In the present study three types of agricultural waste materials, peanut shell, lapsi seeds and energy grass were
carbonized by the same carbonization methods using mineral acids at elevated temperature. The resulted charcoals
having approximately 60% carbon content were applied as low-cost adsorbents for the removal of Cr(VI)
fromaqueous solutions. The sorption kinetics at pH=1 and the sorption isotherms at different pHswere studied.
Chromium concentration was measured by flame atomic absorption spectrometry (F-AAS) in the residual solution
by an indirect way andwas additionally checked by direct measurement using an XRF spectrometer. The adsorption
isotherms weremodeled by Langmuir and Redlich–Peterson equation. In order to achieve the maximal
adsorption pH=1 was found to be optimal at every investigated charcoals. The maximal adsorption capacity
varied between 205 and 230; 85 and 138; 34 and 40; and 30 and 33 mg g−1 at pH=1; 2; 3; and 4 respectively
at the different charcoals. The obtained pseudo-second-order rate constant was k2=4.0×10−4 g mg−1 min−1
at each type of activated carbons. The bond of Cr(VI) to the functional groups of charcoal seems to be irreversible
in the case of dried Cr(VI) saturated charcoals. Both the model studies and the dissolution experiments provided
evidence for this result. Itwas supposed on the basis of our results, that Cr(VI) bonds chemically to the activated
carbon consequently the Cr(VI) saturated charcoals had no more contaminating effect in the environment.