Chemical precipitation processes valorizing two waste streams amalgamating Fe-rich welding wastewater and P-rich swine slurry leachate into FePO4

Abstract

Phosphorus (P) is a finite resource, necessitating regulated extraction. This study recovered P from solid swine slurry (SSS) as FePO₄ through acid leaching and precipitation. Two systems—conventional batch stirred reactor (CBR) and fluidized-bed reactor (FBR)—were used to recover phosphorus as iron phosphate from SSS. Optimal P leaching was achieved with 0.16 mol/L HCl and an L/S ratio of 60 mL/g, reaching 99% leaching efficiency. FePO₄ was precipitated by adding Fe(III)-rich industrial wastewater at a 1.6:1 molar ratio and controlling the mixing solution pH to 4.5. The CBR system achieved 95.3% P removal, while the FBR reached 52.4% crystallization and 96.2% total P removal. Analyses confirmed the FePO₄ purity, with FBR products having lower water content (7.1%) compared to the batch system (91.8%). This study demonstrates the potential for P recovery by converting Fe-rich industrial wastewater and SSS-derived P into FePO₄.