Mineral-enriched biochar produced from metal-cutting fluid sludge delivers enhanced phosphate recovery

Phosphate recovery via mineral-enriched biochar has attracted widespread attention, but studies investigating the uptake are limited. In this study, we prepared novel Al/Fe-rich biochars by a one-step process of pyrolyzing metal-cutting fluid sludge (MCFS) at various temperatures (500, 600, and 700 °C) to facilitate phosphate recovery from aqueous solutions. The findings revealed that the MCFS-based biochar was rich in mineral metal oxides and possessed a well-developed pore structure, significant surface area, and functional groups, all of which contributed to the creation of active sites for phosphate adsorption. The Langmuir model revealed that MCFS-500 efficiently adsorbed phosphate from aqueous solutions, demonstrating an outstanding sorption capacity of 92.58 mg P/g. The Fe and Al hydroxides and oxides present within biochar play significant roles in the phosphate adsorption process. Overall, the MCFS-derived biochar presents a cost-effective and feasible method for phosphorus recovery, introducing an innovative approach for both the secure disposal of MCFS and the recovery of phosphate from wastewater.