Valorization of Foundry Waste into Iron-Based Coagulant and Ceramic Additives

Abstract Wastewater purification from suspended and colloidal impurities remains a critical challenge for industrial and municipal water management. This study proposes a sustainable iron-based coagulant synthesized from foundry waste, enabling simultaneous wastewater treatment and industrial waste recycling. The magnetic fraction of foundry dust (Fe ≈ 47.7 wt%) was leached with HCl to produce an iron-containing coagulant, while the non-magnetic fraction was evaluated for ceramic applications. The obtained coagulant demonstrated high purification performance at an optimal dose of 37.5 mg/L, achieving > 95% removal of suspended solids within pH 5–7 across three types of model wastewater (clay 5 g/L, glaze 10 g/L, dairy 40 mL/L). Compared to commercial FeCl 3 , the experimental coagulant required up to 6–12 times lower dose to reach 97–98% clarification efficiency. This effect is attributed to the simultaneous presence of iron species and polysilicic flocculants formed during waste acid treatment. Additionally, leaching residues and the non-magnetic fraction were successfully incorporated (10–30 wt%) into artistic ceramics without compromising density or water absorption. The proposed approach demonstrates a dual environmental benefit – valorization of iron-rich industrial waste and reduced chemical consumption during coagulation – contributing to SDG 6 (Clean Water and Sanitation) and SDG 12 (Responsible Consumption and Production).