Adsorption of lead(II) onto organic acid modified rubber leaf powder: Batch and column studies

• Citric acid and monosodium glutamate have been successfully functionalised onto rubber leaf surface and were compared.
• Pb(II) adsorption onto the surface fits the pseudo-second order kinetic model.
• CARL follows Langmuir type adsorption but MGRL follows Freundlich type adsorption.
• Adsorbents can be used in the continuous column mode.
• Maximum adsorption capacities for the adsorbents, CARL and MGRL are 97.19 and 109.95 mg/g, respectively.

This study evaluated the Pb(II) sorption capacities of two chemically modified biosorbents which are citric acid modified rubber leaf powder (CARL) and monosodium glutamate modified rubber leaf powder (MGRL). The raw rubber leaf powder (RLP) was modified to improve its effectiveness in removing the Pb(II) ions in an aqueous solution. CARL was prepared by esterification of citric acid onto the cellulose structure while MGRL was prepared by functionalising monosodium glutamate onto the epoxy activated rubber leaf powder. The sorption performance of the sorbents was examined by pH, kinetics and isotherm experiments. The adsorption of Pb(II) was much more favourable at higher pH. The rate limiting step in the adsorption process for both adsorbents was chemisorption and both adsorbents had a better fitting to the pseudo-second order kinetic model. The maximum capacities of Pb(II) calculated by the Langmuir isotherm by CARL and MGRL were 97.19 and 109.95 mg/g, respectively. In column experiments, the breakthrough time was found to decrease from 25 to 5 min for CARL and 37.5 to 10 min for MGRL with an increase in Pb (II) concentration from 20 to 60 mg/L. The Thomas and Yoon–Nelson models had a good fit with the fixed bed column data. Different column parameters such as column adsorption capacity and 50% adsorbate breakthrough were calculated. It was found that the adsorption capacity and performance of MGRL was superior to CARL in both batch and fixed bed column studies.