AWWA ACE54497

This work investigates the influence of silica on both corrosion rates and iron release using a batch reactor set-up under continuously stirred aerated conditions. Cast iron coupons were placed in four reactors with the same type of water except each with a different level of added silica: 0.5, 10, 25, or 50 mg/L as SiO2. Silica had profound effects on iron release. Higher levels of silica caused more iron release to the water during the entire length of the experiment, and shifted particles to smaller sizes. Silica also greatly affected the type of scale that formed on the iron coupons by incorporation into the scale. Scale from the low silica reactors was fairly uniform and easy to physically remove from the coupons, while the scale from the high silica reactors contained many black spots, was denser and was harder to remove. Scale from the highest silica reactor also developed obvious tubercles. Corrosion rates also decreased at the highest level of silica, as did the rate of byproduct release. Includes 27 references, figures.