Effect And Mechanism Of Flotation Reagents On Desulfurization And Deashing Of Bituminous Coal

With the decrease of high-quality coal resources and the enhancement of mechanized coal mining in China,a large number of high ash and high sulfur fine coal slimes have been produced.Traditional flotation reagents can not meet the demand for desulfurization and deashing of these difficult floated slimes.In this paper,JZ bituminous coal and GS bituminous coal were taken as the research objects,the collector and frother were emulsified with surfactants,and the mechanism of emulsified flotation reagents was discussed.The desulfurization and deashing effect of depressants on bituminous coal flotation was also studied,and its mechanism was analyzed by adsorption test,FTIR and XRD.Firstly,kerosene was emulsified with non-ionic surfactants Span20 and Tween80,anionic surfactant sodium dodecyl benzene sulfonate(SDBS)and cationic surfactant cetyltrimethylammonium bromide(CTAB).The results showed that the clean coal yield and combustible matter recovery of JZ bituminous coal flotation were improved after kerosene emulsification.Kerosene emulsified by Tween80 and Span20 had little effect on the deashing,and the flotation perfection index of kerosene emulsified by Span20 was slightly better than Tween80,but the ash rejection of kerosene emulsified by SDBS and CTAB decreased greatly and the flotation perfection index decreased.Kerosene emulsified by Span20 with different quality ratio of oil to water had little effect on the flotation of JZ bituminous coal,and the emulsified kerosene with ratio of oil to water of1:1 had better stability.Similarly,kerosene emulsified by Span20 improved the clean coal yield and combustible matter recovery of GS bituminous coal flotation.This was because the surfactant interacted with the oxygen-containing functional groups on the coal surface through hydrogen bond and other ways and covered the polar surface,which led the reduction of the charge carried by the coal particles,the enhancement of the hydrophobicity and increasement of the floatability,so as to improve the flotation effect.Secondly,surfactants sodium oleate(SO),CTAB and Span20 were used to emulsify sec-octyl alcohol.The results showed that the flotation effects of sec-octyl alcohol emulsified by SO-Span20 and CTAB-Span20 were similar,but the stability of sec-octyl alcohol emulsified by CTAB-Span20 was better.Under high collector dosage,emulsified sec-octyl alcohol had little effect on JZ bituminous coal yield,but the deashing effect was better and the flotation perfection index was improved;At low collector dosage,sec-octyl alcohol emulsified by CTAB-Span20 improved the flotation yield of GS bituminous coal.This was because the surfactants reduced the surface tension of water,made the impurity minerals easier to be wetted and retained in the slurry,and produced more dense and stable bubbles,which promoted the floating of coal particles.In the flotation deashing test of JZ bituminous coal,carboxymethylcellulose sodium(CMC)showed a strong inhibitory effect on kaolinite and other impurity minerals,which significantly increased the ash rejection of clean coal,but the yield decreased.Through the adsorption test of kaolinite and low ash coal on CMC,it could be seen that the adsorption capacity of CMC on the surface of kaolinite was about four times that of coal.This adsorption difference increased the surface charge of particles which enhanced the electrostatic repulsion and promoted the dispersion of coal and impurity mineral particles.It was the inhibition of CMC that significantly reduced the flotation rate of JZ bituminous coal,and its flotation process conformed to the classical first-order kinetic model.Under the flotation conditions of 400 g/t emulsified kerosene,100 g/t emulsified sec-octyl alcohol and 125 g/t CMC,the ash rejection reached 47.93%.In the flotation desulfurization and deashing test of GS bituminous coal,sodium silicate(SS)achieved good sulfur rejection and ash rejection,and did not have a great impact on the yield of clean coal.Through the analysis of various forms of sulfur content in clean coal obtained under different conditions,it was found that flotation reagents emulsification improved the removal of iron sulfide sulfur,and SS improved the rejection of iron sulfide sulfur and sulfate sulfur,but they had little effect on the removal of organic sulfur in coal.FTIR and XRD analysis showed that SS inhibited pyrite and significantly reduced the content of impurity minerals such as kaolinite,quartz and calcite.According to the fitting results,the flotation process of GS bituminous coal under the action of SS also conformed to the classical first-order kinetic model.After adding SS,the flotation rate did not decrease,but increased slightly.Under the flotation conditions of 1200 g/t emulsified kerosene,150 g/t emulsified sec-octyl alcohol and 400 g/t SS,the sulfur rejection and ash rejection reached 33.20% and 48.92% respectively.