Effect Of Surface Modification Of Low Rank Coal Pickling On Flotation And Its Mechanis

With the continuous improvement of mechanized mining degree and mining quantity of low-rank coal in China,the quantity of fine low-rank coal and ash content have also risen sharply.Low-rank coal contains a large number of oxygen-containing functional groups and polar groups.The surface of low-rank coal is rough,the pore is developed,and it is easy to oxidize and slime,which results in poor hydrophobicity of low-rank coal surface,difficulty in mineralization,low flotation efficiency,high drug consumption and difficult to enter industrial application.Therefore,improving the flotation efficiency of low rank coal is an important technical problem that must be faced and urgently solved in the field of coal preparation.Therefore,Sheng 6 lignite and Zhuanlongwan coal were taken as the research objects in this paper,starting from the surface characteristics of low-rank coal,research on the influence of different modification conditions(pickling concentration,pickling time,pickling temperature)on induction time,flotation efficiency and degree of surface hydration of low-rank coal.Using modern analytical testing methods to study the changes of surface properties and flotation efficiency of low-rank coal after pickling,and then analyze the mechanism of the effect of low-order coal surface modification on coal-to-bubble mineralization.The coal quality characteristics of the two coal samples were analyzed by XRD,FTIR,XPS,SEM and other modern analysis methods.The results show that the ash content of the two coal samples is high,and there are a large number of oxygen functional groups,especially SHM coal samples.The highest content of oxygen functional groups is C-O-C/C-OH,The impurity minerals in the two coal samples are mainly quartz,followed by clay minerals(including kaolinite,oblique silica,and Ge zeolite).The surface of the two coal samples is rough,especially in the SHM coal sample,there are a large number of cracks and depressions.In addition,ZLW coal sample is medium-sized floating coal,while SHM coal sample is the most difficult to float coal.The results of induction time show that with the increase of the concentration of acid solution,the induction time of the two coal samples decreases sharply first and then decreases gradually until it is gentle.With the increase of pickling temperature,the induction time of the two coal samples decreased first and then increased.When the temperature was 70 °C,the induction time was the smallest.With the lengthening of the pickling time,the induction time of both coal samples decreased.And when the time reaches 7h,the induction time is the lowest.However,the reduction of the induction time of the ZLW coal sample is much larger than the reduction of the induction time of the SHM coal sample.The results of flotation test of coal samples show that with the increase of the concentration of acid solution,the recovery curves of combustibles of the two coal samples have the same trend,which increases sharply at first and then decreases to a flat level.The pickling temperature and pickling time have improved the flotation effect of the two coal samples,but the effect is not significant.When the pickling temperature is 70 °C,the recoverability of the combustibles of the two coal samples is the highest,when the pickling time is 7h,the recovery rate of combustibles of coal samples is the highest.In addition,with the increase of hydrochloric acid concentration,the increase rate of flammable body recovery rate of ZLW coal sample(100.01%)is much larger than that of SHM coal sample(91.82%).The hydration degree formula f=0.4k-1 was derived by Einstein's viscosity theory to characterize the degree of hydration on the surface of coal samples under different modification conditions.The results show that the modification of the two coal samples by acid washing can reduce the degree of hydration on the surface of the coal sample,and the degree of hydration of coal surface can be affected by increasing pickling temperature and prolonging pickling time appropriately.The degree of hydration on coal surface is the lowest when the temperature is 70 C or the pickling time is 7 h.By investigating the surface properties of the two coal samples before and after pickling,it is concluded that the surface roughness of the SHM coal sample is large and there are a large number of depressions and pores compared with the ZLW coal sample.Therefore,when the two coal samples are pickled with a hydrochloric acid solution,the surface area of the SHM coal sample is more in contact with the hydrochloric acid solution.It is more advantageous for the organic group to undergo a substitution reaction with the chloride ion,so that the oxygen-containing functional group is removed more.But the minerals encapsulated in coal or embedded in cracks are not easy to dissociate,so the removal rate of minerals is low..In addition,the content of oxygen functional groups and minerals on the surface of SHM coal sample is higher,so even if the content of hydrophilic minerals and functional groups on the surface of coal sample is reduced,the improvement effect of surface hydrophobicity of SHM coal sample is far worse than that of ZLW coal sample.Therefore,the improvement of the SHM coal sample flotation effect is far lower than that of the ZLW coal sample.This paper has 38 figures,28 tables and 106 references.