Opportunities of Integrating Slow Pyrolysis and Chemical Leaching for Extraction of Critical Raw Materials from Sewage Sludge

Slow pyrolysis is a promising technology to convert sewage sludge into char: stable solid product with high carbon and phosphorus content. However, due its heavy metals content, char use in agriculture avoided many European Union (EU) countries. This study aimed test solution, based on integrating slow chemical leaching, separate other inorganics from char, obtaining an inorganic P-rich fertiliser C-rich usable for industrial purposes. The was first characterized then processed 3 kg/h reactor at 450 °C 30 min. resulting by leaching acid (HCl, HNO3) alkali (KOH) reagents extract compounds. To optimize the extraction, three case studies have been considered. obtained contained around 78% d.b. (dry basis) of inorganics, 14% C, Al, almost 5% P. tests enabled 100% P, Mg, Ca char. remaining mainly (27%) silica (42%), surface area up 70 m2/g, as adsorbent or precursor sustainable materials.