Domenico Caputo

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.

Preparation and characterization of polyethylenimine-modified mesoporous silicas as CO2 sorbents

Abstract Functionalization of MCM-48 and SBA-15 mesoporous silicas with polyethylenimine (PEI) has been achieved using the wet impregnation technique, and the obtained materials have been tested as media for CO 2 adsorption. Increasing PEI loading resulted in decreasing of the surface area and pore size of the potential adsorbents. PEI-modified mesoporous systems did not sorb any N 2 at 77 K, on the contrary both materials were able to sorb large amounts of CO 2 at 348 K and at very low pressure. At PEI loading of 50 wt% in MCM-48 and 44 wt% in SBA-15 adsorption capacities over 6 wt% were obtained. CO 2 desorption from the mesoporous silica samples under vacuum was close to 100%. These materials could be successfully used as sorbents to capture CO 2 after combustion or as H 2 stream purification media.

A preliminary investigation on kinetics of zeolite A crystallisation using optical diagnostics

Abstract Preliminary data concerning the monitoring in situ of the zeolite A crystallisation from clear solutions are reported. Experiments were performed at 60 and 70°C with fresh and aged solutions having the following composition: 8.6Na 2 O·0.18SiO 2 ·Al 2 O 3 ·150H 2 O. The formation of early phases in the crystallisation process were followed using diagnostics such as dynamic light scattering (DLS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The comparison of the available data seems to indicate the formation of a precursor phase (like gel) in the case of not aged solution. Conversely, crystallisation in aged solution seems to proceed without intermediate phases. At the same time, an investigation on the kinetics aspects of the zeolite A crystallisation was carried out. As far as the reproducibility test is concerned, the chemical system selected showed good results on a large number of tests.

Synergistic effect of vegetable protein and silicon addition on geopolymeric foams properties

Organic–inorganic hybrid foams based on an alkali alumino-silicate matrix were prepared using different foaming methods. Firstly, silico-aluminate inorganic matrix, activated through a sodium silicate solution, was prepared at room temperature. The obtained viscous paste was expanded by means of silicon metal redox reaction in alkaline media in combination with protein-assisted foaming. The foamed systems were hardened at defined temperature and time and then characterized by FTIR, scanning electron microscopy, and compression tests. The high temperature behavior and specific surface area were also evaluated. The experimental findings highlighted that the combination of silicon metal and vegetable protein allowed tailoring hybrid foams with enhanced properties: good yield strength and thermal resistance typical of geopolymeric foam with a ductile behavior (toughness) and low density typical of organic foams.

Chromium removal from water by ion exchange using zeolites and solidification of the resulting sludge in a cement matrix

Abstract A method is presented to remove and segregate Cr 3+ present in some industrial wastewaters using zeolites, on the basis of two important properties jointly exhibited by them: cation exchange and pozzolanic activity. Zeolites, namely synthetic species A and X, chosen because of their marked selectivity towards multivalent cations, were beforehand used as cation exchangers in order to remove the pollutant cation from water. Zeolitic sludge containing Cr 3+ was afterwards solidified in a cement matrix, taking advantage of its excellent reactivity towards lime arising from cement hydration. Various amounts of zeolites A and X were explored in reactions with simulated and real Cr 3+ -containing wastewater, demonstrating that 3g of zeolite X or 4g of zeolite A were able to bring Cr 3+ concentration from 45 mg/liter to values lower than the law limit (2 mg/1) in reasonable time. Subsequent safe stabilization of Cr 3+ -bearing sludges was obtained, provided that the amount of Portland clinker in the blend was not lower than about 25%. In fact the resulting materials showed mechanical strengths much higher than those recommended for landfilling (0.44 MPa) and very satisfying leaching properties.

Data processing of cation exchange equilibria in zeolites: a modified approach

After reviewing the fundamental literature concerning the equilibrium of binary cation exchange reactions on zeolites, this paper provides a straightforward procedure of computation of their thermodynamic parameters, Kα and ΔGo, based on a method of evaluation of cations activity coefficients in solution, which is simple and accurate and is equipped with a sufficiently large data-base. The computation procedure was tested on isothermal equilibrium data of Cd2+ and Zn2+ exchange for Na+ in zeolite A at 25.0°C and 0.05, 0.10, and 0.50 total normality, by calculating their Ka and ΔGo and by comparing these results to those obtained evaluating the cations activity coefficients through a reference largely used method and to previous literature data. The results obtained show that the proposed methods give results in good agreement with those obtained with the reference method so that it appears to be a good alternative for the determination of cation activity coefficients in solution.

Iron-activated carbon nanocomposite: synthesis, characterization and application for lead removal from aqueous solution

The removal of Pb(II) ions from aqueous solution by adsorption on an Iron-Activated Carbon (IAC) nanocomposite was investigated. Removal studies were carried out in a batch system, and the effects of various operating parameters, such as solution pH, solid to liquid ratio and initial concentration were evaluated. Experimental design was carried out using central composite design (CCD) with response surface methodology (RSM). According to the RSM results, the optimum adsorption conditions for Pb(II) removal by IAC were pH = 6.5, solid to liquid ratio of 3 g L−1 and initial lead concentration of 10 mg L−1. Under these optimum operating conditions, 96.5% of Pb(II) was removed by the IAC nanocomposite. The equilibrium adsorption data were well described by the Freundlich isotherm. The maximum adsorption capacity of IAC was 121.9 mg g−1 for Pb(II). It was observed that the adsorption kinetics of Pb(II) on the IAC could be well analyzed with a pseudo-second-order model.

A chromium-based metal organic framework as a potential high performance adsorbent for anaesthetic vapours

In this work, a chromium-based metal organic framework (Cr-MOF) was synthesized, characterized and tested for the adsorption of a model highly ozone-depleting anaesthetic (sevoflurane). Adsorption isotherms were measured at different temperatures e.g., 283, 298, 313 and 328 K on both Cr-MOF and a conventionally used reference adsorbent. At the temperatures used in this study, the Cr-based MOF showed a significantly higher sevoflurane (selected anaesthetic) equilibrium adsorption capacity compared to the reference sample, although adsorption on the selected MOF did not take place on all active sites (i.e., it did not expose its coordinatively unsaturated sites). Moreover, sevoflurane adsorption on Cr-MOF was found to be fully reversible in the 283–328 K temperature range, and the adsorbent was fully regenerated by vacuum treatment at ambient temperature. The semiempirical Sips model was successfully used to fit sevoflurane adsorption data, substantially confirming the phenomenological aspects of the process inferable from the experimental results.

Hybrid geopolymeric foams with diatomite addition: Effect on chemico-physical properties

Organic–inorganic hybrid foams were prepared by using metakaolin or diatomite as a partial (or total) replacement of metakaolin, as precursor and metal silicon and whipped protein as blowing agents. The foamed systems were cured at defined temperature and time and then characterized by chemical point of view through Fourier transformed infrared spectroscopy and X-ray diffraction and by mechanical and morphological point of view by compression tests and scanning electron microscopy. The experimental findings highlighted that the replacement of diatomite in the formulation affected the morphological structure of the foams and consequently their mechanical properties, due to a different chemism between the sodium silicate and the solid phase. In particular, the consolidation mechanism in the diatomite based-hybrid foams changed from geopolymerization to a silicate polycondensation. Consequently, mechanical performances enhanced with increase of the diatomite content.

Safe trapping of Cs in heat-treated zeolite matrices. Part 2

Abstract Safe trapping of cesium was investigated by heat-treating at various temperatures a Slovakian clinoptilolite-rich tuff sample, previously subjected to exhaustive exchange with Cs + . The influence of temperature on the process effectiveness was studied and the mechanism of Cs + immobilization explained. Treating the Cs-exchanged material, at 1000°C results in zeolite breakdown and the formation of an amorphous, likely glassy, phase, which safely encapsulates the polluting cation, as it has been demonstrated by standard leaching tests. This study indicates that clinoptilolite-rich tuff is a good candidate for immobilization of cesium, taken up by ion exchange.