Potential application of termite mound for adsorption and removal of Pb(II) from aqueous solutions

Abstract

The morphological and mineralogical composition of a termite mound from Ilorin, Nigeria was investigated with a view to understand its sorption properties. The termite hill soil was subjected to some spectroscopic analyses such as X-ray fluorescence (XRF) and Scanning Electron Microscopy. The XRF results revealed that the adsorbent contains a large fraction of Silicon, Iron and Aluminium minerals. The organic matter (OM) content expressed as percentage carbon was 3.45% while the high value of cation exchange capacity of 14.0 meq/100 g is in agreement with high percentage OM, which signifies high availability of exchangeable ions. The maximum Pb(II) adsorption capacity of the mound was found to be 15.5 mg/g. Batch adsorption experiments were carried out as a function of contact time, ionic strength and pH. Maximum and constant adsorption was observed in the pH range of 2–5.5. The experimental results of Pb(II) adsorption were analyzed using Langmuir, Freundlich, and Temkin isotherms. The Langmuir and Temkin isotherms were found to fit the measured sorption data better than Freundlich. The constants obtained from the Langmuir model are maximum sorption value, Qm = 18.18 and Langmuir energy of adsorption constant, b = 0.085, while the constants of the Freundlich model are the intensity of adsorption constant, n = 0.134, and maximum diffusion constant, Kf = 1.36. The adsorption data for Pb(II) was found to fit well into the pseudo-second order model. Desorption experiment was conducted using different concentrations of leachant and this was repeated three times to determine the life span of the adsorbent. It was observed that 0.2 M HCl had the highest desorption efficiency for reuse.