Study On The Law Of Ammonia Nitrogen Migration And Transformation In Underground Reservoir In Coal Mine Area

Bulianta mine in Shendong mining area of Shenhua Shendong Coal Group was chosen as the research area in this paper.The coal gangue packed in the underground reservoir and mine water of the mining area were taken as the research objects.XRD/XRF,scanning electron microscope（SEM）,low temperature liquid nitrogen adsorption capacity test and some conventional detection and analysis technology are used.On the basis of the detection and analysis of the mine water and gangue,combined with the hydrogeological environment of the underground reservoir in the research area,through the indoor column simulation experiments were carried out to study the migration and transformation of ammonia nitrogen（NH₄⁺-N）in the underground reservoir of the mining area.The main conclusions are as follows:（1）The test results of XRD/XRF showed that illite is the main clay mineral of the gangue,accounting for 43.3%.Moreover,the BET specific surface area of the gangue is6.95m²/g,which has the characteristics of large specific surface area,strong adsorption and abundant pore structure.There were obvious over standard phenomena of NH₄⁺-N and total nitrogen（TN）the influent water in the underground reservoir（W₁）and the coal roof aquifer drenches water（W₃）in the study area.After the pretreatment of coal gangue in the underground reservoir,the removal rate of"three nitrogen"could reach over 96.99%.Therefore,the gangue filled in the underground reservoir has a positive removal effect on the nitrogen in the mine water.（2）Under the condition of Darcy flow rate of 2.0（±0.06）m L/min and 25℃,the migration velocity（v）and dispersion coefficient（D_L）of NH₄⁺-N are only 0.07 of the corresponding value of tracer Cl^-,and the retardation coefficient（R_d）is 14.35,which further proved that coal gangue has strong adsorption and retardation effect on migration of NH₄⁺-N.Before 170.0h,the contents of NO₃^--N and NO₂^--N began to increase markedly with the accumulation of NH₄⁺-N concentration.Results of the calculation of nitrogen balance showed that the reduction of NH₄⁺-N was 537.38mg,of which the adsorption accounted for 37.07%.It was concluded that the decrease of 62.93%of NH₄⁺-N quality was closely related to NO₃^-,NO₂^-and gaseous nitrogen-containing substances produced by nitrification and denitrification.It is easy to enrich NO₂^--N by incomplete reduction of NO₃^--N,and the maximum value of NO₂^--N was 2.15mg/L.（3）During the process of column simulation experiment,the overall p H value showed a slowly rising trend and was always higher than the influent solution,which was related to the consumption of H⁺in the process of increasing nitrite content in the later stage of the experiment and the dissolution of the alkaline substances on the gangue surface.After the conductivity value reached the highest value（373.9μS/cm）in 176.0h,it decreased to343.5μS/cm,which was correlative with the enhancement of nitrification and the escape of nitrogen produced by denitrification,which resulted in the decrease of ion contents in water body.With the later"three nitrogen"content tending to be stable,the EC value fluctuated between 335.0μS/cm and 349.8μS/cm.The study of this paper is of great significance to the evaluation of the evolution mechanism of mine water quality and the prevention and control of environmental risks in the underground reservoirs of ecologically fragile mining areas in Western China.