Adsorption of reactive dyes from aqueous solution by dirty bentonite

• Magnesium hydroxide coated bentonite was elaborated using novel method.
• High maximum adsorption of reactive dyes on dirty bentonite achieved.
• Kinetic data were well described by the pseudo-second order model.
• The pH exerts significant impact on ion adsorption with variable charge surfaces.

The preparation of magnesium hydroxide coated bentonite, B–Mg(OH)2 composite, and its capacity to remove anionic reactive dyes; Procion blue HP (PB) and Remazol brilliant blue R (RB) from aqueous solution were reported in this study. The adsorbent was characterized by X-ray fluorescence analysis, X-ray powder diffraction, thermal gravimetric analysis, Brunauer Emmett Teller surface area analysis; scanning electron microscopy, and Fourier transform infrared spectroscopy. The effectiveness of B–Mg(OH)2 composite to remove dyes was examined at different initial concentrations, pH, temperature and ionic strengths. At pH = 2, the maximum dye adsorption was found as 98.2% for RB and 87.8% for PB. Kinetic studies revealed that adsorption follows a pseudo-second-order model, and rate constants were evaluated. The Langmuir monolayer adsorption capacities of PB and RB in aqueous solution were estimated at 298 K as 40.22 and 66.90 mg/g, respectively. A temperature uptake from 278 K to 313 K induced an increase of adsorption for both dyes and the process was found to be physiosorptive, endothermic and spontaneous. Higher concentration or more valence of anions of electrolytes in dye solution caused decreasing dye adsorption efficiency of B–Mg(OH)2 composite.

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