Adsorption of Cr(VI) ions onto powdered activated carbon synthesized from Peganum harmala seeds by ultrasonic waves activation

Chromium is a toxic and carcinogenic heavy metal that is found in high concentrations in industrial liquid tanning wastewater. Therefore, the elimination of this element from the wastewater to prevent its entry into the aquatic environment, which is the objective of this study, is of prime importance. To start with, the powdered activated carbon (PAC) was prepared via activation of the Peganum harmala seeds (PPS) using ultrasonic waves. Subsequently, its ability, as an adsorbent, to capture Cr(VI) ions from the wastewater was examined at different conditions. The characterization study revealed the successful preparation of PAC with high activation of PPS. In addition, it was found that the prepared PAC possessed excellent adsorptive properties in terms of morphology, functional groups, surface area, and pore size. The kinetic and isotherm studies established that the adsorption process was simultaneously comprised of chemical and physical reactions of Cr(VI) ions on the multilayer and heterogeneous adsorption sites of the PAC. The removal efficiency of 20 mg/L Cr(VI) concentration by 10 g/L PAC concentration of > 99% was reached at pH = 3, mixing speed = 200 rpm, and contact time = 30 min. These results demonstrated the excellent ability of PAC for the removal of Cr(VI) ions from contaminated solutions via the adsorption process. Therefore, this study recommends that PAC that is prepared from the activation of PPS by ultrasonic waves be used as a highly efficient treatment agent in the adsorption process of Cr(VI)-loaded wastewater.