امتزاز بعض الصبغات القاعدية من المحاليل المائية على البنتونيت السعودي - Adsorption of some basic dyes from aqueous solutions on Saudi bentonit

Thesis
الرشيدان, سلوى بدر عبدالرزاق . 2011
Publication Work Type
ماجستير
Publishing City
الرياض
Conference Date
Thesis Type
دكتوراه
School
جامعة الملك سعود
Publication Abstract

Adsorption of cationic dyes on clay can be considered as a simple, fast and economic method for their removal from water and wastewater. Bentonite, a natural clay mineral, can be effectively used as an adsorbent for the removal of cationic dyes from wastewater. The composition and mineral analysis of bentonite were determined by X-Ray florescence (XRF) and X-Ray diffraction (XRD). The specific surface area (SSA) and cation exchange capacity (CEC) were also determined. It was found that bentonite has a (SSA) of 589 m2/g and (CEC) of about 80 meq/100g. Also the point of zero charge (PZC) was determinate; the Saudi Bentonite does not has PZC.
In this study we investigated the equilibrium of the adsorption and the factors which affects the adsorption of two cationic dyes, which are namely Rhodamine B and Methylene Blue onto raw bentonite. The adsorption of both dyes was studied under several conditions: pH of solution, Ionic strength, bentonite dose and temperature. It was found that the adsorption processes decreased at pH 8 and 10 and were not affected by pH for the adsorption of Methylene Blue on bentonite. The adsorption processes were not affected by the Ionic strength for Methylene Blue and slightly influence on the adsorption of Rhodamine B. The removal capacity have no change after adding 0.5 g of adsorbent that means the adsorption process can occur with 0.5 g (the least amount) of adsorbent. The adsorption of Rhodamine B and Methylene Blue has shown a good agreement with pseudo-second order model. In addition, the Intraparticle diffusion model fit well with Rhodamine B other than Methylene Blue.
The experimental equilibrium data obtained were applied to the Langmuir and Freundlich isotherm equations. By considering the experimental results and adsorption models applied in this study, it can be concluded that The experimental data of the adsorption of Rhodamine B at different temperatures were fitted well by the Freundlich adsorption isotherm, while the adsorption of Methylene blue were fitted well by the Langmuir adsorption isotherm.
The values of enthalpy ΔH and entropy ΔS for adsorption of both dyes are estimated to be -12.29 kJ mol−1, -26.32 J mol−1 K−1 for Rhodamine B and -27.153 kJ mol−1, -57.03 J mol−1 K−1 for Methylene Blue. The negative values of ΔH suggest that the process is exothermic and the negative value of ΔS suggests a decreased in randomness at the solid/solution interface. The free energy of adsorption for both dyes were -8.76, -9.99, -10.18, -9.83 kJ mol−1 for Rhodamine B, whereas -10.3, -9.345, -8.77, -8.72 kJ mol−1 for Methylene Blue at 298, 308 , 318 and 328 K respectively. The ΔG values were negative therefore the adsorption was spontaneous.