Image analysis study of mill products from batch tests on Brunswick mining and Smelting mill tailings

An image analysis study was performed to determine the behaviour of sphalerite during laboratory batch tests on recovering zinc from a sample of Brunswick Mining and Smelting mill tailings containing 1.8 wt % zinc. A zinc concentrate grading 45.5 wt % zinc with a recovery of 62% had been obtained in the laboratory batch tests by regrinding to 80% minus 18 pm, floating a rougher concentrate, and cleaning five times. Image analysis studies of the products showed (1) that regrinding increased sphalerite liberation to 77.5% from 39%, (2) that 70% of the free and 35% of the unliberated sphalerite were recovered in the final concentrate, (3) that the free sphalerite grains lost in the rougher and first cleaner tails were all sizes, (4) that the free sphalerite grains lost in the second to fifth cleaner tails were smaller than 18 pm with most being smaller than 4 pm, and (5) that the unliberated sphalerite grains recovered in the final zinc concentrate were larger than 4 pm. These results explain why good recoveries were obtained from the reground mill tailings, and provide new data on the recovery of free and unliberated sphalerite from a low grade feed by conventional flotation.