Biochar characterization and a method for estimating biochar quality from proximate analysis results

Biochar has gained significant interest in the literature, mainly for its ability to improve soil quality and sequester carbon. This work investigated if results from proximate analysis could be used to assess the quality of the biochar. Normally, ultimate analysis results are used for this purpose. A large set of data was collected from literature and various mathematical correlation were investigated to determine if quality parameters such as carbon mass fraction and H/C and O/C mol ratios could be estimated from proximate analysis results. It was determined that the mass fraction of carbon in the biochar could be correlated to the mass fractions of volatile matter (VM), fixed carbon (FC), and ash (ASH) by the relationship C = 0.474 × VM+0.963 × FC+0.067 × ASH. The mass fraction of oxygen in biochar could also be correlated to VM, FC, and ASH, while hydrogen was best correlated to a relationship with VM, FC, and VM/FC. Atomic ratios, such as H/C and O/C, used for biochar classification by international standards and carbon sequestration potential, were best correlated to VM/FC by the expressions H/C = 0.379 × VM/FC+0.251 and O/C = 0.188 × VM/FC+0.035. The developed correlations were proven to accurately classify biochar when the biochar had been made at ≥400 °C.