Controlling the Composition and Magnetic Properties of Nano-SrFe₁₂O₁₉ Powder Synthesized from Oily Cold Mill Sludge...

This paper proposes a new method for producing nano-SrFe₁₂O₁₉ powder by the citrate precursor route using solid waste as a source of iron. This solid iron-containing waste, which exists in the form of an oily sludge, is produced by a cold rolling mill. This sludge was first subjected to a process, including sulfuric acid leaching, oxidation, precipitation, and nitric acid leaching, to obtain an iron nitrate (Fe(NO₃)₃) solution. Next, the Fe(NO₃)₃ solution was mixed with a strontium nitrate (Sr(NO₃)₂) solution obtained by subjecting strontium carbonate to nitric acid leaching. Subsequently, citric acid, as chelating agent, and ammonia water, as precipitating agent, were added to the mixed solution to form a gel. The gel was dried and spontaneously combusted, then annealed at different temperatures for 2 h in flowing air. The effects of the Fe³⁺/Sr²⁺ molar ratio and annealing temperature on the formation, morphology, and magnetic properties of SrFe₁₂O₁₉ were investigated. The results showed that single-phase SrFe₁₂O₁₉ powder was obtained by decreasing the Fe³⁺/Sr²⁺ molar ratio from the stoichiometric value of 12 to 11.6 and increasing the annealing temperature to 1000 °C for 2 h. Adjustment of the Fe/Sr molar ratio to 12 and the annealing temperature to 900 °C enabled the magnetic properties to be optimized, including saturation magnetization (Ms) 80.2 emu/g, remanence magnetization (Mr) 39.8 emu/g, and coercive force (Hc) 6318 Oe.