Characterization of different types of bentonites and their applications as adsorbents of Co(II) and Ni(II)

Abstract

In this research, the natural bentonite clays collected from different areas in Iran were utilized as adsorbent to study the removal behavior of different Iranian bentonitic clays vs. Ni(II) and Co(II) from their aqueous solutions. The original bentonite clays were characterized with the help of pH, Swell Index, Sediment Index, granulometric (screen) analysis, cation exchange capacity measurement, powder X-ray diffraction, X-ray fluorescence, scanning electron microscopy with energy dispersive atomic X-ray; Brunauer, Emmett, and Teller surface area measurements; and Barrett, Joyner, and Halenda pore size distribution analysis, Fourier transform infrared spectroscopy. While the thermal stability of the samples was studied using thermo gravimetry (TGA-DSC), adsorption experiments were conducted under some constant solution conditions and the removal of Co²⁺ and Ni²⁺ ions from their aqueous solutions was tested on various bentonite types and certain bentonite characteristics including pore size, surface properties, etc. The maximum adsorption of 92% took place on sample A1 in the removal process of Co²⁺ and Ni²⁺. The adsorption capacities followed the order of Co²⁺> Ni²⁺ in single-component systems for sample A2 and A3. The results showed the prevailing metal removal process was adsorption and cation exchange with the initiation in precipitation.

Keywords:

• Adsorption
• Bentonite
• Co(II) and Ni(II)
• Nano-porous Montmorillonite
• Cation Exchange