Process design for the magnetic recovery of iron from desulphurised hot metal slag

Abstract

Desulphurised Hot Metal Slag (DHMS) from ArcelorMittal South Africa Newcastle Works was beneficiated using a drum magnetic separator under dry conditions. DHMS particle sizes from -1400µm to 106µm were classified into nine size classes and their behaviour under basic magnetic separation parameters was observed. The nine size classes were then consolidated into four classes; -1400+850µm, -850+300µm,-300+106µm and -106µm size respectively. The aforementioned particle size classes were used to study the effects of magnetic separation parameters on iron recovery in more detail. It was observed that low intensity dry magnetic separation did not work effectively for particle sizes that are 106µm and below. Particles in this size range i.e. below 106µm were found to have a relatively low iron content of < 18% in the feed and after magnetic separation, their magnetic stream was only upgraded to 25% Fe, which is below the satisfactory grade thresh hold. The most optimal magnetic recovery was achieved when particles below 106µm were excluded and the remaining size classes of the DHMS were collectively upgraded from 55.26% Fe to 69.47% Fe. However, the sulphur content in the final product stream was still relatively high at 2.58% S compared to the 2.91% S initially in the feed. The aforementioned results were obtained at a feed rate of 11g/s, splitter position at 75% fully open and at a magnetic field strength of 641 gauss. The test work was considered a success since the final product has sufficient iron content for use as a high-sulphur source of iron during the production of high sulphur steel grades in the steel making process. A conceptual process flow sheet to achieve this level of beneficiation of DHMS was proposed and a high level feasibility study indicates that the capital expenditure for the process is approximately R3.1 million with a one year payback period. The net present value was positive at R1.71 million while the internal rate of return (IRR) was found to be 23%. This indicates that this project would be worthwhile for operations that are currently disposing at least 18 375 tons of DHMS per year which could otherwise be economically recovered.