Palladium(II) Chloride Complex Ion Recovery from Aqueous Solutions Using Adsorption on Activated Carbon

The process of palladium­(II) chloride complex ion adsorption on activated carbon was investigated. The influence of variable parameters such as the initial concentration of the Pd­(II) complex (from 0.04 to 2.25 mmol·kg–1) and temperature (from 294 to 348 K) was determined. Experiments were conducted in the solution with pH equal to 0 and 1. It was found that the Freundlich adsorption isotherm describes the process better than the Langmuir model. The observed sorption capacity as high as q 294K = 42.4 mg·g–1 and q 323K = 67 mg·g–1 for activated carbon was found at 294 and 323 K, and it is increasing with temperature increase. The obtained results showed that the palladium­(II) complex may react with functional groups present on the surface of activated carbon. The thermodynamic parameters such as the equilibrium constant and heat and entropy of adsorption were derived. The enthalpy value is equal to −6.7 kJ·mol–1, and the entropy is equal to −23 J·mol–1·K–1. It is suggested that, during chemisorption of palladium­(II) chloride complex ions, the palladium dichloro-oxide or PdCl2 is formed on the surface of activated carbon.