Characterization and Flotation of BOF Dust for Zinc Removal

摘要

Reduction of zinc impurities is a prerequisite for recycling of BOF (Basic Oxygen Furnace) Sludge to the blast furnace operations. Results from SEM (Scanning Electron Microscope) and XRD (X-Ray Diffraction) analyses indicated a disproportional distribution of zinc in different sized fractions of the sludge, with higher levels of zinc accumulating in the finer fractions. Specks of zinc impurities were observed around spherical iron cores. This shell-like distribution seems to reflect the pattern of zinc volatilization and condensation out of the BOF. A mechanism for the release of zinc from molten iron during oxygen lancing was proposed. Flotation was examined as a possible method to reduce the zinc content of BOF sludge to an acceptable level. The experimental approach involved floating zinc-bearing phase(s) from the slurry into a small mass as a froth product and leaving the zinc depleted residue in the cell as a tailing product. Sized fractions of flotation products were analyzed for zinc and iron to confirm prior flotation testing with coarse fraction (+38 μm), which indicated a reduction of the zinc content of the tails to about 0.36% (from 1%). Further tests were carried out using an experimental design approach to find out the statistical significance of various flotation parameters. In view of encouraging results from the flotation experiments, a preliminary cost analysis was undertaken for a possible industrial scale application. It was estimated that fixed capital cost of a 200 TPD treatment facility could be about $950,000 CAN.