| The development and utilization of rare earth, as other resources, has the characteristics of grievous human interference, prominent environmental pollution, deteriorated ecological seriously, etc. Moreover, the ecological problems caused by rare earth resources development were concealed by its application value especially in agriculture, and the comprehension about the entironment of rare earth mining area was always rested on superficial phenomena such as soil erosion, vegetation deterioration, etc. At present, the study on the ecological environment of rare earth for the influence of rare earth resources development is relatively fragmented and not systemic, in addition, mainly focuses on the geochemical behaviors of rare earth in agriculture after its entering into the soil environment. Three representative rare earth mining area (rich yttrium rare earth style mining area in Longnan, low yttrium and low europium style rare earth mining area in Xunwu, and middle yttrium and rich europium style rare earth mining area in Xinfeng) in Jiangxi Province, China, were chosen as study objects, combined with field sampling, laboratory simulation analysis method, the characteristics of soil environment and geochemical behaviors of rare earth metals were researched. The main conclusions could be drawn as follows:(1) Characteristics of soil fertility and rare earth metals contamination of representative rare earth mining areas in Gannan region. Soil comprehensive fertility in the mining area and its downstream were all low, soil comprehensive fertility in mining area was rank III (Barren), and rank II (medium) of its downstream. The soil of all rare earth mining area presented acid or faintly acid; the content of soil organic matter in mining area and its downstream were low; the base saturation ions ran off seriously, the cation exchange capacity reduced with the increase of soil acidity; nutrient elements in soil was washed away partly, the content of NPK in mining area and its downstream was in short condition, and the availability of nutrient elements was low. The soil comprehensive fertility presented time effect appearance with the history of exploitation of rare earth mine.The rare earth content in the soil environment of rare earth mining area was high, rare earth metals pollution in soil was serious. The total content of rare earth in soil was connected with time and conditions of exploitation, for instance, the exploitation time of Xinfeng rare earth mining area was short, the total content of rare earth in soil environment was highest. Rare earth metals in the soil environment of rare earth mining area had high bioavailability. The bioavailability of rare earth metals in the soil environment in rare earth mine of shorten exploitation history was more higher.(2) Time effect about acidification of soil and water environment and rare earth metal distribution in the vertical profiles of the soil in rare earth mining area. Soil environment of mining area influenced greatly by rare earth resource exploitation, soil acidity was relative stronger, soil acidification of layer A was greatest, it’s strong acidic until October2011; soil acidification of layer B was also rather strong, and had obvious trend of acidification; but soil acidification of layer C was weak acidic, and had weak trend of acidification. Soil of layer A, B and C in downstream of mining area all acidified seriously, the acidification was a process of from surface to inner, namely, layer A was most seriously(attained to strong acidic), layer B and C took second place. Compared with soil environment, the change of water body pH was not marked.In soil environment of rare earth mining area, the contents of total rare earth and rare earth in bioavailability fractions were all extreme high, the content of rare earth in soil of layer A and B decreased year after year, rare earth metals migrated to the area of low altitude and vertical direction, and relative steady in soil of layer C. The content of rare earth in bioavailability fraction was in a state of increasing year by year, but it’s higher in April (rainy season) than in October (dry season) of the same year, however, in soil of layer B and C, kept in a statue of high value relatively. Rare earth metals in soil environment of downstream in mining area had an obvious characteristic of superficial conglomeration, viz. the content of rare earth metals in soil of layer A increased obviously, layer B took the second place, and raised faintly in layer C, so as to rare earth in bioavailability fractions.(3) Effect of rare earth acid mine drainage on the changes of soil physicochemical properties, content and availability of nutrient elements and transformation of fractions, accumulation, migration and availability of rare earth metals. Inputting of rare earth acid mine drainage could stress the transformation of fractions of rare earth metals, caused rare earth transform intensely to activity fractions, and rare earth metals in activity fractions migrated to horizontal and vertical direction by transportation of hydraulic power and eluviation of rare earth acid mine, rare earth metals occurred diffusion, adsorption, migration and accumulation from mining area to downstream of mining area, ultimately, brought about reduction of the content of rare earth in residual fraction and the total content of rare earth metals, and spreading of rare earth metals contamination.(4) Effect of simulated acid rain and rare earth metals pollution on soil acidification, soil enzyme activities and activation, transformation of fraction, migration and accumulation of rare earth metals in soil environment of rare earth mining area. Simulated acid rain of different pH value had various effects on soil acidification and leaching content, the stronger the acidity of simulated acid rain, the severer the soil acidification, the greater the amount of rare earth leaching out. During the leaching out process, it might exist fraction transformation of rare earth metals.After leached by simulated acid rain, tailings acidized seriously, the stronger acidity of simulated acid rain, the more serious of soil acidification. After incubated by single and combined contamination of La and Ce, vegetable soil pH changed unconspicuously, but for rare earth leachate, it’s serious. The change of urease activity accorded with hormesis effect of RE. Treated with different incubation solution, the inhibition level of urease showed the order respectively of RE leachate> La+Ce> Ce> La. Accordingly, catalase activity was inhibited, and then promoted slightly. The inhibition level of urease showed the order respectively of RE leachate> La+Ce> La> Ce. Urease was more sensitive to RE contamination than catalase.Generally, soil comprehensive fertility in representative rare earth mining area of Gannan region was infertile, the phenomena of nutrient element losing and rare earth metals pollution were all serious, simultaneously, which presented time accumulation effect in some degree. The content and availability of rare earth were high, rare earth acid mine drainage and acid rain could promote soil acidification, the change of physicochemical properties, losing of nutrient elements, the change of soil enzyme activities and transformation of fraction, leaching out of rare earth metals which were activated, and then brought about pollution diffusion of rare earth, existing potential ecological risk. |
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