Adsorption of chloride complexes of platinum group metals by silicas chemically modified simultaneously with mercaptopropyl and aminopropyl groups with various molar ratiosстатьяИсследовательская статья
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Аннотация:The adsorption behavior of chloride complexes of platinum group metals (Pd(II), Pt(II)/Pt(IV), Rh(III), Ir(III)/Ir(IV), Ru(III)/Ru(IV), Os(IV)/Os(VI)) on aminopropyl- and mercaptopropyl-functionalized silica was systematically studied as a function of concentration of grafted groups, ligand molar ratio, metal oxidation state, hydrochloric acid concentration, pH, temperature, and phase contact time. It was shown that kinetically labile chloride complexes of Pd(II), Pt(II), and Os(VI) are quantitatively extracted (recovery of 98-99%) at room temperature in the range of 6 M HCl - pH 6, with the time of attainment of adsorption equilibrium not exceeding 5 min due to complexation with mercaptopropyl groups of the adsorbents. In contrast, kinetically inert chloride complexes of Pt(IV), Rh(III), Ir(IV), Ru(III), Ru(IV), and Os(IV) are extracted via an anion-exchange mechanism by interacting with protonated primary amino groups of the adsorbents. Upon increasing the temperature or prolonged storage of the adsorbents with adsorbed platinum group metal ions, these ions migrate from the amino groups and coordinate with the grafted mercaptopropyl groups. Using electron paramagnetic resonance, luminescence, Fourier transform infrared spectroscopy, and diffuse reflectance spectroscopy, the interaction mechanisms of platinum group metal ions with the adsorbent?s functional groups and their oxidation states in surface complexes were determined.
