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Demonstration of a Pulsed Limestone Bed Process for the Remediation of Acid Mine Drainage from Metal Mines
Demonstration of a Pulsed Limestone Bed Process for the Remediation of Acid Mine Drainage from Metal Mines |
2004 | ||
| Author(s): Sibrell, Philip L., Principal Investigator, U.S. Geological Survey | U.S. Geological Survey, Leetown Science Center, Kearneysville, WV, 2004 | ||
| Mine: | Waste Type: AMD | Contaminant(s): acid | Technology Type: pulsed limestone bed |
| Keywords: limestone, armoring, pulsed fluidized bed reactor, carbon dioxide | |||
| Abstract: A novel acid mine drainage (AMD) treatment process based on limestone neutralization has been developed and patented at the Leetown Science Center in Kearneysville, WV. Limestone is an attractive candidate for acid neutralization because of its ready availability and low cost. In a cost comparison of reagents for acid neutralization, limestone is less than one-third the cost of hydrated lime and less than one-twentieth the cost of caustic. Because of its significantly less corrosive nature, limestone is also less hazardous to ship and handle, and the risk of overtreatment of impaired waters is low. Despite these advantages, limestone has not been used widely in the past due to limitations such as slow dissolution rate and armoring (formation of an impervious coating on the limestone surface). Some researchers recommend that limestone be used only for AMD sources containing less than 50 mg/L acidity or 5 mg/L iron. Recent research at the U.S. Geological Survey has shown that armoring can be avoided and the rate of limestone reaction increased by use of pulsed fluidized bed reactor technology, combined with pressurization of the reactor with carbon dioxide. Pulsing of the limestone bed allows for vigorous mixing of the limestone sand, resulting in high attrition rates, and helping to keep the limestone surface clean. The carbon dioxide increases the rate and extent of limestone dissolution, decreasing retention time by a factor of 100 or more. This enhancement of limestone neutralization allows for much wider use of the more economical limestone than was previously thought possible. Waters containing up to 1,000 mg/L acidity and 200 mg/L iron have been successfully treated with the process. The pulsed limestone bed technology was recognized in 2001 with a Federal Laboratory Consortium Technology Excellence award. The technology has been used on coal mine drainage in Maryland and Pennsylvania and showed good performance, but it has not been demonstrated on AMD from hard rock mines. The aim of this project, which is scheduled to run from May 2004 through Dec 2007, is to demonstrate the applicability of the pulsed limestone bed AMD neutralization process to metal mining AMD effluents, which typically have elevated acidity and metal concentrations relative to coal mine drainage. Secondary objectives include testing the performance of the innovative carbon dioxide recycling system, characterizing the sludge produced by the process, and developing operating cost estimates for economic comparisons to existing processes. | |||
| For more information online: Detailed project information for Study Plan Number 05009  |
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