Ash Reduction Research On Low-rank Coal With High Slime Content

The reserves of low-rank coal in China is very big, but its utilization rate is far less than high-rank coal. Because of the low degree of coalification, the high ash content, the many oxygen-containing functional groups on the surface and the poor hydrophobic property, the flotation performance of low-rank coal is bad. And low-rank coal is fragile, it is easily mixed with a large number of coal slime, its argillization degree is high, so the separation is more worse. This paper aimed at ash reduction of low-rank coal with the high slime content and high ash content to conduct a series of reseaches.With the1#and2#low-rank coal slime of the Xizhao coal preparation plant as the research object, in order to reduce the ash of the clean coal, three ways were adopted including direct flotation, desliming flotation and gravity separation. The direct flotation has chosen more than ten kinds of flotation collector that have direct or reverse effect for the flotation of coal sample, desliming flotation aimed to the0.045-0.5mm material after screening, and gravity separation combined the coal slurry cyclone gravity separation column (Φ50mm) with the hydrocyclone (Φ50mm). The results of the tests were obtained as follows:1.The collectors (kerosene and N9858), cationic surfactant, anionic surfactant, non-ionic surfactant were used respectively for the flotation of1#coal sample, the results show that the effect of kerosene, cationic and anionic surfactants on the flotation are not ideal, only oil soluble span80(15%) and have a prominent role to promote the flotation effect.2.Several representative reagents were chosen the desliming flotation experiments for1#coal sample, the results of these experiments show that the coal sample’s hydrophobicity is improved obviously and its optional sex is improved after desliming.3. Three kinds of inorganic salt (NaCl, CaCl2and FeCl3) were selected for the flotation experiments of2#coal sample in the condition of the collector’s dosage is2500g/t and the foaming agent’ dosage is100g/t, their results were compared with the results of before adding inorganic salt to flotation system, it suggests that the addition of inorganic salt is not effect on the flotation of coal slime.4. The pH value of ore slurry was adjusted by using hydrochloric acid and caustic soda, and then conducted the pH experiments for1#coal slime, the results show that there is the best consequence when the coal slime are in alkaline conditions of pH=11.5. In the flotation systems after adding dispersant sodium hexametaphosph-ate and sodium silicate eliminate the effect of the fine mud on the coal surface, and further improve the flotation results.6. The best optimum condition of flotation experiments are that:the dosage of N9858is2500g/t, the dosage of frother is100g/t, the pH value of ore slurry is11, and the content of sodium hexametaphosphate is1000g/t. The best results are obtained that the production rate of cleaned coal is47.15%, the ash of cleaned coal is11.27%, combustible recovery is61.29%, and flotation perfect degree is44.56%.7. The gravity separation test researches were conducted under the conditions of different structural parameters including the cone structure, the diameter of underflow pipe and overflow pipe and different feed pressure by using the small diameter (Φ50mm) new type water-only cyclone. The results show that the ash of underflow is about80%and+0.045mm material of the overflow is only6%. It realizes efficient separation of the coal slime.8. Combining the new type water-only cyclone with the hydrocyclone can reduce effectively-0.045mm material of the overflow and the pollution of high ash fine coal and reduce the ash of clean coal to18%. This method is an effective way to reduce the ash and improve the quality for difficult-floated coal slime.