Oil shale ash, which is a by-product from oil shale processing, was converted into an adsorbent by alkali hydrothermal activation using sodium hydroxide. The alkali-treated ash was studied for its capacity to remove lead and cadmium ions from aqueous solutions. The results of the study showed that the adsorption of lead and cadmium ions by the modified oil shale ash depended on adsorbent concentration, ash particle size, contact time and pH of solution. When the initial concentration of an aqueous solution was 10mg/L and that of the adsorbent 5g/L, 91% of lead and cadmium ions was removed from the solution. The adsorption isotherm data of the alkali-treated oil shale ash were fitted to the Langmuir isotherm model with R2 of 0.9995 and 0.9963 at 20 ℃. The scanning electron microscopic (SEM) analysis showed that after modification the porosity of the ash increased and, as a result, complex spatial networks were formed, which provided sufficient space for the adsorption of lead and cadmium ions. The energy dispersive spectrometric (EDS) analysis confirmed the adsorption of lead and cadmium ions in the modified oil shale ash sample, while in the control sample these elements were absent. Its excellent adsorption capacity and efficiency makes the alkali-treated oil shale ash a good candidate for heavy metals removal from wastewater.
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