Physico-Chemical Removal of Cu (ii) and Cd (ii) Ions from Contaminated Water Using Recyclable Montmorillonite-Cellulose Nanocomposite

Abstract

Economic and efficient remediation of contaminated water has been studied extensively, however very little attention being paid on the fate of the spent adsorbents. The present work aimed at synthesizing a nanocomposite adsorbent, its characterization and determination of its adsorption efficiency and capacity in removing Cu (II) and Cd (II) ions from contaminated water. The nanocomposite was synthesized by intercalating biopolymer (cellulose) molecules into the interlayer spacing of sodic-Montmorillonite, Na-MMT. The adsorbent was thereafter characterized comprehensively by X-ray diffraction (XRD) to determine the degree of intercalation, Fourier transform infrared spectroscopy (FTIR) to determine the chemical structure by applying IR radiation to the sample, X-ray fluorescence (XRF) to determine the mineralogical composition, Scanning electron microscope (SEM) to describe the morphology and surface area measurement by Brunauer-Emmett-Teller (BET) isotherm studies. Batch studies were carried out on Cu (II) and Cd (II) ions adsorption to determine the influence of adsorption parameters such as; initial metal ion concentration, pH, contact time, adsorbent dosage and temperature on the metal ions uptake. Optimal adsorption efficiencies were achieved at; a contact time of 35 minutes, adsorbent dosage of 80 and 140 mg/50 ml for the adsorption of Cu (II) and Cd (II) ions, respectively, pH of 4 using 20 mg/L solutions and at lower temperatures. The data obtained from batch experiments had highest agreement with Freundlich isotherm with R2 being 0.956 and 0.992 for the adsorption of Cu (II) and Cd (II) ions, respectively. The adsorption capacities (Kf) were 16.1 mg/g and 11.1 mg/g for Cu (II) and Cd (II) ions, respectively. Pseudo-second order model gave the best fit with the experimental data for adsorption kinetics study with the calculated qe values being in par with experimental values and higher R2 values of 0.993 and 0.998 for Cu (II) and Cd (II) ions, respectively. From thermodynamic studies, the negative values of ΔG⁰ and ΔH⁰ indicate that the adsorption of Cu (II) and Cd (II) ions was spontaneous and exothermic, respectively. The negative values of ΔS⁰ indicate that the adsorption process resulted into reduced randomness at the solid/liquid interface. Aqueous ammonia exhibited the best regeneration efficiency for the spent adsorbent materials with a 94 % removal efficiency of Cu (II) ions at the 20th adsorption cycle. The results indicate that MMT-cellulose nanocomposite material has a great potential for use in water remediation strategies.