Simulation And Control Of REE Migrations Under Rainfall Condition In Ionic Rare Earth Mining Area,South China

Ionic type rare earth is a kind of valuable middle-heavy rare earth resource that is only found in southern China.In recent years,due to the continuous exploitation of ionic type rare earth mining area,the soil structure of the mining area suffered serious damage,vegetation types decreased,soil anti-erosion capability dramatically weaken,additionally,heavy rainfall in flood season and occur in surface runoff,resulting in that the water and soil loss in the mining area is particularly serious.Followed by a large amount of rare earth tails gangue migrate to the soil environment in downstream by runoff scouring and interflow leaching,cause soil microbial activity and biochemical process and availability recession,and caused downstream river network and groundwater system to serious pollution.This study takes HNK and Water and Soil Conservation Science and Education Park in Changting County of Fujian Province as the study area,in order to study the basic characteristics of rare earth vertical and lateral transfer,field artificial rainfall experiment and column elevation experiment were conducted,and analyse the benefits soil and water conservation measures on rare earth migrations resistance,reveal that the internal mechanism of rare earth migration and control effect of different water and soil conservation measures on rare earth migration under rainfall condition in ionic rare earth mining area,in southern China.The main results are as follows:(1)On the basis of artificial rainfall experiment,totals of runoff and sediment yield are 2971.3×10-3L?14.87×10-3 kg during the rainfall,respectively.With the extension of rainfall duration,the rates of runoff and sediment yield increase firstly,then decrease,and finally stabilize.REE contents and REE migrations in runoff and sediment increase firstly,then decrease,and fainally gradually tend to be stable.(2)During each rainfall period,REE contents in runoff and sediment fluctuate are 5.57?20.33 ?g·L-1 and 116.2?290.7 mg·kg-1,respectively.The unit content and the total amounts of REE migration in runoff and sediment are 10.91?g·L-1,32.42?g,228.23mg·kg-1,3393.79×10-3mg,respectively.Both HREE contents and HREE migrations are higher than LREE contents and LREE migrations in the runoff,but it shows the opposite in sediment.(3)Leaching experiment showed that the total amounts of REE leaching was the range of 48.63×10-3?1109×10-3?g·L-1 in the soil column,and with the ascendi ng of leaching times,the amount of REE leaching fluctuating reduction.the previ ous 8 times,the amounts of REE leaching was larger variation,and fluctuated wi thin 138×10-3?1109×10-3?g·L-1.then,it was in low value and stable leaching state,the amount of REE leaching are within 49.63×10-3?149×10-3?g·L-1.(4)Before the leaching experiment were conducted,the topsoil of REE contents was highest.After leaching,REE contents were obviously reduced in the first layer soil,REE contents were significantly increased in the second layer soil(The main is the Ce element),REE content in third layer and fourth layer soil were slightly changed,REE content in the fifth layer soil were almost unchanged.and REE contents of variation tendency before leaching are in accord with REE contents of variation tendency after leaching in the same layer soil.(5)The statistical data of runoff and sediment under water and soil conservation measures in 2007-2016 showed that the average annual runoff reduction rates and the average annual sediment reduction rates of five kinds of soil and water conservation measures(the whole slope coverd by grass,closed forest,low-effect masson pine fertilization,mixture of trees with shrubs and herb,enrichment planting masson pine)were 65.41%,69.29%,63.42%,86.19%,72.59%and 91.87%,84.21%,81.54%,94.13%,81.75%,respectively.(6)Under three kinds of rainfall levels(rainstorm,moderate rain and sprinkle),the REEs migrations intensity of runoff and sediment lower than those in control plot under five kinds of soil and water conservation measures,respectively,which was the largest in moderate rain.The HREE migrations intensity of sediment were 82.29%,81.25%,78.38%,75.35%and 77.05%lower than LREE migrations intensity under five kinds of soil and water conservation measures.Except the whole slope coverd by grass,the LREE migrations intensity of runoff were 55.68%,40.38%,85.76%and 85.94%lower than HREE migration intensity under four kinds of soil and water conservation measures.