Psidium guvajava L Leaf Powder — A Potential Low-cost Biosorbent for the Removal of Cadmium(II) Ions from Wastewater

In the present investigation, an evaluation has been made of the adsorption of Cd(II) ions onto Psidium guvajava L leaf powder (PGL). Scanning electron micrographs of the powder as-prepared showed that PGL possessed an irregular texture consisting of globular and elongated grains. The porosity of the structure was also noted. After adsorption of Cd(II) ions, ca. 30% of the powdered grains on the resulting surface showed a pixel concentration of Cd(II) ions, indicating the adsorption of Cd(II) ions by selective grains. The FT-IR spectra of the as-prepared powder and the Cd(II) ion-loaded powder were similar but the absorption bands were shifted by 5–35 cm⁻¹ after the adsorption process. The experimental parameters chosen for adsorption studies included time, pH, particle size, temperature, adsorbate, biosorbent, anions and Pb(II) ion concentrations.

The kinetic data followed linear and non-linear pseudo-second-order kinetics. The adsorption of Cd(II) ions increased from zero to 60.39% as the pH of the aqueous solution was increased from 2 to 3.5, with a further increase in pH to 5.5 resulting in a marginal increase in the extent of adsorption to 63.7%. The isothermal data were well fitted by the Freundlich adsorption model. On the basis of the Langmuir isotherm model, the maximum loading capacity was calculated as 31.15 mg/g. The presence of chloride or sulphate anions had an adverse effect on the Cd(II) ion uptake by PGL. Lead(II) ions were adsorbed preferentially from binary Cd(II)/Pb(II) ion solutions, thereby decreasing the Cd(II) ion uptake. The thermodynamic parameters for the process were also estimated.