Formatted Title
Ball Milling as an Emerging Destruction Technique for PFAS-Contaminated Soils
Background/Objectives
PFAS-containing products, particularly aqueous film-forming foams, have been used extensively at airports, refineries, and military locations for several decades, leading to complex soil contamination problems that require remediation. However, the burden of resolving the environmental issues associated with widespread industrial and commercial use of PFAS is incredibly complex as these chemical compounds are extremely persistent upon release to the environment while also being linked to negative health effects. Due to the recalcitrant properties of PFAS, there are limited technologies capable of both effective destruction as well as scaling to a level required to treat PFAS-related problems, for example, highly contaminated soil. As such, destruction treatment of PFAS in contaminated soils has been identified as a critical priority area in the USA and around the world; in particular, the development of scalable technologies to address real-world challenges. Ball milling, also known as mechanochemical destruction (MCD), is a novel treatment method that can destroy PFAS by exploiting the mechanical energy induced by high velocity ball-to-ball and ball-to-surface collisions within reaction vessels. Recent research has revealed that ball milling is highly capable of destroying PFAS in real-world impacted matrices.
Approach/Activities
The objective of ongoing R&D in this area is to apply ball milling to authentic PFAS-contaminated soils and sediments, with a goal to inform process optimization and future scale-up activities. Benchtop ball milling devices are used to process impacted samples over designated milling periods under variable operational conditions. High rates of destruction (e.g., >99%) are typically achieved without the need for high temperatures, toxic additives, solvents, or extreme pressures which are usually employed in other destruction techniques. To quantify the destruction of PFAS by ball milling, interval samples are generally analyzed using a wide range of techniques, including liquid chromatography tandem mass spectrometry (LC-MS/MS), total organic fluorine (TOF), extractable organic fluorine (EOF), nontargeted high resolution mass spectrometry, and solid-state nuclear magnetic resonance (SSNMR). This approach leads to a holistic evaluation of PFAS destruction during ball milling, accounting for both physical and chemical transformations. Additionally, this strategy de-risks pilot-scale development and subsequent full-scale design / implementation.
Results/Lessons Learned
Initial results have revealed high PFAS destruction efficiencies for contaminated soil subjected to ball milling treatment. The analytical regime allows for the comparison of the destruction rates for various PFAS subgroups, short-chain versus long-chain PFAS, and branched versus linear isomers. The degradation progression of each PFAS subgroup produced variable and irregular concentration curves compared to one another. Nevertheless, all PFAS subgroups present in the contaminated soil were reduced to below the limit of detection for the analytical method used (LC-MS/MS) by the end of ball milling treatment works.
This presentation will provide an in-depth analysis of PFAS destruction by ball milling, with a focus on real-world matrices and progressive system development toward technology scale-up. Observations and explanations of trials will encompass fundamental mechanochemical theory alongside destruction mechanisms, reaction initiation, kinetics, and fluorine fate. The outcomes of this work will lead to a technology demonstration program that will establish the scalability of MCD as an effective PFAS destruction technique for PFAS-laden solids, with a focus on contaminated soil originating from firefighting training sites.