Effect of ageing on biochar properties and pollutant management

Biochar is a carbon-rich pyrogenic material for multifunctional environmental applications such as carbon sequestration, soil amendment, and pollutant management, etc. Owing to long-term existing in the soil, biochar would inevitably suffer from natural geochemical weathering. Such ageing process could pose nonnegligible impacts on the physicochemical property and functionality of biochar. For an object-oriented design of biochar under different application ageing conditions, the latest research progress on ageing methods, biochar properties, and pollutant sorption performance needs to be fully understood. Specifically, the effect of soil components on biochar ageing is critically reviewed, which is of importance but not fully explored so far. The decrease of ash in aged biochar can inhibit the adsorption of heavy metals. The loss of aromatic components and the formation of three-dimensional water clusters during the ageing process have a negative impact on high-temperature biochar (>500° C) for organic pollutants adsorption. For long-term soil remediation, these results remind us to carefully use high-ash biochar for heavy metals and high-temperature biochar for organic pollutants. The interaction between soil minerals and biochar can form organometallic complexes and change functional groups to enhance the oxidation resistance of biochar. In the present review, the current research on biochar ageing are critical reviewed, and the further researches are prospected including developing advanced artificial ageing methods, exploring the impact of soil components on biochar ageing, and clarifying the long-term environmental behavior of modified biochar.