Removal of copper by oxygenated pyrolytic tire char: Kinetics and mechanistic insights

The kinetics of copper ion (Cu(II)) removal from aqueous solution by pyrolytic tire char was modeled using five different conventional models. A modification to these models was also developed through a modified equation that accounts for precipitation. Conventional first- and second-order reaction models did not fit the copper sorption kinetics well, indicating a lack of simple rate-order dependency on solute concentration. Instead, a reversible first-order rate reaction showed the best fit to the data, indicating a dependence on surface functional groups. Due to the varying solution pH during the sorption process, modified external and internal mass transfer models were employed. Results showed that the sorption of copper onto oxygenated chars was limited by external mass transfer and internal resistance with and without the modification. However, the modification of the sorption process produced very different results for unoxygenated chars, which showed neither internal nor external limitation to sorption. Instead, its slow sorption rate indicates a lack of surface functional groups. The sorption of Cu(II) by oxygenated and unoxygenated chars was also found to occur via three and two distinct stages, respectively.

Graphical abstractChange in pH with copper sorption at 297 K, initial concentration 25 ppm. The percentage of Cu removal onto oxygenated pyrolytic char (P550250) is much higher than that onto unoxygenated char (NoPPO).Figure optionsDownload full-size imageDownload high-quality image (69 K)Download as PowerPoint slideResearch highlights► The kinetics of copper ion (Cu(II)) removal by pyrolytic tire char was studied. ► Mechanistic insights into adsorption are provided. ► A reversible first-order reaction rate provided the best fit to the experimental data. ► Oxygenated tire chars were found to be able to precipitate copper from solution. ► Surface chemistry plays an important role in sorption processes.