Lithic controls on the removal of iron and remediation of acidic mine drainage

The remediation of streams adversely affected by acidic mine drainage often employs limestone as a neutralization agent. However, metal precipitation on the limestone surface can render it ineffective. This investigation reports preliminary field and laboratory results demonstrating that, in the presence of a mixture of limestone and sandstone, iron preferentially precipitates on the sandstone surface, and iron removal from aqueous solution is greater than with either of the materials alone. First, a river in Tennessee (USA) with preferential iron precipitation was characterized with respect to water quality and lithic surface morphology. Second, a field experiment where lithic samples were placed in an Ohio stream receiving coal mine drainage demonstrated that iron hydroxide preferentially coats quartz-rich lithologies. Finally, laboratory experiments confirmed enhanced iron removal in the presence of mixed lithic surfaces. Based on these results, the use of multiple lithic surfaces, particularly in-stream, has the potential to provide improved methods for the treatment of acidic mine wastes.