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Surface reactions of magnetite and maghemite with dissolved and added ions in process water
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Reactions between mineral surfaces and dissolved species in process water, both inorganic and organic play an important role in mineral processing. Reverse flotation of finely comminuted iron ore is sometimes employed in order to remove the phosphorous mineral apatite. An anionic collector, designed to specifically adsorb at the calcium specific surface sites of apatite is added, rendering the apatite particles hydrophobic properties. However, some of the collector adsorbs also at the magnetite surfaces, thereby introducing undesired characteristics to the upgraded iron ore concentrate.Of this reason, magnetite and maghemite surfaces and their interactions with the most abundant and important ions in the process water during flotation, and their potential influence on collector adsorption at magnetite was studied. Maghemite was included in the experiments, since previous work had shown that oxidation of the magnetite surface into maghemite may occur during the processing of the iron ore concentrate. The complex system that the dissolved ions in the process water and the iron oxide particles constitute at flotation and agglomeration was divided into smaller subsystems.The protolytic characteristics for the magnetite-H+ and maghemite-H+ systems proved to be similar when their modelled intrinsic surface complexation constants were compared. However, the surface site density of magnetite was found to be 50 % greater than for maghemite. Both potentiometric titrations and ATR-FTIR spectroscopy were used to study and characterize the adsorption of silicate. The results from the surface complexation modelling suggested that the silicate adsorbed as monodentate surface complexes at the maghemite surfaces. The results showed a silicate adsorption maximum at pH 8.5 to 9.5 for both iron oxides. Within this range pH, the surface complex ΞFeOSiO(OH)2 - was proposed as the dominating surface specie in the maghemite-silicate system.The iron ore pellet additive olivine proved to release substantial amounts of Mg2+ when immersed in water, indicating that olivine probably is the main source of Mg2+ to the process water. Thus, the surface characteristic of olivine particles in water suspensions was studied. Since olivine proved to be a significant source of magnesium ions, adsorption of Mg2+ at maghemite and magnetite was studied and modelled. The results suggested that magnesium ions adsorbed as a mix of mono- and bidentate surface complexes when the number of surface sites was in excess. Increased amounts of Mg2+ i.e., ≥1 Mg2+ site-1, resulted in a model including only monodentate surface complexes.Experiments involving competitive adsorption of carbonate and silicate showed that added silicate replaced adsorbed carbonate. Other competitive experiments, with Mg2+ and Ca2+, showed that Mg2+ had a stronger affinity for the magnetite surface than Ca2+. The preferential adsorption of Mg2+ at the iron oxide surface may then have protective properties, by preventing adsorption of the calcium specific collector. Results from both in-situ ATR-FTIR spectroscopy and contact angle measurements indicated also that added Mg2+ reduced the adsorption of collector and thereby increased the wettability of the magnetite surfaces.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2012.
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Research subject
Chemistry of Interfaces
Identifiers
URN: urn:nbn:se:ltu:diva-18556Local ID: 9263618d-c009-451b-a4d0-3dc1d8272cf6ISBN: 978-91-7439-503-7OAI: oai:DiVA.org:ltu-18556DiVA: diva2:991565
Note
Godkänd; 2012; 20121017 (ricjor); DISPUTATION Ämne: Gränsytors kemi/Chemistry of Interfaces Opponent: Professor Jean-Francois Boily, Kemiska institutionen, Umeå universitet, Ordförande: Docent Lars Gunneriusson, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet Tid: Torsdag den 29 november 2012, kl 10.15 Plats: C305, Luleå tekniska universitetAvailable from: 2016-09-29 Created: 2016-09-29Bibliographically approved

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