6 September 2023

Ball milling cleans soil of persistent fluoride


Researchers in New Zealand are testing a solution against fluoride pollution. The technique has made it possible to degrade per- and polyfluoroalkyl substances (PFAS) at the molecular level with 99.9 percent efficacy

by Matteo Cavallito


A group of researchers has successfully tested a system for the removal of fluoride-based pollutants, the so-called PFAS or per- and polyfluoroalkyl substances said an article released by the University of Auckland, in New Zealand. The findings assume considerable importance given the hazardous nature of these substances contained in various products – including fire extinguisher foam – that are extremely difficult to dispose of.

The operation, says a study published in the journal Environmental Science Advances, was carried out in the laboratories of the university. And, the article states, it “destroyed 99.88 percent to 100 percent of PFAS in soil from a decommissioned New Zealand Defence Force firefighting training site and in firefighting foam.”

The procedure

The researchers relied on a procedure known as “ball milling,” a system that closely resembles the typical mortar-and-pestle-based crushing technique used in cooking. In this case, however, the operation is carried out by a machine capable of moving the balls at particularly high speeds to the point of degrading PFAS at the molecular level.

The initiative, which has involved scientists at the New Zealand university working with the U.S. Environmental Protection Agency, is based on a multi-year experiment.

“Laboratory benchtop experiments at the University from 2018 to 2023 typically involved 10 to 30 small metal balls colliding to destroy PFAS in soil, in firefighting foam, and in media such as activated carbon, which is used to remove PFAS from water,” the article explains. “The process left an inert powder suitable for being a grinding additive or non-hazardous fill.”

The dangers of fluoride compounds

Not surprisingly called forever chemicals because of their persistence in soils, PFASs are highly stable substances that appear in products designed to resist grease and water and are not easily biodegradable, Scientific American magazine previously noted.

These compounds are typically found in fluorinated pesticides – those that contain one or more fluorine atoms in their molecular structure – considered to be particularly effective in combating plant pests.

Benefiting their antiparasitic action, in fact, is precisely their recognized chemical stability, which promotes their prolonged action while limiting the ability to dispose them. It is estimated that the half-life of some fluorurates – that is, the time it takes for their presence in the environment to be halved after spraying – can be as long as 2 1/2 years.

A global problem

In 2022, a research by Stockholm University found that the presence of PFAS in stormwater on a global scale exceeds the safety limits set by several national and supranational authorities. Such as those of the United States, Denmark, the Netherlands and the European Union. And that “atmospheric deposition also leads to global soils being ubiquitously contaminated.”

New Zealand is no exception where PFAS contamination is present at military air bases and civilian airports, notes the University of Auckland.

“In addition to the known PFAS-contaminated locations, there are likely many more unknown sites yet to be identified through active investigation from both governmental and private entities,” said Kapish Gobindlal, a researcher at the University of Auckland and Environmental Decontamination Limited and co-author of the study. “We’re likely just at the tip of the iceberg.”