Chemical Interactions between Cr(VI) and Hydrous Concrete Particles

Abstract

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 Cr1 - 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.

Application of the Rietveld method to assess chromium(VI) speciation in chromite ore processing residue

“…However, CACs were never previously reported as the primary Cr 6+ -containing phases in COPR. Weng et al [19] and Meegoda et al [20] studied COPR obtained from N.J. deposition sites, but were not able to identify Cr 6+ -containing phases by XRPD. Hillier et al [21] investigated COPR deposited in Scotland and reported the following phases as candidates for Cr 6+ speciation: hydrogarnet, hydrocalumite and ettringite.…”

Enhancement of electrokinetic remediation of hyper-Cr(VI) contaminated clay by zero-valent iron

“…Clearly, the original form of Cr(VI) in soil has been converted to less toxic Cr(III) after EK treatment. Under acidic condition, Cr(VI) can be rapidly reduced to Cr(III) by both Fe(II) and/or organic matter [3,32,33]. During the EK remediation, albeit, the soil without contained the available reductive substances, the occurrence of Cr(VI) reduction was showed [13,14].…”

Stabilization of a Chromium-Containing Solid Waste: Immobilization of Hexavalent Chromium

“…The concentration values in most of the cases were clearly above the 5 ppm limit, and they even exceeded 40 ppm. Given the great insolubility of Cr(OH) 3 , 24 this behavior indicates speciation of the chromium as Cr(VI). It can also be observed that some of the minimum values of chromium occur in the pH interval between 6.5-7.5, precisely in the interval where the greatest solubilization of zinc and cadmium occurs.…”

“…This is corroborated by the bibliography consulted. 24 Considering these results, it was decided to maintain the pH for the reduction reaction of the Cr(VI) at values greater than but close to 6.…”