Production Behavior Of Acid Mine Drainage (AMD) And Effects Of AMD On Migration And Transformation Of Heavy Metals In Soil-Plant System

The Acid mine drainage(AMD)pollution is one of the environmental problems in the mining area that needs to be solved urgently.In this study,based on the basic process,pyrite biological oxidation,of AMD generation,the effects of temperature and pyrite concentration on pyrite biological oxidation has been explored.The effect of secondary iron minerals attached to the A.ferrooxidans on ferrous ions biological oxidation has been revealed.Finally,the effect of AMD on soil characteristics,crop growth,heavy metal migration and transformation has been revealed when the AMD enter the calcareous soil-plant system.The results show that:(1)both temperature and pyrite concentration can regulate the biological oxidation process of pyrite,and then affect the generation behavior of AMD.Compared with the concentration of pyrite,the regulation of temperature is remarkable.(2)In iron-rich acidic sulfate environment,the adsorption of A.ferrooxidans LX5 by bio-schwertmannite in iron-rich acidic sulfate environment can decrease the system Fe²⁺ biological oxidation efficiency and weaken the system acidification degree.(3)When the simulated AMD enter the calcareous soil,the presence of CaO + MgO contents in soil promoted Fe²⁺ in AMD converted into Fe³⁺,and that major ions(H+,Fe,SO^2-₄)in AMD were trapped in the soil.When the ratio of AMD volume to soil mass reached 10 mL/g,the total phosphorus(total P)and total potassium(total K)did not significantly change;the available nitrogen(available N)and total nitrogen(total N)increased;and the organic matter,available phosphorus(available P),available potassium(available K),Cr,and Cd contents in soil decreased.With the increase of AMD volume to soil mass ratio,the Lolium perenne L.germination rate decreased and the cumulative amount of Cr in the Lolium perenne L.increased.The soil conditions could not support Lolium perenne L.germination when the AMD volume to soil mass ratio was 10 mL/g.(4)The simulated AMD enter the calcareous soil-plant system reduced the soil pH to below 7.00 at the seedling stage,and its increased to7.21 to 7.58 when they reached maturity.With the addition of AMD,the total salt content in the soil increased to 8 to 8.45 g/kg,which was 5.37 to 5.67 times that of CK treatment in the same period.Moreover,the growth of the plant were inhibited,the dry matter mass of the plant was reduced,and the weight of plant above ground is always much higher than the weight of plant below ground.AMD enter calcareous soil,which is beneficial to the dissolution of heavy metals Cu,Cr,Mn and Ni in seedling soil.and increase the residual content of Cu,Zn,Ni,Cr,and Mn in mature soil.The addition of AMD had no significant effect on the dissolution of Mn in the soil.The addition of a small amount of AMD can promote the dissolution of Cr in the soil.Cu,Zn,and Cd in plants are mainly accumulated in the roots of plants,and the addition of AMD reduces the content of Cr and Ni in the root.The findings of this study will clarify the influence of temperature and pyrite concentration on AMD production behavior,and reveal the regulatory effect of secondary iron mineral encase microorganisms on AMD production.Furthermore,the results of this study also reveal to the effects of AMD on soil characteristics,crop growth,and the migration and transformation of heavy metals in soil-plant systems after AMD entered the calcareous soil system.Relevant results provide data support for revealing AMD generation and AMD pollution behavior of calcareous soil when AMD enters in to the soil system.