Aiding Effect Of Surfactants On Centrifugal Dewatering Of Coarse Coal Slimes

Coal washing is the foundation of its cleaning and efficient use.Because of the fact that water is used in most of washing process,the products would contain some water.There is very little research on dewatering of coarse coal slime in China and other countries,so most of the coal preparation plants are troubled by the same problem that the moisture of coarse coal slime is higher than what they want.It brings bad effects to the production storage,transport and downstream industries.It is necessary to find a method by which the moisture of coarse coal slime can be reduced effectively.In this research,Primary Alcobol Ethoxylate(AEO)surfactants,Polyethylene glycol sorbitan monolaurate(Tweens),alkylphenol ethoxylates(OP)surfactants,sodium fatty alcohol polyoxyethylene ether carboxylate(AEC)surfactants are used respectively to do dewatering experiments.Tunlan coal,Liuwan coal,Lijiahao coal and Majialiang Coal are the subjects of dewatering in the centrifuge.According to the dewatering results of Tunlan coal and Liuwan coal when using different surfactants in different dosages,the better dehydration agents are selected to do dewatering experiments on Lijiahao coal and Majialiang coal.The results show that almost all surfactants in the study have an aid effect on dewatering of the coal that is highly metamorphosed and has low content of oxygen such as Tunlan coal and Liuwan coal.However,there still exist some certain surfactants having no dewatering aid effect or having a dewatering aid effect only when they are used in a large dosage.That's because the surfactants are poor water solubility or even oil-soluble,which leads to bad contact with coal(OP-4,OP-7,AEO-3,AEO-4).Or the surfactants have high solidification point,so they are diffused slowly in the water and low efficiency of spreading on the surface of coal(Tween-40,Tween-60).The better surfactants selected also have a good aid effect on dewatering of Majialiang coal which has low content of oxygen like Tunlan coal and Liuwan coal.However,they have no aid effect on dewatering of Lijiahao coal which metamorphosed lowly and has high content of oxygen.The contact angle of coal and the surface tension of centrifugate are measured respectively when surfactants are used and when surfactants are not used.The thickness of the hydrated film on the surface of coal is measured by Atomic Force Microscopy(AFM)separately when surfactants are used and when surfactants are not used.Also,the surface of coal particle is scanned by scanning electron microscope(SEM).The contact angles of coal surface with Tween-20?Tween-40?Tween-60?Tween-80 and Tween-85 are 72.70°?71.70°?71.95°?73.50°and 75.25°respectively.All are higher than that of blank sample which is 68.25°.When using tween-85 with a concentration of 200 g / t and 400 g / t,the thickness of the hydration film on the surface of coal sample is 5.90 nm and 5.88 nm respectively,which is 1.92 nm and 1.94 nm thinner than that of the blank sample.The surface tension of the centrifugal fluid gradually decreases with the increase of the dosage of the medicament.The SEM scanning images of large particle coal show that the fine particles adsorbed on the surface of coal are obviously reduced after using tween surfactants.Therefore,the surfactant can promote centrifugal dehydration.The study indicates that one reason that the surfactants can have a good aid effect on dewatering in the centrifuge is that the coal on which surfactants are adsorbed is modified hydrophobically.As a result of the coal being modified hydrophobically,the hydrophilicity of coal decreased and the hydrated film turns thin.The other reason is the washing effect of surfactants to the larger coal particles.Fine particles adsorbed on the surface of coarse coal particles can't be washed down easily.They have large specific surface area and contain high moisture.When surfactants are used,the fine particles are washed down and centrifuged out with the centrifugate.So the moisture of coal dewatered in the centrifuge and using the surfactant is lower than the moisture of coal only dewatered in the centrifuge.It is also found that the surface tension of centrifugal liquid can be an indicator of aid effect when centrifuging.In addition,the influence of residual surfactant in the centrifugal fluid on the subsequent flotation is studied.The results show that the yield of clean coal increased after using filter aid,so the residual filter aid in the centrifugal fluid is beneficial to the subsequent flotation test.Tween-80 is selected as a filter aid for industrial testing at the Majialiang Coal Preparation Plant.The results show that Tween-80 has a certain effect on the filtration aiding of the Majialiang coal,and the clean coal moisture of the spiral sorter can be reduced from 12.28% to 10.43%.