4A Type Zeolite Research Articles

Contribution of calorimetry to the understanding of competitive adsorption of calcium, strontium, barium, and cadmium onto 4A type zeolite from two-metal aqueous solutions

The contribution of isothermal titration calorimetry is discussed to elucidate the mechanism of competitive adsorption of free Ca2+, Sr2+, Ba2+, and Cd2+ cations onto 4A-type zeolite from aqueous solutions at 298 K. The individual adsorption isotherms for these cations and the related enthalpy of displacement curves were compared between single-metal and two-metal systems. Separate dilution runs carried out under the same experimental conditions provided evidence that the dilution phenomenon made no significant contribution to the total cumulative enthalpy effect. In the light of the observations made in the present study, it is postulated that divalent cations exchanged with extra-framework sodium in different crystallographic locations within the zeolite structure. The binding affinity of individual cations for the zeolite surface was established to decrease in the following order: Sr ≈ Ba > Cd > Ca, in line with the increasing endothermic character of the displacement process. The experimental ΔdplHcum values in two-metal systems were also compared with the theoretical ones obtained by summing up the individual metal contributions as measured in appropriate single-metal systems. In the case of the Sr(II) + Cd(II) system, the competition became noticeable above a total amount adsorbed of 1 mmol g−1, as indicated by great differences between the experimental and theoretical enthalpy values. For the Sr(II) + Ba(II) and Sr(II) + Ca(II) systems, the sequence of site occupation was found to be modified as a result of competition. The effect was particularly pronounced for strontium which gave more exothermic contribution to the total enthalpy of displacement.

Hips/zeolite hybrid composites as active packaging materials: Structure and functional properties

Desiccant composites were prepared from seven high impact polystyrene copolymers (HIPS) with different butadiene content and dispersed droplet size to study the effect of structure on their functional and application properties. A 4A type zeolite was used as desiccant. The thermodynamic analysis of structure development revealed that the embedding of the zeolite into the polybutadiene droplets is the thermodynamically favored process. Comparison of composite stiffness to theoretically predicted values indicated that considerable embedding occurs during composite preparation. The extent of embedding depends on zeolite content, but also on other factors like butadiene content and the droplet size of the elastomer. Composite stiffness and strength decreases with increasing extent of embedding, while functional properties are dominated by zeolite content. The initial rate of water adsorption increases, while overall rate decreases with increasing desiccant loading. Embedding influences only the initial rate of water adsorption which decreases slightly with increasing extent of encapsulation.

Removal of 137Cs and 90Sr from low-level radioactive effluents by hexacyanoferrate loaded synthetic 4A type zeolite

Copper hexacyanoferrate was imbued on pores of synthetic zeolite and the formation of needle shaped copper hexacyanoferrate microcrystals was confirmed by XRD and SEM. Batch equilibrations showed that the sorbent has good affinity for Cs and Sr which was further confirmed from column studies. It is established that a substantial amount (>8000 bed volumes) of low level waste contaminated with 137Cs and 90Sr can be treated in fixed bed column. The sorbent, owing to its low cost, simple preparation process and excellent 137Cs and 90Sr removal performance, is expected to find wide spread application in nuclear industry.

Effect of Matrix Characteristics on the Properties of High-Impact Polystyrene/Zeolite Functional Packaging Materials

Desiccant composites were prepared from seven high-impact polystyrene copolymers and two homopolymers (polystyrene, PS) to study the effect of structure and elastomer content on their functional and application properties. Composites containing an 4A type zeolite up to 50 vol % were homogenized in an internal mixer and then compression molded to 1 mm thick plates. The water absorption capacity of the composites increases strongly with zeolite, but decreases slightly with increasing polybutadiene content. The overall rate of water adsorption decreases with increasing zeolite content, and it is influenced quite significantly by the amount of elastomer as well. Zeolite and elastomer contents determine both functional and application properties, but structural parameters also play a role. The size of the dispersed butadiene droplets, the amount of PS embedded into them, as well as the encapsulation of the zeolite into the droplets also influence all properties to a smaller or larger extent.

ChemInform Abstract: Synthesis of the 4A-Type Zeolite from Pretreated Red Opalite.

Synthetic 4A-type zeolite was obtained from a natural raw material of volcanic origin which was thermally and chemically pretreated. The procedures are described together with the characteristics of the zeolite. The 4A-type zeolite prepared in the described way exhibits about 70% of crystallinity when compared with the commercial products and a somewhat lower surface area.

Inorganic Amendments to Decrease metal Availability in Soils of Recreational Urban Areas: Limitations to their Efficiency and Possible Drawbacks

The use of three inorganic materials as potential immobilizers of metals in soils has been studied by monitoring metal availability by EDTA extraction, the Simple Bioaccessibility Extraction Test (SBET) and extraction with a mixture of organic acids (OA). The SBET test was the most suitable for risk assessment in soils of recreational areas. The materials were a 4A-type zeolite, tri-calcium phosphate and ‘slovakite’, a synthetic sorbent developed for remediation of metal-polluted soils. Adsorption/desorption experiments of metals by the isolated materials showed that all materials caused a strong retention of metals from solutions, with negligible release by dilution. When added to soils of three parks, zeolite and, to a much lesser extent, slovakite caused some increase in soil pH. Despite this increase of pH, zeolite is often the least effective amendment for decreasing metal availability estimated by any method, and even sometimes seems to cause some increase, as well as an increase of soil electrical conductivity. In contrast, slovakite causes a decrease of available metals as estimated by EDTA and SBET, but by SBET the effect seems to be steadily reduced after the first samplings, so that after 300 days the metals extracted by this method are very similar to the data for the blanks. Despite the differences in pseudo-total metal contents, few differences are noticeable among parks. In general, these amendments are scarcely efficient in the case of neutral urban soils like those studied here. Other techniques are needed for controlling and, eventually, decreasing metal pollution hazard in soils of recreational areas.

Nepheline and Carnegieite Ceramics from A‐Type Zeolites by Microwave Heating

The thermal disintegration processes of A‐type zeolites and the properties of the materials that were formed after microwave heating (at 2.45 GHz) were studied. The thermal disintegration of 4A‐type zeolite proceeded as follows: disintegration at ∼880°C, followed by transformations to high‐carnegieite 1 at ∼920°C, nepheline (in nepheline(4A) form) at ∼990°C, and high‐carnegieite 2 at ∼1254°C (further heating led to melting at ∼1526°C). High‐carnegieite 1, nepheline(4A), and high‐carnegieite 2 efficiently absorbed microwaves. Cooling of the molten material yielded low‐carnegieite that contained some impurities. The change of 3A‐type zeolite proceeded as follows: disintegration at ∼910°C and transformation to nepheline (in nepheline(3A) form) at ∼1006°C. In 3A‐type zeolite, in contrast to 4A‐type zeolite, carnegieite did not form before the crystallization of nepheline(3A). Nepheline of high purity and carnegieite with some impurities were synthesized easily by heating 3A‐ and 4A‐type zeolites, respectively, using microwaves. These results suggest that the microwave heating of zeolites can be used to prepare some ceramic materials.

4A zeolite synergistic agent in new flame retardant intumescent formulations of polyethylenic polymers — study of the effect of the constituent monomers

4A type zeolite adducted in the intumescent ammonium polyphosphate (APP)/pentaerythritol (PER) system, additives in fire retardant (FR) polyethylenic-based formulations (ethylenic co/terpolymers), leads to a synergistic FR effect. This study concerns ethylenic co- or terpolymers. It shows the part played by the polymeric matrix on the fire-proofing performances which depend on the chemical nature and amount of comonomer in the polymer. Further, the thermal analyses confirm the effect of the polymeric matrix and show the participation of oxygen in the formation of the intumescent coating. Measurement of the performances using the cone calorimeter puts forward that the zeolite causes different degradation of the intumescent materials and thus the formation in fire of a more thermally stable coating.

Synthesis of the 4A-Type Zeolite from Pretreated Red Opalite

Synthetic 4A-type zeolite was obtained from a natural raw material of volcanic origin which was thermally and chemically pretreated. The procedures are described together with the characteristics of the zeolite. The 4A-type zeolite prepared in the described way exhibits about 70% of crystallinity when compared with the commercial products and a somewhat lower surface area.

Thermogravimetric studies of a Cr(III)- and Zr(IV)-exchanged new synthetic zeolite (Deolite)

Commercial Deolite, a desiccant with properties similar to those of 4A-type zeolite, has been interacted with Cr(III) and Zr(IV) cations to prepare cation-exchanged derivatives of Deolite. This work is devoted to the discussion of the TG, DTA and DTG behaviour of the exchanged derivatives of Deolite. Similar studies have also been carried out on other synthetic zeolites by earlier workers [1–4].

Electron spin resonance studies of methyl radicals trapped on 4A type zeolite

Three kinds of methyl radicals were observed with different heat treatments of Linde 4A type zeolite. The first is the normal methyl radical; the second is the abnormal methyl radical, type I, having additional coupling with one extra proton; and the third is the abnormal methyl radical, type II, having large coupling with one of the three protons. These three different radicals are stabilized on the zeolite heat treated at ca. 65, ca. 80, and ca. 250$sup 0$C, respectively. It was revealed by experiments using CD$sub 4$ that a hydrogen atom liberated from irradiated CH$sub 4$ is most probably stabilized on the zeolite surface and converted into H$sup +$, which causes the additional coupling noted in the abnormal methyl radical I. The fact that the $sup 13$C-hyperfine coupling of the abnormal methyl radical, type II, gives axial symmetric tensors and shows a trend of A/sub parallel/ (75.8 G) greater than A/sub perpendicular to/ (10.5 G) indicates that this methyl radical interacts with the surface through a 2P/sub pi/ unpaired-spin orbital and rotates about the C$sub 3$ symmetry axis. The relation of each type of methyl radical with the trapping environment as well as the probable geometry of each radical ismore » discussed. (auth)« less