Theme: 07. Per- and Polyfluorinated Alkyl Substances (PFAS)

Topic Area: 7e. Ex Situ PFAS Treatment: Soils/Solids and Other Waste Streams

Formatted Title:

Reuse of PFAS-Contaminated Soil at a Remote Mine Site in Australia Using a Circular Economy Approach

Background/Objectives:

At an iron ore mine site in the Pilbara Region of Western Australia, diffuse PFAS contamination was found during a facility upgrade near a former truck wash bay. The soil leachate contained PFAS levels of around 1,350 ng/L as determined by the Australian Standard Leaching Procedure (ASLP) using deionized water as the leaching fluid. PFAS species detected in the leachate included PFOS, PFOA, 6:2 FtS, PFHxS, PFHpA and PFPeA.

The site owner assessed a number of options to manage the soil. Immobilization using a carbon-mineral sorbent, followed by onsite reuse of the treated soil, was chosen as the most cost-effective and sustainable solution. Landfill was not a viable option due to the remote site location, and thermal destruction and soil washing were considered uneconomical and impractical for this low level PFAS contamination. The relatively low carbon footprint of the immobilization process was also a key consideration.

Approach/Activities:

Contaminated soil samples were collected from the site and sent to an offsite laboratory for treatability testing using a proven carbon-mineral sorbent at dosage rates of 1% to 5%. After samples were mixed with the sorbent, water was added to around 15% final moisture content and the samples were left to fix for 48 hours before being sent to an accredited commercial laboratory for leachate generation using ASLP using deionized water as the leaching fluid. Twenty-eight PFAS analytes were measured using LC-MS-MS analysis and the results were assessed against the National Environmental Management Plan (NEMP) for PFAS management.

After the treatability study, full-scale treatment was carried out at a dosage rate of 1.5% using an excavator with a sieve bucket to perform the mixing, and a water truck for dust suppression and to assist the binding process. After treatment, validation samples were collected and sent to an accredited laboratory for PFAS leachability analysis.

Results/Lessons Learned:

Results from the treatability trial showed that a 1% addition of the carbon-mineral sorbent was sufficient to reduce the leachability of all PFAS species detected to below the Level of Reporting (LOR) in soil leachates. It was decided that a dosage of 1.5% would be used in the field to take into account scale-up factors.

PFAS leachability reductions in validation samples collected from the full-scale treatment were consistent with the treatability study results, with all relevant PFAS species being reduced to below the LOR in the leachates.

This project demonstrates a sustainable and cost-effective option for managing low level PFAS contamination at remote mine sites. The ability to reuse treated soil onsite and the reduced carbon footprint of immobilization compared to other treatment options, were major considerations for the site owner in line with the principles of a circular economy.

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Wesley Alport