Study On The Mechanism Of Enhancing Low-rank Slime Filtration With Combined Filtration Aids

Filtration has a long history,which is one of the common methods for solid-liquid separation.In mineral separation industry,filtration is an indispensable process.With the increase of mechanization degree of coal mining and the decline of coal quality,the output of fine coal is increasing,and the proportion of coal processing is increasing,in which poor dewatering results increasingly attracted people's attention.Based on industrial production,the most representative low-rank coal slime samples were taken from a Coal Preparation Plant belonging to Shenhua Shendong Coal Group.Low-rank coal slime has a low dewatering rate and a high moisture content of filtration cake due to it's small particle size,rich hydrophilic oxygen-containing functional groups and poor hydrophobicity.In order to fully understand the properties of the test samples,the test samples were tested by modern equipment such as X-ray diffractometer,Fourier transform infrared spectroscopy,industrial analyzer,laser particle size analyzer and contact angle measuring instrument.On the basis of literature research and experiments,the application status and shortcomings of filter aids are summarized,and their mechanism is analyzed.Based on the mechanism,a combination of filter aids to enhance the dewatering of low-rank coal slime is proposed.The test results showed that the combined filter aid can improve the filtration speed and reduce the moisture content of filter cake.The improvement mechanism of filtration was analyzed by the means of three-dimensional X-ray imaging system,on-line particle size detection system,surface tensiometer and fluid simulation.The test results show that:1)For filtration,Cetyltrimethylammonium bromide(cationic surfactant)is better than sodium dodecylbenzene sulfonate(anionic surfactant).The dehydration effect of non-ionic polyacrylamide is better than that of anionic and cationic polyacrylamide,but the molecular weight and ionicity of flocculant for filter aid should not be too high.The effect of non-ionic polyacrylamide is more notable than anionic and cationic polyacrylamide,but the molecular weight and ionicity of flocculant for filter aid should not be too high.2)The combined filter aid is superior to the traditional surfactant filter aid and flocculant filter aid in reducing the moisture content of filter cake and improving the filtration speed.3)The results of three-dimensional X-ray imaging system show that the inner pore of filter cake is not uniformly distributed.The pore rate and fractal dimension in the top of filtration cake is higher than that in the bottom of filtration cake.The average pore size in the top of filtration cake is smaller than that in the filtration cake.The combination of filter aids can reduce the fractal dimension of the pore and increase the porosity at some positions of the cake,so as to improve the filtration effect.4)Fluid simulation shows that the flow field inside the cake is complex.With the increase of hydration on the surface of particles and the decrease of pore size,the average flow velocity of filtrate decreases,and the decrease rate of dynamic pressure increases,which leads to the decrease of dehydration speed.The combined filter aid can improve the hydrophobicity of the particle surface,weaken the hydration effect and reduce the flow resistance of the pore side wall to the filtrate,besides,combined filter aid can widen the capillary pore size,thereby improving the filtration speed.