Innovative adsorbents based on bentonite mining waste for removal of cationic dyes from wastewater.

Waste rock from bentonite mining (WRBM) was evaluated as potential adsorbents for removing crystal violet (CV) and methylene blue (MB) cationic dyes from contaminated water. The waste samples (AM01, AM02, and AM03) were collected from different locations of the bentonite mine and characterized through X-ray diffraction, X-ray fluorescence, Fourier-transform infrared spectroscopy, N2 adsorption/desorption, and cation exchange capacity. The adsorption efficiency of CV and MB dyes was investigated through the effect of initial concentration, contact time, pH, the dosage of adsorbent, and temperature. Sample AM02 showed the largest surface area (69.13 m2/g) and the best adsorptive performance for both dyes, with removal more significant than 90%. The adsorption of CV and MB in the waste followed the Langmuir isothermal model. Samples AM01 and AM02 followed the pseudo-second-order (PSO) kinetic model, while AM03 better fitted the Elovich kinetic model. The enthalpy (ΔH), entropy (ΔS), and Gibbs energy (ΔG) were evaluated as adsorption parameters. The process of adsorption of CV and MB dyes in the waste was predominantly endothermic and occurred spontaneously. WRBM samples proved to be a promising candidate for removing cationic dyes present in water.

Adsorption Behavior of Crystal Violet and Congo Red Dyes on Heat-Treated Brazilian Palygorskite: Kinetic, Isothermal and Thermodynamic Studies.

The effect of heat treatment on the adsorptive capacity of a Brazilian palygorskite to remove the dyes crystal violet (CV) and congo red (CR) was investigated. The natural palygorskite was calcined at different temperatures (300, 500 and 700 °C) for 4 h. Changes in the palygorskite structure were evaluated using X-ray diffraction, X-ray fluorescence, thermogravimetric and differential thermal analysis, N2 adsorption/desorption and Fourier transform infrared spectroscopy. The adsorption efficiency of CV and CR was investigated through the effect of initial concentration, contact time, temperature, pH and dosage of adsorbent. The calcination increased the adsorption capacity of palygorskite, and the greatest adsorption capacity of CV and CR dyes occurred in the sample calcined at 700 °C (Pal-700T). The natural and calcined samples at 300 and 500 °C followed the Freundlich isothermal model, while the Pal-700T followed the Langmuir isothermal model. Adsorption kinetics results were well described by the Elovich model. Pal-700T showed better adsorption performance at basic pH, with removal greater than 98%, for both dyes. Pal-700T proved to be a great candidate for removing cationic and anionic dyes present in water.