Banca de DEFESA: PRISCILA LIRA DE MEDEIROS

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : PRISCILA LIRA DE MEDEIROS
DATE: 27/06/2023
TIME: 14:00
LOCAL: Auditório do Programa de Pós-graduação em Ciência do Solo da UFRPE
TITLE:

Geochemistry of rare earth elements, uranium and thorium in Chromic Luvisols formed on amphibolites in climosequence, brazilian semi-arid region

KEY WORDS:

argiluviation. tracers of pedogenetic processes. soil forming factors.

PAGES: 122
BIG AREA: Ciências Agrárias
AREA: Agronomia
SUBÁREA: Ciência do Solo
SPECIALTY: Gênese, Morfologia e Classificação dos Solos
SUMMARY:

Considering the current protagonism of REE and U and Th radionuclides, the scarcity of geochemical data on these elements and the difficulty in identifying the process of soil damage, this work was carried out, with the aim of evaluating the geochemistry of REE, U and Th in Luvisols originating from amphibolites along a climosequence (drier, intermediate and less-dry zones) in the Brazilian tropical semi-arid region, and test if these elements can be used to trace lessivation process. To analyze the geochemistry of REE, U and Th, petrography and soil analyzes (physical-chemical and mineralogical) were used. Descriptive statistics of the data and Pearson's correlation were performed, with the aim of knowing the relationship between ETR, U and Th and the physicochemical properties of the soils. The concentrations of REE, U and Th were obtained, and the fractionations between LREE and HREE (La/Yb)N, between LREE (Yb/Tm)N and between HREE (Gd/Tb)N to know the effect of weathering in the mobilization of REE; and the fractionation between LREE, MREE and HREE, associated with Ce and Eu anomalies, and the vertical distribution of Th, in order to trace the process of lessivation; and the Th/U and La/Th ratios, to understand the effects of weathering on the geochemical signature of radionuclides in Luvisols. The pluviometric gradient towards the less-dry zone contributed to: 1) an increase in the concentration of REE, U and Th; 2) slight enrichment in HREE, especially at depth, due to greater mobility and high content in the underlying rock, but without modifying the geochemical signature of low REE fractionation, positive Ce anomaly and negative Eu anomaly; 3) enrichment of U to the detriment of Th (Th/U <1), modifying the Luvisol geochemical signature of these elements, although the La/Th ratio was little affected; 4) relative increasing in the proportion of heavy minerals, in the crystallinity of Fe oxides and in the kaolinite content, contributing to the increase in the concentration of REE, U and Th. It was possible to identify the occurrence of the lessivation process in the formation of the Bt horizon of the Luvisol in the less dry zone by analyzing the distribution of REE and Th in the soil profile. The pH and the Fe content were determinant in the distribution of REE in the soils; the contents of Fe, Ti, CO, sand and silt and the CTCp correlated with the concentration of U, and only the CTCp with that of Th. Soil properties that were changed from a drier to a less dry zone are strongly dependent on formation processes, modulated by the intensity of weathering, which is mainly controlled by the rainfall index (climate factor), and directly affect the concentration and distribution of ETR, U and Th in semi-arid Luvisols. 

COMMITTEE MEMBERS:
Presidente - VALDOMIRO SEVERINO DE SOUZA JUNIOR
Interno - YGOR JACQUES AGRA BEZERRA DA SILVA
Externa ao Programa - ***.067.914-** - MARILYA GABRYELLA FERNANDA DE SOUSA - UFRPE
Externa à Instituição - PAULA RENATA MUNIZ ARAUJO - UFRPE
Externo à Instituição - TIAGO OSORIO FERREIRA - USP