| 摘要 | 矿山开发引起的环境问题是全球性的问题,越来越受人们的重视,已成为环境地球化学研究的一个重要领域.长期以来,由于AMD有较低pH值和较高的金属含量,加之其对生态环境影响的严重性而备受关注,并取得了若干重要研究进展.在碳酸盐岩地区的矿山环境中,由于其矿石类型、围岩类型以及选矿工艺的不同形成的矿山水体常呈中性,甚至碱性.而这类水体也能有相当含量的重金属,也可导致水文生态系统灾难性的变化.然而,相对酸性矿山水而言,碳酸盐岩矿山环境（碱性水体）重金属元素地球化学研究显得非常薄弱.碳酸盐岩矿山环境作为矿山环境的重要类型之一,人们完全有必要去了解这类环境中重金属元素的迁移释放和沉淀过程.论文通过对低硫化物、高碳酸盐岩矿山周围各种环境要素中重金属矿物学、存在形态的系统研究,辅以硫同位素和REE的示踪手段揭示了碳酸盐岩山区金属矿山开发过程中重金属元素的释放迁移的地球化学过程. |
| 其他摘要 | The environmental impact resulted from mining activities is serious and ubiquitous all over the word. It has drawn much attention of geochemists, and has become one of important aspect in the environmental geochemistry. People have paid much attention to studies on AMD (Acid Mine Drainage) due to its acidity and high metal content, and have obtained significant research progresses. The chemistry of mine drainage can bis affected by many factors, including the type and abundance of metal-bearing sulfides in ore and wall rock, and smelting process. Mine waters of netural or alkaine pH values can still show a high concent of dissolved metals which have a significant impact on the aquatic ecosystem. However, environmental geochemistry in the carbonatite-rich mine area have been poorly addressed compared with AMD. The environmental geochemistry of carbonatite-rich mine, an important type in the mine environment research, is worth of further study on the releas and deposition of heavy metals. The study on environmental geochemical processes in the carbonatite-rich mine area reveals the mechanism of mine impact on the environment, and is of significance to the studies on elemental cycle, mining rehabilitation, environmental assessment, ecological effect, and so on. Besed on the research of mineralogy, geochemical partitioning of heavy metals, sulfur isotope and REE in environment around low sulfide, high carbonate deposits, Some ideas and conclusions were obtained as the following: 1 Due to the special type of ore and wall rock and technique of smelting, the waste pH values, one of dominant factors controlling the metal releasing, is often neutral to slightly or strongly alkaline. The distribution of heavy metals in the waste residue pile is related to the type of waste residue and the piling time. These metals are detained mainly in the slags layer. With prolongation of piling time, the content of heavy metals in the slags decreases gradually due to weathering. The natural releasing processes of Pb, Zn and Cd. in the slags can be primely described with minus-exponent equation. The relative order of mobility of metals in the waste residue is Cd>Zn>Pb. These metals are hazardous to environment because of their high total contents and long time of release. 2 In general, Concentrations of heavy metals tend to increase as the size fractions get finer. However in the slags, the coarser paticles show similar or even higher heavy metal contents than finer ones. The crystallization during smelting and sequentially secondary metal-bearing minerals formed from weathering controlled the release of heavy metals in the waste residues. Heavy metals in the carbonate fraction and Fe-Mn oxide fraction are the most significant geochemical partitioning controlling the release of metals in the mine wastes. Weathering processes and/or pH values are likely to be responsible for the decrease in the exchangeable fraction in the mine wastes. Although the relative partitioning of heavy metals in exchangeable fraction is very low, the exchangeable fraction in the slages contains high content of heavy metals. Heavy metals in exchangeable fraction have the highest solubility to show the highest potential bioavailability in contrast to the other chemical forms. Heavy metals in the carbonate fraction of mine slags may be released, when pH values of slags decreased, such as resulted from acid deposition, to enough low to dissolve the carbonatite. 3 The physical transport of streams or rivers are very important mechanism in the dispersion of heavy metals in Hezhang Pb-Zn mine area. Although the mobility of heavy metals is controlled a certain extent by the rock in drainage basin itself and by the aquatic chemistry in the carbonatite-rich mine area, concentration of dissolved metals are comparatively high as that of other rivers disturbed by mining. Concentration Etnd mobility of dissolved metals are controlled by a series of complex geochemical reactions including sulfide oxidation, precipitation and dissolution of secondary minerals, coprecipitation, ion exchange reaction, and adsorption/desorption reaction. 4 The water in the carbonatite-rich mine area shows different physical-chemical characteristics from other mine drainage. It is often alkaline or srongly alkaline. To a certain extent, the oxidation of sulfide and releasing of heavy metals were controlled by the chemical characteristics of hydrological environment. This process gave rise to the formation of the metastable secondary metal-bearing minerals on the surface of sulfide in the sediment. The secondary minerals can be effective scavengers of contaminants in water. When hydrological condition changes, the secondary minerals can dissolve and release heavy metals into the solution. Therefore, the geochemical partitionings of heavy metals in the sediment are a consequence of oxidation of sulfide and neutralization of carbonate minerals. Distribution, transportation, disperesion and accumulation of heavy metals in the sediment downstream are a result of interaction among the contaminants, hydrological condition and suspended matter transportation in the rivers. 5 In the carbonatite-rich mine area, the most important parameter effecting the mobilities of dissolved metals is the pFI of water. Heavy metals derived from oxidation of sulfides can be adsorbed on the surface of suspended matter and/or ooze. The heavy metals can be released into solution again due to the influence of aquatic chemstry and hydrological dynamics. Therefore, the water quality can be possibly affected by the hydrogeochemical processes such as precipitation, flowing and resuspending1. Due to the special geological and hydrological characteristics of drainage basin, the suspended matter and sediment settling from the water column may play a signifbatnt role in the migration of metals in surface waters. Concentrations of heavy metals in the suspended matter and sediment are not obviously affected by elutriation of stream and dilution of tributary stream. This feacture does not change even in the distant reach downstream. Therefore, the suspended matter and sediment are the potential source of heavy metal contamination to the waters for industry and agriculture use. High SPM content in water is also Em important pollution to the catchment area. |
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