Activated Carbon from Olive Wastes as an Adsorbent for Chromium Ions Removal

Adsorption of Chromium ions (VI) and (III) in aqueous solution was investigated using activated carbon prepared from olive wastes, by one step physical activation with steam. After adsorbent material characterization using adsorption capacity of methylene blue, iodine and phenol, BET surface area, Fourier Transform InfraRed (FT-IR) spectroscopy, pHpzc, surface functions based on the Boehm method and, Scanning Electron Microscopy (SEM), the effect of different parameters (initial pH, absorbent dosage, initial concentration of solutes, time) on the adsorption of chromium ions were carried out in a batch system. The obtained activated carbon has a large specific surface area of 1050,9 m2/g and good adsorption capacity for iodine (1017 mg/g) and methylene blue MB (349 mg/g), which confirm that its structure is essentially composed of micropores (61 % of the surface) and mesopores. It has a basic chemical nature. Experimental results showed that the adsorption capacity of the prepared activated carbon was strongly dependent on solution pH. It was found that the initial pH of 2.0 was most favorable for Cr(VI) adsorption, and basic pH was best for Cr(III) removal. The adsorption process was studied using two kinetic models (pseudo-first order and pseudo-second order) and three functions isotherms (Langmuir, Freundlich, Temkin). The results showed that the adsorption process follows the pseudo-second order kinetics and the adsorption data were found to agree with the Langmuir isotherm model. Maximum adsorption capacity for Cr (VI) was 74,9 mg/g at pH 2, and 14,3 mg/g at pH 9 for Cr (III), and was comparable to results reported by other researchers working on activated carbon prepared from various solid wastes. Temperature effect was determined using the thermodynamic parameters. Negative values of ΔH0 and ΔG0 proved the feasibility of the adsorption process with its spontaneous and exothermic natures. Tests of desorption were performed in three different media: neutral (distilled water), acidic (2N hydrochloric and acetic acid solutions) and alkaline (2N NaOH solution). The magnitudes of desorption efficiency in the acetic acid medium were 94% and 71% for Cr(VI) and Cr(III) respectively.