Study On Phytoremediation To Rare-earth Tailings Area In Mianning Of Sichuan Province

The exploitation of the mine would change the original environment on a large scale and destroy the ecosystem which is surrounding the areas of mine. Especially the exploitation of metal mines not only spent a lot of land resources, but also make the land which has been mined lost the balance of primordial ecosystem. The activities associated with mining would generate a lot of tailings. And the tails contains heavy metal pollutants that can easily cause environmental pollution when it is stored on the surface of soil. It is easy for these wastes to get physical change, chemical change or biological change that could release a lot of toxic heavy metal elements to the environment which could lead to pollution of surroundings and impact seriously on people's normal life.In recent years phytoremediation became one of the ideal approaches for improving the injured ecosystem and reducing the heavy metals pollution in soil. Compared to traditional physical, chemical and other repair techniques phytoremediation is inexpensive, convenient and can prevent of the secondary pollution. The key part of phytoremediation is the selection and utilization of the plants for restoring the heavy metals polluted areas, including pioneer plants, metal-tolerant plants and accumulators or hyperaccumulators.In order to recover the ecosystem in the rare-earth tailing area in Mianning of Sichuan, firstly we investigated the mine field and analyzed the samples which were got in the mine field in the laboratory, and studied the status of soil contamination in mine field and surroundings. After that, we chose 10 kinds of plants which grew better than the other plants in the tailing field and distributed broadly in the rare-earth tailing areas, and we researched the features on absorption and accumulation of heavy metals in 10 plants, hoping that could construct a foundation for screening out of some metal-tolerant plants and accumulators or hyperaccumulators in order to provide some species for the vegetation restoration in the field of rare-earth tailings. The main conclusions as follow:1. The pollution of heavy metals in the rare-earth mining area are serious. The highest concentration of Pb in the soil is 2050 mg·kg^-1 as 52 times as reference value. The pollution of heavy metal Zn, Cu, Cd and As are not very serious. The highest concentration of Zn in the soil is 3 times more than the control value, the highest concentration of Cu in the soil is almost same with the control value and the highest concentration of Cd in the soil is 5 times more than the control value.2. We evaluated the pollution of rare-earth area by using N. LNemerow index. From the single pollution index we can see the pollution index of Pb and Cd are higher than the other elements we studied and the index of Cu, Zn and As are less than 1. So the soil of mining area is contaminated mostly by Pb and Cd. The N.L.Nemerow comprehensive pollution index of rare-earth mining area is the highest, which is 3. And the order of pollution level was: the tailing field>the area of washing rare-earth>the soil surrounding the tails>agricultural land. The comprehensive pollution index of the tailing field, the area of washing rare-earth and the soil surrounding the tails are more than 2, which indicated these areas are moderately polluted by heavy metals.3. We analyzed the determination of heavy metals in 10 kinds of plants. The Pb content of up-ground part's of Artemisia annua L is the highest among the 10 plants, which achieved 203.09 mg·kg^-1; the highest determination of Zn in the shoot of plants is Herba Artemisiae Scopariae, which is 95.01 mg·kg^-1; the shoot of Chenopodium ambrosioides L accumulated 4.93 mg·kg^-1 Cd, that is the hightest in the 10 species; the highest determination of Cu in the shoot of plants is Ambrosia artemisiifolia L, which achieved 13.25 mg·kg^-1. The TF and EC for Pb of Ambrosia artemisiifolia L are higher than the other plants, so Ambrosia artemisiifolia L has the ability to recover the soil which is contaminated by Pb. The Pyracantha fortuneana has the highest TF to Zn, and the Herba Artemisiae Scopariae has the highest EC to Zn.So they can repair the pollution of Zn. The Buddleja lindleyana L and Chenopodium ambrosioides L are capable of rehabilitating the soil with pollutant Cd. Centaurea picris Pall is more effective than the other plants in restoring the soil which is polluted by Cu.4. There are 3 vegetation succession stages in the rare-earth tailings area, that are bare land, early herbaceous plants and herbaceous-shrub vegetation community.5. Phytostabilization is more suitable than phytoextration in restoration to rare-earth tailing field.