Adsorption kinetics and mechanism of cationic methyl violet and methylene blue dyes onto sepiolite (original) (raw)
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Adsorption kinetics and mechanism of maxilon blue 5G dye on sepiolite from aqueous solutions
Chemical Engineering Journal, 2008
The use of sepiolite for the removal of maxilon blue 5G from aqueous solutions at different contact times, stirring speeds, initial dye concentrations, pHs, ionic strengths and temperatures was investigated. The adsorption process attained equilibrium within 60 min, which was an economically favorable requisite, in addition to the local abundance of the raw material. The extent of dye removal increased with increasing initial dye concentration, contact time, pH and temperature, and decreased with increasing ionic strength. On the other hand, stirring speed had no important effect on adsorption process. The adsorption process was found to be endothermic and physical in nature. Four kinetic models, the pseudo-first-and second-order equations, Elovich equation and the intraparticle diffusion models were selected to follow the adsorption process. Kinetic parameters, rate constants, equilibrium adsorption capacities and related correlation coefficients for each kinetic model were calculated and discussed. It was shown that the adsorption of maxilon blue 5G onto sepiolite could be described by the pseudo-second-order equation. The diffusion coefficients were calculated and found to be in the range of 3.625 × 10 −8 to 12.100 × 10 −9 cm 2 /s. Various thermodynamic activation parameters such as enthalpy of sorption H*, Gibbs energy change G* and entropy S* were estimated. The positive value of H* and G* shows the sorption process is endothermic and not spontaneous. The negative value of entropy S* shows the decreased randomness at the solid-liquid interface during the sorption of dye ions onto sepiolite particles. In addition, an activation energy of sorption has also been determined based on the pseudo-second-order rate constants. The activation energy of system (E a) was calculated as 19.25 kJ/mol. Sepiolite, an inexpensive and easily available material, could be an alternative for more costly adsorbents used for dye removal in wastewater treatment processes.
The temperature, pH and ionic strength effects on the adsorption of crystal violet (CV) by raw, base activated and Al-saturated sepiolite samples were studied. Al-saturated sepiolite has relatively weak ability for CV adsorption compared to the raw clay, whereas the highest adsorption observed for the base activated sepiolite may be due to the Na þ ions replaced part of Mg 2þ located at the edges of the channels. Different thermodynamic parameters for raw and pre-treated sepiolite samples indicate the adsorption of the dye component on a non-uniform surface.
Adsorption studies of aqueous basic dye solutions using sepiolite
Desalination
Sepiolite, low cost, locally available and natural mineral was studied as an adsorbent for the removal of Basic Astrazon yellow 7GL from aqueous solutions and batch contact tests. The kinetics of the adsorption process was tested for the pseudo-first order, pseudo-second order reaction and intra-particle diffusion models. The rate constants of adsorption for all these kinetic models were calculated. Good correlation coefficients were obtained for the pseudo-second order kinetic model. Langmuir, Freundlich and Dubinin-Radushkevich isotherm models were applied to the experimental equilibrium data by changing temperature. The isotherm constants were determined by using the linear regression of these models. The monolayer coverage capacities of sepiolite for basic dye were found to be in the range of 62.5–88.5mg/g at different temperatures. Thermodynamic studies showed that the reaction for dye uptake by sepiolite is endothermic in nature. Based on the optimum parameters sepiolite was a...
Desalination, 2010
The adsorption behavior of crystal violet (CV + ) from aqueous solution onto a manganese oxide-coated (MCS) sepiolite sample was investigated as a function of parameters such as initial CV + concentration, contact time and temperature. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms. The Langmuir monolayer adsorption capacity of MCS was estimated as 319 mg/g. The pseudo-first-order, pseudo-second-order kinetic and the intraparticle diffusion models were used to describe the kinetic data and rate constants were evaluated. The values of the energy (E a ) , enthalpy (ΔH ≠ ) and entropy of activation (ΔS ≠ ) were 56.45 kJ/mol, 53.90 kJ/mol and −117.26 J/(mol K), respectively, at pH 6.5. The quite high adsorption capacity and high adsorption rate of MCS will provide an important advantage for use of this material in basic dye solutions.