Mechanochemical synthesis of calcium-biochar for decontamination of arsenic-containing acid mine drainage

Ca-biochar is an efficient material for As(III)-containing acid mine drainage (AMD) decontamination, while it is challenging to fabricate Ca-biochar with oyster shell waste as the Ca source due to its complex structure. Herein, a mechanochemical method was proposed to activate oyster shell waste and wood waste for Ca-biochar design and production, and its efficacy and relevant mechanisms for AMD detoxification were evaluated. The smaller size Ca-biochar produced by the medium-speed ball milling showed a higher As(III) removal (74.0 %) compared to high-speed ball milling (60.9 %), attributed to the formation of finer Ca(OH)₂ while avoiding particle aggregation, which could release more Ca (89.0 mg/g) and alkalinity for the co-precipitation of As. Meanwhile, wood-based biochar substrate served as a platform for co-precipitation, and its surface functionality supported the oxidative immobilization of As. This study presents a promising route for upcycling food and wood waste to produce Ca-biochar for AMD decontamination.