Optimization of Carob Shells Biomass Activation by Nitric Acid for Heavy Metals Sequestration from Contaminated Water

Abstract

This study reports the use of agro-waste (carob shells) as a precursor for the synthesis of activated carbon by nitric acid activation. The prepared adsorbent was used for the removal of cadmium and cobalt ions from aqueous media. In order to optimize the preparation conditions for the high removal efficiency of heavy metals, the Box-Behnken design was used to correlate activation agent ratio g(HNO3)/g(carbon), reaction time, and activation temperature to the removal efficiency of metals. The experimental result shows that the rise in activation temperature strongly decreases the removal of both metals. This result suggests a low energy demand for the activation of carob shells by HNO3. The sample prepared at optimum conditions was characterized by DRX, SEM, FTIR, and surface groups titrations in order to obtain information on its structural, morphological, and surface properties. It has also been found that equilibrium data are well correlated to the Langmuir model with adsorption capacities of 125.52 and 69.01 mg/g, respectively, for Cd(II) and Co(II).