The present study focuses on the adsorption of Pb(II) by the H-form of titanosilicates (ETS-4, GTS-1) and clinoptilolite. The H-forms were prepared by first exchanging the extra-framework cations—Na+, K+, Ca2+, etc.—with NH4+, and by subsequent thermal treatment for obtaining H-forms. The purity and thermal behaviour of the initial, NH4+, and H-forms of ETS-4, GTS-1, and clinoptilolite were analysed by powder XRD, while the morphology and size of the particles were determined by SEM. The chemical composition of the solids and the solutions was obtained by WDXRF and ICP-OES, respectively. The kinetics research of the Pb(II) adsorption processes was based on WDXRF and ICP-OES. The H-forms of the materials displayed favourable properties for the adsorption of Pb(II). The best behaviour in this respect was demonstrated by GTS-1 when compared to ETS-4 and clinoptilolite.

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Natural zeolite (clinoptilolite)-based geopolymers were synthesized using alkali aluminate solution, including aluminate anodizing waste solution. The effect of calcination of the clinoptilolite sample at 900°C was investigated. The samples were studied by powder X-ray diffraction, thermal analysis, scanning electron microscopy and N2-specific surface area. The alkali aluminate-activated clinoptilolite geopolymers are characterized by satisfactory compressive strength (up to 37 MPa), low density and acceptable shrinkage. The clinoptilolite geopolymer obtained contains an X-ray amorphous phase and newly formed phillipsite and zeolite NaP. The presence of zeolite phases in the geopolymer agglomerate could be beneficial in products with specific qualities and properties, such as ion exchange, passive cooling, antimicrobial activity, etc.

Experiments with dropwise alkalization of a 0.1 M ZnSO4 solution with 1M NaOH were carried out to establish the formation order of Zn-hydroxy-sulfate minerals (osakaite, namuwite, and lahnsteinite). During the controlled alkalization with 1M NaOH of a 0.1M ZnSO4 solution, namuwite (osakaite), lahnsteinite and wulfingite are successively formed. The obtained precipitates were characterized by powder X-ray diffraction (XRD) and SEM-EDS methods. The formation conditions and regions of stability of osakaite and namuwite are at near circumneutral pH (6.5–7), while lahnsteinite is stable at high pH (11–12). This explains the wider distribution of namuwite and osakaite in nature. The isomorphic substitution of Zn2+ cation with Cu2+ in the hydroxide layer of the Zn-hydroxy-sulfate minerals during controlled alkalization was studied using mixed 0.1M ZnSO4 + CuSO4 solution (molar ratio Zn:Cu = 4:1 and 1:1). During controlled alkalization of mixed Zn-Cu sulfate solutions, 25% copper cations are isomorphic incorporated in the namuwite (osakaite) and lahnsteinite structures. It was determined that this Cu2+ content is the upper limit of the isomorphism and corresponds to the occupation of 1/3 of octahedral positions.

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