Introducing a recycling method for iron oxide from cold forming mild scale and its application in alkyd resin-based primer paint

Millions of tons of iron oxide-rich sludge waste are generated yearly by the steelmaking industry, posing significant environmental disposal challenges. This study aimed to develop a sustainable and economical technology by recycling this secondary material, specifically cold-forming oxide sludge, into a high-performance iron oxide pigment for use in corrosion-resistant coatings. The methodology involved a multi-stage purification process applied to the raw sludge: initial drying, separation of organic contaminants using a methanol solvent, magnetic separation to remove residual iron, and subsequent fine mechanical milling using a jet mill. The resulting powder was subjected to a crucial heat treatment at 400 ℃ to homogenize the microstructure. Finally, the refined iron oxide powder was mixed with an alkyd resin base and additives to successfully formulate a dark brown, liquid anti-rust and corrosion primer paint. The structural and chemical purity of the recovered pigment were characterized using XRD and XRF, while particle size and morphology were determined via DLS and SEM analysis, which indicated a particle size of approximately 50 to 100 nm. The performance of the final paint was rigorously validated against the ISIRI 4817 standard, employing tests such as salt spray (ASTM B117), pull-off adhesion (ASTM D4541), scratch resistance, humidity exposure, and resistance to petroleum solvents. The material characterization confirmed the successful recovery of the desired iron oxide phases (Fe 3 O 4 , Fe 2 O 3 , and Fe). The final primer paint demonstrated excellent barrier and mechanical properties, achieving a high adhesion rating (5B per ISO 2409), a satisfactory viscosity of 103.5 KU, and passing the 240-hour salt spray test with minimal defect rating. These results conclusively validate the feasibility of using waste steel sludge to produce a high-performance, anti-corrosion primer paint.