Release of Aluminum from Clays in an Acid Rock Drainage Environment

Abstract

Aluminum concentrations in low pH acid rock drainage (ARD) commonly exceed the freshwater aquatic toxicity threshold. An Al-containing ARD released from pyritic sandstone and shale fill along US. Interstate 80 in Center County, Pennsylvania has adversely impacted a former fishing stream. This ARD consistently contains low concentrations (<2 mg/L) of Fe and high concentrations (≈48 mg/L) of Al. Batch experiments conducted with kaolinite and H/Al-bentonite clays and clay soils collected from the Centre County, PA area suggests that synthetic brackish ARD enhances the release of Al from these clays, compared to synthetic acid (sulfuric) only and non-brackish ARD. This implies that highway deicing salts in road runoff could aggravate the leaching of Al from pyritic rocks used as fill or exposed in road cuts. Likewise, the use of ARD to enhance the production of natural gas from tight shales could result in the leaching of Al. Quantification of levels of Al released from field clays could be critical when considering remediation strategies.