In the iron and steel industry, the production of narrow particle size distribution (PSD) for pellet feed making with acceptable liberation of valuables from the iron ore is very difficult. This study has been carried out to achieve desired pellet feed with narrow PSD and maximum liberation of hematite from the iron ore. The iron ores have been collected from three different sources (mines in Karnataka state) and milled. The iron ores and the blend feed samples were analyzed in the Optical Microscope (OM) and Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCAN) to understand the PSD and percentage of hematite liberation. The new approach is adapted to identify the retention time (RT) of the iron ore in the mill, and the total RT taken for the blend sample in the Bonds ball mill is considered as the reference grinding time for milling in the Laboratory Ball Mill (LBM). The desired narrow PSD (150/+10m) with acceptable hematite liberation is achieved at an optimal grinding time of 7min in the LBM.
The present research work is in joint collaboration with NITK, Surathkal, and JSW Steel Pvt. Ltd., Ballari. The authors are thankful to the management of JSW and MHRD, India, for all the support extended during the course of this research work.
Hanumanthappa, H., Vardhan, H., Mandela, G.R. et al. Investigation on Iron Ore Grinding based on Particle Size Distribution and Liberation. Trans Indian Inst Met 73, 18531866 (2020). https://doi.org/10.1007/s12666-020-01999-5
The application of vertical mills in regrind circuits is consolidated. This type of mill is now attracting interest in primary grinding applications, due to its higher efficiency when compared to ball mills, which are usually used at this stage. In this study, a coarse sample of iron ore was tested in a pilot scale grinding circuit with a vertical mill. Other three samples of pellet feed had already been tested with the methodology used in this study. The sample of coarse iron ore was characterized in laboratory tests carried out in a small batch ball mill. Selection and breakage function parameters were determined from the laboratory tests. The parameters were then used for simulating the pilot scale tests using Modsim software. The model previously implemented in Modsim has been successfully applied to represent the vertical mill operated with different ores. The simulations produced particle size distributions that were very close to the actual size distributions, and the predictions were accomplished only by imputing the calibrated parameters from the batch tests, the power draw and the feed size distribution of the pilot tests. The methodology is therefore useful for scale-up and simulation of vertical mills, only requiring laboratory tests that can be carried out in standard laboratory batch ball mills with small amounts of samples.
Laboratory-scale batch grinding tests were performed on 2 sieve size fractions of the almost pure hematite mined at the Carajas mine of CVRD Brasil. Good first-order kinetics of grinding were obtained, both for dry grinding and for grinding with water, using the Bond test levels of ball load and powder load. However, the primary breakage distribution functions were not dimensionally normalized, as smaller particles produced proportionally more fines on primary breakage, possibly due to internal porosity of the ore. The test results were scaled to the conditions of a pilot-scale mill in normal closed circuit, and a ball mill simulator was used to predict the capacity, circulating load and size distributions, employing the size selectivity values calculated from the balance around the hydrocyclone. The simulation results were in reasonable agreement with the observed values. The technique was then extended to predict the behavior of a full-scale mill at a capacity of 308metric tons/h and a circulating load of nearly 600%. Agreement between simulated results and plant test results was reasonable except that the simulator predicted a product (overflow) size distribution with a higher sharpness index than observed. The reason for this discrepancy is not known.