Study On The Interaction Mechanism Between Colloids And Iron In Groundwater In Closed Coal Mine Areas

The number of coal mines shuttered in China has risen year after year as a result of the coal industry’s“de-capacityization”and“carbon neutral,carbon peak”target requirements.Colloids are abundant in groundwater and can adsorb and carry heavy metals due to their enormous specific surface area and adsorption sites.This can affect the migration and transformation of heavy metals and other pollutants in groundwater.The groundwater of closed coal mines is typically characterized by high iron pollution.In order to analyze the characteristics and water chemistry types of groundwater in the closed mine area for this study,groundwater samples were collected at the site of the closed coal mine area.The colloids in the groundwater were extracted in a graded manner,and the colloids morphology and composition were analyzed by scanning electron microscopy（SEM）and energy dispersive spectroscopy（EDS）,and the colloids content was calculated by the weight method.In the meantime,inorganic colloids represented by Si O₂,and organic colloids represented by humic acid,humic acid-Si O₂composite colloids were chosen,and the effects of various hydrogeochemical conditions on the hydrodynamic diameter and Zeta potential of colloids coexisting with Fe were examined by carefully taking into account the groundwater chemical conditions in the study area.In order to study the migration behavior of colloids coexisting with Fe in the medium under the conditions of various influencing factors,indoor experiments using quartz sand as the test medium were used to simulate the adsorption and migration patterns of colloids coexisting with Fe in the aquifer under different hydrogeochemical and hydrodynamic conditions.The following are the primary conclusions:（1）The dissolution of iron-bearing minerals in coal-bearing strata and the Fe structures left in the roadways after the mine closed are the sources of the study area’s high total Fe content in the water samples.The p H of the groundwater in the studied region ranges from 7.35 to 8.33,and the predominant anions and cations are HCO₃^-and SO₄^2-;the TDS content is correlated with the conductivity and major ion content.The Ca-SO₄ type of water chemistry dominates in the mine area’s groundwater,and organic colloids with irregular colloid forms and concentrations ranging from 67 to 116 mg/L are the most prevalent in the particle size range of 100KDa～0.45μm.（2）The physicochemical properties of the colloids coexisting with Fe under different water chemistry conditions are different.The hydrodynamic diameters of different types of colloids coexisting with Fe differed from small to large in the order of Si O₂ colloids,humic acid colloids,and complex colloids.The particle size of the three types of colloids coexisting with Fe gradually increased with the increase of ionic strength,and the effect of Ca²⁺on the particle size of colloids in suspension was greater than that of Na⁺.When Si O₂ colloids coexisted with Fe,the zeta potential of suspension decreased with the increase of colloid concentration,while when humic acid colloids and composite colloids coexisted with Fe,the zeta potential of suspension increased with the increase of colloid concentration.With the increase of ionic strength,the absolute value of Zeta potential of colloidal suspensions coexisting with Fe tended to be close to 0,and the suspensions tended to be unstable.（3）At various water chemistry circumstances,the medium’s ability to bind Fe changed.Fe was less likely to be absorbed by the medium when Si O₂ colloids and Fe coexisted,and this tendency increased as colloids concentration and ionic strength rose.Contrarily,when humic acid colloids and composite colloids coexisted with Fe,Fe was more effectively absorbed by the medium than when no colloid were present.This adsorption also increased when colloids concentration and ionic strength rose.Moreover,regardless of the existence of colloids,the adsorption of Fe by the medium increased with an increase in ionic strength.（4）Colloids coexisting with Fe migrate in a different way depending on the hydrogeochemical and hydrodynamic environment.The migration ability of Fe in the medium significantly deteriorates when Si O₂ colloids coexisting with Fe move by raising the ionic strength and lowering the flow rate.The ability of Fe to migrate when humic acid colloids coexisting with Fe do so increases as the ionic strength and flow rate do.The migrating ability of Fe increased with increasing ionic strength and flow rate in the composite colloids coexisting with Fe,while the effect of flow rate on migration was less significant.Under the same hydrochemical and hydrodynamic conditions,Si O₂ colloids have the strongest ability to co-operate with Fe migration,followed by composite colloids,and humic acid colloids are the weakest.There are 32 figures,16 tables and 107 references in this thesis.