Air heating-alkaline hydrothermal production of artificial humic acid: Rapid and efficient humification of waste biomass

Natural humic acid (NHA) is formed by plant remains through a long geochemical and biochemical processes and is essential for soil fertility. However, the long natural formation process and the inadequacy of artificial humification methods limit its wide application. In this study, artificial humic acid (AHA) is efficiently prepared from cypress sawdust by a simple air heating-alkaline hydrothermal process. Multiple characterisation analyses reveal the reasons for the increased humification potential of sawdust after air heating and suggest possible reaction mechanisms. The results show that the yield of AHA after air heating at 240 °C and hydrothermal reaction is as high as 37.01%, which is higher than the yields reported in similar literature. Compared with commercial mineral potassium humate, the artificial potassium humate shows superior root growth promotion in wheat hydroponics experiments. This study provides a circular sustainable development pathway that biomass derived from the soil and returns to the soil after humification.