Environmental Compliance of Ferrous Waste Moulding Sand and Best Foundry Practices for Hazardous Metals (Mn, Ni, and Cr)

The circular economy approach aims to reduce raw material use and limit landfill disposal of industrial by-products. In the metal casting industry, waste foundry sand (WFS) disposal is a persistent financial and environmental challenge due to hazardous metal contamination. This study assessed three South African ferrous foundries’ sand streams—virgin, fettling/shot blast, and moulding/shakeout—using the toxicity characteristic leach procedure (TCLP) under the South African Waste Management Act. Results showed that while virgin sand was inert, fettling/shot blast and shakeout sands contained elevated Cr (0.024–1.02 mg/L), Mn (62–97 mg/L), and Ni (0.14–3.26 mg/L), exceeding inert waste thresholds (Cr: 0.05 mg/L; Mn: 0.5 mg/L; Ni: 0.07 mg/L). The shakeout sand, which accounts for 50–70% of total foundry waste, was the most critical stream. Particle size analysis revealed that the majority of sand (70%) falls between 600 and 75 µm, with hazardous metals concentrated in fine fractions (150 µm) had low leachability and characteristics comparable to virgin sand. A simple size segregation treatment reduced hazardous metal content by up to 93–97%, rendering 75–85% of shakeout sand inert, while only 10–15% (fine portion) required hazardous waste disposal. These findings highlight that targeted removal of fines can substantially reduce disposal costs and environmental risk, supporting greener and more sustainable foundry operations.