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In this study some characterization tests of acidic pumice were performed using various techniques such as Mercury Intrusion Porosimetry (MIP), Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), Thermal Analysis (DTA-TG), FTIR and its electrokinetic properties in water such as zeta potential (ZP), isoelectrical point (IEP), indifferent, specifically adsorbing and potential determining ions were determined. The results showed that (i) pore dimensions of the irregular or oval and fibrous cavities of the pumice varied between 0.05 μm and 2 mm depending on its particle size and these cavities usually did not intersect each other; (ii) as the pumice particle size decreases, both total pore volume and total pore surface area significantly decrease as well; (iii) pumice maintained its thermal stability approximately up to 900°C; (iv) pumice had a negative surface charge between pH 1.8 and 11.4; and (v) Cl − , Br − SO 4 2− , Na + , Al(OH) 2 + and Ca 2+ ions were indifferent, C 16 H 33 (CH 3) 3 N + , Al 3+ and Al(OH) 2+ cations were specifically adsorbing and, H + and OH − ions were potential determining ions for acidic pumice.

The adsorption behavior of quaternary ammonium cationic surfactants with different hydrocarbon chain lengths, i.e. HDTMA (hexadecyltrimethylammonium), TDTMA (tetradecyltrimethylammonium) and DDTMA (dodecyltrimethylammonium), onto clinoptilolite has been investigated. The adsorption isotherms of these surfactants are correlated with the z potential curves of clinoptilolite. Accordingly, the applicability of the hemimicelle hypothesis to the adsorption of cationic surfactants at the clinoptilolite/water interface considering in the electrical double layer (EDL) of clinoptilolite is discussed. Even though the adsorption occurs in the EDL of clinoptilolite, the adsorption of HDTMA, TDTMA and DDTMA onto clinoptilolite is not conveniently described by the hemimicelle hypothesis. The absence of all expected marked increase in the z potential curves at the hemimicelle concentration is ascribed to the large external cation exchange capacity (ECEC) of clinoptilolite. The hydrocarbon chain length of surfactant molecules is found to have a significant effect on the ion exchange as well as hydrophobic interaction mechanisms. The effectiveness of both ion exchange and hydrophobic interactions increases with increasing chain length, and so the greatest surfactant adsorption onto clinoptilolite was obtained by HDTMA.

The effects of La 2 O 3 additions up to 5 wt.% on the thermal stabilities of sol-gel derived alumina gels were studied. Observations were made on pore size, total pore area, phase changes at various sintering temperatures and times. XRD, Hg-porosimeter, DTA-TG techniques were employed. The addition of La 2 O 3 to the sol-gel derived alumina gels raised the g-Al 2 O 3 to a-Al 2 O 3 transformation temperature to 1200 C. This significantly improves the thermal stabilities of alumina gels, that are employed in ceramic membranes.

In the present paper, the effects of suspension pH and charge density of anionic polyacrylamide (PAA) on flocculation behavior of two different natural stone suspensions (NSS) marble and travertine were investigated by settling rate and turbidity as indicators. The flocculation of NSS occurs even when the natural stone (NS) powders and the flocculants carry the same sign of the charge. The polymer bridging mechanism is responsible for flocculation of marble and travertine suspensions. The settling rate of NSS exhibits an optimal balance between the flocculating power of the polymer resulting from its expanded position in suspension due to its anionicity degree and the repulsive forces between the negatively charged NS powders and anionic flocculants. At high pH of 11, the settling rate of both natural stones increased significantly with each polymer except the 40% anionic polymer. In contrast, at low pH of 6, the supernatant turbidity of both suspensions was at the minimum level with no significant difference between them. However, when considering the settling rates, each polymer except the nonionic one showed different flocculation performances. The settling rate and turbidity results are analyzed in the light of zeta potential data to identify the mechanism of polymer uptake onto NSS. D