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

摘要

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