A Study of Polyacrylamide-Pumice Composite for Fast Removal of Copper Ions from Aqueous Solutions: Synthesis, Kinetics and Thermodynamics

In the present work, a polyacrylamide-pumice stone (PAAm-PMC) composite has been synthesized and used as an adsorbent for the fast removal of copper ions from wastewater. The PAAmPMC composite was synthesized by the conventional free radical polymerization method and characterization has been done by Fourier Transform Infrared Spectroscopy (FT-IR) and Scanning Electron Microscope (SEM). Effects of various parameters on the adsorption capacity of the synthesized PAAm-PMC composite were studied and optimized. The optimized values of various parameters found were: contact time (60 minutes), pH value of solution (6.5), composite dose (0.05 g), Cu(II) concentration (1500 mg/L), and temperature (323 K). The kinetic studies reveal that the rate of adsorption of copper on the composite, increases with time and the maximum adsorption achieved for copper ions is similar to 96 %. The fast adsorption kinetics followed pseudo-second-order kinetics when modified composites were used. Among three different isotherm models, Langmuir adsorption isotherm model has been found to be the best-correlated model with experimental data-based on a higher correlation coefficient with a maximum Langmuir loading of 500 mg/g. The positive entropy during the adsorption process for both the materials (Delta S-0= (55.6855 J/(mol.K) for PAAm and 151.0737 J/(mol.K) for PAAm-PMC at 303K) suggests, that the adsorption process is thermodynamically favorable and increases with the increase in temperature. Gibbs free energy values are found to be higher for composite material suggesting higher equilibrium constant values (Delta G(0) = -5.0191 kJ/mol for PAAm vs -8.0059 kJ/mol PAAm-PMC at 303K). Structural strength and stability of the synthesized composite can be accessed, as modified composites were used up to three times for the adsorption removal of Cu(II) ions from waste-water, after regeneration. These investigations confirmed that the synthesized PAAm-PMC composite can work as an effective adsorbent for the economical and fast removal of Cu(II) ions from wastewater.