Engineered biochar composite with minerals: organo-mineral interactions, physicochemical changes, and implications for practical application

Abstract Engineered biochar materials are under development for a wide range of environmental applications. Many of these engineered materials combine biochar with minerals such as non-clay silicates, clay minerals, oxide minerals, and carbonates, or are manufactured through the co-pyrolysis of mineral additives with the biomass, both forming organo-mineral complexes. In this review, we provide an exploration of the mechanisms of organo-mineral interactions, physicochemical changes, and real-world practical applications. We first provide an overview of organo-mineral interactions between biochar and minerals in the natural environment to offer insights into organo-mineral interactions in engineered biochar composites. Secondly, we propose a classification of biochar composites with minerals. A quantitative analysis of physicochemical changes in engineered biochar composites is presented, revealing an increase in ash content and polarity, with either improved or degraded porous structure. Based on these physicochemical changes, enhancement mechanisms of the mineral components are assessed. These mechanisms primarily involve direct stabilization of biochar carbon (C) and indirect negative priming when applied to soil, nutrient delivery, introduction of functional groups for adsorption/immobilization, and reduced toxicity to support microbial colonization and improve soil health. In addition, evidence for the practical application of biochar-mineral composites is presented, including field studies for soil applications and pilot-scale non-soil applications such as in wastewater and stormwater treatment. Finally, challenges and future research directions are proposed, including examining the molecular binding mechanisms between minerals and the C matrix, investigating the reversibility of mineral attachment and the long-term effectiveness of composites, and exploring emerging non-soil applications of novel biochar composites with minerals. Graphical Abstract