Sulfur Reduction by Wet Grinding Circuit Optimization of Golegohar Iron Ore Complex

Wet separation circuit of Golegohar iron ore plant includes comminution by overflow discharge ball mills and separation by low intensity magnetic separators. The average sulfur content of the concentrate is more than 1.2 %, which is higher than allowable limits for de-sulfurization and pelletizing plants (0.8 % and 0.1%, respectively). This problem is due to the low liberation degrees of sulfur bearing minerals (pyrite) discharging the ball mills. In this research, the optimum product size (P80; 80% passing size) to achieve the acceptable level of sulfur in the product by Davis tube test was found to be 100 microns. In order to increase the grinding efficiency and reach to the desired liberation degrees, the ball charge level and solids percent were studied as the main role playing factors. At the 33% ball charge and 68 percent solids, mill product particle size reduced from original size of 137 microns to 106 microns. The modification which were implemented in the whole circuit are increasing solid percent from 47 to 65%, increasing ball charge level from 27 to 33 volumetric percent and finally adding 20 mm diameter steel balls in mill No.2 with the usual 30mm balls. Mean residence time of materials in the ball mill were determined by tracing method to be about 8 minutes and was used to determine the time needed to achieve stability. Sampling over a period of a few months in the plant indicated that the product size is adjusted at 110 microns with 95 % confidence. After modification in the plant, due to finer mill discharge, the sulfur reduction criterion (ratio of feed sulfur content and wet concentrate) increased by 19% (relative).