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OPTIMIZATION OF A PULSED LIMESTONE BED REACTOR AT THE ARGO TUNNEL IN IDAHO SPRINGS, COLORADO
Citation:
MILLER, A., P. SIBRELL, T. WILDEMAN, AND D. R. BLESS. OPTIMIZATION OF A PULSED LIMESTONE BED REACTOR AT THE ARGO TUNNEL IN IDAHO SPRINGS, COLORADO. Presented at Sixth International Conference on Acid Rock Drainage (ICARD), St. Louis, MO, March 27 - 29, 2006.
Impact/Purpose:
To inform the public.
Description:
Acid Mine Drainage (AMD) is an unintended consequence of coal and metal mining that adversely affects thousands of miles of streams both in the eastern and western regions of the U.S. A novel AMD treatment process based on limestone based on limestone neutralization has been developed and patented at the Leetown Science Center in Kearneysville, West Virginia. Limestone is an attractive candidate for acid neutralization because of its ready availability and low cost. Also, because of its less corrosive nature, limestone is less hazardous to 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 including slow dissolution rate and armoring (formation of an impervious coating on the limestone surface). Recent research at USGS has shown that armoring can be avoided and the rate of limestone reaction increased by use of a 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, helping 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 100 mg/L acidity and 200 mg/L iron have been successfully treated with the process. Application of the enhanced limestone process could help alleviate acid and metal contamination on a wider scale than more expensive alternate alkaline sources.