Experimental Study On The Effect Of Surface Modification On Fine Low-rank Coal Dehydration

Due to the high degree of mechanization technology in mining and mineral processing,a large amount of secondary fine slime has been produced in recent years.As consequence,the coal slurry treatment has become a great challenge to most coal preparation plants,especially the slurry dewatering for long flame coals,non caking coals and other steam coals.The surface of low rank coals is known to have many oxygen-containing functional groups and abundant natural capillary pores.For that reason,most low rank coals are strongly hydrophillic and their slurries are geneally of difficulty in detwatering.Although extensive studies have shown that high rank coal slimes could be effectively dewatered using surfactants,little work has been done with respect to dewatering ow rank coal slimes.In view of this,different ionic type surfactants and inorganic salts with different valence states were used to modify the surface of fine-grained low-rank coal to improve the dehydration effect,and the filter-assising mechanism was analyzed.It provides a reference for the selection of reasonable dehydration agents for low-rank coal preparation plants,and also brings some help to other researchers in this direction.The coal ash used in the test is 32.05%,the fine particle grade?-0.074mm?content is 79.02%;the high density grade(+1.6 g·cm^-3)in the coal sample accounts for 55.66%of the whole sample,and its surface contains Many hydrophilic groups?-OH,CO,C=O,Si-O-Si,etc.?;the impurity minerals in coal samples were mainly quartz,chlorite,kaolinite,muscovite and pyrite.In the single factor exploration test of filter aid,the inorganic salt shows that the greater the ion concentration,the higher the ion valence state,the better the dewatering effect of the slime.When the surfactant is used for dewatering of coal slime,the dehydration effect of DTAC in cation is better than that of CTAB.The anionic dehydration effect is not good,and the non-ionic Tween85 has the best dehydration effect.When the inorganic salt and the surfactant act synergistically,the dehydration effects of the Tween85 group and the sodium oleate group were significantly improved,and the filter cake moisture of the cationic DTAC group was increased.The effects of coal slurry water pH,chemical agitation adsorption time,slime density and slime particle size on the synergistic drainage of inorganic salts and surfactants were explored.When the slime water is acidic,the filtration speed can be increased.When neutral,the filter cake moisture can be reduced.The adsorption equilibrium time of the DTAC group,the Tween85 group and the sodium oleate group are about 120s,240s and 300s respectively;the higher the slime density,the filter cake moisture The higher the filtration rate,the smaller the filtration rate;when the coal slurry has a large content of coarse coal,the moisture of the filter cake is greatly reduced,and the filtration speed is also significantly increased.When the content of the fine coal is large,the opposite is true.Studying the effect of inorganic salts on the surface tension of surfactant solutions,Inorganic salt ions can promote the filtration of nonionic and anionic surfactants,but have an inhibitory effect on cationic surfactants.From the effect of filter aid on the zeta potential of coal slurry surface,the higher the cationic valence state of inorganic salt,the more significant the positive displacement of Zeta potential,the more obvious the compression electric double layer;DTAC and Tween85 can cause the zeta potential to move forward,oil Sodium is the opposite.From the perspective of increasing the contact angle of the coal sample after the treatment,the surfactant+inorganic salt>single surfactant>single inorganic salt.From the infrared spectrum analysis,it can be seen that the three surfactants can bond with the hydrophilic functional groups on the coal surface,which reduces the hydrophilic area of the coal surface and promotes the dehydration effect;FeCl3 can promote nonionic and anionic surfactants and pro-The water functional group is bonded,but the opposite is true for the cationic surfactant.From the SEM analysis,Tween85 has a"washing"effect on the shale powder on the surface of the coal particles;and ferric chloride can further promote the"washing"effect.From the hydration of coal samples,the higher the valence and concentration of inorganic salts,the lower the hydration degree;the DTAC is significantly faster than the Tween85 and sodium oleate,and the final hydration value of Tween85 in reducing the rate of hydration.Lower than DTAC and sodium oleate.