Toxicologia Ambiental e Analítica

Evaluation of the Application of Carica papaya Seed Modified Feldspar Clay for Adsorption of Pb+2 and Cu+2 in Aqueous Media: Equilibrium and Thermodynamic Studies

Abstract

Kabir A Sanusi, Babayo A Umar and Isyaka M Sani

Feldspar clay sample obtained from Federal Institute of Industrial Research Oshodi (FIIRO), Lagos, Nigeria was modified with Carica papaya seed to obtain CPS-modified feldspar clay Composite. The SEM of modified and unmodified samples showed irregular crystal structures. FTIR results proved the surface modification of the Feldspar at –Al–O and –Si–O centers. The CPS-modified adsorbent presented with broader peaks of inner –OH. Modification of feldspar clay sample with papaya seed decreased its PZC from pH 4.34 to 3.50 while its Specific Surface Area (SSA) was increased from 12.58 m2g−1 to 18.64 m2g−1. Modification with Carica papaya seed increased the adsorption capacity of feldspar clay from 18.26 mg/g to 45.81 mg/g for Pb (II) and 12.57 mg/g to 46.18 mg/g for Cu (II) at 308°K. Increasing temperature and initial metal ions concentration was found to increase the adsorption of both metals onto both adsorbents suggesting an endothermic adsorption reaction. The simultaneous presence of electrolyte in aqueous solution with Pb and Cu (II) was found to decrease the adsorption capacity of CPS-modified adsorbent for Pb and Cu (II). The thermodynamic calculations for the modified feldspar clay sample indicated an endothermic nature of adsorption (ΔHmean+4.38 kJ mol−1 for Pb (II) and +3.81 kJ mol−1 for Cu (II)) and an increase in entropy as a result of adsorption of Pb (II) and Cu (II) (ΔSmean−21.75 J mol−1 K for Pb (II) and −18.32 J mol−1 K for Cu (II)). The small positive values of free energy change (ΔGmean) indicated that the adsorption of Pb (II) and Cu (II) onto the modified adsorbent may require some small amount of energy to make it more feasible. Modeling equilibrium adsorption data obtained suggested that CPS-modified adsorbent sample has homogeneous adsorption sites and fit very well with Langmuir adsorption model. CPS-modified feldspar clay sample show some very good potentials as a low-cost adsorbent for the adsorption of Pb (II) and Cu (II) from aqueous solutions.