Lu, et al (2024) Effects of low molecular weight organic acids on adsorption of Cd(II) by Auricularia auriculaspent substrate-derived 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: Types and reaction sequence. Environmental Chemistry and Ecotoxicology. https://doi.org/10.1016/j.enceco.2024.09.001

Spent substrate-derived biochar, sourced from Auricularia auricula, has shown potential for cadmium (Cd) remediation in contaminated soils. A recent study evaluated how low molecular weight organic acids (LMWOAs)—like tartaric (TA), citric (CA), and malic acids (MA)—affect the biochar’s ability to adsorb Cd ions under various reaction sequences. These acids, common in root exudates, play a critical role in rhizosphere soil chemistry.

Four reaction setups were studied: simultaneous mixing of Cd, biochar, and LMWOAs; pre-reacting Cd with LMWOAs before biochar addition; pre-reacting Cd with biochar before adding LMWOAs; and pre-reacting biochar with LMWOAs before Cd exposure. Results showed that LMWOAs influenced both Cd adsorption and desorption dynamics. While TA facilitated adsorption, CA and MA hindered it, especially when introduced before Cd or biochar.

Functional groups on biochar, including carboxyl and hydroxyl groups, were key to these interactions. TA promoted better retention of functional groups, while CA and MA displayed reduced adsorption efficiency under specific sequences. These variations highlight the complex interplay between biochar surface properties and organic acid behavior.

The study underscores the need to consider reaction sequences in biochar applications for soil remediation. Optimizing the timing of biochar addition relative to crop growth and organic acid secretion can enhance its effectiveness in immobilizing toxic metals like Cd. Future work should explore how real-world soil 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 variations influence these mechanisms.