Banca de DEFESA: SÁVIO ROBERTO MARTINS

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : SÁVIO ROBERTO MARTINS
DATE: 26/02/2024
TIME: 14:00
LOCAL: Auditório do prédio do PPGCS-UFRPE
TITLE:

Rare earth element geochemistry in regolith derived from syenite under a climatic gradient in the state of Pernambuco

KEY WORDS:

Weathering, Regolith. Climate-soil relationship, Saprolithology.

PAGES: 105
BIG AREA: Ciências Agrárias
AREA: Agronomia
SUBÁREA: Ciência do Solo
SPECIALTY: Química do Solo
SUMMARY:

A comprehensive understanding of the dynamics of various elements and processes occurring in the soil profile is only achieved through the joint study of the soil-saprolite system. This is especially true for rare earth elements (REE), whose unique characteristics allow them to participate in chemical processes and reactions essential to the pedosphere. REE comprise a group of 17 chemical elements, corresponding to Sc, Y and the 15 lanthanide elements, from lanthanum to lutetium. These elements are commonly divided into two groups: light rare earth elements (LREE: La-Sm) and heavy rare earth elements (HREE: Eu-Lu). However, knowledge about the distribution and behavior of these elements in the soil profile is limited, especially in tropical regions, where weathering and pedogenesis processes are intense and variable. In this way, a climate gradient can provide crucial information about the response of these elements to climate variation and its implications for soil and vegetation. Thus, studies that associate climate and REE geochemistry are relevant to the scientific community because they can serve as indicators of important geochemical changes to the environment. Aiming to study the geochemistry of REE in the soil profile, samples were collected from 3 soil profiles (P1 at the base, P2 in the intermediate position and P3 at the top), distributed at different altitudes and, consequently, under a climatic gradient, from a climate drier and hotter at the base to a wetter and colder climate at the top of the Triumph Massif. These samples were prepared and subjected to analysis to determine the content of: 1) total clay, 2) organic carbon (TOC), 3) major elements (Al2O3, BaO, CaO, Cr2O3, Fe2O3, MgO, MnO, P2O5, K2O, SiO2, Na2O e TiO2), 4) minor elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Ho, Er, Tm, Yb, Lu and Y), 5) pedogenetic Fe (Fed) and 6 ) forms of iron linked to low crystallinity phases (Feo). Chemical weathering measurement indices were calculated, relationships between REE were calculated, normalization of REE in relation to the “upper continental crust” (UCC) was performed and the content of total clay, TOC and pedogenetic iron forms were correlated with the contents of LREE and HREE in the respective soil profiles. The relationship between climatic variation and the geochemistry of the profiles was evident and influenced the attributes measured in the profiles in the three positions: 1) the highest levels of larger more mobile elements such as K were determined in P1, due to lower rainfall in this position, 2) the weathering indices indicate more intense weathering in the position with the highest precipitation in P3, 3) the normalization of the REE indicated the enrichment of the LREE, depletion of the HREE and positive Eu anomaly in P1 and P2, thus as uniformity in P3, probably due to greater humidity at the top, 4) the climatic gradient affected the distribution of pedogenic iron forms in the profiles and Feo had higher content in P1, under semi-arid climate, just as Fed had higher content in P3 under climate humid, 5) the clay content varied from P1 to P3, due to the effect of climate on weathering, 6) organic matter was incorporated in different ways, depending on the position of the profile in the climatic gradient, with a drastic decrease in depth in P1 and moderate in the other profiles, 7) LREE correlated well with clay content, Feo and Fed and 8) HREE correlated well with TOC. The data presented indicate that the climate gradient significantly shapes the geochemistry of syenite-derived soil profiles, making this an important result for studies that aim to relate climate to REE geochemistry in soil profiles around the world.

COMMITTEE MEMBERS:
Presidente - JEAN CHEYSON BARROS DOS SANTOS
Externo à Instituição - FABRICIO DE ARAÚJO PEDRON
Externo à Instituição - LUIZ HENRIQUE VIEIRA LIMA