Investigation of a basic dye adsorption from aqueous solution onto raw and pre-treated bentonite surfaces

The effects of temperature, pH and ionic strength on the adsorption of crystal violet (CV+) by raw, Ni-saturated (Ni-), Co-saturated (Co-) and Zn-saturated (Zn-) bentonite samples were investigated. The amounts of CV+ adsorbed in equilibrium at 298.15 K were 0.27, 0.37, 0.49 and 0.54 mmol g−1 bentonite, which correspond to 108%, 148%, 196% and 216% of the cation exchange capacity (CEC) of the raw, Ni-, Zn- and Co-saturated bentonite samples, respectively. The adsorption of the dye on these samples is pH-independent within the range (2.5–8.5), and it increases with ionic strength from 0 to 0.6 mol l−1. Thermodynamic and Langmuir parameters showed that cation-saturated bentonite samples have relatively stronger ability than the raw bentonite towards the crystal violet (CV+) cation.