Adsorption equilibrium and kinetics of polyvinyl alcohol from aqueous solution on powdered activated carbon

In this study, powdered activated carbon (PAC) was used to remove polyvinyl alcohol (PVA) from the aqueous PVA solution. The adsorption kinetics has been studied pertaining to various initial PVA concentration and PAC dosage. The rates of adsorption were found to conform to the second-order kinetics with good correlation. Boyd plot confirmed that external mass transfer was the rate-limiting step in the sorption process. The adsorption isotherm obtained resembled with H-type of isotherm, which indicated a high affinity of the solute for the sorption sites. The Freundlich model appeared to fit the isotherm data better than the Langmuir model. The thermodynamic parameters such as ΔH°, ΔS° and ΔG° were evaluated from the slope and intercept of linear plot of log Kc against (1/T) × 1000. The change in entropy (ΔS°) and heat of adsorption (ΔH°) of PAC was estimated as 1.45 kJ mol−1 K−1 and 365 kJ mol−1, respectively. The free energy of the adsorption at all temperatures was negative indicating a spontaneous process. The maximum PVA removal of 92% was obtained at a pH of 6.3 and contact time of 30 min for an adsorbent dose of 5 g/L.