Experimental Study On Treatment Of Acid Mine Drainage With PRB Combination Materials

China is the world’s largest coal producer and consumer.For a long time,coal energy has made great contributions to Chinese rapid economic development.However,with the advancement of“Energy Supply-side Structural Reform”,after a large number of coal mines were closed,the gobs were no longer drained.Under the replenishment of atmospheric precipitation and other water sources,the gobs were filled with water.The sulfur-containing minerals in the gobs reacted with water to generate sulfuric acid,which makes acid mine drainage.When the acid mine drainage from coal mines enters the water cycle directly or indirectly,it will pollute the ecological environment and affect people’s production and life.Therefore,it is necessary to treat the acid mine drainage.In this paper,loess and steel slag were used as materials for the treatment of acid mine drainage.Firstly,the pH enhancement effect and Fe²⁺and Mn²⁺removal effect of loess and steel slag on acid mine drainage at different treatment time and different dosage conditions and steel slag at different particle sizes were studied by static experiments;meanwhile,the structure,morphology,element distribution and content of loess and steel slag before and after treatment of acid mine drainage were characterized by X-ray Powder diffractometer,Scanning Electron Microscope and X-ray Energy Dispersive Spectrometer,and the results were combined with kinetic models to analyze the mechanism of Fe²⁺and Mn²⁺removal by loess and steel slag.Secondly,the effect of different ratios of loess/steel slag materials on the pH enhancement of acid mine drainage and the removal of Fe²⁺and Mn²⁺at different flow rates were studied through dynamic experiments,and the ability of different ratios of loess/steel slag materials to remove Fe²⁺and Mn²⁺was evaluated according to the effluent quality.The main findings of this study include:（1）The longer the loess treatment time and the larger the dosage,the better the treatment effect of acid mine drainage.Loess can increase the pH of the solution to neutral within 15min,the removal rate of Fe²⁺and Mn²⁺increased rapidly within 60 min,and the removal rate of Fe²⁺continued to increase with time after 60 min,while the removal rate of Mn²⁺increased but the increase was small;the increase of loess dosage has a nearly linear relationship with the increase of Fe²⁺and Mn²⁺removal rates.After the treatment of acid mine drainage,the CaCO₃of loess decreased,a small amount of CaSO₄was produced on the surface,the porous structure was replaced by fillers with no obvious structure,the content of Caelement on the loess surface decreased,and the content of Fe and Mn elements increased.The removal of Fe²⁺and Mn²⁺by loess is more in line with the pseudo-second-order kinetic model.CaCO₃in loess dissolves in water and produces OH^-,which combines with H⁺to raise the pH value.Combined with the results of loess characterization analysis and kinetic model fitting results,the removal of Fe²⁺and Mn²⁺by loess is mainly chemical adsorption.（2）The treatment effect of steel slag on acid mine drainage was improved with the increase of treatment time,the increase of dosage and the decrease of particle size.The increase of pH value and the removal of Fe²⁺by steel slag have been increasing with time,and the removal of Mn²⁺is basically saturated at 180 min;the increase of steel slag particle size will reduce the ability of steel slag to treat acid mine drainage,especially the removal effect of Mn²⁺;the increase of slag dosage was nearly linear with the increase of pH value,Fe²⁺and Mn²⁺removal rate.Fe（OH）₃precipitates on the surface of the steel slag after the treatment of acid mine drainage,the porous structure is replaced by the petal-like structure,and the content of Caelement on the surface of the steel slag decreased the most,the Fe element content increased significantly,and the Mn element content was not significantly enhanced.The removal of Fe²⁺and Mn²⁺by steel slag is more consistent with the pseudo-first-order kinetic model and the intra-particle diffusion model.The CaO in the steel slag reacts with water to generate OH^-,which combines with H⁺to raise the pH value.According to the results of steel slag characterization analysis and kinetic model fitting,it can be seen that the removal of Fe²⁺by steel slag is mainly by chemical precipitation,and the removal of Mn²⁺is mainly by adsorption.（3）In the dynamic experiment of simulating the permeable reactive barrier,it is better to treat acid mine drainage when the volume ratio of loess/slag is 15:15（column B）than the volume ratio of loess/slag is 25:5（column A）.The days when the pH value of the effluent of columns A and B were kept above 10.00 were 7 days and 19 days,respectively.The removal rates of Fe²⁺in the effluent were 70.74%and 85.85%,and the removal rates of Mn²⁺in the effluent were 37.97%and 68.66%,respectively.In the early stage of the dynamic experiment,the combined loess/steel slag materials can release enough alkaline oxides to raise the pH value to alkaline.At this time,the precipitation effect of the combined materials on Fe²⁺and Mn²⁺is much greater than the adsorption effect,but with increasing the flow rate to shorten the hydraulic retention time and the loess/slag combined material being consumed,the ability of the loess/slag combined materials to raise the pH value decreased,and the removal of Fe²⁺and Mn²⁺changed from precipitation to adsorption,and the effluent concentration of Fe²⁺and Mn²⁺increased,and finally the effluent Mn²⁺concentration was greater than the influent Mn²⁺concentration.