The Research Of Pollution Produced By Rare-earth Tailings And The Rule Of Migration For Heavy Metal Element Pb In Mianning, Xichang

Based on the status of rare-earth mine production and environment in XiChang MianNing County, we started an environmental impact assessments and research on the rare-earth mining and wash-dressing tailings and studyed the migration and transformation activities of heavy metal existed in rare-earth tailings using the method of speciation analysis. The results of investigation and research showed that the environmental quality of MaoNiuPing rare-earth mining area is closely related with the rare-earth mine. The flour dust, waste liquid and tailings produced by activities of excavation and wash-dressing of rare-earth mining, which have caused a rapid increase of particulate matter in air and migration harmful heavy metal. By the contrastive analysis ,the distribution and concentration of heavy metals in different regional environment which has different distance and relations with rare-earth areas was compared in this article. The test results showed that there are various heavy metals concentration levels of the solid environmental samples in the rare-earth mining areas. itself of rare-earth mine contained a large number of heavy metals, the largest proportion of harmful heavy is Pb, the content is to 3220mg/kg in rare-earth raw ore , wash-dressing tailings reached 2410mg/kg, the environmental samples affected by rare-earth mine tailings in this area have the same high Pb content, for example the soil in the mining area Pb is to 2050mg/kg, underwater sediments in NanHe's downstream Pb content is as high as 3120 mg/kg, while the regional environment has not been affected is much lower, such as the mountain areas of against the wind, residential areas and farmland, Pb content of the soil only in the 100mg /kg around. All kinds of aquatic system in rare-earth mining area and surrounding regions has different Pb content, tailings leachate is to reach of 4.85mg/L, the river water samples in the middle of MaoNiu River containing Pb is to 1.34 mg/L, in the water sample downstream of tailings reservoir of Nan River is to 1.55 mg/L, which are far higher than the national surface water quality standards for value, and the upper reaches of the Nan River water samples Pb content is much lower. In addition to existing the high-Pb, Cd was found in some sample in local environment, other harmful heavy metals content are lower. Therefore, heavy metals Pb is the main security risks for local environment.To deal with the data of static test by using method of clustering and principal component analysis, which made us draw some conclusion that: the influencing force of solid-liquid ratio, reaction time and size is similar; factors leaching solution of citric acid content, inorganic anion concentration is similar; factors leaching solution "hardness", humic acid content is similar; the EDTA content of leaching solution is another sort. The force of all factors on Pb's speciation change decreased in order of EDTA content of leaching solution, the other organic acids, easily-produced insoluble salt inorganic anions, cations calcium and magnesium content, another factors. By using dynamic leaching test to research the relation of pH, the continuous leaching volume with Pb's speciation change in tailings. From the test results and the test results of the analysis of mathematical statistics, we can know that the pH value is less than 4, Pb is susceptible to leach out of the tailings, but pH value is between 4 and 7, there is little Pb leaching from the tailings. With the increase of continuous leaching volume, the leaching Pb content will be increasing in turn at the volume is 500mL to 2000mL, while 2000 mL slowly start to reduce. The statistical analysis results obtained by Two-factor variance showed that the leaching solution pH and the continuous leaching volume have some effects on change of all forms of Pb, especially on oxidable form.All factors of the solution acidity, redox potential, calcium and magnesium soluble salt content and humic acid content as the influencing factors to research the migration and transformation rule of Pb in solution. From the test results we can come to some conclusions as follows: the neutral or weak alkaline solution, including the large amount of calcium and magnesium solution, a solution containing less organic matter, soluble Pb content will be less in the solution; Fixed pH value, the solution potential value turn smaller, soluble Pb will reduce.In order to resolve all problems produced by the heavy metal released from rare-earth tailings, we have taken some measures to dispose tailings and improve the quality of the environment, such as the method of storage, phytoremediation, recycling, harmless transferring, strengthen supervision and management, raising awareness of environmental protection.