Adsorption of methylene blue and zinc ions on raw and acid-activated bentonite from Morocco

Adsorption of methylene blue (BM) and zinc ions on raw and acid-activated Moroccan bentonite composed of montmorillonite (88 mass%), a mixture of quartz and K-feldspar (9 mass%), calcite (3 mass%) and insignificant amounts of organic matter was evaluated at 25 °C using UV–visible and atomic absorption spectrometry. The adsorption capacity of MB and Zn ions by raw bentonite were about 2.2 and 1.1 mmol/(g of bentonite) and the best-fit isotherm models were those of Harkins–Jura and Langmuir. Acid-activation of the bentonite reduced the maximum uptake of MB and Zn ions by 30 and 95% and the best-fit models of the isotherms were Freundlich and Dubinin–Radushkevich for MB and Zn ions respectively. The reduced adsorption was associated with partial collapse of the montmorillonite particles and the formation of amorphous silica.