Characterization And Regulation Mechanism Of Low Rank Coal Hydrophobicity Based On Surface Energy Distribution

The poor natural floatability of low rank coal is the bottleneck problem restricting the utilization of low rank coal resources.Many studies showed that there were many oxygen-containing functional groups on the surface of low rank coal,and the oxygen-containing functional groups could interact with water molecules through hydrogen bond,therefore deteriorating the hydrophobicity of low rank coal surface.In recent years,researchers improved the surface hydrophobicity of low rank coal mainly by adding surfactants and composite agents.Although many kinds of reagents were used,there was a lack of unified measurement to improve the surface hydrophobicity of low rank coal.This is mainly because the surface properties of low rank coal are heterogeneous,so it is necessary to comprehensively characterize the surface properties of low rank coal.The surface energy distribution of low rank coal is a series of surface energy values under different surface coverages.Compared with the contact angle,the surface energy distribution can more comprehensively characterize the hydrophobicity of low rank coal surface.Firstly,through experimental exploration and theoretical analysis,the conditions such as temperature,probe reagent,coverage range,sample particle size range and density range required for the measurement of surface energy distribution of low rank coal were determined.After that,the relationship between the surface energy distribution and the contact angle,the relationship between the contact angle and the surface functional groups,and the relationship between the surface energy distribution and the composition of the functional groups of low rank coal were established through the micro infrared test,the contact angle test and the surface energy distribution test on the same testing area.Then,the relationship between the flotation effect of low rank coal and the surface energy distribution was established through the surface energy distribution test and micro flotation test.It was innovatively proposed that high energy characteristic value representing a small part of the surface?₉₀ was the key factor determining the hydrophobicity of low rank coal.According to this conclusion,the reagent selection strategy for improving the hydrophobicity of low rank coal was proposed.Finally,the selectivity of low rank coal maceral reagent adsorption was studied by using the characterization of surface energy distribution,and the relationship between low rank coal composition structure,low rank coal surface energy distribution and low rank coal hydrophobicity improvement reagent selection was further clarified.The main conclusions are as follows:In the study of the relationship between functional group composition and contact angle of low rank coal,the micro-infrared test and contact angle test were carried out on the testing areas of polished low rank coal samples,and semi-quantitative ratios PACHal/PAC=O?1700+PAC=Car/PAC=O and(2PACHal+PAC=Car)/(3PAC=O?1700+PAC=O?1650)were proposed as indexes affecting the surface hydrophobicity of low rank coal,which quantitatively reveals the relationship between the functional group composition and hydrophobicity of low rank coal.In the study of the relationship between the surface energy distribution of low rank coal and the contact angle,the testing areas in the contact angle test were used to test the surface energy distribution.The results showed that with the increase of surface energy distribution characteristic value?₉₀,the contact angle showed a decreasing trend.The results showed that the aromatic structure was the main reason for the increase of the nonpolar component of surface energy;The carbonyl structure was the main reason for the increase of the polar component of surface energy.In the study of surface energy distribution and flotation effect of low rank coal,the relationships between surface energy distribution,flotation rate and flotation recovery were studied.The results showed that in the flotation process,the materials with lower surface energy can float faster,while the materials with higher surface energy can float slower.In the surface energy distribution,the high energy characteristic value representing a small part of the surface?₉₀ was the key factor determining the hydrophobicity/floatability of low rank coal.The selection strategy of flotation reagent for low rank coal based on the adjustment of surface energy distribution should be:the calculated adhesion work W_adh between low rank coal and the reagent by using the surface tension of reagent molecules and the characteristic value?₉₀ should be greater than the corresponding adhesion work between water and low rank coal;The Gibbs function of low rank coal in water interacting with air bubble?G_pwb in the low coverage(n/n_m<0.05)should be changed to negative after the conditioning of reagent;Amphiphilic agent molecules containing both polar and nonpolar ends should be used in combination with nonpolar hydrocarbon oil agents,and combined with the characterization of surface energy distribution to avoid reverse adsorption.