Lime Sludge Has Many Uses: FOX Environmental Engineer Publishes Graduate Work

11 Lime Sludge Publication TLL.pdf

A special issue of the publication, “Land Contamination and Reclamation” was recently published by EPP Publications, based in the United Kingdom.  The focus of the special issue was “The Utilization of Wastes as Construction Materials.”  The last three articles were based upon graduate research done by FOX Engineer, Rob Baker.  Rob was also one of the authors in each of the three articles.

The first article details the results of feasibility studies for using lime sludge for the following applications:

• Replacement for mined limestone in dry scrubbing processes in coal-burning power generation plants.
• Replacement for mined limestone in cement kilns.
• Neutralization of acidic industrial wastewater.
•  Dust control on gravel roads.
• Use as fill material in road construction.

When lime sludge is dewatered and dried, it is mostly calcium carbonate, or the same substance chemically as limestone.  Dried lime sludge is fine grained and was classified as a silt size material with a large available surface area.  During the feasibility study phase, only one of the five potential applications proved to be ineffective.  This was using lime sludge as dust control agent on gravel roads in Story County. 

 Lime sludge proved to be effective in reducing sulfur dioxide and NOx gases in the Ames Power Plant; however the material was not dried adequately and it plugged the scrubber.  To be fair, the scrubber’s feed system was not specifically designed for the lime sludge product.  Given proper processing of the lime sludge product, and an appropriate feeding system, using lime sludge in dry scrubbers remains a sustainable option for electric utilities.  The solution creates a local beneficial use for a locally produced byproduct.  It is a way for a community to honor a commitment to “green” practices.

Lime sludge was effective in neutralizing acidic  wastewater from a food processing facility. The feasibility experiment was conducted at Warren Foods. An acidic wastewater, a byproduct of making pasta food products, was dosed with dried lime sludge.  Normally, the wastewater would have been treated with sodium hydroxide, a common man-made chemical.  When lime sludge was added to the acidic water instead of the sodium hydroxide, the calcium carbonate acted as a buffer, and neutralized the acid. 

 This application would also be considered “sustainable” or “green” because it found a use for regionally produced, stockpiled byproduct as a replacement for a manufactured chemical that is most likely sourced from outside the state.

Production of portland cement has occurred at Lehigh Cement in Mason City, Iowa.  One of the necessary ingredients for making portland cement is calcium carbonate, which is usually sourced from mined limestone. 

Taking advantage of the chemical equivalence to mined limestone, 20 tons of dried lime sludge was used as a direct replacement in cement production.  80 tons of cement was produced, containing about 15% of lime sludge, and the product passed the quality control testing provided to the research team. 

Since mining of limestone was occuring within a very short distance of the cement manufacturing facility, using the lime sludge as a replacement was not a beneficial solution for this particular facility.

The second and third articles went into great detail regarding the engineering properties of lime sludge when used as a soil material, as well as testing and analysis of various mix designs of lime sludge and fly ash mixtures. 

 Both lime slude and fly ash are by-products or waste from water treatment and local power generation, respectively.  If mixtures of these products were beneficially used, the solution avoids adding to unproductive stockpiles. 

 Since fly ash is already widely used as an admixture to strengthen fill materials, it has relatively low stockpiles in Iowa.  It was logical to minimize the amounts of fly ash product used in the lime sludge mixtures for economic reasons. 

 The second article provides almost all of the testing and analysis data needed to evaluate lime sludge as a soil fill material for a project.  This testing information would normally need to be paid for through a construction project’s design fees, and was provided at a much lower cost though publication of this research. 

The third article documented the construction of a test embankment, using full-scale construction equipment, as well as in-situ testing of the lime sludge/fly ash mix fill product.  In-situ testing was repeated in fall, winter and early spring seasons to capture wet/dry and freeze/thaw cycles.  The test embankment demonstrated that no special construction methods or equipment were necessary to use these mixtures.

The second and third articles were written with the designer and builder in mind.

The main sponsor of this research was the Iowa Department of Transportation’s Highway Research Board.  The city of Ames, the Newton Water Works,  the Cedar Rapids Water Department, the Des Moines Water Works, and the West Des Moines Water Works made susbtantial contributions to research funding. 

Special thanks goes to Christopher Jones, DMWW; John Dunn and Phil Propes, of the city of Ames; Marty Hoffert of the Newton Water Works; John Luther, West Des Moines Water Works; John North of the Cedar Rapids Water Department (now retired); Scott Adair of Kelderman Lime; BMG Biosolids of Boone; the Ames Power Plant; the Ottumwa Generating Station; Lehigh Cement; Warren Foods (now T. Marzetti, Inc.); and the Story County Engineering Department for their support during the research phase.  
 
Contact:
FOX Engineering Associates, Inc.
Rob Baker, P.E.
800.433.3469
www.foxeng.com