Minerai de fer | EPFL Graph Search

vignette|Rocher formé de minerai de fer rubané, vieux de d'années environ (Musée minéralogique de Dresde). Le minerai de fer est une roche contenant du fer, généralement sous la forme de sulfures, carbonates ou oxydes. L'hématite (oxyde) est le principal minerai utilisé par l'industrie sidérurgique. La teneur en fer des minerais est variable (25 % à 70 %), de sorte que la teneur du minerai est un critère souvent plus important que sa distance géographique d'un point de vue économique. Ils sont transformés avant d'être utilisés en haut fourneau pour la fabrication de l'acier. Histoire Histoire des mines de fer L'abondance de minerai de fer riche a permis le maintien d'une caractéristique originale de la sidérurgie par rapport à la métallurgie extractive des non ferreux : la forte proportion de centres sidérurgiques éloignés des mines. En effet, il est nettement plus économique de transporter sur des milliers de kilomètres un minerai comportant 55 % de fer (minerais brésil

The Emancipation of Destruction – Transforming Gällivare (Suède)

Linus Godet

Gällivare is a remote city in the middle of the northern Swedish wilderness. The city was established as iron ore was found in the ground just over a century ago. Until the 60's the mining industry and the city grew together in what seemed to be a perfect symbiosis. But as times changed and the industry had to adapt to a globalized market and bigger production volumes, the symbiosis was broken. The mines started expanding at a much higher speed, and the same industry that once founded the city is now threatening its whole existence. The last decades have been a story of destruction and relocations. The problems of dealing with destruction and relocating people have overshadowed the needs for visions and dreams. Experts from all over the world have gathered to solve the situation. The first step will be to build a knowledge center for cities in movement. Gällivare offers a very rare context. Most of the moving cities of the world are moved within a short period of time, while Gällivare is moving step by step every year. Many moving cities are actually disappearing as the inhabitants are forced to move, which makes documentation and research very difficult. Gällivare offers the opportunity to take part of the whole process, from planning to relocation. The knowledge center is the starting point for the visionary work of transforming Gällivare.

2009

An alternative model for the formation of hydrous Mg/Ni layer silicates ("deweylite"/"garnierite") in faulted peridotites of New Caledonia: II. Petrography and chemistry of white and green clay infillings

Gabrielle Dublet

This study, which complements a first mineralogical work, presents detailed petrographic and chemical data on the sequences of clay infillings commonly found in serpentine veins of reactivated faults from the New Caledonian peridotite formation. Chemical trends and transfers established from the outer serpentine fringe to the inner clay infilling, as well as from the white (deweylite) to the greenish (garnierite) parts of the veins, enable us to decipher the processes and conditions involved in the redistribution of Mg and Ni along reactivated faults. As commonly reported from studies of peridotite formations worldwide, two main chemical trends are distinguished. In New Caledonia, these trends belong to distinct periods of tectonic activities associated with the dislocation and early alteration of the ophiolite nappe. They result from two kinds of Ni-ore-forming processes and reveal a significant decrease in the mobility of Ni over time. The first process relates the step-by-step alteration of serpentine species into talclike (TL) minerals to the sequential leaching of Mg and Fe, together with their local replacement by Ni in octahedral sites of the newly formed TL minerals. The TL minerals are thus considered as the main Ni-bearing phases (pimelite) of the ore. The large-scale redistribution of Mg and Ni during a first period of tectonic activity and alteration leads to the differentiation of white (Ni-free) and olive-green (Ni-rich) clay infillings along the reactivated faults. The second process belongs to a second period of tectonic activity and alteration where most of the serpentine species have been converted into TL minerals without major Ni enrichment (formation of a second sequence of milky white and turquoise clay infillings). Redistribution of Mg and Ni occurs over shorter distances from the transition of Mg-rich to Ni-rich clay infillings (or breccias). It results from oscillatory phenomena and self-organised precipitation processes leading to cyclic and inverse Mg and Ni variations in alternating bands of contrasted optical anisotropy. The early redistribution of Ni and the significant decrease in the mobility of this element from the first to the second period of tectonic activity provide better constraints on an alternative model for the genesis of the Ni-silicate ore.

E SCHWEIZERBARTSCHE VERLAGSBUCHHANDLUNG2019

From 2D to 3D Characterization of Materials Subjected to Extreme Pressure and Temperature Conditions

Farhang Nabiei

Planetesimal were the first planetary objects to form in the solar system, which later grew to make the proto-planets. Most of these bodies were differentiated as a result of internal heating. Several differentiated bodies have, then, been accreted following the giant impacts to create the terrestrial planets. As a result of these impacts, the newly formed Earth was molten and completely differentiated. Subsequent crystallization has given rise to Earth's current structure. In order to bring new constraints on the differentiation and melting relationship in the planets we have studied natural and synthetic samples corresponding to different stages of planetary evolution through state of the art electron microscopy techniques. We have, first, looked at carbonaceous materials in a ureilite meteorite (Almahata Sitta MS-170). Thin sections from ureilite diamonds were prepared with the focused ion beam (FIB) are observed by transmission electron microscopy and spectroscopy. The morphology of graphite bands in diamonds indicated that they result from the diamond to graphite transformation during a shock event. Moreover, the diamonds in this meteorite with crystallite sizes as large as ~20 ÎŒm can only form under static high-pressure condition of planetary interiors. We have, also, found three types of diamond inclusions in our samples. The majority of these inclusions are euhedral Fe-S inclusions. However, each of these inclusions has three phases, namely: kamacite (Fe, Ni), troilite (FeS), and schreibersite ((Fe, Ni)3 P). The chemical analysis of the intact inclusions shows them to be a stoichiometric phase, (Fe, Ni)3(S, P), that can only form above 21 GPa. The ureilite parent body (UPB) should have had the size about that of Mars to exert necessary pressure to grow the diamond inclusions in the core-mantle boundary. The other two types of inclusions are the Al- and Mg- free chromite, Cr2FeO4, and Ca-Fe phosphates that were previously observed only in iron meteorites. Our results suggest that the diamonds and their inclusions were formed from an S-rich metallic liquid. In the second part of the thesis, we have studied melting and fractional crystallization of the lower mantle using a laser-heated diamond anvil cell (LH-DAC). San Carlos olivine is used as a proxy to the mantle composition. The recovered samples are first analyzed with the 3D chemical tomography using a dual beam FIB instrument. The molten region in all the samples at pressure range from 30 to 71 GPa have at least three distinct zones: a ferropericlase shell (Fp), an intermediate bridgmanite (Brg) region and the Fe-rich melt core. Thin sections from the center of the same samples are analyzed with TEM and energy-dispersive x-ray (EDX) spectroscopy. The results from the samples heated at 45 GPa for 1, 3, and 6 minutes demonstrated that the temperature gradient in the heated zone shrinks through the time and, thus, the crystallization continues toward the center of the heating. Consequently, the melt becomes richer in iron. The melt core also gets more iron-rich with increasing pressure. In fact, in ~70 GPa we observe an Fe-O core with small Si and Mg concentration. This implies that the melt at the bottom of the mantle could become denser than the solid phases and sink down. The presence of the iron-rich melt or the oxides crystallizing from such a melt can explain the ultra-low velocity zones (ULVZs) found in the seismic surveys of the core-mantle boundary.

EPFL2017

From 2D to 3D Characterization of Materials Subjected to Extreme Pressure and Temperature Conditions

Farhang Nabiei

EPFL2017

Gabrielle Dublet

E SCHWEIZERBARTSCHE VERLAGSBUCHHANDLUNG2019