In drinking water distribution systems, chromium (Cr) may be extensively accumulated in corrosion scales of iron pipe, and the chromium solids may advertently be oxidized by residual disinfectant chlorine to form hexavalent chromium Cr(VI). Since Cr(VI) is highly toxic and carcinogenic, its release in drinking water is undesirable. This study investigated the mechanisms of Cr(VI) release from cast iron corrosion scales, using two cast iron pipe sections collected from drinking water distribution systems in the United States. The oxidation of iron corrosion scales by residual disinfectant chlorine resulted in the release of Cr(VI) and it exhibited a three-phase kinetics behavior: a fast phase within the first 2 hour, a subsequent transitional phase from 2 to 12 hour and a slow phase from 12 hour to 7 day. X-Ray Absorption Spectroscopy (XAS) analysis confirmed that zerovalent Cr(0) coexisted with trivalent Cr(III) solids in the corrosion scales. Zerovalent Cr(0) exhibited a much higher reactivity than Cr(III) in formation of Cr(VI) by chlorine, which indicated that zerovalent Cr(0) was the main source of Cr(VI) release in drinking water systems. Thus, different water conditions were investigated in order to control the Cr(VI) release from Cr(0), including pH, alkalinity, hardness,  phosphate concentration and silicate concentration. These findings provides a new insight to understand the Cr(VI) release in drinking water distribution systems, that is, direct oxidation of Cr(0) by chlorine, and the control strategies for inhibiting the formation of Cr(VI) in drinking water.

Mechanism of hexavalent chromium formation from iron corrosion scales and its control strategies in drinking water distribution systems

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.