Experimental study on hard-to-float coal slime flotation

with an aim to overcome the difficulties in flotation of difficult-to-float coal slime, an experimental study is conducted with the 1/3 coking coal slime as the target. Flotability analysis shows that the density fractions of the slime are predominantly in the 1.4～1.8 g/cm³ intermediate range with a yield of 62.87% and an ash of 18.24%, and it contains a high proportion of middlings, regarding it to be poor in selectivity; and the flotation concentrate is contaminated by fine slime as the < 0.045 mm size in the slime has a high yield of 32.67%, a factor causing the poor flotability of the slime. As indicated by results of batch flotation test, cleaning test on ash reduction as well as the cleaning plus tailings scavenging combined test, when flotation of the slime is carried out with the dosage of agent of 1.0 kg/t and the use of kerosene and secoctanol at a ratio of 4:1, the ash of the concentrate cannot be lowered to the required value simply through a roughing process.Result of test on ash reduction through timed-release cleaning process shows that a concentrate product with a yield of 25.01% and an ash of 11.57% and a yield of middling of 52.70%, with the ash of the concentrate being up to the required level; however, through only the cleaning process, the yield of tailing is excessively high and the middling fails to get effectively separated. By using one roughing + one cleaning + two scavenging combined process, the yield and ash of concentrate are 47.64% and 11.75%, respectively, and the yield and ash of middling are 35.65% and 23.64%, respectively, with the ash of tailing being as high as 80.21%, all up to the standards in quality indicators; and by using such a process, the yield of concentrate can see a rise of yield by 16.80 percentage points while the yield of middling is lowered by 17.17 percentage points due to the possibility of its sufficient separation, in comparison with the use of one roughing + two cleaning + two scavenging process. It is noted that in treating the difficult-to-float coal slime, appropriate increase of scavenging processes can improve flotation efficiency and quality indices of products, and the use of the one roughing + one cleaning + two scavenging process can lead to effective separation of the middling in tailing product of roughing process in a separate manner for reducing the possibility of contamination of concentrate by fine slime while ensuring the high ash of tailing product.