Chemical interaction mechanisms of metals, inorganics anions, organic acids and protein on purified material, artificial soil and cropland soil

Author(s)

Matheus Sampaio Carneiro Barreto

• Document type: Doctoral Thesis
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2019-09-05

Examining board members

Luis Reynaldo Ferracciú Alleoni; Hudson Wallace Pereira de Carvalho; Tiago Osorio Ferreira

• Advisor: Luis Reynaldo Ferracciú Alleoni

Abstract

The soil is a complex system with several phases, where abundant interfaces phenomena happen, which determines the mobility/availability of nutrients and contaminants into the environment. The deep understanding of these chemical mechanisms is a challenge, and it is often necessary to use models with reduced numbers of components and high purity, in order to isolate the effects of environmental variables such as minerals type, pH and time. Also, sophisticated analytical techniques may be used to elucidate the mechanisms involved at atomic and molecular scales. Here, mechanisms of some chemical reactions for some nutrients such as P and Zn, macromolecules such as protein and humic substances, as well as a contaminant such as Cd and As were evaluated, using pure systems, artificial soil or soil samples from cultivated areas. The main conclusions were: (i) the previous adsorption with citrate decreased P adsorption on hematite surface. The P-hematite surface complex in bidentate configuration had a faster absorption than the monodentate, and the bidentate was preferentially desorbed by citrate; (ii) As(V) was adsorbed on inner and outer- sphere complexes on the hematite and hausmannite surfaces, hausmannite showing a higher adsorption than hematite. The transformation from hausmannite to manganite should increase As(V) adsorption an its stability, thus hausmannite could be a good option as As(V) filter; (iii) the adsorption on hematite surface promoted a prominent conformational change in the secondary structures of BSA protein, toward a less \"packed\" and more \"unfolded\" protein forms, and the pH near the isoelectric point maximized its adsorption; (iv) Ca increased the adsorption of humic substances in the minerals present in weathered soils. Ternary complexes \"mineral-Ca-humic substances\" were responsible for this increment; and organic molecules less humified and/or with lower molecular weight were preferentially adsorbed on minerals\' surfaces; (v) less Zn was adsorbed at pH 4.5, which was preferentially retained in aluminosilicate minerals, while at pH 6.5, more Zn was adsorbed and Zn sorbed on Fe oxide, and Zn-P precipitates were identified. However, after 6 months, these ones decreased or disappeared, and the fraction of Zn sorbed to aluminosilicate minerals incresed; (vi) Cd and Zn are rapidly adsorbed on soils under native vegetation or highly fertilized agricultural soils, and agricultural soils adsorb more these metals than soil under native vegetation. These metals, however, were easily desorbable by EDTA; (vii) the soil mineralogy determined the main Zn fractions adsorbed on the soil, the fraction of Zn adsorbed to kaolinite was present in all soil samples, regardless of origin and management; agricultural management and time increased the amount of Zn in less mobile fraction, and Zn associated with P was present in highly fertilized soils. (AU)

• FAPESP's process: 16/05870-1 - SPCIATION AND KINETIC ADSORPTION AND DESORPTION OF Cd AND Zn IN SOILS OF OLERACEUS CROPS HIGHLY FERTILIZER
• Grantee: Matheus Sampaio Carneiro Barreto
• Support Opportunities: Scholarships in Brazil - Doctorate