Adsorption of methylene blue, crystal violet and congo red from binary and ternary systems with natural clay: Kinetic, isotherm, and thermodynamic

The adsorption of Methylene Blue (BM), Crystal Violet (CV) and Congo Red (CR) onto natural clay from Agadir region in the binary and ternary system was carried out. All the parameters influencing the adsorption of three dyes were studied namely effect of percentage, contact times (20-120 min), initial dye concentration (100-600 mg L-1), temperature (22-50 degrees C), and dye solution pH (2-12). The obtained results showed that the adsorption of MB, CV, and CR is highly dependent on the initial dye concentration, the temperature, and the dye solution pH. The kinetic study was performed by applying two kinetic models, the pseudo-first-order and the pseudo second-order. According to the obtained results, the pseudo-second-order model is better described the adsorption of dyes onto natural clay. The adsorption isotherms were studied such as Langmuir, Freundlich, the obtained results indicate that the adsorption followed the Langmuir model with correlation coefficients which are very close to 1. The maximum adsorption capacities for three dyes are 202.13 mg g(-1) for MB (MB + CV), 289.59 mg g(-1) for MB (MB + CR), 281.31 mg g(-1) for MB (MB + CV + CR), 179.28 mg g(-1) for CV (CV + MB), 289 mg g(-1) for CV (CV + CR), 280.61 mg g(-1) for CV (CV g MB + CR), 253.53 mg g(-1) for CR (CR + MB), 240.06 mg g(-1) for CR (CR + CV) and 264.54 mg g(-1) for CR (CR + MB + CV). The thermodynamic study showed that the adsorption of dyes in the binary and ternary system is spontaneous, physical and endothermic.