UNEP Chemicals

Remediation of Abandoned Coal Mines Using Coal Combustion Products

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Courtesy of UNEP Chemicals

A slurry of mine water and coal combustion fluidized bed ash (FBA) was injected into an abandoned coal mine in Eastern Oklahoma in July 1997. Oil-field technology was used to inject 1.8 Gg (418 tons) of FBA through five wells in 15 hours. Alkaline minerals in the FBA neutralized acidity and imparted alkalinity to the mine water. Thus, this remediation method uses the waste from an industrial process to remediate environmental damage causes in associated resource extraction activities. Prior to injection, the seep water had a pH of 4.4, was acidic (acidity over 400 mg/L as CaCO3), and had relatively high metal concentrations (in mg/L: Fe - 200; Mn - 7; and Al - 6). As of June 1998, the seep water had a pH of 6.3, alkalinity of approximately 140 mg/l as CaCO3 (though it was still net acidic), and lower metals concentrations (in mg/L: Fe - 120; Mn - 5; and Al - 0). About 15 months after injection, however, the seep water returned to the pre-injection condition. It is hypothesized that longer and more effective treatment can be realized if larger quantities of FBA are injected. In this paper, the results of the FBA injection project are discussed.

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