Equilibrium and kinetic studies for Cd(II) adsorption from aqueous solution on Terminalia catappa Linn leaf powder biosorbent

Abstract

Terminalia catappa Linn,(TCL) leaf (almond leaf) powder was tested as a biosorbent in a batch adsorption system. The samples with and without Cd(II) adsorption were characterized using FTIR and SEM-EPMA techniques. Loading of Cd(II) onto to TCL powder resulted in shift of various band positions (5 to 51 cm(-1)) in the FTIR spectrum. The EPMA of Cd(II) loaded powder showed that Cd(II) was not uniformly distributed on the surface but only on specific sites. The experimental parameters chosen for adsorption studies were: pH (2.0 to 6.0), contact time (5 to 120 min), adsorbate concentration (50 to 500 mg L(-1)), adsorbent concentration (0.25 to 5.0 g per 50 mL adsorbate), anions and Pb(II) concentration. With the increase in pH from 2.0 to 4.0, Cd(II) adsorption increased from 0.86 to 13.79 mg g(-1) and with the further increase in pH to 5.5 only marginal increase to 14.12 mg g(-1) was observed. Presence of chloride, sulphate or Pb(II) adversely affected Cd(II) adsorption onto TCL. The kinetics of adsorption could be best described by the pseudo-second-order equation. The three equilibrium models namely, Langmuir, Freundlich and Redlich-Peterson fitted well to the isothermic experimental data for TCL with regression coefficients of > 0.97. The maximum uptake capacity of the biosorbent was estimated to be 35.83 mg g(-1).