Case Studies Of The Water Environmental Geochemistry Of Mines In Guizhou Province

Heavy metals contamination caused in mine exploitation has become a global environment concern. This problem is getting worse with the development of economy, and has been scarcely addressed. The mine environment shows a close relation to the region geologic setting. For instance, outcrops such as carbonate and granite, could result in different impacts of mine substance. In Guizhou province, the extensively distributed carbonate makes the surface water slightly alkaline, and would consequently lead to distinct impacts on mine environment. Mine water acts as essential media for heavy metals generation, migration and precipitation, thus the geochemical characteristic of heavy metals in mine water is a key to the understanding of mine impacts on the surrounding environmentThe objective of this study was to conduct case studies on mine water environment in carbonate area, so as to understand the knowledge of mine substance dififusion and migration. This study primarily addresses the environmental impact of toxic substance from Pb-Zn mine, Hg mine and Au-mine, as well as the contrast of distinct migration characteristic of heavy metals. This research would help to remedy the mine environment and provide fundamental evidences for sustainable development of the society. The mine tailings of three mines (Shanshulin Pb-Zn mine, Wanshan Hg mine, and Yata Au mine) and their downstream environment have been investigated in detail, and primary conclusions are listed below:1. The aqueous environment of three mines were all seriously affected by the substance from the mine tailings. In the vicinity of the mine tailing dump of shanshulin Pb-Zn mine, the water contains 6780 μg/g of Pb, and 7971 μg/g of Zn. The leachate of Wanshan calcines dump contains 1200 ng/L of Hg. In Yata mine area, the As and Sb concentrations are 618 μg/1 and 206 μg/L in the downstream water, and 532 μg/g and 122 μg/g in the sediment.2. The mine waters in the study area are alkaline or slightly alkaline, owing to the carbonates as well as liming in the preliminary treatment of mine drainage. Thealkalinity of surface water enhances the sorption of cationic heavy metals- Pb, Zn and Hg, whereas on the other hand, it prompts the dissolution of anionic heavy metals- As and Sb. It could be implied that in carbonate areas, different means should be applied to the remedy of cationic and anionic heavy metals contamination,3. the diffusion and migration of mine toxic substances correlate mainly with suspended solids as well as dilution by other streams. The cationic heavy metals, such as Pb, Zn, and Hg, migrate mostly along with suspended solids, whereas the anionic heavy metals such as As and Sb, migrate predominately as dissolved ions and would be attenuated primarily by dilution process. In Shanshulin Pb-Zn mine area, the stream water is quite turbid and contains a quantity of suspended solids, so Pb and Zn were mostly sorbed and is able to migrate along with suspended solid over a long distance, giving rise to a high level of Pb and Zn in sediment The impact of particulate heavy metals on environment is more important than that of dissolved heavy metals. In Wanshan area, despite the mine water is very dear and contains much less suspended solids, Hg was still found to be controlled by the sorption on suspended solids. In Yata area, the As and Sb in water, similarly as SO42*, show conservative behavior and attenuate only when diluted by other streams.4. During the oxidation of sulflde minerals, SO42' is.released along with heavy metal ions, therefore sulfur concentration and sulfur isotope are closely correlated with heavy metals in mine waters. Obvious difference of sulfur concentration and sulfur isotopic value between mine source and other sources makes sulfur isotope an appropriate Variable for tracing the migration of mine-source heavy metals.5. According to the characteristics of the heavy metals migration in mine waters, it was concluded that the environmental threats of Pb, Zn and Hg in the mine tailing could be mitigated via the control of suspended solids (e.g. construction of tailing dams etc.), whereas innovative ideas would be imperatively expected for the control of As and Sb migration.