【作者】 罗颖；

【导师】 刘埔；

【作者基本信息】 贵州大学 ， 地质工程， 2023， 硕士

【摘要】 酸性矿井水（AMD）对环境的污染不仅表现在采矿过程中,在矿井闭坑后仍会对环境造成巨大威胁。贵州省高硫煤炭资源分布广泛,煤矿闭坑的增多势必会对岩溶地下水系统的水质造成影响。而当闭坑矿井采空区上覆为碳酸盐岩地层时,AMD在回弹过程中会与之相互作用,但这一反应过程尚不明确。因此,本课题利用室内实验,通过设计不同的水动力条件、不同碳酸盐岩地层厚度、不同AMD初始pH值、不同AMD初始Fe²⁺浓度四个影响因素,来研究闭坑矿井地下水在回弹的过程中,AMD与碳酸盐岩接触并反应的水文地球化学过程。重点分析了四个不同影响因素下反应过程中各水化学参数的变化特征,并阐明了各因素对各参数的影响规律;根据空间上的取样测试结果,揭示了AMD在反应过程中的时空变化机制;采用矿物饱和指数SI、Eh-pH图、XRD、SEM-EDS、Ca²⁺/Mg²⁺释放量等多种手段来解析碳酸盐岩对AMD的缓冲机制;并构建了AMD-碳酸盐岩-地下水相互作用的数学模型。取得的主要研究成果如下:（1）反应过程中各水化学参数的变化特征:各组实验pH值均表现为先快速上升,再缓慢上升并逐渐趋于平稳的趋势。Fe在反应过程中均表现为先下降再趋于平稳的趋势,当水动力条件改变之后,Fe的下降速率加快;而各组实验Mn在反应过程中总体呈下降趋势。（2）各因素对pH、Fe、Mn的影响:当水动力条件越强,AMD的pH值上升的越快;水动力条件的增强有利于Fe、Mn浓度的降低,在相同水动力条件下,Mn的降低速率要小于Fe。当碳酸盐岩的地层厚度越大时,pH值的上升速率越快,Fe、Mn的下降速率亦越快,且地层厚度的改变对Fe的影响大于Mn。在淹没阶段,初始pH值越低,AMD的pH上升速率就越慢,在排水阶段初期,初始pH值越低,pH的上升速率越快。反应过程中,初始pH=3更加有利于Fe、Mn浓度的降低。当AMD的初始Fe²⁺浓度越高时,Fe浓度的下降速率越快,初始Fe²⁺浓度对Mn浓度的降低具有一定的影响,表现为初始Fe²⁺增高会抑制Mn浓度的降低。（3）AMD在空间上的扩散机制:在淹没阶段,岩溶地下水的补给使得水平方向上AMD中H⁺、Ca²⁺、Fe、Mn的扩散表现为从远离补给端扩散到补给端的过程。垂直方向上,AMD中H⁺、Fe、Mn的扩散总体上是自下而上的;H⁺浓度在整个反应过程中均出现上下分层的现象,Fe、Mn浓度在反应前期出现上下分层的现象,在反应后期逐渐趋于一致,而Ca²⁺则是向四面八方而扩散的。在排水阶段,水流流速是AMD扩散的主控因素,总体而言,水流流速的加快使得各离子浓度趋于一致。（4）碳酸盐岩对AMD的缓冲机制:碳酸盐岩对AMD的pH的缓冲机制为方解石和白云石消耗AMD的H⁺,从而提升AMD的pH值。碳酸盐岩对AMD的缓冲效应与AMD自身的pH值相关,表现为当AMD的初始pH值越低,碳酸盐岩所起到的缓冲效应就越大,且水动力条件越强、碳酸盐岩的地层厚度越大、初始AMD的Fe²⁺浓度越低时,碳酸盐岩对AMD的pH的缓冲就越快。针对闭坑矿井地下水回弹并与碳酸盐岩接触的这一反应过程,提出了如下概念,反应过程中Ca²⁺/Mg²⁺的释放量可作为碳酸盐岩与AMD反应的缓冲因子。碳酸盐岩对AMD重金属的缓冲机制为:提高溶液的pH而引起Fe（Ⅱ）的氧化,Fe（Ⅱ）氧化过程中会释放·OH并生成纤铁矿（γ-FeOOH）和针铁矿（α-FeOOH）的沉积物。Mn在反应过程中主要是以吸附或共沉淀的方式来降低。（5）AMD-地下水-碳酸盐岩反应的数学模型:pH在淹没阶段的数学表达式均遵循一元一次线性函数,而排水阶段数学表达式均表现为底数为e的指数函数。Fe、Mn在淹没阶段和排水阶段的数学表达式均表现为底数为e的指数函数。更多还原

【Abstract】 Acid mine water（AMD）pollution to the environment is not only manifested during the mining process,but also poses a great threat to the environment after mine pit closure.High-sulfur coal resources are widely distributed in Guizhou Province,and the increase of coal mine pit closures will inevitably affect the water quality of karst groundwater systems.And when the closed pit mine void area is overlain by a carbonate formation,AMD will interact with it during the rebound process,but this reaction process is not yet clear.Therefore,this project uses indoor experiments to investigate the hydrogeochemical processes of AMD contacting and reacting with carbonate rock during the rebound of groundwater in closed pit mines by designing four influencing factors:different hydrodynamic conditions,different thickness of carbonate rock strata,different initial pH of AMD,and different initial Fe²⁺concentration of AMD.The characteristics of the changes of each water chemistry parameter in the reaction process under four different influencing factors were focused on,and the influence law of each factor on each parameter was elucidated.The spatially sampled test results reveal the mechanism of spatio-temporal variation of AMD in the response process.Various means such as mineral saturation index SI,Eh-pH diagram,XRD,SEM-EDS,Ca²⁺/Mg²⁺release were used to resolve the buffering mechanism of carbonate rock to AMD;and a mathematical model of AMD-carbonate-rock-groundwater interaction was constructed.The main research results obtained are as follows.（1）Characteristics of the changes in each water chemical parameter during the reaction.The pH values of all groups of experiments showed a trend of rapid increase,then slow increase and gradual stabilization.Fe showed a trend of decrease and then stabilization during the reaction process,and the decrease rate of Fe was accelerated when the hydrodynamic conditions were changed;while Mn in all groups of experiments showed an overall decreasing trend during the reaction process.（2）Effect of each factor on pH,Fe,and Mn.When the hydrodynamic conditions are stronger,the pH of AMD rises faster;the enhanced hydrodynamic conditions are favorable to the decrease of Fe and Mn concentration,and the decrease rate of Mn is smaller than that of Fe under the same hydrodynamic conditions.when the thickness of the carbonate formation is larger,the pH rises faster,and the decrease rate of Fe and Mn is also faster,and the change of the formation thickness has a greater effect on Fe than Mn.in the flooding stage,the lower the initial pH,the slower the pH rise rate of AMD.The lower the initial pH value,the slower the pH rise rate of AMD,and the lower the initial pH value,the faster the pH rise rate at the beginning of the drainage stage.During the reaction,the initial pH=3 was more favorable to the reduction of Fe and Mn concentration.When the initial Fe²⁺concentration of AMD was higher,the rate of decrease of Fe concentration was faster,and the initial Fe²⁺concentration had a certain influence on the decrease of Mn concentration,which showed that the increase of initial Fe²⁺would inhibit the decrease of Mn concentration.（3）Spatial diffusion mechanism of AMD.In the inundation stage,the recharge of karst groundwater makes the diffusion of H⁺,Ca²⁺,Fe and Mn in AMD in the horizontal direction appear as a process from far from the recharge end to the recharge end.In the vertical direction,the diffusion of H⁺,Fe and Mn in AMD is generally bottom-up;the H⁺concentration is stratified up and down throughout the reaction process,the Fe and Mn concentrations are stratified up and down in the early stage of the reaction,and gradually converge in the late stage of the reaction,while Ca²⁺is diffused in all directions.In the drainage stage,the water flow rate was the main control factor for the diffusion of AMD,and in general,the acceleration of the water flow rate made the concentration of each ion converge.（4）Buffering mechanisms of carbonate rocks against AMD.The buffering mechanism of carbonate rocks on the pH of AMD is that calcite and dolomite consume H⁺of AMD,thus raising the pH of AMD.The buffering effect of carbonate rock on AMD is related to the pH value of AMD itself,which shows that when the initial pH value of AMD is lower,the buffering effect played by carbonate rock is greater,and the stronger the hydrodynamic conditions,the greater the thickness of the stratum of carbonate rock,and the lower the initial Fe²⁺concentration of AMD,the faster the buffering effect of carbonate rock on the pH of AMD.For this reaction process of groundwater rebounding and contacting with carbonate rocks in closed pit mines,the following concept is proposed:the amount of Ca²⁺/Mg²⁺released during the reaction can be used as a buffering factor for the reaction of carbonate rocks with AMD.The buffering mechanism of carbonate rocks against AMD heavy metals is:increasing the pH of the solution and causing the oxidation of Fe（Ⅱ）,which releases·OH and generates deposits of fibrous iron ore（γ-FeOOH）and needle iron ore（α-FeOOH）during the oxidation of Fe（Ⅱ）.Mn in the reaction process is mainly reduced by adsorption or co-precipitation.（5）Mathematical model of AMD-groundwater-carbonate rock reaction.The mathematical expressions of pH in the flooding stage all follow a linear function of unity,while the mathematical expressions in the draining stage all exhibit an exponential function with base e.The mathematical expressions of Fe and Mn in both the flooding and draining stages exhibit an exponential function with base e.The mathematical expressions of Mn in the flooding and draining stages all exhibit an exponential function with base e.更多还原