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    Effect of crystallinity and surface silanol groups on rheological properties of different sepiolites
    (Oficyna Wydawnicza Politechniki Wroclawskiej, 2022) Cinar, Mustafa; Guelgoenuel, Ilhan; Ozdemir, Orhan; Celik, Mehmet S.
    In this study, differences in the rheological properties of three different types of brown sepiolites (K1, K2, and K3) along with one beige (B) sepiolite with different physicochemical properties were explained based on their crystallinity and level of surface silanol groups. Towards this aim, SEM images, XRD and chemical analyses, cation exchange capacity (CEC), and water absorption tests were conducted along with surface area measurements and time-dependent pH profiles. The pH profiles at 3% by wt. revealed that each sepiolite sample attained the equilibrium at different times. These differences showed a parallel behavior with the degree of crystallinity. While sepiolite with better crystallinity (K1) was rather slow in reaching the equilibrium pH, the sepiolites with poor crystallinity (B and K3) reached their equilibrium pH more quickly. The rheological studies conducted with different sepiolites at 3% solids concentration exhibited time-dependent flow of the Bingham plastic model and thixotropic. Differences observed in the rheological behavior of sepiolites were found to correlate with the fiber size, CEC, surface area, and water absorption. The results further indicated that sepiolites with low crystallinity or high level of surface silanol groups (K3 and B sepiolites) show the best rheological properties.
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    Effect of roughness and shape factor on flotation characteristics of glass beads
    (Elsevier, 2016) Hassas, Behzad Vaziri; Caliskan, Hidayet; Guven, Onur; Karakas, Firat; Cinar, Mustafa; Celik, Mehmet S.
    The effect of surface roughness and shape factor on behavior of particles in flotation has been investigated. Surface roughness of various degrees was applied on spherical glass beads of 150 + 106 mu m by means of acid etching. The same procedure was also performed on ground glass beads of the same size interval with different shape factors. The effect of these variations on surface morphology of particles was investigated in terms of flotation recovery, contact angle, and bubble-particle attachment. An Atomic Force Microscope (AFM) was used for surface roughness characterizations and a correction methodology on roughness measurements of spherical particles is proposed. A digital image analyzer was used for shape factor characterizations. It is shown that increase in surface roughness improves the flotation recovery, contact angle, and bubble attachment. Shape factor, however, was found to be more predominant in flotation and bubble attachment. This is attributed to the effect of sharp edges of ground particles which triggers the film rupture process and shortens the attachment time. (C) 2015 Elsevier B.V. All rights reserved.
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    Improved flotation of heat treated lignite with saline solutions containing mono and multivalent ions
    (Oficyna Wydawnicza Politechniki Wroclawskiej, 2018) Ozdemir, Orhan; Ersoy, Omer F.; Guven, Onur; Turgut, Hatice; Cinar, Mustafa; Celik, Mehmet S.
    Flotation of lignites is inherently difficult. However, pre-heat treatment of coal is also known to make coal surfaces more hydrophobic possibly through removal of water entrapped in the structure of coal. In this context, the objective of this study was, therefore, to determine changes in the hydrophobicity of some lignites under moderately controlled heat treatment, and correlate the flotation response of lignites in different salt solutions of NaCl, KCl, CaCl2, and MgCl2 without using any reagent. The results of flotation tests suggested that, under the present test conditions, it was possible to float thermally pre-treated lignite samples of partially hydrophobic character in salt solutions in the absence of collector and frother. In addition, the effect of heat treatment on hydrophobicity, and in turn flotation was explained by a theoretical model based on extended DLVO interactions to quantify the effects of both heat treatment and salt concentration on bubble-particle interactions. The results of theoretical modeling suggested that the removal of hydrogen containing groups from coal surfaces significantly contributed to the electrical double layer and hydrophobic forces that governed the magnitude of energetic barrier and also the extent of bubble-particle attachment.