Selectivity Of Clinoptilolite Research Articles

Antibacterial activity of Na-clinoptilolite against Helicobacter pylori: in-vitro tests, synergistic effect with amoxicillin and stability of the antibiotic formulated with the zeolite

Abstract Helicobacter pylori is a bacterium whose pathogenic strains cause severe gastroduodenal diseases. Ammonium plays a crucial role in the survival of H. pylori , and potentiates the effect of a toxin produced by the bacterium. This research has evaluated the possibility to exploit, against H. pylori growth, the selectivity of clinoptilolite towards ammonium. A specifically-prepared material containing 90% Na-clinoptilolite and H. pylori reference strain ATCC ® 43504™ have been used to perform in-vitro tests. The viable colony count test has evidenced, compared to the zeolite-free control, a decrease in bacterial growth from 13 to 87% for Na-clinoptilolite concentrations from 0.5 to 8 mg/mL. H. pylori growth has been inhibited in media containing 30 mg/mL of Na- clinoptilolite, whereas the same concentration of NH 4 -clinoptilolite, prepared through exchange from the Na-form, has allowed bacteria proliferation. The disc diffusion test revealed the existence of a synergy between amoxicillin trihydrate and Na-clinoptilolite, as the diameter of inhibition halo caused by the antibiotic has increased by 24% in growth media containing 0.125 mg/mL of Na-clinoptilolite, and by at least 70% for a zeolite concentration of 0.250 mg/mL. Conversely, NH 4 -clinoptilolite has not affected inhibition halo of amoxicillin. The results lead to correlate the antibacterial activity of Na-clinoptilolite with its ability to remove ammonium by cation exchange. Na-clinoptilolite does not affect the solid state stability of amoxicillin trihydrate, as determined by XRD and HPLC analyses performed on a physical mixture stored for 18 months at 20 °C and relative humidity of 20, 50, and 80%.

Release of lead from Pb-clinoptilolite: managing the fate of an exhausted exchanger

The selectivity of clinoptilolite toward Pb2+ has stimulated many studies aimed to evaluate the metal uptake. Conversely, the management of a Pb-bearing clinoptilolite has not received the same attention, although it can release a harmful metal. This work aims to evaluate the possibility to control, through thermal treatments, the release of lead from a Pb-clinoptilolite, prepared to simulate the condition of highest dangerousness of an exhausted exchanger. A zeolite-rich rock from Sardinia (Italy) has been processed, obtaining a powder with almost 90 % (wt.) of clinoptilolite. This material has been initially Na- and then Pb-exchanged, reaching a Pb2+ content of 2.28 meq/g. The lead release has been tested before and after 2-h heating at eight different temperatures from 200 to 900 °C. The unheated material releases 64 % of the lead. Heating weakly affects lead release up to 400 °C (54 %), but higher temperatures determine an abrupt reduction from 44 % at 500 °C to 1 % at 700 °C, when the zeolite breakdown occurs. At 800 °C the nucleation of Pb-feldspar and silica polymorphs begins. Basically, the material heated at 900 °C does not release lead (0.03 %), because the metal is trapped in the lead feldspar, whose content attains 42 % (wt.). This solid-state transformation does not involve the emission of lead vapors, another significant environmental aspect.

Solid phase extraction–inductively coupled plasma spectrometry for adsorption of Co(II) and Ni(II) from radioactive wastewaters by natural and modified zeolites

Natural and modified clinoptilolite as low-cost adsorbents have been used for adsorption of Co(II) and Ni(II) from nuclear wastewaters both in batch and continuous experiments. Zeolite X was also synthesized and its ability towards the selected cations was examined. Kinetic and thermodynamic behaviors for the process were investigated and adsorption equilibrium was interpreted in term of Langmuir and Freundlich equations. The effect of various parameters including the initial concentration, temperature, ionic strength and pH of solution were examined to achieve the optimized conditions. The clinoptilolite was shown good sorption potential for Co(II) and Ni(II) ions at pH values 4–6. Based on desorption studies, nearly 74 and 85% of adsorbed Co(II) and Ni(II) were removed from clinoptilolite by HCl. The Na+ and NH4 + forms of clinoptilolite were the best modified forms for the removal of investigated cations. It is concluded that the selectivity of clinoptilolite is higher for Co(II) than Ni(II). The synthesized zeolite showed more ability to remove cobalt and nickel ions from aqueous solution than the natural clinoptilolite. The microwave irradiation was found to be more rapid and effective for ion exchange compared to conventional ion exchange process.

Trapping the lead ion in multi-components aqueous solution by natural clinoptilolite

To study whether natural clinoptilolite could selectively capture Pb 2+ ion in the aqueous solution containing salt and glycine as well as nitrosamines, the natural zeolite was utilized in the complex solution with pH value of 1.2 in comparison with other porous materials such as zeolite NaZSM-5 and activated carbon. Clinoptilolite exhibited the highest capability in adsorbing Pb 2+ ion in the solution at 37 °C, achieving the capacity of 7 mg/g, two times more than that by other zeolites and six times over that by activated carbon, and the adsorption equilibrium could be achieved within 2 h. The impacts of solid–liquid ratio, initial concentration of Pb 2+ and the competition of other metal ions or volatile nitrosamines on the adsorption were examined, and the change in Gibbs energy for the ion-exchanged of Pb 2+ ion by clinoptilolite was discussed, through which the ion-exchange process was proven to be spontaneous. Moreover, both the selectivity of clinoptilolite toward Pb 2+ ion in complex solution and the venial toxicity of clinoptilolite on the viability of RAW264.7 cells were investigated in this article.

Sorption-Analytic, Microcalorimetric and ab Initio Study of Ion-Exchange Equilibria Involving Mg2+ and Ca2+ Cations on Clinoptilolite

The exchange equilibrium between Mg2+ and Ca2+ ions and the corresponding microcalorimetric ion-exchange heats were studied on two clinoptilolite (Cli) samples. Using the experimental values of the ion-exchange constants (free energies) and heats (enthalpies), reliable estimates of the entropy were obtained for the direct (Mg2+-Ca2+-Cli) and inverse ion-exchange reactions. It was shown that the sign (negative or positive) of the ion-exchange free energy in the case under study was determined essentially by the entropy constituent of the ion-exchange process. The selectivity of clinoptilolite towards Ca2+ cations rather than to Mg2+ cations was demonstrated. The ab initio calculations undertaken confirmed the experimental results and provided structural information concerning the localisation of ions in the crystalline environment. In particular, it was shown that the 10-membered structural clinoptilolite rings provide favourable positions for hydrated Ca2+ cations. The energy gain of the system arising from the Ca2+-Mg-Cli exchange was -E = 8.0–3.4 kJ/mol depending on the localisation sites for the Ca2+ cations; these values are in acceptable quantitative agreement with experimental data for the exchange enthalpy variation –ΔH = (7.3-8.4) kJ/(g equiv). Data were obtained for the energetics of interaction of Ca2+ and Mg2+ ions with water molecules located in the first and second hydration spheres.

Adsorption of Pb and Cd by amine-modified zeolite

Natural zeolites, known for their excellent sorption properties towards metal cations, are widely used for the purification of wastewaters. The selectivity of clinoptilolite, a common zeolite mineral, for Pb is known to be particularly high, whereas its selectivity for Cd is often lower. Extraordinarily high sorption capacities for soft metal cations were observed in the case of thiol-functionalized silica gels and clays. In order to enhance the zeolites’ sorption capacity for Cd, we treated natural heteroionic and Na-clinoptilolite in aqueous suspensions with cysteamine and propylamine solutions and investigated the sorption of Cd and Pb to amine-modified zeolite by a series of batch experiments. Stability constants for amine sorption on all zeolite samples at room temperature and 50 °C were obtained. Partial dimerization of cysteamine explains the enhanced sorption of this compound. In contrast, amine treatment did not enhance the adsorption capacity or selectivity of the clinoptilolite towards Cd and Pb. Instead, the amounts of adsorbed heavy metals decreased stoichometrically with increasing sorption of cysteamine and propylamine. This reduction can be explained by the blockage of channels by amine molecules and revealed that the modification of zeolites with mercaptoamines does not enhance the sorption capacity of zeolite for Cd and Pb.

An Equilibrium Ion‐Exchange Study on the Removal of NH4 + Ion from Aqueous Effluent Using Clinoptilolite

The present work concerns an equilibrium study of naturally occurring clinoptilolite as an ion‐exchange medium; the clinoptilolite has been used for the removal of the NH4 + ion from a model aqueous effluent of the Landfill Leachate Assisted Froth Flotation (LLAFF) process. The other principal cations involved were sodium and calcium, and the anion was chloride. A number of experimental tests with constant ionic strength in solution were conducted; these were performed to further validate the feasibility of using clinoptilolite to remove NH4 + ion from the LLAFF effluent. The experimental data obtained were well described by the law of mass action. A binary‐component equilibrium study revealed a value for the binary separation factor αNH4 +, Na+ of 5.5; this value was relatively unaffected by the total salinity under the experimental conditions. Values for the intra‐particle diffusion coefficient and the maximum ion‐exchange capacity were also obtained; the latter was affected by total salinity. Results from the binary‐component and multicomponent studies have revealed the selectivity of clinoptilolite for ammonium over other cations under the compositional conditions of the model LLAFF effluent: The selectivity sequence is K+ > NH4 + > Na+ > Ca2+. The factors that influence the selectivity of clinoptilolite for NH4 + in LLAFF effluent have been ascertained; in particular, it has been found that small quantities of Ca2+ in the effluent have a deleterious effect on both selectivity toward ammonium and ammonium ion‐exchange capacity.

Studies on the use of clinoptilolite for ammonia removal from leachates

Abstract The removal of ammonia from leachates has been studied using clinoptilolite as an ion‐exchanger. The performance of the zeolite was examined under various conditions such as single column and columns in series with and without leachate recycling. The experimental results have shown that under certain conditions the ammonia removal is very effective although all the available sites of the exchanger are not covered despite the high selectivity of clinoptilolite for this particular ion.