Alkalinity generation in a vertical anoxic limestone drain (VALD) at an abandoned coal mine discharge near Hartshorne, Oklahoma was evaluated. The VALD consists of a 9-m 2 abandoned vertical air shaft filled with approximately 22 m of >90% CaCO 3 limestone overlying approximately 34 m of dolomitic stone. The VALD and a downstream passive treatment system were designed to treat a net-acidic discharge (~40 L/min) characterized by elevated concentrations of metals (Fe 765 mg/L; Mn 18 mg/L; Na 1900 mg/L), anions (Cl-225 mg/L; SO 4 2-7800 mg/L), with pH 5.4 and net-acidity 1400 mg/L. System construction was completed in late 2005, but discharge from the VALD did not occur until January 2007 due to a prolonged regional drought. Upon initial discharge, alkalinity concentrations from the VALD outflow were 550±14 mg/L. During the first year of operation, alkalinity concentrations consistently remained >400 mg/L. The effects of elevated pCO 2 , mine water ionic strength, detention time, and other factors impacting alkalinity concentrations exiting the VALD were assessed. It appears that multiple factors, especially the brackish nature of these particular mine waters, influence treatment effectiveness. In addition, the down-gradient 12-cell passive treatment system is effectively removing metals and discharging net alkaline waters to the receiving stream.
Abstract. Remediation of underground mines can prove to be a difficult task, given the physical constraints associated with introducing amendments to a subterranean environment. An acid mine abatement project, involving an in-situ chemical treatment method, was conducted by the University of Oklahoma. The treatment method involved the injection of an alkaline coal combustion by-product (CCB) sluny into a flooded mine void (pH 4.4) to create a buffered zone. Injection of the CCB sluny was possible through the use of equipment developed by the petroleum industry for grouting recovery wells. This technology was selected because the CCB sluny could be injected under significant pressure and at a high rate. With higher pressure and rates of injection, a large quantity of sluny can be introduced into the mine within a limited amount of time. Theoretically, the high pressure and rate would improve dispersal of the sluny within the void In addition, the high pressure is advantageous in fracturing or "breaking-iiown" obstructions to injection. During the injection process, a total of 418 tons of CCB was introduced within 15 hours. The mine did not refuse any of the material, and it is likely that a much larger mass could have been added. One injection well was drilled into a pillar of coal. Normally this would pose a problem when introducing a slurry; however, the coal pillar was easily fractured during the injection process. Currently, the pH of the mine discharge is above 6.5 and the alkalinity is approximately 100 mg/Las CAC0 3 •
Abstract. The Oklahoma Conservation Commission conducted a demonstration project to investigate the feasibility of treating acid mine drainage by chemically altering the characteristics of the mine water. The treatment method involved the injection of an alkaline coal combustion byproduct directly into a flooded underground mine. The project was based on the premise that the alkaline materials in the ash would create an in-situ chemical condition that would result in acid neutralization, metal precipitation, and would impart alkalinity to the mine drainage. Alkaline injection technology (AIT) was successful at raising pH and alkalinity, while reducing acidity and metals loading, but the duration of the treatment and the environmental significance was temporary. After 15 months, the water quality characteristics appeared to approach pre-injection conditions. However, after reviewing the water quality data from the past 4 years there are statistically significant reductions in acidity (23%), iron (18%), and aluminum (47%), and an increase in pH (0.35 units). Presumably, the mine environment has reached equilibrium with the alkalinity introduced to the system. A second study is currently underway to determine if the total amount of alkalinity was actually limited in the system or if there are other factors involved that limit the effectiveness of AIT.
Flooded underground mines pose a difficult problem for remediation efforts requiring hydrologic information. Mine environments are hydraulically complicated due to sinuous travel paths and variable hydraulic gradients. For an acidic mine remediation project, conducted by the University of Oklahoma in conjunction with the Oklahoma Conservation Commission, a tracer study was undertaken to identify basic hydrologic properties of a flooded coal mine. The study was conducted to investigate the possibility of in-situ remediation of acidic mine water with the use of alkaline coal combustion by-products. Information on the rate of flow and "connectiveness" of injection wells with the discharge point was needed to develop a treatment strategy. Fluorescent dyes are not typically used in mine tracer studies because of the low pH values associated with certain mines and a tendency to adsorb ferric iron precipitates. However, Rhodamine WT was used in one tracer test because it can be detected at low concentrations. Due to poor recovery, a second tracer test was undertaken using a more conservative tracer-chloride. Each tracer produced similar travel time results. Findings from this study suggest that Rhodamine WT can be used under slightly acidic conditions, with mixed results. The more conservative tracer provided somewhat better results, but recovery was still poor. Use of these tracers has provided some valuable information with regard to mine hydrology, but additional questions have been raised.
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