Detailed Research Information

Detailed project information for
Study Plan Number 05009

Branch : Restoration Technologies Branch

Study Plan Number : 05009

Study Title : Demonstration of a Pulsed Limestone Bed Process for the Remediation of Acid Mine Drainage from Metal Mines

Starting Date : 05/01/2004

Completion Date : 12/31/2007

Principal Investigator(s) : Sibrell, Philip L.

Primary PI : Sibrell, Philip L.

Telephone Number : (304) 724-4426

Email Address : philip_sibrell@usgs.gov

SIS Number :

Primary Program Element :

Second Program Element :

Status : Active

Abstract : BACKGROUND
Acid mine drainage (AMD) is an unintended consequence of coal and metal mining that adversely affects thousand of miles of streams both in the eastern and western regions of the U. S. Estimated costs of remediation for the state of Pennsylvania alone using current technology range upwards of 5 billion dollars (1). A novel AMD treatment process based on limestone neutralization has been developed and patented at the Leetown Science Center in Kearneysville, West Virginia (2). 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, Hedin and others (3) found that limestone was less than one third of the cost of hydrated lime, and less than one twentieth of the cost of caustic. Also, because of its significantly less corrosive nature, limestone is 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 including 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 (Here, acidity is defined as the amount of base required to bring the pH of the AMD influent up to 8.3, following an oxidizing pretreatment to convert metals to a more hydrolysable form.) or 5 mg/L iron (4). 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, 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 1000 mg/L acidity and 200 mg/L iron have been successfully treated with the process. The pulsed limestone bed (PLB) technology was recognized in 2001 with a Federal Laboratory Consortium (FLC) Technology Excellence award. Thus far the technology has been tested on several samples of coal mine drainage in Maryland and Pennsylvania, and has performed well, but has not been demonstrated on hard rock AMD such as is typically found in the western U. S. Application of the enhanced limestone process to these areas could help alleviate acid and metal contamination on a wider scale than more expensive alternate alkaline sources.
OBJECTIVES
The primary objective of this research 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 of the performance of the innovative CO2 recycling system, characterization of the sludge produced by the process, and development of operating cost estimates for economic comparisons to existing processes.
HYPOTHESIS TO BE TESTED
1. Use of inexpensive limestone to neutralize the bulk of the acidity within the AMD influent will result in cost savings versus the more expensive lime or sodium hydroxide.

2. Metal hydroxide sludge density, settleability and filterability will be improved by the limestone process versus lime or sodium hydroxide.

3. Recovery and recycle of CO2 will be improved through the operation of a packed column stripping tower in conjunction with an unconventional horizontal CO2 scrubber/absorber.

4. The strong agitation and attrition forces developed by the pulsed fluidized limestone bed will prevent armoring of the limestone particles by the AMD influent.

5. Carbon dioxide stripped from the treated AMD effluent can be utilized for reacidification of the AMD to neutral pH for release to the watershed.

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Branch :	Restoration Technologies Branch
Study Plan Number :	05009
Study Title :	Demonstration of a Pulsed Limestone Bed Process for the Remediation of Acid Mine Drainage from Metal Mines
Starting Date :	05/01/2004
Completion Date :	12/31/2007
Principal Investigator(s) :	Sibrell, Philip L.
Primary PI :	Sibrell, Philip L.
Telephone Number :	(304) 724-4426
Email Address :	philip_sibrell@usgs.gov
SIS Number :
Primary Program Element :
Second Program Element :
Status :	Active
Abstract :	BACKGROUND Acid mine drainage (AMD) is an unintended consequence of coal and metal mining that adversely affects thousand of miles of streams both in the eastern and western regions of the U. S. Estimated costs of remediation for the state of Pennsylvania alone using current technology range upwards of 5 billion dollars (1). A novel AMD treatment process based on limestone neutralization has been developed and patented at the Leetown Science Center in Kearneysville, West Virginia (2). 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, Hedin and others (3) found that limestone was less than one third of the cost of hydrated lime, and less than one twentieth of the cost of caustic. Also, because of its significantly less corrosive nature, limestone is 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 including 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 (Here, acidity is defined as the amount of base required to bring the pH of the AMD influent up to 8.3, following an oxidizing pretreatment to convert metals to a more hydrolysable form.) or 5 mg/L iron (4). 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, 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 1000 mg/L acidity and 200 mg/L iron have been successfully treated with the process. The pulsed limestone bed (PLB) technology was recognized in 2001 with a Federal Laboratory Consortium (FLC) Technology Excellence award. Thus far the technology has been tested on several samples of coal mine drainage in Maryland and Pennsylvania, and has performed well, but has not been demonstrated on hard rock AMD such as is typically found in the western U. S. Application of the enhanced limestone process to these areas could help alleviate acid and metal contamination on a wider scale than more expensive alternate alkaline sources. OBJECTIVES The primary objective of this research 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 of the performance of the innovative CO2 recycling system, characterization of the sludge produced by the process, and development of operating cost estimates for economic comparisons to existing processes. HYPOTHESIS TO BE TESTED 1. Use of inexpensive limestone to neutralize the bulk of the acidity within the AMD influent will result in cost savings versus the more expensive lime or sodium hydroxide. 2. Metal hydroxide sludge density, settleability and filterability will be improved by the limestone process versus lime or sodium hydroxide. 3. Recovery and recycle of CO2 will be improved through the operation of a packed column stripping tower in conjunction with an unconventional horizontal CO2 scrubber/absorber. 4. The strong agitation and attrition forces developed by the pulsed fluidized limestone bed will prevent armoring of the limestone particles by the AMD influent. 5. Carbon dioxide stripped from the treated AMD effluent can be utilized for reacidification of the AMD to neutral pH for release to the watershed.
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U.S. Department of the Interior \|\| U.S. Geological Survey 11700 Leetown Road, Kearneysville, WV 25430, USA URL: http://www.lsc.usgs.gov Maintainer: lsc_webmaster@usgs.gov Last Modified: October 21, 2002 dwn Privacy Policy and Disclaimers \|\| FOIA \|\| Accessibility