Nandu River Basin In Hainan Island Typical Soil In The Rare Earth Element Geochemical Characteristics

In recent years, the research of rare earth elements (REEs) in soil and agricultural is very active, especially the application of the rare earth fertilizer has been developed vigorously, and it has become a hot spot of geochemical research about trace element. The results show that in a certain concentration range, rare earth elements can promote the growth of microorganisms in the soil and enhance its activity, improve soil fertility, improve soil nutrient cycling capacity of ecosystems and promote growth and development of crop. China is a big country rich in Rare earth resources, nearly accounting for 80% of global reserves, and it has a wealth of firsthand information. The soil environmental impacts of rare earth are more and more concerned. In order to study of REEs systematically and comprehensively, and make them for our use, the study on geochemical behavior of REEs in the soil is essential.The Nandu River is the biggest river of Hainan Island. The article selects the soil of typical area in the Nandu River Basin as the research object. A large number of sampling and the use of advanced testing techniques conducted the special studies of REEs. A systematic study has been made on the content, distribution, fractionation, distribution patterns of REEs in soil in this thesis. The background value of REEs in soil of the typical area in Nandu River Basin could be obtained from the thesis. It can guide agricultural zoning, land improvement, application of rare earth fertilizer and ensure the coordinated development of agriculture and ecology. So this thesis has important practical significance.With the purpose of understanding the geochemical characteristics of REEs in soil of the typical area in Nandu River Basin, ICP-MS method is used to get the REEs contents of 100 surface soil samples and 40 soil samples for 5 soil profiles in the typical area of Nandu River Basin. This paper analyzes the horizontal characteristics of REEs in surface soil and the vertical distribution characteristics of REEs in soil profile, REEs contents, fractionation and anomaly of Ce and Eu. The main results are as follows:(1)The gross of REEs (ΣEE) in surface soils of study area is between 18.75mg/kg and 237.59mg/kg, with an average of 103.22mg/kg. The standard deviation is 42.47, and the coefficient of variation is 0.41. The content of light rare earth elements (LREEs) is between 14.74mg/kg and 225.18mg/kg, with an average of 92.21mg/kg. Its standard deviation is 39.07, and its coefficient of variation is 0.42. While the content of heavy rare earth elements (HREEs) is between 3.64mg/kg and 19.63mg/kg, with an average of 11.01mg/kg. Its standard deviation is 4.06, and its coefficient of variation is 0.37. The ratio of LREEs and HREEs is between 3.67 and 18.14, and the average ratio is 8.32, much bigger than 1. These numbers indicate that LREEs and HREEs in surface soil fractionate significantly, and the surface soil in researched area is typically rich in LREEs. (2) REEs content of surface soil exists a certain characteristic in the horizontal distribution. REEs content of the longitudinal area (area A) which is influenced closely by the Nandu River is higher than the transverse area (area B) which is less affected by water. The average gross of REEs in surface soil of the longitudinal area is 115.10mg/kg, while the transverse area is only 84.64mg/kg. And the coefficient of variation of gross REEs in transverse area is 0.64, higher than the longitudinal area (0.24).(3) According to REEs calculation of 100 surface soil samples in the typical area of Nandu River Basin, the standard value of Eu (8Eu) is between 0.38 and 1.00, with an average of 0.79, less than 1.05, showing a negative anomaly, loss of Eu. And the standard value of Ce (δCe) is between 0.83 and 2.61, with an average of 1.29, the overall performance of positive anomaly, relative rich in Ce.(4) The test data on the chondrite-normalized and North American shale-normalized are got. In 2008 Yuan Jianping measured parent material brick red basalt REEs data in Hainan Island. Comparing the two, we can find they show a certain similarity that from the morphological point of view they both right tilt, and both rich in HREEs. All respects show typical features of continental crust, and indicate that the main source of the material is terrigenous.(5) There is a certain rule in the average gross of REEs (ΣREE) in vertical profiles of the soil in the typical area of Nandu River Basin, which is in order of the middle layer>upper>floor. The average LREEs and HREEs also follow this rule. Particularly the distribution of LREEs is almost the same distribution withΣREE. The reason may due to tropical of Hainan Island, and the climate is warm and humid, so REEs move easily. The surface soil is leached strongly, causing REEs enrichment in the deposition layer.(6) The ratio of LREEs and HREEs in the soil profile is between 8.23 and 10.93, and this ratio is much bigger than 1, indicating that the fractionation of LREEs and HREEs is serious, and the soil is rich in LREEs. The distribution rule of LREEs is almost the same with HREEs, which explains that to some extent LREEs is the main part ofΣREE, and it also proves that the soil rich in LREEs.(7) Chondrite-normalized REEs distribution patterns of the soil profile are the right partition curve slope, and Ce present positive anomaly.δCe is in order of middle> upper> floor, and the upper and middle layer of soil presents significant positive anomaly, while the underlying soil shows no abnormality or weak positive anomaly. Distribution patterns of Eu indicate a negative anomaly, loss of Eu.δEu is in order of floor> middle> upper, that the closer to surface soil loss of the more REEs, because Eu occurs oxidation reduction reaction during the process of the soil development. With the continued development and maturation of soil, loss of Eu is superimposed constantly, so the process of soil development is the process of gradual increase loss of Eu.