Biochar modified with iron could turbocharge the removal of agricultural pollutants and boost sustainable farming in many other ways too, a new study shows.
The study reviewed dozens of papers on biochar and found that while regular biochar is already making gains on farmland—helping to increase soil health, retain water, and sequester carbon—the innovative process of “surface doping with metals” like iron can significantly up the ante of this agricultural additive, the researchers say.
Take the fact that iron can initiate reactions to accelerate the breakdown of pollutants in the soil, and others that make it bind to specific ingredients that farmers might want to extract from their land. Seeding biochar with tiny fragments of iron also increases its surface charge, which enhances its ability to bind to various ingredients. Iron-modified biochar has increased surface area and porosity, too.
This combination of increased area and the increased ‘stickiness’ of biochar with iron enables it to latch on to more pollutants as they move through the water and soil. Several papers the researchers reviewed show that modified biochar attracts more phosphates (from fertilizer pollution), harmful heavy-metals like arsenic and chromium from contaminated soils, and even microplastics, compared to regular unmodified biochar. It also does a better job of drawing in pesticides from water and soil, they found.
Meanwhile, several more studies show iron-rich biochar affects the behavior of soil microorganisms in ways that reduce their nitrous oxide output, and so may also help to limit greenhouse gas emissions from farms. And, the enhanced soil amendment is better able to trap nutrients and release them more slowly into the soil—which could improve fertilizer efficiency and reduce its polluting load on farms.
An added bonus is that with the many methods now available to modify biochar with iron—from pyrolizing the organic material along with iron salts, to actively adding metal nanoparticles to its surface after the fact—scientists have many tools to tailor-make this material to suit specific challenges, such as attracting pollutants or allowing the slow-release of nutrients. The fact that iron is recyclable and can be recouped from industrial waste streams means there would also be sustainable sources of iron available to make modified biochar.
As the review shows, this substance is evolving fast to meet agriculture’s challenges. But even with all the work that’s already been done, a lot more research is needed still, to investigate its potential and safety out in the field, the review authors say.
For now, it remains a tantalizingly simple solution to “unlock a new level of performance” from biochar, they add.
Islam et. al. “Advances in biochar modification for environmental remediation with emphasis on iron functionalization.” Biochar X. 2025
Image: © Anthropocene Magazine
