Alessio Langella

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.

Italian zeolitized rocks of technological interest

Large areas of Italian territory are covered by thick and widespread deposits of zeolite-bearing volcaniclastic products. The main zeolites are phillipsite and chabazite spread over the whole peninsula, and clinoptilolite recorded only in Sardinia. A trachytic to phonolitic glassy precursor accounts for the formation of the former zeolites characterized by low Si/Al ratios (⩽3.00), while clinoptilolite is related to more acidic volcanism. The genesis of most of these zeolitized deposits is linked to pyroclastic flow emplacement mechanisms characterized by quite high temperatures and by the presence of abundant fluids. The main utilization of these materials has been and still is as dimension stones in the building industry. Currently, limited amounts are also employed in animal farming (dietary supplement, pet litter and manure deodorizer) and in agriculture as soil improvement and slow-release fertilizers. New fields of application have been proposed for these products on account of their easy availability, very low cost, their high-grade zeolites (50–70%), and good technological features such as high cation exchange capacities and adsorption properties.

Influence of zeolites on the sintering and technological properties of porcelain stoneware tiles

Low-cost zeolitic rocks are promising substitutes for feldspathic fluxes in ceramic bodies, since their fusibility, modest hardness and high cation exchange capacity (CEC) should improve grinding and sintering. Five large-scale Italian deposits of natural zeolites with different mineralogy were characterised and tested in porcelain stoneware bodies. Their behaviour during processing was appraised and compared with that of zeolite-free bodies. Zeolites increased the slip viscosity during wet grinding, causing a coarser grain size distribution and consequently some drawbacks in both unfired and fired tiles. After overcoming this hindrance by dry grinding of zeolite rocks, the technological behaviour of zeolite-bearing tiles appear to be similar to that of current porcelain stoneware, though with larger firing shrinkage and residual closed porosity.

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.

Methods of determining cation exchange capacities for clinoptilolite-rich rocks of the Logudoro region in Northern Sardinia, Italy

Clinoptilolite-rich materials from widespread pyroclastic and epiclastic deposits of northern Sardinia were investigated to assess their cation exchange properties and to find the most reliable experimental method to determine their cation exchange capacity (CEC). The CECs were evaluated using a cross exchange method (CEM) and a batch exchange method (BEM). The CEM resulted in values 30–35% lower than the theoretical or expected CEC calculated from the chemical analyses of the clinoptilolite-rich materials. The BEM resulted in CECs 6–12% lower than the expected CECs. Various parameters, such as the grain-size of powders (<64 µm and 125–250 µm) and replacement cation (Na+, K+, Li+, Cs+, NH4+, Ca2+, Mg2+, Sr2+) were evaluated in order to optimize the cation exchange process, i.e. enhance complete exchange. The particle size did not affect the exchange process appreciably. The type of replacement cation had a substantial effect on the experimental CEC determined by the BEM. The NH4+ and Cs+ replacement solutions resulted in the best experimental CECs ranging between 75% and 94% of the theoretical CEC with NH4+ as the replacement cation and 79% and 88% of the theoretical CEC with Cs+ as the replacement cation. The exchange efficiency was also measured as a function of ammonium concentration in the replacement solution (0.50, 1.00, 2.00 and 3.00 M). Experimental CECs ranged between 94% (0.5 M NH4Cl solution) and 99% (1 M NH4Cl solution) of the theoretical CEC for one epiclastic rock sample and between 79% (3 M NH4Cl solution) and 87% (2 M NH4Cl solution) of the theoretical CEC for one pyroclastic rock sample.

Building stone and related weathering in the architecture of the ancient city of Naples

Abstract The survey of materials constituting the buildings of the ancient city centre of Naples and of their decay typologies was carried out. Reports were entered in a database which enabled us to draw two thematic maps in a digital format: one of materials and lithotypes, and one showing weathering. On this basis, quantitative evaluations of the lithotypes were carried out. The research pointed out that the use of different lithotypes was mainly as a result of their availability and/or ease of exploitation. Furthermore, the importance of the preservation of the quarrying sites was stressed, both for their historical and cultural interest and, above all, for possible forthcoming provisioning finalized to restorations. The analysis of the results, made on a geo-mineralogical basis, as well as the thematic maps, gives a basic tool which will be very useful to those professionals involved in preservation of cultural heritage.

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.

Evaluation of Natural Phillipsite and Chabaziteas Cation Exchangers for Copper and Zinc

ABSTRACT Chabazite and phillipsite, two zeolites widespread in many volcaniclastic deposits in central-southern Italy, were evaluated as cation exchangers for the removal of copper and zinc from aqueous solution. Equilibrium and kinetics of copper and zinc exchange reactions for sodium were investigated in order to verify the selectivity and the uptake rate of both zeolites for these heavy metals. Thermody-namic quantities, such as equilibrium constant, K a, and δG′, as well as rate constant, K, were computed, and they showed that Na-chabazite displays a moderate selectivity and a favorable kinetics for copper, whereas in all the other cases uses in wastewater treatment are not recommended.

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.

Surface modified natural zeolite as a carrier for sustained diclofenac release: A preliminary feasibility study

In view of zeolite potentiality as a carrier for sustained drug release, a clinoptilolite-rich rock from California (CLI_CA) was superficially modified with cetylpyridinium chloride and loaded with diclofenac sodium (DS). The obtained surface modified natural zeolites (SMNZ) were characterized by confocal scanning laser microscopy (CLSM), powder X-ray diffraction (XRPD) and laser light scattering (LS). Their flowability properties, drug adsorption and in vitro release kinetics in simulated intestinal fluid (SIF) were also investigated. CLI_CA is a Na- and K-rich clinoptilolite with a cationic exchange ability that fits well with its zeolite content (clinoptilolite=80 wt%); the external cationic exchange capacity is independent of the cationic surfactant used. LS and CLSM analyses have shown a wide distribution of volume diameters of SMNZ particles that, along with their irregular shape, make them cohesive with scarce flow properties. CLSM observation has revealed the localization of different molecules in/on SMNZ by virtue of their chemical nature. In particular, cationic and polar probes prevalently localize in SMNZ bulk, whereas anionic probes preferentially arrange themselves on SMNZ surface and the loading of a nonpolar molecule in/on SMNZ is discouraged. The adsorption rate of DS onto SMNZ was shown by different kinetic models highlighting the fact that DS adsorption is a pseudo-second order reaction and that the diffusion through the boundary layer is the rate-controlling step of the process. DS release in an ionic medium, such as SIF, can be sustained for about 5h through a mechanism prevalently governed by anionic exchange with a rapid final phase.