Long-Term Leaching of Metals from Concrete Products

The long-term leaching of metals from concrete products made with spent abrasive media was investigated using a sequential extraction procedure employing both an acidic extraction fluid and seawater. By using seawater, leaching behavior under conditions encountered in the environment (especially coastal areas) can be determined. Chromium, cadmium, and lead concentrations were substantially less for the seawater sequential extractions than for the acidic sequential extractions. The environment created during the acidic sequential extractions resulted in the leaching of substantial amounts of alkalinity from the concrete, and leachate pH levels dropped below 4 where metals are highly soluble. Also, as only one-tenth of the alkalinity that leached in the acidic extractions leached in the seawater extractions, the integrity of the calcium matrix within the concrete seemed to play a role in the successful stabilization of cadmium and lead. Acidic extraction tests provide more severe conditions than concrete products are likely to encounter in real-world applications.