Chemical Interactions between Cr(VI) and Hydrous Concrete Particles

Chemical interactions between Cr(VI) and concrete particles in synthetic groundwater solutions were studied. Results indicate that redox, adsorption, and precipitation are the three major reactions occurring at the concrete−water interface. The solution pH plays a significant role in determining the characteristics of chromium reaction behavior with concrete materials. In acidic systems, Cr(VI) species are removed from the solution by reduction reactions. At pH < 4.0, Cr(VI) reacts with aqueous Fe(II) ion, derived from the Fe-containing minerals of concrete materials, and is subsequently reduced to Cr(III). A simple stoichiometric relationship was observed for Cr(VI) reduction by concrete particles. As Cr(III) is not adsorbable in this pH region, it becomes released into the solution phase. The Cr(III) concentration is then governed by the solubility of Cr(OH) 3 (s) and/or Fe x Cr 1 - x (OH) 3 (s) precipitates as solution pH increases. In the pH range from 4.0 to 9.0, an adsorption reaction is mainly responsible for Cr(VI) removal.