Study On The Attachment And Spreading Behavior And Mechanism Of Compound Collector At The Low Rank Coal / Water Interface

Low rank coal is an important part of coal production and supply in China.It has the characteristics of low metamorphism,high water content,high content of oxygen functional groups on the surface,poor hydrophobicity and many pores on the surface.All these characteristics affect the adsorption of traditional hydrocarbon oil collectors on the surface of low rank coal,resulting in high reagent consumption and low flotation efficiency.In order to solve these problems,this paper uses the dodecane ester complex collector to strengthen the flotation process of low-rank coal,and proves the adhesion behavior,spreading wetting behavior and spreading driving mechanism of dodecane ester complex collector at the solid/liquid interface under the flotation condition,which provides the basis for the improvement of quality and high-efficiency flotation of low-order coal.In this paper,Daliuta coal is used as the test coal sample,the dominant particle size of the test coal sample is-0.045 mm,the ash content is 22.59%,and the content of fine coal slime is high;the gangue in the coal sample is mainly quartz,kaolinite and calcite,and there are a lot of cracks on the surface of low rank coal;the coal sample contains a variety of oxygen-containing functional groups,among which the content of hydrophilic groups(C-O,C=O,O-C=O)reaches 52.8%.In addition,the contact angle of coal sample is 57.5 °,and its hydrophobicity is weak.Dodecane,ethyl butyrate,ethyl octanoate,ethyl dodecanoate,dodecane-ethyl butyrate,dodecane-ethyl octanoate and dodecane-ethyl dodecanoate were selected as the research objects.The effects of different collectors on the induction time,adhesion strength,wetting heat and infrared spectrum of low rank coal surface were studied.The results show that the order of induction time is: dodecan-ester< ester< dodecane,which shows that the combination of collectors shortens tehe induction time and strengthens the adhesion effect between the collectors and coal particles.The results of EDLVO theoretical calculation show that: in the long range,the dodecane-ester compound agent and ester have no obvious advantages over dodecane,but in the short range of force,the effect of dodecane ester composite collector and coal particle is stronger due to the hydrogen bond formed between the polar group of ester and coal surface and the hydrophobic effect of dodecane.In the analysis results of wetting heat and infrared spectrum,dodecane-ester compound collector has great wetting heat release,and the polar and non-polar groups contained in the collector form stableadsorption with the polar and non-polar groups on the surface of low-rank coal respectively,which enhances the adhesive strength of the collector and makes it difficult to fall off.The spreading behavior and driving mechanism of dodecane-ester compound collectors at the low rank coal/water interface and the influence of coal surface roughness on spreading behavior were studied.The results showed that the absolute spreading coefficient of different collectors in the spreading process of low rank coal/water interface was ethyl butyrate> dodecane> dodecane-ethyl butyrate> ethyl octanoate> dodecane-ethyl octanoate> dodecane-ethyl dodecanoate> ethyl dodecanoate.The smaller the absolute value of spreading coefficient is,the stronger the adsorption of collector on coal surface is.The order of equilibrium contact angle is opposite to spreading coefficient.The spreading speed is mainly affected by the viscosity of collector.The higher the absolute value is,the faster the spreading speed is.According to the molecular dynamics model,the molecular substitution length λof the dodecane ester complex collector is the comprehensive distance of the point of the surface hydrophobicity of the low rank coal,which is smaller than the substitution distance of the single collector,and the molecular exchange frequency of the dodecane-ester compound collector is obviously smaller than that of the single ester.The higher the molecular exchange frequency is,the faster the spreading speed is,the easier the collector spreads and the smaller the activation free energy is.The combination of dodecane and ester can promote the spread of collector droplets at the low rank coal/water interface,make the spread more thorough,but also have some adverse effects on the spread speed of the three-phase contact line.The decrease of roughness will enhance the surface hydrophobicity of low rank coal,increase the equilibrium contact angle,reduce the spreading coefficient and the molecular substitution length of micro droplets,and promote the spreading of micro-droplets.However,the decrease of roughness reduces the actual wetted area of the droplet,slows down the energy consumption of the system,and slows down the free energy decline speed of the spreading system.The experimental results show that the collection effect of ester collector is better than that of dodecane under the condition of single collector;when dodecane-ester collector is used,82.38% of clean coal yield and 8.84% of clean coal ash can be obtained under the condition of 3kg/t of the best dosage.The compound collector can promote the spread and adhesion of droplets on the surface of low rank coal,so as togreatly enhance the collector’s collection ability,improve the recovery rate of clean coal and ensure its selectivity.There are 53 pictures,16 tables and 121 references in this paper.