Comparative cadmium adsorption study on activated carbon prepared from aguaje (Mauritia flexuosa) and olive fruit stones (Olea europaea L.)

• We use a new renewable precursor material to get activated carbon.
• Two precursors are used in order to get activated carbon at the same conditions.
• The sample AG0.75_600 shows a high mesoporous area and high superficial acidity.
• AG0.75_600 has the highest adsorption capacity at the lowest impregnation ratio.
• AG0.75_600 is a potential adsorbent for removing heavy metal ions.

This study assesses the capacity of activated carbons, prepared from Mauritia flexuosa (AG series) and Olea europaea L.   (OL series) fruit stones, to adsorb cadmium ions. These carbons were activated chemically through phosphoric acid solution, using impregnation ratios of 0.75, 1.0, and 1.5gH3PO4/gprecursor1.5gH3PO4/gprecursor. The impregnated precursor material was subsequently activated at 400, 500 and 600 °C. The physicochemical characteristics of precursors and activated carbons were analyzed by thermogravimetric analysis (TGA), nitrogen adsorption–desorption isotherm (SBET), Boehm’s titration, and scanning electron microscopy (SEM). Kinetic assays were evaluated from solutions containing 10 ppm of cadmium (Cd(II)). Within each series, the activated carbons with higher adsorption capacity turned out to be AG0.75_600 and OL1_600 with 8.14 and 9.01 mg g−1, respectively at pH 2. Among 26.33 and 24.83 mg g−1, respectively at pH 5. Both activated carbons were characterized by the highest mesoporous area and acidic surface functional group compared to other activated carbons (of each series). The obtained isotherm correlations fit better according to a Langmuir model and this was confirmed with a Redlich–Peterson model (with G values close to 1). The adsorption process of cadmium ions took place mostly in adsorption sites of uniform energies.