Research On The Pollution Assessment And The Transport Characteristics Of Heavy Metals In A Typical Nonferrous Metal Mine

Resources and environment are the essential conditions on which human being could survive, breed and develop. Now, people pay more and more attention to and attach more importance to these questions such as lack resources, environmental pollution and ecological deterioration. How to study the nonferrous metal production and its pollution treatment technology and facilitate harmony development between nonferrous metal industry and environment is one of emphasis research areas of hi-tech project. Therefore, the research topic is very important both in theory and in practical values.In this research, a typical nonferrous metal mine was taken as studied object. Based on sample, test and analysis of the water and the soil near the studied object, the transport characteristics of heavy metals and pollution assessment in mining activities were investigated.In summary, the dissertation includes the following contents and contributions:(1) The process and behavior of release and transport of heavy metals in the mining area were explained in theory. Mining operation moves the valuable ores in underground to the surface. Mineral milling and metallurgical processes made the ores into new products of which the construction and chemical composition of minerals were changed. Consequently, during the processing, heavy metals will release and transport to ecological environment, which bring heavy metals pollution seriously.(2) By searching the process of mining activities, the fault tree of heavy metals pollution was built which indicates tailings are the most serious field of heavy metals pollution. The emphasis of preventing and controlling the heavy metals pollution of mine should be concentrated on the area of the tailings pollution.(3) The polluted mechanism could be explained as following: sulfide mineral oxidation of tailings produced waste water acidification, and then, a series of chemical reactions in acid condition occur which bring heavy metal ions to environment. Also, some mathematic models for describing the transport characteristics of heavy metals from acid mine drainage to soils were established, depended upon hydrodynamics, underground leakage theory and so on.(4) By analyzing the heavy metal concentrations and their correlation, it indicates that mining area has been polluted by heavy metals seriously. The average contents of Zn, Pb, Cd, Cu and As in soils of studied area are 2 803.73 mg·kg^-1, 1 787.50 mg·kg^-1, 5.37 mg·kg^-1, 357.40 mg·kg^-1 and 46.61 mg·kg^-1 respectively. They are 29.20, 21.90, 0.83, 13.10 and 0.71 times of environmental background values of soils. Among them, Zn, Pb and Cu pollution is very serious, and Cd and As pollution is unobvious. There was a positive correlation among heavy metals concentration. The correlated coefficient between Zn and Pb was 0.9, which indicates that the pollution status corresponds to the same polluted sources.(5) The system pre-estimation theory was used to establish the mathematic models for forecasting the heavy metal concentration of pollution in tailing area based on the history measuring data from 1994 to 2002. The forecasting results show that Pb, Zn, Cd and As concentrations near the tailing dam in 2022 will reach 1.191².710 times compared with the case in 2002.(6) Three-step extraction procedure set by European Bureau of Reference was applied to extract heavy metals fractionation of the soils. The testing results show that heavy metals are thedominant status in associated with residual fraction and least associated with reducible fraction. Lead and zinc are primarily associated with the residual fraction of 61.5% and 43.0% respectively.(7) Intimated method and synthetic index were applied to assess a polluted river near the mine. The assessment result indicates the river has been polluted by heavy metals which synthetic index is 25.08. The contamination of Pb2+ and Zn2+ is rather serious.(8) Depending upon the polluted features of various mining activities in the mine, the contaminated soil area was divided into four zones which were polluted by tailings, mine drainage, dust deposition in wind and spreading minerals during vehicle transportation respectively. Ranking of pollution intension of different zones from heavy to light is in the sequence of tailing zone, mineral transportation zone, mine drainage zone, and dust deposition zone. The Nemero indexes are 177.60, 65.54, 9.76 and 8.99 respectively, which show the pollution intension of tailings is the heaviest.(9) The ecology risk assessment index in the mine was computed. The heavy metals toxic response coefficient and ecology harm coefficient were also calculated and discussed. The average ERI (ecology risk index) among 28 samples was 418.26. The general environmental quality of studied area became considerabe deterioration. Risk of heavy metals pollution is very high in the mine.(10) Some policy suggestions for preventing and controlling the environmental pollution by heavy metals in mining activities were put forward, which claimed the most effective approach is to increase the mineral processing recovery ratio and reduce discharge of the tailings in order to prevent heavy metal contamination. Nowadays, the key measure is to disseminate scientific knowledge of preventing and controlling environmental pollution by heavy metals, encourage and support scientific research and technological development, and expand the scope of mine environmental impact assessment. Meanwhile, the state should promulgate feasible policies to encourage and support the comprehensive recovery and rational utilization of tailings, and adopt economic and technical policies and measures that facilitate the comprehensive use of tailings.