Wang, et al (2024) Effects 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 magnesium oxide on cadmium immobilized by microbially induced carbonate: Mobilization or immobilization in alkaline agricultural soils? Environmental Pollution. https://doi.org/10.1016/j.envpol.2024.124537

A recent study explored the potential of combining biochar and magnesium oxide (MgO) with microbially induced carbonate precipitation (MICP) to immobilize cadmium (Cd) in alkaline agricultural soils. This research is crucial as cadmium contamination in soils, particularly in Asia, poses significant health risks through crop uptake.

MICP relies on urease-producing bacteria to hydrolyze urea, producing carbonate that can precipitate with heavy metals like Cd, thereby immobilizing them. While MICP has shown promise in neutral or acidic soils, its effectiveness in alkaline soils, which have a naturally high 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, is less understood.

The study conducted various treatments on agricultural soils from Baiyin, Gansu Province, to analyze how the number of MICP treatments and calcium chloride concentration affect Cd immobilization. The researchers found that early MICP treatments could immobilize exchangeable cadmium and increase residual cadmium. However, over time, soil processes like nitrification could dissolve these precipitates, potentially reactivating cadmium.

Adding biochar and MgO to the MICP process enhanced cadmium immobilization. Four treatments with MICP-biochar-MgO were more effective than a single treatment, achieving passivation rates of 40.7% for exchangeable cadmium and 46.6% for bioavailable cadmium. The primary mechanism involved forming cadmium hydroxide (Cd(OH)2), with additional contributions from cadmium carbonate formation.

Despite the positive results, the study noted an increase in soil salinity, which warrants caution. This research highlights the potential of using combined MICP-biochar-MgO treatments for remediating heavy metal-contaminated soils, particularly in alkaline environments, and calls for further investigation to optimize these methods while mitigating side effects like salinity.