Boosting the extraction of humic acid from HCl-activated weathered coal catalyzed by oxygen vacancy-rich CuO nanoparticles

Abstract

The efficient extraction of humic acid (HA) from weathered coal is crucial for its high-value utilization. However, conventional methods often suffer from low extraction yields and insufficient product purity. To address these limitations, this study proposes a novel synergistic strategy combining “hydrochloric acid activation pretreatment” with “catalytic oxidation”. Specifically, weathered coal was first pretreated with hydrochloric acid to enhance its hydrophilicity and remove impurities. Subsequently, the activated coal was subjected to targeted oxidative degradation using hydrogen peroxide (H₂O₂) catalyzed by CuO nanoparticles rich in oxygen vacancies. This synergistic process significantly enhanced the HA extraction yield from a baseline of approximately 50% in the raw coal to over 91.5% (based on the residue). Characterization results revealed that the hydrochloric acid treatment effectively improved the pore structure and surface properties of the weathered coal. Meanwhile, the oxygen vacancies in the CuO nanoparticles greatly promoted the activation of H₂O₂ to generate hydroxyl radicals (˙OH), which efficiently cleaved the macromolecular cross-linked structures in the coal. This work develops an efficient and green method for extracting HA from weathered coal and provides a new catalytic chemical pathway for the high-value utilization of coal resources.