Experimental Study On The Effect Of Electrochemical Action On The Surface Properties And Water Absorption Of Coal

Coal seam water injection plays an important role in dust control,hard coal softening,top coal caving,rock burst prevention and coal and gas outburst prevention.At present,the research of coal seam water injection mainly focuses on the influence of water injection parameters and methods on coal seam water injection,but seldom considers changing the characteristics of coal and rock.In view of this,the electrochemical modification experiments of the long flame coal from Suancigou Coal Mine of Inner Mongolia Yitai Group,the coke coal from Shaqu Coal Mine of Shanxi Huajin Coking Coal Co.,Ltd.and the anthracite from Sihe Coal Mine of Shanxi Jincheng Anthracite Coal Industry Co.,Ltd.are carried out,and the effect of the electrochemical modification is analyzed.The main work and conclusions are as follows:?1?The moisture,ash,volatile matter,fixed carbon,maximum reflectance of vitrinite,macerals,minerals,chemical composition,element composition,pore structure and mechanical properties of long flame coal,coking coal and anthracite were tested.The test results show that the lower degree of metamorphism is long bituminous coal,with undeveloped internal and external fissures,low hardness,low brittleness,high porosity,large pore structure and strong hydrophilicity;the medium degree of metamorphism is coking coal,with high hardness and stable properties;the anthracite has the highest degree of metamorphism,hard texture,high brittleness,micropore development,large specific surface area and high aromatization degree.The CMC of SDS was0.008 mol·L^-1 at 25?measured by conductivity method.The variation of surface tension of SDS solution with solution concentration was measured by surface/interfacial tensiometer.?2?Based on the electrochemical electrophoresis principle and electrochemical oxidation reaction principle,an electrochemical modification device was built.Deionized water,0.05mol·L^-1Na₂SO₄ and 0.05mol·L^-1SDS were selected as electrolytes,and the potential gradients were 0V·cm^-1?0.5V·cm^-1?1V·cm^-1?2V·cm^-1 and 4 V·cm^-1,respectively.The electrochemical modification experiments of long flame coal,coking coal and anthracite were carried out.?3?The surface properties of long flame coal,coking coal and anthracite before and after modification,such as surface groups,pH value,Zeta potential and coal/water dynamic contact angle,were tested.The results show that with the increase of the degree of metamorphism,the oxygen-containing functional groups of natural coal samples decrease.With the increase of potential gradient,the number of oxygen-containing functional groups on the surface of modified coal sample increases.Zeta potentials of the three coals are all negative potentials,and the electronegativity decreases with the increase of the degree of metamorphism.After electrochemical modification,the modified coal sample/solution dispersion system in the anode region is acidic,and the pH value decreases exponentially with the increase of potential gradient,while the Zeta potential moves linearly and positively with the increase of potential gradient;the modified coal sample/solution dispersion system in the cathode region is alkaline,and the pH value increases exponentially with the increase of potential gradient,and the Zeta potential increases exponentially with potential gradient.The increase moves in an exponential direction.The oxidation reaction in the anode area produces H⁺,and the reduction reaction in the cathode area produces OH^-.The acidic ions in the anode area dissolve and guide the pore and fissure of coal body by electroosmosis.The alkaline ions make clay minerals separate from coal body and move to the anode by electrophoresis.The dynamic contact angle between coal and water is measured by mechanical method,which avoids the disadvantage of large deviation of the results obtained by optical method due to the heterogeneity of coal and rock materials,and cannot accurately characterize the overall wettability of coal and rock.With the increase of metamorphism degree,the coal/water dynamic contact angle of coal sample increases.With the increase of metamorphism degree,Zeta potential of coal sample moves towards positive charge direction,and dynamic contact angle of coal/water increases.The dynamic contact angle between coal and water decreases with the increase of potential gradient.?4?The water absorption of three kinds of coal samples with different metamorphic degree before and after modification was tested.The results show that the saturated water content of natural coal samples decreases with the increase of coal metamorphism.The water absorption of three kinds of coal samples with different metamorphic degree has similar block size effect.With the decrease of coal sample size,the faster the water absorption rate of coal sample is,the greater the saturated water absorption rate is.When the block size is 0.3-0.5mm,the saturated water absorption of natural coal samples from long flame coal is 12.85%,that of natural coal samples from coking coal is 7.48%,and that of natural anthracite coal is 5.99%.The saturated water absorption of natural coal samples of long flame coal is 11.21%,that of natural coal samples of coking coal is 6.05%and that of natural coal samples of anthracite is 4.75%when the lump is 45-50 mm.The saturated water absorption of coal sample is changed by electrochemical modification.The electrochemical modification of deionized water as electrolyte improves the saturated water absorption of coal samples,but the modification has little effect.The electrochemical modification of sodium sulfate as an electrolyte reduces the saturated water absorption of coal samples.The electrochemical modification of SDS as an electrolyte improves the saturated water absorption of coal samples.When the block size is 45-50mm,the saturated water absorption of the modified longflame coal in the anode area of SDS solution electrochemical modification increases by 9.3%,the saturated water absorption of the modified coke coal increases by 6.7%,the saturated water absorption of the modified anthracite increases by 5.14%,the saturated water absorption of the modified longflame coal in the cathode area of SDS solution electrochemical modification increases by 10.51%,and the saturated water absorption of the modified coke coal increases by 6.86%.The saturated water absorption of modified anthracite increased by 5.67%.