Phosphorus partitioning and recovery of low-phosphorus iron-rich compounds through physical separation of Linz-Donawitz slag

摘要

The Linz-Donawitz(LD) steelmaking process produces LD slag at a rate of about 125 kg/t. After metallic scrap recovery, the non-metallic LD slag is rejected because its physical/chemical properties are unsuitable for recycling. X-ray diffraction(XRD) studies have indicated that non-metallic LD slag contains a substantial quantity of mineral phases such as di- and tricalcium silicates. The availability of these mineral phases indicates that LD slag can be recycled by iron(Fe)-ore sintering. However, the presence of 1.2wt% phosphorus(P) in the slag renders the material unsuitable for sintering operations. Electron probe microscopic analysis(EPMA) studies indicated concentration of phosphorus in dicalcium silicate phase as calcium phosphate. The Fe-bearing phases(i.e., wustite and dicalcium ferrite) showed comparatively lower concentrations of P compared with other phases in the slag. Attempts were made to lower the P content of LD slag by adopting various beneficiation techniques. Dry high-intensity magnetic separation and jigging were performed on as-received samples with particle sizes of 6 and 3 mm. Spiral separation was conducted using samples ground to sizes of less than 1 and 0.5 mm. Among these studies, grinding to 0.5 mm followed by spiral concentration demonstrated the best results, yielding a concentrate with about 0.75wt% P and 45wt% Fe.