A new study demonstrates that agricultural and medicinal plant residues can be transformed into a highly effective material for removing toxic heavy metals from contaminated water and soil while also improving crop productivity. Researchers developed a phosphorus-modified biochar derived from residues of Salvia miltiorrhiza, a widely used medicinal herb, and showed that the material can simultaneously immobilize harmful metals and enhance soil fertility.
Heavy metal pollution, particularly from lead and cadmium, is a persistent environmental problem worldwide. These contaminants can accumulate in soils and water, enter the food chain, and pose serious risks to human health. Conventional remediation techniques such as chemical precipitation, ion exchange, and membrane filtration are often expensive or technically demanding. Biochar, a carbon-rich material produced by heating biomass under limited oxygen, has emerged as a promising alternative because it is relatively inexpensive and environmentally friendly.
In the new research, scientists enhanced the performance of biochar by modifying it with phosphate during its preparation. The resulting material, called 3K-BC, was produced by pyrolyzing residues from Salvia miltiorrhiza at high temperature and incorporating potassium phosphate. Analytical techniques confirmed that phosphate groups were successfully integrated into the biochar structure, creating additional reactive sites that can bind heavy metals.
Laboratory experiments revealed that the modified biochar exhibited remarkable adsorption capacity. It could capture up to 361.82 milligrams of lead and 123.03 milligrams of cadmium per gram of material. These values are higher than those reported for many previously studied biochars, highlighting the effectiveness of the modification strategy.
"The modified biochar shows strong potential as a low-cost and efficient adsorbent for heavy metal pollution," the researchers explained. "By introducing phosphate groups into the biochar structure, we significantly enhanced its ability to immobilize toxic metals while maintaining environmental compatibility."
The study also investigated how the material works at the microscopic level. Multiple mechanisms contribute to metal removal, including surface adsorption, precipitation reactions with phosphate, complexation with oxygen-containing functional groups, and cation exchange processes. Together, these interactions stabilize heavy metals and prevent them from migrating through soil or water systems.
Beyond laboratory solutions, the team evaluated the material in soil experiments. When applied to contaminated soil, the phosphorus-modified biochar significantly reduced the bioavailability of lead and cadmium. The proportion of mobile and easily absorbed metal forms decreased, while more stable forms increased. This transformation lowers ecological risks and limits the likelihood that crops will accumulate toxic metals.
The researchers also examined how the biochar affects plant growth. Pot experiments using Ligusticum chuanxiong, a traditional medicinal plant that is often affected by heavy metal contamination, showed encouraging results. Application of the modified biochar increased plant yield by 61 percent and enhanced the concentration of key medicinal compounds. Even under heavy metal stress, the total effective components of the plant increased by more than 22 percent.
"These results demonstrate a dual benefit," the authors noted. "The material not only stabilizes heavy metals but also improves soil conditions and promotes plant growth."
An additional advantage of the approach is sustainability. Residues from traditional herbal medicine production are often treated as waste. Converting these byproducts into functional biochar creates a circular solution that simultaneously addresses waste management and environmental remediation.
As heavy metal contamination continues to threaten ecosystems and food safety worldwide, innovations like phosphorus-modified biochar offer a promising pathway toward cleaner soils and safer agriculture. By combining waste recycling with pollution control, the technology could support more sustainable environmental management and agricultural production in the future.
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Journal Reference: Yuan, J., Liu, Y., He, Q. et al. Phosphorus-modified biochar from salvia miltiorrhiza dregs: synthesis, characterization, and dual-functional synergy for heavy metal immobilization and soil fertility augmentation. Biochar 8, 30 (2026).
https://doi.org/10.1007/s42773-025-00540-5
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About Biochar
Biochar (e-ISSN: 2524-7867) is the first journal dedicated exclusively to biochar research, spanning agronomy, environmental science, and materials science. It publishes original studies on biochar production, processing, and applications—such as bioenergy, environmental remediation, soil enhancement, climate mitigation, water treatment, and sustainability analysis. The journal serves as an innovative and professional platform for global researchers to share advances in this rapidly expanding field.
