Equilibrium and kinetics of lead adsorption onto tyre char

The disposal of the waste tyres represents one of the most difficult global problems ever encountered. Pyrolysis of waste tyre is considered as an alternative process for recovering some of the value in waste tyres. The process is very energy intensive. There will be 30-40 weight % solid tyre char produced; hence the process economy depends strongly on its application and market value. In this study, the tyre char was investigated as an adsorbent to remove lead from aqueous solution. The maximum lead adsorption capacity was 135 mg/g at pH of 5. At low pH (< 3.75), less adsorption was observed due to the electrostatic repulsion between Pb2+ and the positively charged external surface of the tyre char. At higher pH (> 3.75), the external surface became negatively charged, resulted in a higher lead adsorption. The adsorption mechanism was quite complex, and three possible mechanisms were identified, including ion exchange, surface complex formation and adsorption. The isotherm was best fitted with Langmuir-Freundlich isotherm with a Langmuir monolayer capacity of 135.5 mg/g. The experimental data were analysed using adsorption kinetic models and the pseudo-first order equation was found to be the best fit equation for the adsorption of lead ions onto the tyre char