Sorpcja chromianów na tlenkach żelaza i manganu w zależności od odczynu

Selected synthetic iron and manganese oxides: goethite, ferrihydrite: pyrolusite and mixed MnOx were examined in their capacities to adsorb chromium(VI) from dichromate solutions in the wide range of solution pH: 3.0 - 9.0. Process of chromium sorption showed a strong dependence on pH. The most relevant effects of Cr(VI) sorption were observed under acidic conditions, at pH below 5.5. The efficiency of chromium removal from solution depended strongly on initial Cr concentration which affected solid phase: solution equillibria. All the oxides examined differed in their sorption capacities. Maximum Cr(VI) sorption capacities of iron oxides were estimated as: 13.4 mmol Cr(VI)/100 g for goethite and 47.3 mmol Cr(VI)/100 g for ferrihydrite and proved to be much higher than those of manganese oxides (3.9 - 7.3 mmol Cr(VI)/100 g). Atime necessary for reaching the equillibria varied from 1 hour (for goethite) to 48 hours (for ferrihydrite) and apparently depended on material crystallinity. In strongly acidic conditions, at pH below 3.5, partial dissolution of manganese oxides was observed, which resulted in decreasing Cr(Vl) sorption capacities. Thus, a maximum sorption of Cr(VI) on manganese oxides occured at pH about 3.5 Iron oxides did not dissolve while decreasing pH even slightly below 3.0, and the maximum sorption was found at this very low pH, about 3.0.