A green adsorbent for the removal of BTEX from aqueous media

This study reports on the application of ostrich bone wastes (OBW) covalently modified with citric acid as a bioadsorbent for the uptake of various volatile organic compounds such as benzene, toluene, ethylbenzene, and p-xylene. The influence of experimental parameters on the removal behavior was assessed by changing the contact time, the amount of adsorbent, initial pH, temperature, chemical modification process, and initial pollutant concentration. The order of the adsorbate removal on OBW-NaOH-CA was obtained as follows: p-xylene > ethylbenzene > toluene > benzene. The adsorption kinetics of the organic pollutants has been studied in terms of pseudo-first- and -second-order kinetics, and Freundlich and Langmuir isotherm models have also been applied to the equilibrium adsorption data. The results showed that the adsorption process was spontaneous and endothermic in nature and followed a pseudo-second-order kinetic model. The presence of the free carboxyl groups of citric acid raises the density of electron donating groups (with the carboxylic oxygen acting as an electron-donor) on the modified ostrich bone, that is, increasing its favorable interaction with the organic pollutants due to their weakly positive charge at different pH values. The results showed that the immobilized CA on the OBW shifted the surface charge towards a negative value, which promoted the adsorption of BTEX. Furthermore, the prepared bioadsorbent could also be utilized to remove the organic pollutants from real water (Persian Gulf water).