Exposed, open pit mine highwalls contribute significantly to the production of acid mine drainage (AMD) thus causing environmental concerns upon closure of an operating mine. Four innovative technologies were evaluated under the US Environmental Protection Agency's, Mine Waste Technology (MWTP), Prevention of AMD Generation from Open Pit Highwalls Demonstration Project. This project is funded by the US Environmental Protection Agency (EPA) and jointly administered by the EPA and the US Department of Energy (DOE) through an Interagency Agreement. The objective of the field demonstration was to evaluate the technologies ability to decrease or eliminate acid generation from treated areas of the highwall in comparison an untreated highwall area._x000D_
The field demonstration was performed at the Golden Sunlight Mine (GSM) a subsidiary of Placer Dome US, located near Whitehall, Montana. GSM is an operating gold mine._x000D_
The highwall at GSM was divided into five plots measuring 15.24 by 15.24 m and each technology was assigned a plot with the fifth plot being used for comparison as a background control plot. The four technologies were spray-applied. The applied in situ treatment technologies included: a modified, furfuryl alcohol resin sealant, utilising wood and agricultural by-products to coat the rock surface; EcobondTM ARD, a phosphate based process that forms a stable, insoluble compound, coating the rock surface; and two AMD passivation technologies, magnesium oxide and the Dupont technology developed to create an inert layer/coating on the pyrite, preventing oxidation._x000D_
The technologies were evaluated using the following methods: ASTM D 5744-96, accelerated weathering of solid materials using a modified humidity cells; mine wall residual wall rinse sampling; microscopy; and core drilling followed by water injection testing._x000D_
The following paper describes the technologies used for passivation of acid generation from the highwall, the field demonstration, and the testing results from the background and each technology plot.