C. Colella

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.

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.

Use of thermal analysis for the evaluation of zeolite content in mixtures of hydrated phases

Abstract A method, based on water vapour desorption, for the estimation of zeolite content in mixtures of hydrated phases is presented. The accuracy and reliability of the method and the ease of its application are demonstrated through an evaluation of the chabazite and phillipsite contents of Italian tuffs. The method is suitable for more general use provided that the pure phases of the mixture under investigation are available and their thermal features are known.

Evaluation of an intermediate-silica sedimentary chabazite as exchanger for potentially radioactive cations

Intermediate-silica sedimentary chabazite contained in two chabazite-rich tuffaceous rocks has been evaluated as potential cation exchanger for radioactive cation removal from nuclear waste streams. Exchange isotherms have been obtained for the cationic couples Na/Ba, Na/Co, Na/Cs and Na/Sr and the relevant thermodynamic parameters calculated with the help of a computer program. Sedimentary chabazite turns out very selective for Cs þ , fairly selective for Ba 2þ and Sr 2þ , especially at low equivalent fraction of these cations in solution, and unselective for Co 2þ . An expla

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.

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.

Remediation of Cd- and Pb-polluted soil by treatment with organo-zeolite conditioner

The present work is part of a study focused on the use of organo-zeolite conditioner to remediate soil polluted by toxic elements. The Neapolitan yellow tuff (NYT) was utilized as a component of an organo-mineral sorbent/exchanger soil conditioner with pellet manure (NYT/PM) to reduce the mobility of Cd and Pb and recover plant performance in heavily polluted soils from illegal dumps near Santa Maria La Fossa (Lower Volturno river basin, Campania Region, southern Italy). Pot experiments were performed by adding the NYT/PM mixture (1:1, w/w) to polluted soil at the rates of 0%, 25%, 50% or 75% (w/w). Wheat (Triticum aestivum) was used as the test plant. The addition of organo-zeolite NYT/PM mixture significantly reduced the DTPA (diethylene-triamine-pentaaceti c acid)-extractable Cd and Pb from 1.01 and 97.5 mg kg−1 in the polluted soil, to 0.14 and 11.6 mg kg−1, respectively, in the soil amended with 75% NYT/PM. The best plant response was observed in amended soil systems treated with 25% NYT/PM, whereas larger additions induced plant toxicities due to increased soil salinity.

Evaluation of Mechanical and Leaching Properties of Cement-Based Solidified Materials Encapsulating Cd-Exchanged Natural Zeolites

Cheap, naturally occurring, powdered zeolite-bearing materials, containing large amounts of phillipsite and chabazite, are used as a direct addition to water to remove cadmium. The resulting Cd-bearing natural zeolite sludges are subsequently stabilized-solidified in a cement matrix. The solidified wastes are evaluated using an international protocol which involves measuring the mechanical strengths of hardened pastes and a careful characterization of their leaching behaviour by means of different leaching tests. The results of stabilization-solidification runs appear to be positive as good containment of cadmium in the cement matrix is achieved. On the contrary ion exchange runs confirm the moderate selectivity of either phillipsite or chabazite for cadmium, suggesting that the proposed procedure can only be profitably used in the presence of low cadmium loadings and low interfering cations concentration in the wastewaters. The Cd-bearing natural zeolite sludge-Portland cement blends obtained could find ...