Advances and challenges in humic acid production technologies from natural carbonaceous material wastes

Abstract

Humic acids (HAs) play a crucial role in enhancing agro-environmental sustainability by acting as synergistic intermediaries between soil, water, fertilizers, microbiomes, and plant nutrition. Due to the slow nature of natural humification, advanced production and activation techniques are essential for efficient HA production. Cleaner valorization of natural carbonaceous materials (NCMs)—including mining byproducts such as lignite, brown coal, leonardite, weathered coal, and peat—into HAs is critical for advancing the global circular economy and providing sustainable solutions for soil rehabilitation and environmental restoration. This review comprehensively evaluates the latest advancements in HA production and activation technologies from NCMs. Various methods are analyzed, including extraction techniques, catalytic oxidation processes, microbial activation, hydrothermal conversion routes, and solid-phase mechano-activation methods. The findings highlight that catalytic oxidation techniques and free radical mechanisms uniquely enhance HA synthesis, while hydrothermal conversion routes offer an energy-efficient process with high HA yields and a low carbon footprint. This review also examines the reaction mechanisms and functionalization of HAs, detailing their emerging applications in agriculture, environmental management, biofuel production, energy storage materials, clinical treatments, medical and healthcare products, cosmetics, and animal feed supplements. Several improvement strategies for current production and activation methods are identified, and potential future research directions to maximize HA production are outlined. These insights aim to raise awareness within the scientific community about the vast potential of HA production and activation technologies, driving advancements in humification methods and contributing to the growth of a circular economy.