Preventing Pollution from Decommissioned Underground Mines
There are more than 100,000 abandoned underground mines worldwide. Many of these discharge drainage contaminated by acid, heavy metals and salinity. The poor quality drainage is a result of the exposure of sulfidic minerals (such as pyrite) within the mine to atmospheric oxygen. If not managed, pollution can continue for centuries. Solutions for the management of these legacy mines include hydraulic seals which flood the workings and prevent oxygen access to the reactive sulfides, or treatment of the discharge water via costly and ongoing chemical addition. Hydraulic bulkhead seals are difficult to engineer, can be expensive, and have some history of catastrophic failure due to the corrosive nature of the drainage and high working pressures. When water treatment is chosen, it is often considered necessary in perpetuity.
Earth Systems has developed an innovative alternative to water treatment in perpetuity that involves controlling the mine void atmosphere. In the absence of oxygen, the sulfide minerals can no longer react to produce sulfuric acid. In some scenarios, mine void oxygen concentrations can be lowered by sealing mine access points to air, while still allowing water discharge. In these situations, natural sulfide oxidation within the void automatically lowers internal oxygen concentrations, thereby lowering pollution generation rates. At sites where mine access seals are only partially effective, active injection of inert gases (nitrogen or carbon dioxide) into the mine voids may be required to further lower mine void oxygen concentrations.
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