In a study published in Scientific Reports, Hamid Reza Boostani, Mahdi Najafi-Ghiri, and Dariush Khalili investigated the effectiveness of biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More and bentonite clay in immobilizing cadmium (Cd) in contaminated calcareous soils. The research explored the combined use of phosphoric acid-modified biochar and bentonite, an abundant and cost-effective mineral in Iran, to address Cd contamination in agricultural soils.  

The researchers conducted a 90-day incubation study using three levels of bentonite (0%, 1%, and 2% wt.) and five biochar treatments: control, unmodified/phosphoric acid-modified coffee grounds biochar, and unmodified/phosphoric acid-modified municipal solid waste biochar (all at 2% wt.).  

The study revealed that combining municipal solid waste (M) biochar with 2% bentonite (B2​) had a synergistic effect on Cd immobilization. This treatment reduced EDTA-desorbed Cd by 18.7% and exhibited the slowest release rate. The enhanced immobilization was attributed to the transfer of Cd from bioavailable forms to more stable fractions in the soil due to increased pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More and phosphorus levels.  

Conversely, coffee grounds biochar combined with bentonite increased the concentration of Cd in water-soluble and exchangeable fractions compared to using coffee grounds biochar alone. Overall, unmodified biochars proved more effective in stabilizing soil Cd than those modified by phosphoric acid.  

The research concludes that the combination of municipal solid waste biochar and 2% bentonite is the most effective approach for Cd immobilization in contaminated calcareous soils.

SOURCE: Boostani, H. R., Najafi-Ghiri, M., & Khalili, D. (2025). Comparative effectiveness of pristine and H₃PO₄-modified biochar in combination with bentonite to immobilize cadmium in a calcareous soil. Scientific Reports, 15(14301).