Effect of montmorillonite content in natural Saudi Arabian clay on its adsorptive performance for single aqueous uptake of Cu(II) and Ni(II)

Abstract

The effect of montmorillonite content on adsorptive performance of natural Saudi Arabian clay for aqueous uptake of Cu(II) and Ni(II) was investigated under kinetic and equilibrium batch studies. The clay and bentonite used were characterized using scanning electron microscopy (SEM), Brunauer-Emmet-Teller (BET), cationic exchange capacity (CE), energy dispersive X-ray (EDX) and X-ray diffraction (XRD) techniques. The clay was composed of kaolinite and muscovite with lower quartz and calcite contents, while the bentonite was mainly montmorillonite mineral possessing surface area of 20.83 and 44.27 m2/g, respectively. Increase in montmorillonite content in the clay significantly, resulted in decrease in Cu(II) adsorption capacity while increasing the capacity for Ni(II) adsorption. Equilibrium time was found to increase considerably as the montmorillonite content was increased and was higher for the clay compared to the bentonite with 16.38 and 8.66 mg/g maximum adsorption capacities for the metal ions, respectively. For both metal ions and the different montmorillonite content, the experimental data predominantly, fitted pseudo-second-order model (R2 = 0.96–0.999) while both Langmuir and Freundlich isotherm models described well the two ions removal mechanisms (R2 = 0.91–0.99). The two metal ions exhibited divergent behaviors for having distinctive affinities towards the clay and bentonite surfaces, respectively. This suggests that proportion of montmorillonite in clay adsorbents is susceptible to influence different metal ions removal from water in different manner.