Assessing Air Emissions of Study Compounds from Area Sources Found at Mining Sites Using the USEPA Flux Chamber Technology
Air emission assessments performed for the mining industry have focused on two compounds that can be found at some gold mines: hydrogen cyanide used in the gold leaching process, and mercury which is found in the gold ore.
Mining of rock with mineralize gold includes excavation of the ore (surface and/or subsurface), rock hauling, crushing, and heap pile leaching and/or ore processing in tanks. These processes produce overburden and waste rock, which is used in reclamation of the site, and waste water or 'tailings'.
Area sources often included in the site assessment using the USEPA flux chamber technology include: freshly excavated ore, crushed ore stockpiles, heap leach (under leach with cyanide solution, photo 1) and inactive heap leach (photo 2), lechate channels and ponds, mine tailing ponds (photo 3), process tanks (photo 4), waste water clarifier tanks (photo 5), waste rock stock piles, and reclamation areas.
The technical approach developed for the gold mine site assessments are rather involved and include characterization of air emissions from these sources, and they also include sampling that addresses operational, diurnal, and seasonal factors, all of which may affect emissions from these area sources. Hydrogen cyanide emissions as related to fugitive emissions from heap leach process and tank extraction processes involve collecting gas samples from the flux chamber in a basic liquid solution and analysis by an off-site laboratory. Mercury emission assessment can include field screening instrumentation, sorbent tube sample collection and analysis off site, and onsite analysis using a laboratory grade instrument outfit for field assessment (Tekran Analyzer).
Given the remote location of gold mines and the size and complexity of the unit processes or area sources found at the mines, air pathway analyses conducted for this industry are both robust and challenging.
Photo 1: Flux Chamber Testing on Heap Leach
Photo 2: Flux Chamber Testing on Reclaim Land
Photo 3: Flux Chamber Testing on Tailings Pond
Photo 4: USEPA Flux Chamber measuring emissions from Process Tank
Photo 5: Measuring Emission from Process Tank, Clarifier Tank