Registration for the December 2^nd AIPG MN Luncheon registration is now available online. Please register online by Friday, November 28^th.

Advance luncheon registration cost is $21 for non-members and $16 for members. Students may attend free of charge. Same-day luncheon registration cost is $25.

 Sponsorship of the December 2^nd Luncheon is by Barr Engineering Co.

Presentation Title

A “basic” Problem: Neutralizing High pH at a Former Cement Plant

by Ross Lovely and Dr. Allison Haus

Presentation Overview

The City of Duluth partnered with Barr to redevelop a legacy industrial site containing historic slag and cement manufacturing waste. Both byproducts can cause high pH water; storm water on-site has measured pH between 6.5 and 12.5. Annual pH monitoring onsite suggested that pH increases whenever meteoric events cause an influx of water to contact alkalinity-generating waste material.

A series of laboratory tests aimed to determine the most feasible method to reduce pH were designed and executed in Barr’s Duluth laboratory. The tests focused on passive, safe, and low-cost pH-neturalization alternatives tailored to the site constraints, including variations in water flow, water chemistry, and seasonality.

Initial testing of alkalinity of the site water suggested that the water contained very low levels of carbonate, making sulfuric acid addition a poor option for pH-neutralization because of the potential to “overtreat” the water, resulting in acidic drainage. Therefore, other pH-neutralization methods were pursued, more specifically, the addition of acidity through CO₂. A number of delivery methods were evaluated, initially through thermodynamic modeling in Geochemist’s Workbench, and then through kinetic testing in the laboratory, including addition of sodium bicarbonate, CO₂ sparging, aeration, and unpromoted equilibration with atmosphere (the control). CO₂ sparging was found to reduce pH most quickly, while aeration achieved the same effect 100x more slowly, and pH change in the control occurred 1000x more slowly.

Additionally, a more passive treatment technology was explored for treating pH in laboratory testing: the addition of peat. The effectiveness of two types of peat product to lower pH, APTsorbII and sphagnum peat moss, was evaluated in jar and column tests. Jar tests showed that it took roughly twice as much APTsorbII as sphagnum peat moss to adjust the site water to neutral pH, but additional carbonate present in the APT product resulted in water pH that was buffered in the neutral range. Treatment with sphagnum peat moss resulted in water pH as low as 4. Both products caused effluent to be discolored with tannins and particulate organic matter. Column tests evaluated the service life of each material. We found that while sphagnum peat moss did not have such a long service life as the APT, it was less expensive and caused a greater decrease in pH. That said, there is a potential to overtreat with peat moss, resulting in acidic water. Both products were roughly 30 times more effective at reducing pH than equilibration with atmospheric CO₂ alone.

Equilibration with atmospheric CO₂ is already ongoing onsite, evidenced by the precipitate everywhere present. An immediate concern for the client was to identify the prevalent solid onsite coating much of the ground and actively precipitating from surface waters. The concern was that the precipitate might be a soluble salt that had the potential to dissolve with rain events, leading to increases in pH. Barr collected particulate that formed from site water during pH-attenuation, in addition to particulate that formed the whitish crust in areas prone to wetting and drying cycles. Both samples were analyzed by powder XRD and by SEM by Barr’s geochemists in conjunction with University of Minnesota-Duluth characterization facility. The solid was determined to be calcite, a sparingly soluble material that will not readily dissolve in high pH waters onsite.

To achieve immediate short-term reduction in pH with little risk of over treating with no safety concerns, CO₂ sparging appears to be the safest and most low-cost alternative. In the longer-term, Barr recommended that an aerator be placed in the large central storm pond where surface water is collected prior to discharge. This action is favorable to regulators and the public and works well with the sites future use.

 Speaker Biographies

Ross Lovely is a Business Developer with the City of Duluth, assisting businesses large and small with site selection and financing issues and facilitating the construction and maintenance of infrastructure that supports economic development. His work has a significant brownfields focus whereby he works to bring projects to life on legacy and contaminated sites. Ross holds a Masters in Chemistry from the University of Wisconsin-Madison where he specialized in Analytical Chemistry with a focus on ultrafast laser spectroscopy and a J.D. from the University of Kentucky. His past work experience includes time as a practicing attorney and as an Environmental Scientist for Barr.

 Allison Stephenson Haus is a geochemist at Barr, assisting clients with onsite investigations, geochemical modeling and testing; reporting, and regulatory negotiations. She specializes in modeling the chemical speciation of mine tailings water and investigating the geochemical parameters governing mineral precipitation and dissolution. Allison has a PhD in geochemistry from Virginia Polytechnic Institute and State University and completed a Marie Curie post-doctoral fellowship at the Center for National Scientific Research in Toulouse, France. Her research involved low-temperature carbonate geochemistry, particularly the uptake of metals into calcite precipitates.