Co-release Of Heavy Metals And Acid From Coal Gangue And Proccess Simulation

Coal gangue is a coal-associated waste rock and is a type of mining solid waste.Pyrite is the main mineral component of coal gangue acid production,containing pyrite waste coal gangue will produce acid mine waste water（AMD）,resulting in the heavy metals stored in it more easily leached,causing heavy metal pollution in the soil-water-biological environmental system around the coal gangue.This process is closely related to the mineral composition of the gangue,the stockpile environment and its heavy metal distribution pattern.Therefore,it is important to study the acid production and heavy metal release pattern of coal gangue under different environmental factors and explore its related mechanism to provide theoretical basis for the control of acid pollution and heavy metal pollution in regional coal gangue dumps,which is important for the environmental management,land reclamation and ecological reconstruction of mining areas.In this thesis for the sulphur-containing gangue,static simulation experimental method is used to study the acid production law of gangue,setting different initial p H,different oxygen concentration and addition of different low molecular weight organic acid（LMWDOM）conditions,through the analysis of heavy metal release system in the gangue p H,ORP,EC,Fe²⁺,SO₄^2-,heavy metal ions and other changes in the characteristics of the investigation of different environmental factors The influence of different environmental factors on the acid production and synergistic release of heavy metals from gangue;based on the composition of the sulphide minerals of gangue,the study of the oxidative acid production and metal ion release characteristics of different single sulphide minerals and mixed sulphide minerals;the discussion of the influence of light and oxygen on the induction of free radicals in pyrite to reveal the mechanism of light and oxygen on the oxidative acid production of pyrite,the main conclusions are as follows:（1）The gangue specimens used in the experiment were mainly composed of minerals such as quartz,kaolinite and pyrite,of which pyrite is the main effective component of acid production from gangue,which belongs to 222（1）medium-sulphur medium-ash silica-aluminium type gangue（level 1 silica-aluminium ratio）.Under the condition of initial p H 7,the p H of the gangue experimental system decreased to about 3.2 after 13 days.p H reduction can promote further acid production and metal leaching from the gangue.Using SO₄^2-as a measure of the degree of oxidation of sulphur-containing gangue,the concentration of Fe²⁺,Fe_total and SO₄^2-in the experimental system at an initial p H of 2 was about twice that of the initial p H of 5 and 7,but it did not change the acid production mechanism of the gangue.Gangue oxidation acid production is an acid production and alkali production process,gangue acid production is mainly the oxidation process of metal sulfide minerals,and alkali production is the dissolution process of alkaline minerals and certain silicate minerals surface ions of the proton exchange leaching process.（2）Oxygen is the key factor in the gangue pyrite oxidation acid production,the presence of oxygen promotes the production of Fe³⁺,Fe³⁺production further promotes the gangue acid production,the environment of oxygen affects the gangue heavy metal dissolution rate and dissolution rate is not significant,combined with different initial p H conditions on the gangue heavy metal release of experimental results,the gangue heavy metal release to proton release for the main.The presence of oxygen mainly controls the release of heavy metals in the more stable organic bound state and sulphide bound state of the gangue.（3）The addition of LMWDOW on the gangue apparent acid production effect is small,and the experimental group of salicylic acid after the end of the experimental cycle for the addition of Fe_total 130.29mg/L,for the experimental system without LMWDOM Fe_totalconcentration of about 2.5 times,thus increasing the degree of oxidative dissolution of pyrite in the gangue.LMWDOW on the heavy metal dissolution in the gangue has Certain promotion effect,including the addition of citric acid on the gangue of Cr,Cd,Cu and Zn has a certain promotion effect,the addition of glycine experimental group to promote the dissolution of Pb in the stone.（4）In the atmospheric oxygen concentration and light sufficient conditions gangue and pyrite experimental group to produce-OH concentration increases with time,and shows a linear trend,and gangue pyrite iron ore is the effective component of the generation of free radicals.Light and oxygen are important factors influencing the generation of free radicals in pyrite.Oxygen activates the oxidation by increasing the adsorption on the surface of pyrite and promotes the formation of active oxide species-OH.Light easily excites pyrite to generate photogenerated electrons and photogenerated holes,and photogenerated holes have strong oxidizing properties to directly oxidize Fe²⁺on the surface of pyrite to generate Fe³⁺.Pyrite excited photoelectrons are not directly involved in chemical reactions,but in the form of photoelectrons in chemical reactions,it can further react with dissolved oxygen and water and other substances,thus generating active radicals.（5）In mixed sulphide minerals,the sulphide minerals with higher resting potential act as cathodes on which oxidants（oxygen molecules or iron）undergo reduction,while the sulphide minerals with lower resting potential act as anodes and dissolve.When pyrite is mixed with galena or sphalerite,pyrite acts as a cathode and oxygen molecules combine with H⁺in water to produce water molecules,resulting in a constant depletion of H⁺in the reaction system and a mixed the p H of the sulphide mineral experiments showed an increase with time.And the mixed sulphide minerals experiment group due to the electric coupling phenomenon led to the reduction of high-valent metal ions in the reaction system.（6）The release process of heavy metals from coal gangue is not a simple primary reaction,but a process controlled by multiple factors.Using the"shrinkage nucleus model（SCM）"as the heavy metal release model,the fitting results show that the dissolution of Cd in the gangue is mainly controlled by internal diffusion,the dissolution of Cr is mainly controlled by interfacial chemical reaction,and the dissolution of Cu and Pb is controlled by both internal diffusion and chemical reaction.The total length of this thesis is approximately 50,000 words,containing 36 illustrations,23 tables and 132 references.