Sorption of Cd(II) and Pb(II) ions by Nanolimestone from underground water samples from Tehama region of Saudi Arabia

Abstract

Powdered Nano limestone (NLS)  has been investigated as an un-expensive  adsorbent for heavy toxic metals removal from aqueous solutions as cadmium and lead. Batch experiments were carried out, The favorable pH for maximum metals adsorption was at 6.8 for both. The surface area increased in case of  NLS up to 6.2 m²/g.  The adsorption capacity calculated by Langmuir equation was 75.1 mg/g for Cd(II)  and 68.4 for Pb(II) ions at pH 6.8. The adsorption capacity increased with temperature and the kinetics followed a First-order rate equation for both. The enthalpy change (ΔH⁰)  was 25.4 Jmol⁻¹ for Cd(II)  and 20.8 Jmol⁻¹  for Pb(II), while  entropy change (ΔS⁰) was 41.6 JK^-1mol^-1 for Cd(II)   and 38.7 JK^-1mol^-1  Pb(II), which indicate that adsorption process was endothermic and spontaneous in nature. About 25  collected samples of groundwater were tested and found to be contaminated with cadmium and lead elements with different rates, with using NLS as adsorbent able to remove both metals from the samples.  All of the results suggested that the NLS is excellent nano-adsorbents for cadmium and lead contaminated water samples.