Seminário no PPGEM

O PPGEM-CP CONVIDA PARA SEMINÁRIO

Título:  “The Fascinating Geochemistry of Pyrite And Natural Hydrogen”.

Profa. Dra. Corinne Arrouvel

Universidade Federal de São Carlos (UFSCAR), Sorocaba;

Pesquisadora do Instituto de Química da Universidade Federal do Rio de Janeiro (IQ - UFRJ). 

Data: 11 de setembro de 2018

Horário: 16:00 horas

Local: UTFPR-CP - Sala A-128

RESUMO DA APRESENTAÇÃO

Pyrite FeS2 is the most common sulfide mineral and it has captured the interest of humankind since the prehistory. Stones were used to start a fire; its metallic yellow glow did foolish a lot of gold prospectors during the American dream; its euhedral shapes with divine proportions did inspire metaphysical believers and Pythagorean mathematicians living in the South of Italy. Italy is still leading the pyrite market, exporting it and producing sulfur. Recent nanoscience studies are revalorizing pyrite applications for energy materials (i.e. rechargeable batteries, solar cells), in catalysis for hydrogen production and for toxic metal removals. However, a key issue in nanotechnology is to understand thermodynamic and kinetic aspects of the crystal growth as a function of temperature, the pressure and concentration of the elements present in the medium. In addition, framboidal micron-pyrite minerals found in sediments are also related to the primitive life cycle in which the formation and shapes obey to the same crystal growth theories. The first part of the talk will propose some new insights on structural, electronic and magnetic properties of pyrite and related compounds using classical[1] and ab initio simulations (METADISE and VASP software). Combining theory with electron microscopy, we can show that the striations along the <001> directions follow some rules, being visible on {hk0} facets and observed in the mathematical description of golden shapes.

And what is the link between pyrite and natural hydrogen? First of all, abiotic H2 is a recent discovery and seems to be renewable. The community in the village of Bourakebougou in Mali is the first to exploit natural hydrogen though the PETROMA company. New researches indicate that there are natural hydrogen sources in Brazil and in other parts of the world (including Turkey, USA, Oman, Russia) [2]. Nevertheless, its origin and formation on Earth remain poorly understood. Some controversial hypotheses have been formulated to explain its genesis, as primitive hydrogen in the inner core, in mantle rocks or in the continental crust. In this second part of the talk, I will review possible routes for H2 formation and propose new chemical reactions based on simulations (VASP and SUPCRT) and geological data observations (on-going work with Dr. Alain Prinzhofer). Among the favourable reactions, (1) and (2), pyrite and hydrogen are formed even at relatively high temperature and pressure.

 α-Fe2O3 + 4 H2S → 2 FeS2 + 3 H2O + H2    (1)

Fe3O4 + 6 H2S → 3 FeS2 + 4 H2O + 2 H2    (2)

 Hydrogen is a promising substitute fuel to hydrocarbons and ethanol, especially for the transport industry. Indeed, H2 fuel cells and generators are technologies producing energy with zero carbon emission, the sub-product being water. Moving toward green technologies and decentralised energy for a sustainable future is becoming affordable thanks to geochemistry, geophysics and geology......

 [1] Corinne Arrouvel and J.-G. Eon, Understanding The Surfaces And Crystal Growth

     Of Pyrite FeS2, Materials research, accepted (2018)

[2] Alain Prinzhofer and Eric Deville. Hydrogène naturel. La prochaine révolution

     énergétique ?, Ed. Belin, 2015.