Quantitative differentiation of coal, char and soil organic matter in an Australian coal minesoil

Organic inputs from plant establishment are part of the rehabilitation process in restoring coal minesoil function. Soil organic matter (SOM) content could therefore potentially be an indicator of rehabilitation success. Rehabilitated coal minesoils contain inherited coal and char that complicate the attribution of measured total C to recent SOM inputs. We provide proof-of-principle tests of ramped combustion thermal analyses combined with chemometrics (multivariate curve resolution-alternate least squares, MCR-ALS) to quantitatively distinguish between geogenic C, pyrogenic C and SOM C in model mixtures and a coal minesoil from Queensland, Australia. MCR-ALS successfully separated coal and char, and initial estimate thermograms improved the model fits. Geogenic C represented a small proportion of total organic C in the tested unknown minesoils (mean = 9.2%), and a larger contribution from pyrogenic C (mean = 32.4%). Trends in SOM were also consistent with Walkley-Black measurements of organic C. Our combined thermal-chemometric approach represents a robust means of quantifying SOM, distinct from coal and char, though resolution could be improved using multi-element thermograms and additional end-members and soils.