Session: 05-07: Disposal Options and Materials Management Methods

Paper Number: 110272

110272 - Influence of Blending Phosphogypsum to Mitigate Radium Leaching and Promote Reuse as Road Base Material 

The processing of phosphate rock to produce phosphoric acid results in a calcium sulfate byproduct known as phosphogypsum (PG). This byproduct is regulated in the United States as a Technologically Enhanced Naturally Occurring Radioactive Material (TENORM) and is managed indefinitely in monofills or gypstacks. The reuse of this material is inhibited by regulations surrounding radon release and total and leachable ²²⁶Ra concentrations, however increased interest in using PG as a road base material has developed. Many sources of PG cannot be used as a road base material alone largely due to insufficient strength and potential for ²²⁶Ra leaching. This paper investigates the influence of blending PG with common alkaline road base aggregates such as limerock and recycled concrete aggregate (RCA) to reduce ²²⁶Ra leaching from PG amended road base and provide an avenue for widespread reuse. Two sources of PG were investigated for ²²⁶Ra leaching at various pH conditions and blended with each of the two aggregate sources at up to 0,25,50, and 75% (by mass) PG to understand the behavior of  ²²⁶Ra leaching. The results reveal an amphoteric leaching behavior from the PG sources alone. The blending experiment indicates an increase in leaching from PG:limerock blends initially, followed by a reduction with increasing limerock addition, and a decrease in leaching from PG:RCA blends. The amphoteric behavior of the PG paired with the leaching curves for these material blends indicates a mechanism of control of  ²²⁶Ra mobility aside from change in pH, perhaps due to binding of radium by elevated concentrations of Ba, Sr, or Ca in the RCA blends. This data provides novel insight into controlling a limiting factor to PG reuse as a road base material and suggests that blending with RCA could allow for lower ²²⁶Ra mobility from PG blends and allow a larger application of PG reuse and an alternative scenario to end-of-life stacking.

Presenting Author: Kate Weiksnar University of Florida

Presenting Author Biography: Kate Weiksnar is a doctoral research assistant at the University of Florida pursuing her PhD in environmental engineering with a focus in sustainable material management. Kate's area of study includes optimization of environmental performance of industrial byproducts in beneficial reuse scenarios, including reuse of byproducts as supplements to raw materials in concrete manufacture and road construction materials. Kate's recent work focuses on the mobility of trace elements, anions, and radionuclides from phosphogypsum, a TENORM material produced from the phosphoric acid process. This includes identifying approaches to limit element mobility and produce a waste-derived construction product suitable for widespread reuse that maintains the health and welfare of the environment.