The Distribution Characteristics Of REEs’ Forms Of Existence In The Benggang System And Its Prevention And Migration

As a typical granite eroded area in southern China,Changting is typically featured with serious erosion landform.Changting is rich in REE,which has a superposition effect on soil erosion due to mining and erosion of REE resources.In 1940,"Fujian Research Institute"set up a"soil conservation experiment area in Changting county",which means that we has started the soil erosion control in Changting officially.After several large-scale management in recent twenty years,the ecological environment in Changting has been greatly improved.But due to the exploitation of REEs in the research area,the soil pollution in the downstream of the eroded area is becoming more and more severe.Some of the previous studies mainly focus on researching about Benggang or REEs pollution,or only make simple description about them;Some choose to study total migration of REEs and bioavailability;Less attention had been paid to study the system of Benggang-vegetation-REEs,Benggang features of REEs’ five forms of existence and Dicranopteris’prevention effect,especially the study of the inner difference on Benggang of REEs in different forms of existence and the element activity and differentiation process is less concerned;Study of the morphology feature and existence activity are even less than the above ones.REEs morphology feature is an important limiting factor for the migration of REEs in the soil environment.Environmental differences of different subsystems in Benggang have large restrictions on the growth of Dicranopteris.Therefore,the research on the morphology feature of REEs in Benggang system and Dicranopteris’s effect can lay experimental basis for REEs treatment.This study selected Huangnikeng Zhuotian Town as the experimental area,which is a typical compound distribution area of REEs ore and the erosion phenomenon of the Benggang.Sample places are named as follow:Huangnikeng No.1 Benggang place and Huangnikeng No.2 Benggang place.After sampling in the field,the soil samples were measured by ICP-MS.On the basis of the soil variables,REEs content and the distribution difference of different forms in Benggang system,this papar analyzes the effect of Benggang system and the growth of Dicranopteris to the distribution of REEs in soil and the changing features of different elements.Migration,prevention and transformation features of REEs in Benggang system and the effect of Dicranopteris are discussed.The major conclusions are as follows:(1)The LREE/HREE value is expressed as:Uncovered Benggang>Low-coverage Benggang>High-coverage Benggang.The differentiation of REEs is expressed as:The lower coverage contains more the LREE,and cause more loss of HREE.The REEs have been well migrated and prevented.(2)The distribution of REEs in different parts of Benggang system are different.The main characteristics of the changes in the total number of REEs in different parts are:in the catchment,collapsing wall.、colluvial deposit and scour channel contain more LREE,and cause general loss of HREE.The total amount of the 8 REEs after the Gd element is affected not so much,and the total amount of HREE in the CK is stable.(3)According to the horizontal comparison of REEs content according to the bare Benggang,low cover Benggang,and high cover Benggang sequence,the REEs are rapidly lost when the Dicranopteris coverage is reduced.A large amount of Dicranopteris growth can reduce the loss of REEs,and the absorption of REEs through the roots may affect the accumulation rate of REEs in the soil.The difference in Dicranopteris coverage may effect the total amount of REEs and the content of various states in Benggang system are affected by the effect of migration、prevention and transformation.(4)The Ce elements in the bare Benggang,low-coverage Benggang,and high-coverage Benggang are significantly different from other elements in the longitudinal migration comparison within each Benggang and the transverse distribution comparison between Benggang.(5)The REEs morphological differentiation of each subsystem In the Benggang system:the main REEs form of all the subsystems in CK area are in residual-state,which accounts for more than 80%,some reach nearly 95%in most enriched channels;In the uncovered Benggang,channels are major contains residual-stage REEs,and the morphology in catchment、collapsing wall and colluvial deposit is mainly transforming form.The highest enriched subsystem is the catchment,about 76.63%;In Low-coverage Benggang,the main morphology is transforming form.The lower the subsystems is,the more obvious the form become.In High-coverage Benggang,the prevention effects in main Benggang system display as decreasing state,followed by lower place of Benggang system,upper place of Benggang system,channels and collapsing wall.REEs in the water-collecting slope,the middle part of the collapsing wall and the upper part of the Colluvial deposit is mainly in rasidual state.REEs in the upper part of the collapsing wall,the lower part of the collapsing wall and the lower part of the colluvial deposit are rmaily in transforming form.(6)The migration effect of the colluvial deposit is that,prevention effect of REEs of the binding state of carbonate,the binding state of iron and manganese oxide and the binding state of organic matter are not obvious.However,the transforming and residual-state REEs are affected obviously by structural resistance control,and cause more Benggang prevention effect.Compared with the uncovered Benggang,the biological inhibition effect of the growth of Dicranopteris is likely to effect the total amount of rare earth elements in each existing form,and it informants best in the lower part of the colluvial deposit.(7)The content of La element residual in soil is significantly higher,which may be related to the influence of the La element on the roots of Dicranopteris.The total amount of rasidual state of La in soil,rhizosphere soil and non-rhizosphere soil show as:rhizosphere soil>non-rhizosphere soil>soil.This rule reflects the effect of the roots of Dicranopteris on the residual-state of REEs.(8)Dicranopteris will affect the contradiction mode of REEs in the fixed field under it by roots.Surface plants migrate the loss of water and sand,and the roots migrate the water underground,what can directly prevents the way water and soil erosion that affects migration agent,leading to mechanical preventing of Dicranopteris roots.The migration about surface behavior and underground behavior are relatively independent;Root absorption REEs will exert biological preveting on the absorption pattern of relatively active La,Nd and Pr elements,and become a part of Dicranopteris.Therefore,if the Dicranopteris been removed individualy(such as artificial collection and utilization,etc.)in the REEs loss area,it will cause the loss and transfer of REEs.