Value-Added Humic Acid Derived from Lignite Using Novel Solid-Phase Activation Process with Pd/CeO2 Nanocatalyst: A Physiochemical Study

Soil, air, and water pollution caused by lignite is considered a serious environmental problem. Activation methods thus have been developed to extract humic acid from lignite to support the agricultural production as the soil amendment or fertilizer synergist. The traditional activation methods of humic acid from lignite, however, are not environmentally friendly. As the first study, this work developed a novel solid-phase activation method with a Pd/CeO2 nanocatalyst for lignite-derived humic acid. This study analyzed the morphology and structures of the as-synthesized Pd/CeO2 nanocatalyst with various characterization tools. The mechanisms of the Pd/CeO2 nanocatalyst for lignite activation were determined. The Pd/CeO2 catalyst effectively promoted the production of water-soluble humic acids from lignite via KO H solid-phase activation at room temperature. It increased the amount of small molecular active groups and the corresponding small molecules of humic acid. The existence of a strong synergistic effect at the interface sites between Pd/CeO2 nano particles and lignite was one of the key factors for the outstanding catalytic performance. In conclusion, this study has great application perspectives for reducing lignite pollution and increasing humic acid utilization by crops, which can improve the sustainability of the environment and agricultural systems.