Erni Johan

Cs+ and Sr2+ adsorption selectivity of zeolites in relation to radioactive decontamination

Abstract Zeolites are used as adsorbents of cationic elements in the radioactive decontamination process of water, soil and others. We determined Cs+ and Sr2+ adsorption selectivity of some zeolites to know effective zeolite species for the decontamination of radioactive Cs and Sr. A 30 mL mixed solution containing up to 15 mg L−1 of non-radioactive Cs+ or Sr+ and up to 0.50 M of Na+ or K+ was mixed with 0.5 g of Linde-type A, Na-P1, faujasite X, faujasite Y and mordenite. Among the zeolites, mordenite had the highest Cs+ adsorption selectivity, and the selectivity had no correlation to the cation exchange capacity (CEC) of the zeolites. In contrast, Sr2+ adsorption selectivity of the zeolites positively correlated with the CEC of the zeolites; Linde-type A with the highest CEC showed the highest adsorption selectivity, and its adsorption rate was more than 99.9% even in the presence of 0.5 M K+. A simulated soil decontamination experiment of Cs from a Cs-retaining vermiculite by using mordenite and that of Sr from a Sr-retaining vermiculite by using Linde-type A showed decontamination rates of more than 90%.

Proton Adsorption Selectivity of Zeolites in Aqueous Media: Effect of Si/Al Ratio of Zeolites.

In addition to their well-known uses as catalysts, zeolites are utilized to adsorb and remove various cations from aqueous system. The adsorption of the cations is ascribed to the negative charge of zeolites derived from isomorphous substitution of Si by Al. The amount of Na+ adsorption on 4A, X, Y, Na-P1 and mordenite type zeolites were determined in aqueous media, in a two-cation (Na+ and H+) system. Although each zeolite has a constant amount of negative charge, the amount of Na+ adsorption of each zeolite decreased drastically at low pH−pNa values, where pH−pNa is equal to log{(Na+)/(H+)}. By using the plot of the amount of Na+ adsorption versus pH−pNa, an index of the H+ selectivity, which is similar to the pKa of acids, of each zeolite was estimated, and the index tended to increase with decreasing Si/Al ratio of zeolites. These indicate that zeolites with lower Si/Al and higher negative charge density have higher H+ adsorption selectivity, and in fact, such a zeolite species (4A and X) adsorbed considerable amount of H+ even at weakly alkaline pH region. The adsorption of H+ results in the decrease of cation adsorption ability, and may lead to the dissolution of zeolites in aqueous media.

Cs+ decontamination properties of mordenites and composite materials synthesized from coal fly ash and rice husk ash

ABSTRACT Mordenites were synthesized using the natural resource such as coal fly ash and rice husk ash. The Cs+ adsorption rate (100 ppm Cs+, 100 mL) in seawater for the prepared mordenite (1.0 g) was 83.2%. The Cs+ adsorption rate for these mordenites almost depended on the calculated Cs+ exchangeable value (mmol) using the cation exchange capacity (CEC) values. Composite powder materials consisting of mordenite and nanosized magnetite (Fe3O4) (10, 20, 30 wt%) were also synthesized from coal fly ash and rice husk ash. The total Cs+ decontamination rates using the magnetic collection after the Cs+ adsorption in water and seawater were ca. 90% and ca. 70% for the examined 20 wt% magnetite-containing composite material, respectively. Although the elution ratio of the Cs+ ion was ca. 8% from all of the adsorbed Cs+ by the dissolution test in slowly shaken deionized water for 14 days in the case of the Cs+ adsorbed composite material (20wt% magnetite), the Cs+ ion did not elute when the sample was heated at 1000°C and higher temperature due to the Cs+ containment in the glassy phase.

Sorbent-embedded sheets for safe drinking water in developing countries: a case study of lead(II) removal by a zeolite-embedded sheet

Although many kinds of materials for water purification are known, easy-to-use methods that ensure the safety of drinking water for rural populations are not sufficiently available. Sorbent-embedded sheets provide methods for the easy removal of contaminants from drinking water in the home. As an example of such a sorbent-embedded sheet, we prepared a Linde type A (LTA) zeolite-embedded sheet (ZES) and examined its Pb(II) removal behaviour. Different amounts of LTA were added either as powder or as ZES to 0.3 mM Pb(NO3)2 solutions containing 2.5 mM Ca(NO3)2, in which the ratio of the negative charges in LTA to the positive charges in Pb(II) (LTA/Pb ratio) ranged from 1 to 20. After shaking, the mixtures were centrifuged to remove the powder, while the ZES was simply removed from the mixture by hand. The LTA powder removed more than 99% of the Pb(II) from the solution at all LTA/Pb ratios within 1 h, while the ZES removed >99% of the Pb(II) at LTA/Pb ratios of 2 and higher; at the highest LTA/Pb ratio of 20, the ZES removed >99% of the Pb(II) in 30 s. Therefore, the use of appropriate sorbent-embedded sheets enable the facile removal of contaminants from water.