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The discoloration of Methylene Blue has been studied spectrophotometrically in sulfite solution. The reaction proceeds by redox reaction without formation of Methylene Violet Bernthsen, as in the case with a hydroxide. Disappearance of the dye obeys first-order kinetics under the excess of sulfite. The order with respect to sulfite is not a simple first order, other expressions are proposed. The salinity effect to the discoloration rate has been evaluated. The addition of Nacl, Na2SO4, NaNO3, and KSCN inhibits the discoloration, but Na2CO3 increases it. A linear relation between the rate constant and the concentration of the salt added is obtained. The activation parameters Ee, ΔG#, ΔH# and ΔS# were calculated. The discoloration rate increases with the increase of temperature. [ABSTRACT FROM AUTHOR]

Adsorptive removal capacities of renewable and highly available Chaetophora elegans alga have been investigated in this study. To assess the use of this soft water alga to remove organic pollutants from aqueous solution, crystal violet (CV) dye was used as a cationic model molecule. The effect of dye concentrations, pH, adsorbent mass, temperature, and salinity have been evaluated. The algal biomass showed quite interesting adsorption capacity under optimized operating conditions (158.7 mg of dye per gram of biomass at 25° C). The pseudo-first and pseudo-second order kinetic models were applied to the adsorption dynamic data. Pseudo second order model was well in line with the experimental data, suggesting therefore, a probable chemically-based sorption process. Several isotherm models were investigated to monitor the adsorption behavior. The Langmuir-Freundlich isotherm model fitted better the experimental data. The inhibition of the dye adsorption in the presence of different salts suggests that the salt inhibition is rather via an electric double layer. The adsorption thermodynamic parameters ΔG°, ΔH° and ΔS° were calculated. From the values of the thermodynamic parameters, we concluded that the adsorption is endothermic, less ordered and spontaneous. [ABSTRACT FROM AUTHOR]

Adsorption of three dyes methylene blue, methyl red, and fluoresceine onto feldspar have been investigated in this study. To assess the use of feldspar to remove dyes from aqueous solution, the effect of dye concentrations, pH, mass of adsorbent, temperature, and shaking speed have been evaluated. Methyl red and fluoresceine did not show any adsorption at any pH, however methylene blue showed low adsorption. Pseudo-first and pseudo-second order kinetic models were applied to the adsorption data. Pseudo second order model was well in line with the experimental data. Langmuir, Temkin and Freundlich isotherm models were also investigated. According to Langmuir isotherm, the maximum adsorption capacity was estimated as 0.66 mg/g at 40°C. The positive enthalpy indicated that the adsorption was endothermic. The negative values of Gibbs free energy revealed that adsorption was spontaneous. [ABSTRACT FROM AUTHOR]