IRON GEOCHEMISTRY IN SOILS DEVELOPED ON GRANITIC TERRAIN IN A TROPICAL CLIMATE

• Grant number: 25/06945-4
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: June 01, 2025
• End date: May 31, 2026
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Physical Geography
• Principal Investigator: Hermano Melo Queiroz
• Grantee: Ana Beatriz Abade Silva
• Host Institution: Faculdade de Filosofia, Letras e Ciências Humanas (FFLCH). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

Poorly crystallized structures, known as amorphous, are defined by the lack of a crystalline arrangement that characterizes a periodic structure. This fraction of natural metals has a variable chemical composition, mineral structure, and crystallinity, making it prone to rapid alteration when exposed to leaching conditions and acidic pH. In tropical regions, where these conditions occur, there has been few research on this topic, although recent studies emphasize the importance of the crystallinity degree of iron minerals in relation to their capacity for contaminant and nutrient retention and bioavailability, cation exchange capacity (CEC), porosity, and other soil functions. In this context, the aim of this research is to understand the genesis, occurrence, and geochemical behavior of amorphous iron in tropical environments. For this, a granite lithology area, which has considerable geographic distribution in tropical climates, was selected to study the potential occurrence of amorphous iron in an extensive 18-meter soil profile. This sampling will undergo physicochemical and mineralogical analyses: FTIR and sequential iron extraction using the Dithionite-Citrate-Bicarbonate (DCB) and Oxalate methods. Based on these qualitative and quantitative data, it will be possible to conduct a crystallographic characterization of iron throughout the profile, which will help assess its geochemical behavior. Thus, it will be possible to validate the hypothesis that iron oxides are formed in tropical climates. Also, due to their position in the profile, these oxides have been directly transformed into more crystalline iron oxide forms. Finally, we will correlate these transformations occurring at depth to changes in crystallinity and the potential services provided by iron in the soil. (AU)