AWWA ACE68862

This powerpoint presentation begins by providing a brief overview of iron scales and iron release, the difference between corrosion and iron release, scale structure and composition, and iron release from corrosion scales. The study objective was to determine the impact of chloride, sulfate and DIC (bicarbonate) on iron release from an old cast iron pipe section. Experimental setup included the following: 90 year old cast iron pipe section (volume, diameter); sample from center of pipe after 23.5 hours stagnation (72 hrs); measure REDOX, pH, DO, iron, metals (ICAP); slowly fill with adjusted deionized water (2 liters); and, pH 8, DIC 10 and 50 mg C/L, 0 and 150 mg SO4/L, and 0 and 100 mg Cl/L. Key observations on iron release include the following: chloride and sulfate independently increased iron release (23.5 hour samples); increase (and decrease) were rapid; chloride and sulfate impact was NOT additive; DIC decreased iron release (23.5 hour samples); DIC countered impact of chloride and sulfate; and, Larson's ratio and iron release were consistent. Key observations on stagnation include the following: chloride and sulfate increased RATE of iron release (23.5 hour samples); diffusion, corrosion, dissolution rate; chloride and sulfate impact was NOT additive; sulfate did not impact final iron release levels following long stagnation times; chloride had little impact (ie., iron solubility did not appear to be impacted); DIC countered impact of chloride and sulfate; and, DIC reduced iron solubility (impacted the nature of the iron minerals within the pipe scale). Includes figures.