achieved. [ABSTRACT FROM AUTHOR]

Partial and almost complete barium exchange on clinoptilolite is performed and structurally studied for different durations (2 h, 24 h, 72 h, 168 h, 12 d, 22 d) at room temperature and 90 °C of the ion exchange process. Continuing ion exchange up to the 22nd day is proved by EDS analyses data and powder XRD (intensity changes of 020 and 200 peaks). Rietveld structure refinement was first performed on the maximum Ba exchanged clinoptilolite at 90 °C for 22 days (3.04 atoms per unit cell). Four barium positions and 9 H2O sites were refined. The split positions Ba2 and BaK (around M3 site in channel C) were found mostly occupied by 2.23 atoms per unit cell. The rest of refined samples showed different occupations of the positions of incoming Ba2+ and outgoing cations (Na+, Ca2+, K+, Mg2+) during ion exchange, describing extra-framework cationic movements, which are released easily without preferable directions. The exchanges at 90 °C and room temperature were found proceeding similarly up to the 2nd hour, but then at room temperature the process is slowed and at 22nd day 1.64 barium atoms per unit cell are structurally refined. [ABSTRACT FROM AUTHOR]