Adsorption and reduction of platinum(IV) chloride complex ions on activated carbon

The adsorption kinetics of platinum(IV) chloride complex ions on the activated carbon Norit GF40 was investigated. Experiments were carried out at different initial concentrations of Pt(IV) chloride complex ions, temperature, rate of mixing and pH. It was found that the value of activation energy of the studied process is equal to 19.7 kJ/mol. From the ICP MS analysis it was confirmed that platinum ions (Pt(IV) and Pt(II)) are removed from the solution due to the adsorption and are further reduced to the metallic state. Such mechanism was confirmed by XPS analysis which showed that on the carbon surface three forms of platinum species, i.e. Pt(0), Pt(II) and Pt(IV), exist. The presence of platinum in the solution at different oxidation states was also confirmed spectrophotometrically by identification of their characteristic absorption bands. The metallic form of Pt present on the surface of activated carbon was observed in the form of small spherical islands with the diameter not exceeding 500 nm. Those islands consist of smaller, flake-shape particles with a thickness of about 35 nm.