Effect of low-carbon coal gangue on the stability and dissolved organic matter characteristics of co-pyrolysis biochar: insights on pyrolysis temperatures and minerals

Abstract The stability and dissolved organic matter (DOM) characteristics of biochar have an essential effect on carbon emission and migration and transformation of pollutants. In this work, straw biochar and coal mine waste (coal gangue)-straw co-pyrolysis biochar were produced at 300, 450, and 600 °C. The effects of coal gangue on biochar's stability, carbon structure, and the components of biochar-derived DOM were investigated. The results showed that coal gangue enhanced co-pyrolysis biochar's thermal and chemical stability by 1.16%–8.25% and 39.17%–68.36%, respectively. They also promoted the aromatization process of co-pyrolysis biochar when the pyrolysis temperature increased from 300 to 450 °C. The co-pyrolysis biochar-derived DOM content was lower than biochar-derived DOM by 35.79%–55.52%, indicating that coal gangue inhibited the release of DOM. Moreover, coal gangue increased the humification degree of biochar-derived DOM at low pyrolysis temperatures but accelerated the decomposition of aromatic molecules in biochar-derived DOM at high pyrolysis temperatures. The proportion of low-aromatic humic-like substance increased from 1.28% to 50.87% in biochar-derived DOM but from 1.44% to 88.14% in co-pyrolysis biochar-derived DOM with increasing pyrolysis temperature. Thus, the pyrolysis temperature and coal gangue have a synergistic effect on controlling the stability and DOM characteristics of biochar. Moreover, the synergistic effect of three primary minerals in coal gangue (SiO 2 , Al 2 O 3 and Fe 2 O 3 ) is the core mechanisms of impacting the biochar stability and DOM characteristics. This work provides essential information for biochar applications by showing that adding coal gangue can boost the stability of biochar and modify the molecular properties of biochar-derived DOM. Graphical Abstract