Treated oil shale ash and its capacity to remove Cd and Pb from aqueous solutions

Cadmium (Cd) is the most highly toxic heavy metal even at a trace level. In this study, the oil shale ash treated material was used as an adsorbent to remove cadmium and lead (Pb) metals/ions from aqueous solutions. The absorbent treated oil shale material was characterized prior to experimental work using X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The effects of multiple factors on percent metal removal, including contact time, initial ions concentration and pH, are investigated. Results show that the adsorption capacities of Pb and Cd are 29.15 and 23.81 mgg-1, whereas removal efficiencies are 56% and 48% in 10 minutes, respectively. Removal efficiency and time of equilibrium are affected by the metal atomic weight (Pb 207.2 u and Cd 112.4 u) and pH values. The equilibrium isotherms were analyzed using Freundlich and Langmuir isotherm models and described by the Freundlich isotherm model indicating a heterogeneous surface of the adsorbent. The calculated Langmuir adsorption constant and maximum adsorption capacity of adsorbent, KL and qmax, are 1.313*10-2 and 25.25, respectively. The Freundlich adsorption constant KF and the characteristic constant of the Freundlich isotherm n are 0.5234 and 1.39, respectively.