The state of iron in natural zeolites: A Mössbauer study

In situ and ex situ study of the enhanced modification with iron of clinoptilolite-rich zeolitic tuff for arsenic sorption from aqueous solutions

“…However, this result cannot be considered conclusive, since oxidation of the ferrous species may occur on the surface of the zeolite upon contact with air at room atmosphere as observed by Weidenthaler [37], thus appearing as ferric species in the samples T + FeAs1, T + FeAs2, T + FeAs3, and T + FeAs7 in Table 4. The values gathered in this table suggest that Fe 2+ in the T + Fe(II) sample, and Fe 3+ in the T + Fe(III) samples before and after arsenite adsorption have octahedral and tetrahedral coordination, respectively, according to Roque-Malherbe [50] and Fejes [39].…”

Adsorption kinetic of arsenates as water pollutant on iron, manganese and iron–manganese-modified clinoptilolite-rich tuffs

“…It is reasonable to consider that Na, Mg, K and Ca are the extraframework cations that compensate for the deficiency of negative charge in the zeolite network [25,26]. A Mössbauer study [27] of iron-containing zeolitic rocks from several countries (Mexico, Cuba, Czech Republic, and the Russia) showed that iron is located as high spin Fe 3+ in framework tetrahedral sites, in extraframework octahedral sites as free Fe(H 2 O) 6 3+ , and as high spin Fe 2+ in octahedral coordination in extraframework sites or in another aluminosilicate associated with the zeolite. Iron is also located in magnetite contained in the zeolite rocks.…”

Physicochemical and Catalytic Properties of a Modified Natural Clinoptilolite

“…The fact that only 1.6 mole% of Fe 3+ ions present in the original material was extracted is probably due to the fact that Fe3 § is replacing tetrahedral AP + in the framework (Roque-Malherbe et al, 1990).…”

“…The natural clinoptilolite used has a degree of purity higher than 85% (Roque-Malherbe et al, 1990) mordenite, calcite, and or-quartz being the major impurities. The chemical composition of the mineral (wt%) is: SiO2 68.05; A1203 12.3; TiO2 0.40; Fe203 1.34; CaO 3.70; MgO 1.03; Na20 0.43; K20 1.70 and H20 11.06.…”