Carbonation of Mine Water to Increase Limestone Dissolution and Alkalinity Generation

EPA Contract Number: 68HERC21C0049
Title: Carbonation of Mine Water to Increase Limestone Dissolution and Alkalinity Generation
Investigators: Hedin, Robert
Small Business: Hedin Environmental
EPA Contact: Richards, April
Phase: II
Project Period: April 1, 2021 through March 31, 2023
Project Amount: $399,829
RFA: Small Business Innovation Research (SBIR) - Phase II (2021) Recipients Lists
Research Category: SBIR - Mining and Mine Waste Management , Small Business Innovation Research (SBIR)

Description:

Acidic metal-contaminated mine water impacts tens of thousands of miles of streams in the US. Treatment requires neutralization of acidity followed by precipitation and management of the metals. Conventional mine water treatment systems use lime (CaO) or caustic (NaOH) to generate acid-neutralizing alkalinity. The high cost of these conventional technologies has contributed to the bankruptcies of hundreds of mining companies and significantly limited the ability of public reclamation groups to treat polluted mine water at abandoned sites. Lime and caustic are mature technologies and there is little opportunity for substantial cost-decreasing technical advances.

Limestone (CaCO3) is a commonly available alkaline material that can provide acid neutralization at 1/8 to 1/40 the cost of lime and caustic, respectively. However, limestone's use is subject to solubility and kinetic constraints that limit its application to a small subset of the Nation's mine water problems. The Phase I project investigated whether these constraints could be overcome through carbonation of the mine water. The limestone+CO2 technology that was developed was able to double concentrations of alkalinity produced from limestone and quadruple that rate of alkalinity generation. The Phase I findings were implemented at an existing underperforming limestone treatment system where carbonation was able to produce an alkaline discharge from the limestone system for the first time in 30 years. The results indicate that carbonation could improve the treatment effectiveness of existing limestone systems and significantly decrease the size and cost of future limestone systems.

Phase II will advance the technology by developing an improved carbonator device and applying the technology to low pH mine water contaminated with ferric iron, aluminum, and toxic metals. The limestone+CO2 technology will be demonstrated at four full-scale under performing limestone treatment systems in Pennsylvania and at an experimental system at a metal mine site in southwestern Colorado.

The customers for the limestone+CO2 technology are local, state, and federal mine reclamation programs, non-profit watershed restoration groups, private mining companies, and engineering companies that design treatment plants. The technology will compete with lime and caustic based on price. The Phase I results suggest that the primary cost driver for the technology is CO2 utilization and price. Phase II will increase the efficiency of CO2 utilization. CO2 availability and price will be determined through a market analysis that relates potential sources of industrial quality CO2 to acid mine drainage producing regions in the US and provides pricing for various production and transportation scenarios.


SBIR Phase I:

Carbonation of Mine Water to Increase Limestone Dissolution and Alkalinity Generation  | Final Report