An overview of the effect of pyrolysis process parameters on biochar stability

[Display omitted] •Pyrolysis temperature is the dominant processing parameter to biochar stability.•High temperature, long residence time and slow heating rate are preferable.•Biomass feedstock of high lignin content with large particle size are favorable.•Both biochar yield and stability are decisive to carbon sequestration potential. Biochar produced from biomass pyrolysis is becoming a powerful tool for carbon sequestration and greenhouse gas (GHG) emission reduction. Biochar C recalcitrance or biochar stability is the decisive property determining its carbon sequestration potential. The effect of pyrolysis process parameters on biochar stability is becoming a frontier of biochar study. This review discussed comprehensively how and why biomass compositions and physicochemical properties and biomass processing conditions such as pyrolysis temperature and reaction residence time affect the stability of biochar. The review found that relative high temperature (400–700 °C), long reaction residence time, slow heating rate, high pressure, the presence of some minerals and biomass feedstock of high-lignin content with large particle size are preferable to biochar stability. However, challenges exist to mediate the trade-offs between biochar stability and other potential wins. Strategies were then proposed to promote the utilization of biochar as a climate change mitigation tool.