Effect of pH and polymer charge density on settling rate and turbidity of natural stone suspensions

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.AKÜ-BAP

Effect of hydrocarbon chain length on adsorption of cationic surfactants onto clinoptilolite

The adsorption behavior of quaternary ammonium cationic surfactants with different hydrocarbon chain lengths, i.e. HDTMA (hexadecyltrimethylammonium), TDTMA (tetradecyltrimethy- lammonium) 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.İTÜ-BAP

Effects of La2O3 addition on the thermal stability of γ-Al2O3 gels

The effects of La2O3 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 La2O3 to the sol-gel derived alumina gels raised the g-Al2O3 to a-Al2O3 transformation temperature to 1200 C. This significantly improves the thermal stabilities of alumina gels, that are employed in ceramic membranes.TÜBİTA

Preparation and characterization of sol-gel derived 4%La2O 3- Al2O3 ceramic membrane on clay-based supports

In this work, γ-Al 2 O 3 membrane layer (4 wt % La 2 O 3 + 96 % Al 2 O ) was coated on the clay based porous support by using the sol-gel coating. The coating solution was prepared by using boehmite (AlOOH), La-nitrate (La 2 (NO 3 ) 3 .6H 2 O), PVA, distilled water and HNO 3 . The thickness of the γ-Al 2 O membrane layer was between 5-7 µm. Two unprocessed clay samples which were supplied from Kutahya and Balıkesir regions, were used to produce supports for the membranes. Porosities of the supports were varied from 25 to 40% depending on sintering temperatures. Mean 3 pore diameter of the supports were between 0.01-1µm. The mean pore diameter of 4wt%La – Al 2 O 3 membrane layer was around 11 nm and total pore area was 113 m 2 3 / g at 1000 C for 1 hour. 0 2 O

Uptake of aniline and nitrobenzene from aqueous solution by organo-zeolite

Adsorption mechanisms of toxic non-ionic organic contaminants (NOCs), aniline and nitrobenzene, with natural-zeolite andorgano-zeolite (OZ) were investigated in both batch and continuous systems. In batch tests, the adsorption capacity ofaniline and nitrobenzene onto natural zeolite surface is very low or almost nil but becomes significant upon modifying thezeolite surface by hexadecyltrimethylammonium (HDTMA). A partitioning mechanism is proposed to be responsible for the adsorption of NOCs onto OZ. The effectiveness of the partitioning mechanism is directly connected with hydrophobicproperties of the NOCs. The column tests were carried out as an indicator for continuous system. The breakthrough curveswere constructed for OZ/NOC system and the adsorption capacity of NOCs onto OZ under the present conditions weredetermined as 2.36 and 3.25 mg per gram of OZ, for aniline and nitrobenzene, respectively. A schematic model is proposedto account for the adsorption of NOCs onto OZ

Synthesis, characterization and Cr(VI) adsorption properties of modified magnetite nanoparticles

In this study, magnetite (Fe 3 O ) nanoparticles were synthesized by chemical co-precipitation method, coated with silica, and then the surface of silica coated magnetite (Fe 4 3 O 4 @SiO ) nanoparticles was modified with (3aminopropyl)triethoxysilane (APTES) at first. Secondly, attained nanoparticles were characterized by the Fourier transform infrared, X-ray diffraction, transmission electron microscopy, the Brunauer–Emmett–Teller, vibrating sample magnetometer, and zeta-sizer devices/methods. Finally, detailed adsorption experiments were performed to remove hexavalent chromium (Cr(VI)) from aqueous media by synthesized nanoparticles. Mean size and specific surface area of synthesized nanoparticles were about 15 nm and 89.5 m 2 2 /g, respectively. The highest adsorption capacity among used adsorbents (Fe 3 O 4 , Fe 3 O 4 @SiO 2 , Fe 3 O 4 @SiO 2 @L) was attained by Fe nanoparticles and it was determined that adsorption capacity of the other two adsorbents was too low when compared to the Fe nanoparticles. Optimum conditions for Cr(VI) adsorption by Fe 3 O nanoparticles were: pH, 3; temperature, 55 4 C; contact time, 90 min; adsorbent concentration, 0.5 g/l and initial Cr(VI) concentration 10 mg/l. Under these conditions, adsorption capacity and removal percentage of Cr(VI) were found to be 33.45 mg/g and 88%, respectively. 3 O 4 3 O 4AKÜ-BAPK / 14.FEN.BIL.3

Investigation of wear strength of blast furnace slag blended polymer materials

Having symmetrical and balanced material properties, polymer matrix composites are increasingly becoming popular due to easiness of construction and are use in the production of aerospace and automotive structures. In the study, we developed polymer composites based on epoxy resins, containing up to 40 wt.% of blast furnace slag and determined their pin-on-disc dynamic friction, wear, Shore hardness and surface roughness values. Wear tests were performed using a pin-on-disc under dry friction conditions, at the loads of 5, 10, 15 and 30 N, using slip velocity of 0.3 m/s and along distance of 500 m. The hardness and wear resistance values increased with the increase in the content of blast furnace slag. Showing the relationship between wear rate and hardness, an equation with parameters dependent on load was provided. There was an increase in the dynamic friction with an increase in the surface roughness. In addition, dynamic friction was an increasing function of the wear rate. The wear surfaces of the polymer composites were analyzed using scanning electron microscopy. It was observed that the wear rate of the epoxy composites and pure epoxy samples ranged from 19.85 to 171.42 mm /N m. 3TÜBİTAK / 114M15

Investigation of equilibrium, kinetic, thermodynamic and mechanism of basic blue 16 adsorption by montmorillonitic clay

The adsorption of a cationic dye, Basic Blue 16 (BB16), by montmorillonitic clay was studied in detail. Changes in the molecular structure during adsorption were analyzed by FTIR spectroscopy. BB16 adsorption onto the clay mainly results from hydrogen bonding between OH and NH groups of dye molecules and OH groups of clay and electrostatic interaction between the negatively charged clay surface and cationic dye. The montmorillonitic clay dose had an inverse effect on the adsorption performance, while the highest dye removal was 305 mg/g at pH 3.6. An increase in temperature and dye concentration positively enhanced the adsorption capacity of the montmorillonitic clay. Temperature had no effect on the adsorption at a dye concentration less than 500 mg/L, while dye adsorption was positively enhanced at elevated dye concentrations. Three-parameter equations provided higher better fitting than two-parameter equations while the Freundlich model had the highest correlation coefficient and the lowest error values with experimental data. The BB16 adsorption was well followed by pseudo-second order model and the rate of adsorption process was controlled by surface and intraparticle diffusion. Thermodynamic evaluations revealed that the adsorption process was spontaneous and endothermic, while the randomness increased during adsorption. Experimental results indicate that montmorillonitic clay from Eskisehir is a promising adsorbent for the removal of cationic dye molecules from aqueous solutions.TUBITAK /109Y16

Colloidal stability-slip casting behavior relationship in slurry of mullite synthesized by the USP method

This study presents the outcome of a research concerning the relationship between the colloidal stability of mullite powders synthesized by the USP (ultrasonic spray pyrolysis) method and its slip casting behavior. The colloidal stability of mullite slurry has been investigated under three different pH conditions (4.5, 8.9 and 10.9) derived from pH-dependent zeta potential (ZP) curves. Employing these pH values, mullite slurries with 50 wt.% solid content were prepared and slip cast. The microstructures of dried and sintered specimens were examined using SEM. It is concluded that the pH significantly influences the stability and in turn the slip casting behavior of the mullite slurry. In order to prepare homogeneous and stable mullite slurry for efficient slip casting it is preferable to utilize a basic rather than an acidic medium. High pH (i.e. 10.9) tends to leads to more closely packed mullite particles resulting in a homogeneous microstructure and greater structural integrity

Characterization of acidic pumice and determination of its electrokinetic properties in water

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 and Ca 2+ ions were indifferent, C 16 H 33 (CH 3 ) 3 N + ,Al 3+ and Al(OH) 2+ − ,Br − cations were specifically adsorbing and, H + and OH − SO ions were potential determining ions for acidic pumice. 4 2− ,Na + , Al(OH) 2 +AKÜ-BAPK / 07.MUH.0