Adsorption Characteristics of Cadmium from Aqueous Solutions by Acid-Treated Oil Shale Ash

A by-product oil shale ash from Huadian was treated with 5 mol/L nitric acid in order to enhance its adsorption capacity. The acid-treated oil shale ash was used as a low cost adsorbent to remove of cadmium from aqueous solutions. The adsorption capacity of samples to remove of cadmium was evaluated by a series of experiments, and the test results indicated that the adsorption capacity was found to increase with increasing the initial concentration of nickel ions solutions, adsorbent dosages, temperature, and pH of solutions. Langmuir adsorption model was used to fit the adsorption isotherms of raw ash and acid-treated ash with R² of 0.9938 and 0.9954 at 25degC, respectively. When the initial concentration was 100 mg/L, the pH was 6.0, the particle size was <75 mum, the adsorbent dosage was 15 g/L, the agitation speed was 400 r/min and the adsorption temperature was 25degC, the uptake values of raw ash and acid- treated ash were 7.78 mg/g and 10.53 mg/g, respectively.