Characterizing and modeling of oak fruit shells biochar as an adsorbent for the removal of Cu, Cd, and Zn in single and in competitive systems

Abstract

In this study, the oak fruit shells (OFS) were used to prepare a biochar (OFSBC) obtained by one-step pyrolysis process at 700 °C. The obtained adsorbent was characterized to evaluate physicochemical properties and tested for the adsorption of Cu2+, Cd2+, and Zn2+ in an aqueous solution. The results proved that the prepared adsorbent has a large specific surface area (SBET = 520 m2/g), a large number surface functional groups and a developed porosity. The adsorption equilibrium metal ions onto OFSBC was reached after 4 h of contact time with a removal efficiency 95.29 %, 94.63 %, 82.99 % for Cu2+, Zn2+, and Cd2+, respectively. The Avrami fractional order was the suitable model that describes the kinetic adsorption process of metal ions onto OFSBC. The Freundlich isotherm model fits the experimental data slightly better than other models in single systems. The maximum adsorption capacities of Langmuir that were obtained were in the following order 41.97 mg/g, 41.79 mg/g, and 27.00 mg/g for Cu2+, Cd2+, and Zn2+ ions, respectively. In binary systems the equilibrium adsorption of these ions onto OFSBC was found to be antagonistic in nature and is well described by the extended Freundlich model. The thermodynamic study revealed that the adsorption of these metals was spontaneous and endothermic in nature.The regeneration of the adsorbent was tested in 5 adsorption/desorption cycles, with a slight decrease from cycle 1 to cycle 5. The prepared adsorbent could serve as promising material to remove Cu2+, Cd2+ and Zn2+ effectively from wastewater.