Abstract
In this study, Natural Raw Kaolinite (NRK) clay was used as an adsorbent for the investigation of the adsorption kinetics, isotherms and thermodynamic parameters of a cationic dye Safranine-O, also known as Basic Red 2 (BR2) from aqueous solution. The effects of pH, temperature, initial dye concentration and contact time on the adsorption capacity were evaluated and the adsorbent was characterized by XRD, BET and FTIR. The pseudo-first-order, pseudo-second-order kinetic models and the intraparticle diffusion model were used to describe the kinetic data and the rate constants were evaluated. The experimental data fitted very well with the pseudo-second-order kinetic model and also followed intraparticle diffusion model revealing that diffusion is not only the rate-controlling step. The Langmuir Freundlich and Dubinin-Radushkevic adsorption models were applied to describe the equilibrium isotherms and the isotherm constants were also determined. The Langmuir model agrees with experimental data well. The activation energy, change of Gibbs free energy, enthalpy and entropy of adsorption were also evaluated for the adsorption of BR2 onto NRK.
Highlights
Dyes and pigments represent one of the problematic pollutant groups in wastewaters
The Langmuir adsorption isotherm can be written as follows qe KL qmaxCe 1+ KLCe where qe is the amount of Basic Red 2 (BR2) adsorbed onto clay samples at equilibrium, qmax is the theoretical monolayer capacity, KL (L/mol) is the Langmuir equilibrium constant related to the affinity of binding sites and energy of adsorption and Ce is the equilibrium solution concentration
The results showed that the percentage dye adsorption by the raw kaolinite increased significantly as pH increased
Summary
Dyes and pigments represent one of the problematic pollutant groups in wastewaters They are aromatic compounds with various functional groups and can be classified as anionic (direct, acid, and reactive dyes), cationic (basic dyes) and non-ionic (disperse dyes). The permanent negative charge is produced because of isomorphic replacement of Si4+ by Al3+ in the silica tetrahedral sheet or of trivalent metal ions (such as Al3+) by divalent ions Fe2+ and Mg2+ in the alumina octahedral sheet, leaving a single negative charge for each substitution As a result, both the alumina sheet surfaces and the crystal edges have a pH-dependent variable charge caused by broken bonds around the edges and exposed hydroxyl basal [15] [16]. Experimental data were analyzed using the Langmuir, Freundlich and Dubinin-Radushkevic adsorption isotherms
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