Efficient abstraction of nickel(II) and manganese(II) ions from solution onto an alkaline-modified montmorillonite

We tested alkaline-activated montmorillonite as a low-cost adsorbent for simultaneous removal of Ni(II) and Mn(II) ions from solution. The experiment was performed by batch adsorption to evaluate the effects of pH, initial metal ion concentration, particle size, adsorbent dose, contact time and temperature on adsorption. Alkaline modification of montmorillonite increased the specific surface area from 23.2 to 30.7 m2/g and the cation exchange capacity from 90.78 to 94.32 mEq/100 g. The adsorption capacity of the montmorillonite for Ni(II) and Mn(II) ions increased with alkaline modification. The adsorbent was characterized by Fourier transform infrared, X-ray diffraction and scanning electron microscopy. When four isotherms, the Langmuir, Freundlich, Temkin and Dubinin–Radushkevich models, were applied to the experimental data, the best fit was obtained with the Freundlich model. The kinetic data were analysed with pseudo-first order, pseudo-second order, Elovich and intraparticle diffusion rate equations; greater conformity was found with the Elovich equation. Thermodynamic studies revealed a spontaneous, endothermic physical adsorption process.