Michele Pansini

Cu2+, Zn2+, Cd2+ and Pb2+ exchange for Na+ in a sedimentary clinoptilolite, North Sardinia, Italy

Abstract Recent findings of clinoptilolite-bearing volcanoclastic deposits in northern Sardinia promoted a study aimed at evaluating the cation exchange properties of this zeolite in view of a possible future utilization of the parent rock. Isotherms of NH + 4 , Cu2+, Zn2+, Cd2+ and Pb2+ exchange for Na+ at 25°C and 0.1 total normality were obtained and the related thermodynamic quantities Ka and ΔG0 computed. The maximal exchange level was in any case less than 100% for each cation investigated. Good selectivities were recorded for NH + 4 and Pb2+, whereas clinoptilolite proved to be unselective for Cu2+, Zn2+ and Cd2+. The cation selectivity sequence NH + 4 >Pb 2+ >Na + >Cd 2+ >Cu 2+ ≅Zn 2+ was obtained. The results are discussed in the light of literature data, and contrasting performances of various clinoptilolites were ascribed to different cationic compositions of the minerals, due to different minerogenetic conditions, which were proved to affect both cation exchange capacity and selectivity. This led to the conclusion that any practical utilization of a clinoptilolite-rich rock as cation exchanger should be preceded by basic studies on representative samples from the deposit under examination.

Chromium removal from water by ion exchange using zeolite

The possible use of Neapolitan yellow tuff, a widespread zeolitic rock containing phillipsite and chabazite, in the removal of chromium from wastes has been evaluated, either in static experiments or testing fixed beds eluted by solutions of the pollutant in the presence or lack of interfering cations. Results not entirely positive have been collected, because of the moderate selectivity displayed by both zeolites for Cr3+ and of the gradual structure breakdown resulting from the ion exchange process. Nevertheless a profitable employment has been suggested in the decontamination of waters with low chromium content and not too high salinity.

FTIR study of the thermal transformation of barium-exchanged zeolite A to celsian

In this study room temperature X-ray diffraction patterns and FTIR spectra of zeolite A in its Na form, Ba-exchanged zeolite A, hexacelsian, monoclinic celsian and Ba-exchanged zeolite A samples thermally treated at temperatures ranging from 200 to 1000 °C are reported. The combined inspection of room temperature X-ray diffraction patterns and FTIR spectra reveals the following points. 1) The thermal collapse of the microporous zeolite structure goes to completion upon thermal treatment at 200–300 °C; in the resulting amorphous phase the presence of the secondary building units of the zeolite A structure may be detected. 2) Thermal treatment in the temperature range 200–400 °C results in a middle-range order which favours the crystallisation of small crystallites of monoclinic celsian at 500 °C. 3) The further evolution of the amorphous phase in the 500–800 °C temperature range of thermal treatment instead of promoting the crystalline growth of monoclinic celsian, creates a middle-range order favourable to the crystallisation of hexacelsian which occurs at 1000 °C.

Ion exchange selectivity of phillipsite for Cs and Sr as a function of framework composition

Abstract Cs and Sr exchange reactions for Na on sedimentary, hydrothermal and synthetic phillipsites are studied by determining their exchange isotherms at 25°C and 0.1 total normality, and computing the related thermodynamic quantities K a and Δ G °. Sedimentary and synthetic phillipsite, characterized by a higher Si/Al ratio, display good selectivity for Cs and moderate selectivity for Sr. The more aluminous hydrothermal phillipsite displays a lower selectivity for Cs and a higher selectivity for Sr than sedimentary and synthetic phillipsite do. These results, perfectly explainable in terms of field strength of the anionic zeolite framework and of ion charge density, demonstrate that the joint removal of Cs and Sr from water by phillipsite would be possible, provided cheap widespread aluminous phillipsite-rich materials were available.

Evaluation of phillipsite as cation exchanger in lead removal from water

Abstract The ability of phillipsite to remove lead from water was evaluated by determining lead exchange isotherms with sodium- or potassium-exchanged phillipsite and by studying the kinetics of sodium exchange for lead and, lastly, by testing lead uptake in a column, in which fixed beds of sodium-enriched phillipsite tuff grains were percolated by lead-containing solutions. The collected data evidenced a remarkable selectivity of sodium phillipsite for lead in equilibrium experiments, fast kinetics, and massive lead removal from water in column runs, even in the presence of substantial amounts of sodium as interfering cation. The favourable lead elution during regeneration of exhausted phillipsite together with the above mentioned results in the exchange experiments allow to forecast a profitable utilization of phillipsite in lead removal from waste water.

Thermal transformation of Ba-exchanged A and X zeolites into monoclinic celsian

Abstract The thermal transformation of Ba- and (Ba+Li)-exchanged precursors of zeolites A and X into monoclinic celsian has been investigated by X-ray diffractometry, differential thermal analysis, and thermodilatometry. Upon the proper thermal treatment either Ba-exchanged zeolite A or X give rise to the following transformations: zeolite→amorphous phase→hexacelsian→monoclinic celsian. Zeolite A-based precursors are more reactive than zeolite X-based precursors allowing all the reported transformations to occur at far lower temperatures starting from Ba-exchanged zeolite A rather than from Ba-exchanged zeolite X. In particular, starting from zeolite X-based precursors, fully monoclinic celsian may be obtained after 24 h at 1550°C in the absence of Li and after 6 h at 1100°C in the presence of Li, whereas starting from zeolite A-based precursors it may be obtained after 6 h at 1100°C in the absence of Li and by slow heating (1°C/min) up to 900°C in the presence of Li.

THERMAL BEHAVIOR OF NATURAL AND CATION-EXCHANGED CLINOPTILOLITE FROM SARDINIA (ITALY)

The thermal behavior of two clinoptilolites from an epiclastic and a pyroclastic deposit of central-northern Sardinia and of their exchanged forms (Li, Na, K, Cs, Mg, Ca, Sr and ammonium) were investigated by differential thermal analysis and thermogravimetry up to 1000°C. Their thermal stability was studied by evaluating the residual crystallinity (expressed as rehydration capacity) after 2 h thermal treatments at 450, 600 and 900°C. The water loss at 1000°C was linearly related to the radius (r) and the charge (z) of the exchangeable cations by the equations r2/z or r3/z, which are proportional to the inverse of the charge density over the surface or to the charge density over the volume of the cations.The cation composition plays a crucial role in determining the thermal behavior of clinoptilolite. The presence of cations such as Cs or K, which have low surface or volume charge densities, was found to increase the thermal resistance. In particular, the crystallinity of Cs- and K-exchanged forms of both clinoptilolites was not affected by thermal treatment at 450°C and was only slightly reduced by thermal treatment at 600°C.Predicting the thermal behavior of natural and cation-exchanged forms of these clinoptilolites can provide useful information for possible applications in catalysis, in the case of high thermal stability, or for thermal transformation into ceramics or lightweight aggregates.

Dynamic data on lead uptake from water by chabazite

Abstract The possibility of using chabazite, a natural zeolite exchanger, for lead removal from water is examined, testing fixed beds made of Campanian tuff, a volcanic rock rich in such zeolite. Lead breakthrough curves, as a function of pollutant concentration and influent flow rate, are determined and dynamic parameters connected with ion exchange operation calculated. The considerable selectivity of chabazite for lead and the good performances of the beds in the process investigated are emphasized, obtaining also useful indications on the operating conditions under which such processes should be carried out.

Thermal shrinkage of various cation forms of zeolite A

Abstract The thermal shrinkage of Li, Na, K, Cs, ammonium, H, and Ca forms of zeolite A has been investigated by dilatometry up to 650°C. The shrinkages of Li, Na, K, Cs and Ca forms are attributed to the dehydration and partial structural collapse which predominates over the normal thermal expansion and cation migration from one site to another in the zeolitic structure. The ammonium form shows a noticeable shrinkage and a possible catalytic action of the acid sites produced in the zeolite A in the combustion of ammonia evolved upon heating. The H form undergoes collapse at temperatures higher than 350–400°C depending on the heating rate.

Disposal of Lead-Containing Zeolite Sludges in Cement Matrix

The use of phillipsite- and chabazite- rich tuff wastes, from the huge deposits of Neapolitan yellow tuff for removing lead from water has been considered. The effectiveness of the removal process in the presence or absence of interfering cations has been demonstrated. The possibility of using the pozzolanic activity of the exhausted material to stabilize lead in a cement matrix is successfully accomplished, since materials with good mechanical properties and negligible lead release by leaching are obtained. The advantage to dispose of these materials in a segregate landfill instead of a more expensive sanitary landfill is highlighted.