Chemistry / Kimya

Permanent URI for this collectionhttps://hdl.handle.net/11147/4072

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Author: search.filters.author.Shahwan, TalalSubject: search.filters.subject.Calcite

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Now showing 1 - 4 of 4
  • Article
    Citation - WoS: 69
    Citation - Scopus: 77
    Morphosynthesis of Caco3 at Different Reaction Temperatures and the Effects of Pdda, Ctab, and Edta on the Particle Morphology and Polymorph Stability
    (Elsevier Ltd., 2007) Altay, E.; Shahwan, Talal; Tanoğlu, Metin
    Facile precipitation of CaCO3 was performed using aqueous solutions of CaCl2 with Na2CO3 over a wide range of mixing and aging temperatures. The precipitation process was then repeated in the presence of PDDA, CTAB, and EDTA at the mixing temperatures of 30 °C, 50 °C, 70 °C, and 90 °C. The presence of these additives was seen to greatly suppress the formation of aragonite. Among these additives, EDTA was the one that showed the most prominent effects on particle morphology of CaCO3. The sequence of pH adjustment appeared to be a critical factor for the additive functionality.
  • Article
    Citation - WoS: 21
    Citation - Scopus: 21
    Retention of Aqueous Ba2+ Ions by Calcite and Aragonite Over a Wide Range of Concentrations: Characterization of the Uptake Capacity, and Kinetics of Sorption and Precipitate Formation
    (The Geochemical Society of Japan, 2007) Tunusoğlu, Özge; Shahwan, Talal; Eroğlu, Ahmet Emin
    The uptake of aqueous Ba2+, ions by abiogenic calcite and aragonite was studied over a wide range of concentration; 1.0 × 101, 5.0 × 101, 1.0 × 102 5.0 × 102, 1.0 × 103, 5.0 × 104, and 1.0 × 104 mg/L. The uptake process was characterized using ICP-AES, XRPD, SEM/EDS, and FTIR techniques. Up to the initial concentration of 5.0 × 102 mg/L, the uptake of Ba2+ ions was fast and obeyed Lagergren's kinetic model. The equilibrium data were adequately described using Freundlich isotherm model. The overgrowth of BaCO3 (witherite) took place at higher concentrations, in a kinetically slow process and enhanced the uptake of Ba2+ ions. Quantitative XRPD was used to evaluate the fractions of precipitated BaCO3 on calcite and aragonite minerals and monitor their variation with time. At all the studied concentrations, aragonite showed higher removal capacity of Ba2+ and faster uptake kinetics than did calcite. The precipitated crystals appeared to predominantly possess olivary-like morphology with an average particle size of 1-2 μm. EDS was used to reveal the elemental quantities of Ba and Ca after BaCO3 formation on calcite and aragonite surfaces. FTIR spectroscopy was employed to analyze the vibrational modes in carbonate mixtures upon incorporation of Ba2+ by sorption and precipitation mechanisms.
  • Article
    Citation - WoS: 11
    Citation - Scopus: 13
    Study of the Scavenging Behavior and Structural Changes Accompanying the Interaction of Aqueous Pb2+ and Sr2+ Ions With Calcite
    (The Geochemical Society of Japan, 2005) Shahwan, Talal; Zünbül, B.; Akar, Dilek
    The uptake of Pb2+ and Sr2+ ions from aqueous solutions by calcite was studied at various initial concentrations and pH conditions using the batch method under ambient conditions. XRPD, SEM/ EDS, AAS/AES, and DRIFT techniques were used in characterizing the sorption process. The results indicated that the retention mechanism of Ph2+ and Sr2+ ions ranged from ion incorporation to precipitate overgrowth (cerussite, hydrocerussite for Pb, strontianite for Sr) depending on the concentration and pH conditions. The calcite structure seemed to be entirely vanishing upon formation of cerussite and hydrocerussite while partial dissolution of calcite occurred upon strontianite formation. The formation of precipitates showed rapid kinetics, and equilibrium seemed to be reached within about an hour from the start of mixing. SEM analysis showed that cerussite, hydrocerussite, and strontianite had columnar prismatic-like, tabular hexagonal-like, and needle-like morphologies. Based on a nine-month observation period, dry samples of hydrocerussite seemed to show more morphological stability than cerussite. EDS analysis indicated that Pb2+ sorption is more favored than that of Sr2+, particularly in the phase of precipitate overgrowth. DRIFT analysis indicated a change in the symmetry of the carbonate groups in calcite matrix upon uptake of Pb2+ and Sr2+ cations.
  • Article
    Citation - WoS: 43
    Citation - Scopus: 47
    Aas, Xrpd, Sem/Eds, and Ftir Characterization of Zn2+ Retention by Calcite, Calcite–kaolinite, and Calcite–clinoptilolite Minerals
    (Elsevier Ltd., 2005) Shahwan, Talal; Zünbül, Banu; Tunusoğlu, Özge; Eroğlu, Ahmet Emin
    In this study, the sorption behavior of Zn2+ on calcite, kaolinite, and clinoptilolite, in addition to mixtures of calcite with kaolinite and clinoptilolite, was investigated at various loadings and mixture compositions using atomic absorption spectroscopy, scanning electron microscopy/energy dispersive X-ray spectroscopy, X-ray powder diffraction, and Fourier transform infrared techniques. According to the obtained results, within the experimental operating conditions, the sorption capacity was enhanced with increasing amount of calcite in both types of mixtures. Under neutral–alkaline pH conditions and high loadings, the order of Zn2+ retention was observed as calcite > clinoptilolite > kaolinite. The experiments on the retention of Zn2+ by pure calcite under conditions of oversaturation showed that the uptake process proceeds via an initial adsorption mechanism (possibly ion-exchange type) followed by a slower mechanism that leads to the overgrowth of the hydrozincite phase, Zn5(OH)6(CO3)2.