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Expanded perlite and raw perlites of various origins were examined using solid-state NMR and Fourier transform infrared (FTIR) spectroscopies, as well as scanning electron microscopy, in an attempt to correlate the characteristics of aluminosilicate framework with the material's expansion properties. The 27 Al magic angle spinning (MAS) NMR spectra indicated that aluminum atoms in perlite are mainly tetrahedrally coordinated in Q 4 structures not participating in the expansion process; two different octahedral Al species were also identified in perlite. Owing to the tetrahedra−octahedra transformations, perlite may be classified among the metastable materials. The 29 Si MAS NMR and 1 H− 29 Si CPMAS NMR spectra showed that Q 3 and Q 4 units are mostly abundant, a fact that explains the low cation exchange capacity of perlites. Deconvoluted FTIR and 29 Si MAS NMR spectra are consistent regarding the relative Q n intensities which, together with the network geometry, determine the expansibility of raw perlites. The calculated variations of the Si−O−Si angle are more significant than those of the Si−O bond length, remarkably affecting the structure of the aluminosilicate network. Thus, perlite samples of increasingly fragmentary framework exhibit the highest expansion ratios. SEM micrographs monitored the expansion process differentiating between the low-and highexpansibility perlites.

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Interactions of C.I. Basic Blue 3 with potassium humate in aqueous systems were investigated. Both the humic content and dye removal are of crucial significance in relation to water of a desired quality. Dye retention experiments demonstrated that potassium humate is an exceptionally efficient adsorbent. The effect of both the pH and temperature on the adsorption process was investigated. The temperature proved to only slightly influence the extent of dye sorption; contrarily, under mildly acidic conditions (pH = 4.0), the quantity of dye adsorbed was doubled on standing. At this pH value, interactions between the positively charged dye and the dissociated carboxyl groups of humic substances are encountered. This was also supported by the obedience of the experimental data to the pseudo-second-order kinetic model. Three adsorption models, i.e., Langmuir, Freundlich and BET, were fitted to the experimental data; the equilibrium adsorption conformed to the Langmuir and BET isotherm equations on the basis of electrostatic dye–humics interactions, while the fitting of the Freundlich model referred to the heterogeneities of humic substances attributed to their colloidal behavior. Thermodynamic quantities, i.e., enthalpy, entropy and free energy change in the adsorption, were calculated. The low ΔHadsθ values verify the negligible effect of the temperature on the adsorption; ΔSadsθ denotes a thermodynamically favorable reaction, and ΔGadsθ denotes a spontaneous process.