Study On Passivation Of Heavy Metals In Gangue Of Hengshan Mining Area

Hengshan mining area in Northern Shaanxi has an annual output of more than 50 million tons of coal and an annual discharge of 7 million tons of coal gangue.A large amount of gangue accumulation not only takes up land,but also brings serious environmental pollution.The heavy metal elements in the gangue in Hengshan mining area are highly abnormal Studying the occurrence state of heavy metal elements and its passivation repair technology will help solve the problem of heavy metal pollution in the process of gangue stacking,mine filling and utilization.This paper takes gangue in Hengshan mining area as the research object,and systematically analyzes the basic properties of gangue and the occurrence state of metal elements,the passivation effects of medical stone,zeolite,metakaolin and composite passivators on the metal elements such as Cd,Cr,Cu,Ni,Pb and Zn in coal gangue were studied by elemental analysis and BCR continuous extraction methods.The gangue used in the experiment is a kind of high ash gangue,and The main minerals are quartz,kaolinite,mica and carbonate minerals;trace metal elements such as Cd,Cr,Cu,Ni,Pb and Zn in coal gangue are highly abnormal;the metal Cd in gangue mainly exists in the oxidizable state and the residue state,the metals such as Cr,Pb and Zn mainly exist in the reducible state and the residue state,and the metals such as Cu and Ni exist in the exchangeable state and the residue state.According to the differences in the chemical properties of metal elements in gangue,medical stone,zeolite,metakaolin and their composite passivators were screened to reduce the effective state of heavy metals in gangue.Analyzing the passivation agent and passivated gangue by SEM and XRD,it is found that the passivation agent is effectively loaded on the gangue;by BET analysis,it is found that the specific surface area from medical stone,zeolite to metakaolin decreases sequentially;FTIR analysis shows that the surface functional groups of medical stone,zeolite and metakaolin.Among the three single passivators,medical stone has the best passivation effect on metals Ni,Pb and Zn,reducing their effective states by 28.39%,37.12%and 36.33%respectively;Zeolite has the best passivation effect on metal Cd and Cr,which can reduce its effective state by 28.99%and 11.4%.Compared with a single passivator,the composite passivator with the same compatibility of medical stone and zeolite has a significantly higher passivation effect on the metal Cr,Cu,Pb,and the passivation effect of metal Cd,Ni and Zn is similar to that of a single passivator.It shows that there is a synergistic effect between medical stone and zeolite.Through the leaching experiment,the pH value of the leachate before and after passivation of gangue was compared with time and the maximum leaching rate of heavy metals in the leachate was found.After the coal gangue is passivated by medical stone,zeolite,metakaolin and composite passivation agent,the pH value of the leaching liquid increases.The reason is that the passivation agent contains water-soluble alkaline substances or alkaline substances that are leached out,the increase in pH value is proportional to the passivation effect of gangue;the leaching rate of the 6 metals in coal gangue is Cr,Cd,Pb,Zn,Ni,Cu in descending order;after passivation,the leaching rate of these six metals in the gangue is Cr,Pb,Zn,Ni,Cu,Cd;the metal leaching rate in the gangue passivated by the composite passivator is Cr,Zn,Pb,Ni,Cu,Cd in descending order.The leaching solution of Cd,Cr,Cu,Ni,Pb and Zn in the passivated gangue is lower than the "Surface Water Environmental Quality Standard"(GB3838-2015)and "Groundwater Environmental Quality Standard"(GB/T14848-2017)And the metal content requirements specified in the "Sanitary Standards for Drinking Water"(GB5749-2006).