PFAS adsorbent for unsaturated soil zones
PFAS are highly mobile in groundwater systems, due to their high solubility in water. Typically, a large remediation effort is made to contain and treat the vast PFAS plumes, which have formed due to this effect.This is where Fluorolock® comes into play: We developed a clay mineral-based, microscale adsorber which is specifically designed for the treatment of water-unsaturated PFAS infiltrations zones above the groundwater surface.
Limit PFAS leaching before they reach groundwater
With Fluorolock®, PFAS can be effectively adsorbed, immobilized and hence confined within the water-unsaturated zone before being leached into the groundwater accompanied by their distinct fast spreading through the subsurface. A formation of PFAS-plumes can be prevented or interrupted, and remediation efforts can be targeted to small, localized zones, rather than to widespread plumes.
Fluorolock®
- offers irreversible adsorption of long- and short-chain PFAS for long-term immobilization within the unsaturated zone
- results in long-term confinement of the adsorbed PFAS inventory in soils due to robustness of Fluorolock® to periodic drying and re-wetting
- grants ecotoxicological safety, and has been independently tested and verified by a German university
- is injectable as a liquid suspension with common direct push systems
Properties of Fluorolock®
| Patents | DE 20 2019 004 774.3
developed by Intrapore |
|---|---|
| Specific surface Area | ~ 270 m²/g |
| Particle size | ~ 1.5 μm |
| Injection concentration | from 10 to 50 g/L |
| Components |
|
Adsorption of long- and short-chained PFAS
The polymers at the Fluorolock® particle surface provide distinct hydrophobic interactions resulting in the adsorption of long-chain PFAS, e.g., PFOS. Fluorolock® yields adsorption capacities as high as observed for high-performance ACs specifically functionalized for PFAS adsorption. Due to its pH-independent permanent positive surface charge, Fluorolock® facilitates also the adsorption of short-chain anionic PFAS -such as PFBS- due to electrostatic attraction. The exponential rise in PFAS adsorption with increasing PFAS concentration renders Fluorolock® as perfect agent for application in the direct vicinity of PFAS-contaminated sources (Figure 1).
Almost irreversible PFAS immobilization
The major part of PFAS is irreversibly bound to Fluorolock®. This has been confirmed in lab tests: although rigid conditions were repeatedly applied to force a re-mobilization of initially adsorbed PFAS from Fluorolock® (maximum chemical gradients; 48 h shaking). After three desorption steps, where PFAS-loaded Fluorolock® was exposed each time to a PFAS-free solution, in sum ~7% PFOS, ~11% PFBS, ~17% PFOA and ~65% of the initially adsorbed PFHxS were re-mobilized under such strongly desorption-forcing conditions (Figure 2). Alike conditions (shaking, strong chemical gradients) are not expected to occur in nature but rather resemble a stress test for the PFAS-Fluorolock®-binding.
Despite repeated drying of Fluorolock®, no PFAS are additionally released from Fluorolock®. This makes Fluorolock® perfectly applicable in water-unsaturated soils, which are common objects to periodic drying and re-wetting.
Applied within the unsaturated soil zone
Due to its colloidal size, soils can be amended with Fluorolock® by the injection of liquid Fluorolock® suspensions directly into soils. The injected Fluorolock® particles will move through the porous media over a certain distance and finally adhere to the soil pore walls. There, the immobile Fluorolock® particles will adsorb and immobilize the PFAS molecules, which migrate through the soils via percolating soil solution.
In a soil column experiment with four independent replicates, PFAS-containing groundwater (taken from a former military airport) was percolated under water-saturated conditions through soils (taken from the same site). The soil was amended with Fluorolock® or remained unamended (control soil). The presence of Fluorolock® resulted in a distinct immobilization of PFAS within the soil, revealed by effluent PFAS concentrations below the detection limits (Figure 3). Given the applied percolation rate o 2 pore volumes d-1, a contact time of 12 h was sufficient to achieve the observed immobilization. Contrary, unamended soil did not (or only insufficiently) retain the monitored PFAS.
Consequently, Fluorolock® instantly and sustainably immobilized PFAS, which were initially highly abundant in the mobile phase (e.g., groundwater).
Environmentally safe and tested
Fluorolock® proved its environmental compatibility in standardized ecotoxicological assays with plants and multicellular animals (earthworms). An independent German university and experts on environmental matters support an application of Fluorolock® to PFAS-contaminated soils.
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