OPTIMIZATION OF ADSORPTION OF Pb (II) AND Cr (VI) FROM AQUEOUS SOLUTION USING MODIFIED FELDSPAR COMPOSITE: ISOTHERM AND KINETIC STUDIES

In this study modified feldspar composite (MFC) adsorbent based on feldspar and Theobroma cacao podas (TCP) was prepared, characterized and utilized for adsorption of Pb (II) and Cr (VI) in aqueous solution. The results showed that the cation exchange capacity of the modified feldspar composite (30.66 ± 0.21 meq/100 g) was 5 times higher than that of raw feldspar (6.42 ± 0.45 meq/100g). More so, the novel biohybrid material, MFC has a surface area of 53.60 ± 0.3 m2/g and particle size of 105.4 ± 0.18. X-ray diffraction peaks revealed that after the modification process, there is only slight shift in the position of some diffraction peaks of feldspar and the composite material suggestive of the retention of the crystalline properties of the feldspar in the novel composite (MFC). Infrared spectroscopy (FTIR) spectra showed that some functional groups present in the two starting materials were also available on the surface of the composite (MFC) indicating that the intercalation of TCP biomass into feldspar surface was successful. Response surface methodology (RSM) via a five-levels central composite design (CCD) was applied for optimization of metal adsorption onto the adsorbent in 32 experiment runs considering the effect of pH, adsorbent dose, adsorbate concentration and contact time. Optimization results showed that the predicted and experimental values of Pb (14.021, 14.148 mg/g) and Cr (3.428, 3.504 mg/g) were close at the optimum condition of (pH 2, 5, 6; 0.5 g; 100 mg/L; 60-120 min and 3000K). Results of ANOVA analysis revealed the adequacy of the model with the good correlation between R2 values (0.9916-0.9998) and adjusted R2 (0.9919-0.9986) and F value of (≥ 147). Results showed that Pb (II) ions adsorption onto the adsorbents was well fitted to the Langmuir isotherm model while the Cr (VI) ions uptake onto FS and MFC adsorbents followed Freundlich isotherm model. The results of the kinetic studies showed that rate of Pb (II) removal followed pseudo second order model while the rate of adsorption of Cr (VI) onto the FS and MFC adsorbents best fitted pseudo first order model. Owing to its improved cation exchange capacity and eco-friendliness, the modified feldspar composite have a good potential application in wastewater treatment besides other industrial explorations.