Multi-Source Release Mechanism And Control Simulation Of Iron In Underground Water In Closed Coal Mine

The groundwater of closed coal mines mostly shows high iron characteristics.The remaining iron devices are easy to rust after pit closure and flooding,which can form a multi-source iron release system with primary minerals,thereby increasing the risk of groundwater pollution.On the other hand,the hydrothermal and spatial resources of closed mines can be used.This thesis aims at the core issues of groundwater pollution prevention and control in green pit closure and resource utilization of closed mines.Based on the investigation of hydrogeochemical environment and water chemistry model inscription of closed mines,taking multiple sources of iron in groundwater of closed coal mines as the research object,water-rock-gas reaction simulation experiments were carried out using water chemistry analysis techniques as well as microscopic characterization and analytical testing techniques.Electrochemical simulation experiments with pyrite and anchor rods which are representative of iron contamination sources in groundwater were carried out by electrochemical tools.The dynamic pattern of multi-source iron release from groundwater in closed coal mines is systematically studied,and the release mechanism and in situ control pathways are investigated jointly using numerical hydrogeochemical simulations.The main results are as follows.（1）Based on a 15-d simulated experimental study of the water-rock-gas reaction,the multi-source iron release pattern in groundwater of closed coal mines was revealed.The oxidation degree of both pyrite and anchor rod was significantly increased after the reaction of both in acid mine water than when they were reacted separately,and the proportion of oxidized Fe（III）and S（VI）on the surface of both materials was higher after the reaction,which further proved that the parallel presence of pyrite and anchor rod would accelerate the oxidation process of each other in acid mine water.（2）The redox environment brought by the switch between open and closed systems in closed coal mines is an important factor that induces the release of multi-source Fe.From the exploration of the electrochemical mechanism of multi-source Fe release in groundwater of closed coal mines,the oxidation process of pyrite in acid mine water under open conditions includes two processes,namely,the oxidation of pyrite to Fe²⁺and S and further oxidation to SO₄^2-when The process of oxidation of Fe²⁺to Fe³⁺.And the oxidation process of pyrite surface under closed conditions is not obvious,and the reduction process of S occurs on the surface of pyrite.Hydrogen precipitation corrosion occurred at the anchor electrode under both gas phase conditions,but the anchor electrode was less active in the nitrogen environment and less susceptible to oxidation reactions.When in acidic solution,anchor rods are more easily oxidized than pyrite,regardless of the oxygen level.（3）Based on the experimental simulation,the PHREEQC software was applied to establish a model of multi-source iron release from groundwater in closed coal mines,simulate the effects of temperature and p H on the multi-source iron release process in groundwater in closed coal mines,and put forward proposals for the regulation of multi-source iron release in closed coal mines.The results showed that the scarcity of oxygen（dissolved oxygen）greatly inhibited the oxidation of pyrite in the groundwater of the closed coal mine;the acidity of the groundwater environment could be kept at a low level at 25°C,and the solution could be kept in a weakly oxidative state by reducing the oxygen content in the environment;the water temperature could be adjusted to 30°C to reduce the oxidative nature of the environment under the condition of sufficient oxygen.Adjusting p H to 4 can inhibit the production of iron and sulfate at the same time,which also has some effect on controlling acidity.The simultaneous presence of anchor rod and pyrite will greatly accelerate the oxidation process of both.The temperature and p H of mine water can be regulated to achieve the purpose of controlling the pollution caused by the release of iron from multiple sources in closed coal mines.This thesis contains 49 figures,17 tables and 96 references.