Junxia Wang, Shicheng Dong, Haiguang Fu, Nianhua Liu, Chengjie Guo, Xi Li, Xiaoqiang Cui, Youjun Zhang, Beibei Yan, Guanyi Chen
The degradation of soil organic matter and nutrient depletion pose challenges for global agricultural sustainability. In this work, a hydrothermal humification (HTH) process was developed to simultaneously address these challenges by converting K-rich Canna indica biomass waste into artificial humic acids (HA) and K-enriched fulvic acids (FA-K) without external potassium sources. The results revealed that alkali concentration was the dominant factor, with 1 mol·L –1 NaOH yielding the highest HA yield (17.91% at 180 °C) by promoting lignocellulose depolymerization and polycondensation. Increasing alkalinity (≥1 mol·L –1 NaOH) promoted the migration of endogenous K, releasing over 81.54%–91.36% into the liquid phase. The released K + preferentially associated with liquid-phase fulvic acid (LFA), forming −COO-K coordination complexes and reaching concentrations of 50.74–53.62 mg·g –1 under 1 mol·L –1 NaOH conditions. Spectroscopic analyses identified carboxylate groups (−COO – ) as the primary coordination sites responsible for K retention within the oxidized aliphatic frameworks of LFA. A dual-pathway mechanism was proposed in which the lignin-derived aromatics polymerized into HA, while lipid/carbohydrate hydrolysates assembled into carboxyl-rich LFA acting as efficient potassium carriers. This study establishes a sustainable waste-to-resource approach for the concurrent production of humic substances and organic K fertilizers, offering a feasible pathway toward resource circularity and enhanced agricultural resilience.