Potential of Saudi natural clay as an effective adsorbent in heavy metals removal from wastewater

Abstract

This study aims to examine the potential of natural clay mineral from the southern part of Saudi Arabia as an effective adsorbent material for the removal of heavy metal ions of cadmium (Cd) and nickel (Ni) from aqueous solutions. The SEM analysis showed that clay particles had mixed shapes such as elongated rod-like and rectangular shape having rough corners with larger particles of 2-8 µm in size and smaller particles in the sub-micron size range. X-ray diffraction data revealed that clay particles had a good crystalline structure and composed of a mixture of various minerals including feldspar, illite, quartz, calcite, and gypsum. The BET surface area was found to be 35 ± 1 m ² /g and the average pore size and pore volume of 6.5 ± 0.5 nm and 5.7e-02 cc/g, respectively. The X-ray fluorescence analysis of clay showed main compounds of SiO₂ (47.33%), Al₂O₃ (18.14%), Fe₂O₃ (15.89%) with many others such as CaO, MgO, TiO₂, and K₂O in minor quantities. It was found that 1.2 g of clay removed up to 99.5% of Ni and 97.5% of Cd from 40 ppm aqueous solutions. The metal removal efficiencies were increased from around 95% up to 99% by increasing the pH of aqueous solutions from 4 to 11. The adsorption of Ni and Cd ions on Saudi clay was relatively fast, and up to 97% of ions were removed from solution within 45 min. The SEM-EDX and BET analysis for recycled clays further confirmed that the metal ions were removed from water through adsorption onto the clay. The experimental data fitted well with Langmuir and Freundlich isotherms. The maximum adsorption capacity of clay for Cd and Ni from isotherms was found to be 3.3 and 2.7 mg/g respectively. The findings of this study confirm the potential role of Saudi natural clay in wastewater treatment processes as a cheap, environment-friendly and safe natural adsorbent material.