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Instruments / Technical Area	Publication Details	Published
B18-Core EXAFS	Micronutrient availability in Precambrian oceans controlled by greenalite formation Rosalie Tostevin , Imad Ahmed Nature Geoscience 356 DOI: 10.1038/s41561-023-01294-0 Diamond Proposal Number(s): [15859] Show Abstract ▼ Abstract: Metabolisms that evolved in the Archaean era (4.0–2.5 billion years ago) preferentially selected iron, manganese and molybdenum to form metalloproteins, whereas the majority of zinc-, copper- and vanadium-binding proteins emerged much later. The initial preference for these elements is commonly interpreted to reflect their availability in anoxic seawater, with free sulfide proposed as a key influence. While sulfidic waters reduce the availability of zinc and copper, they also remove molybdenum and leave behind vanadium. Furthermore, current geochemical data reflect predominantly ferruginous (Fe2+-rich), rather than sulfidic, conditions. Consistent with this, recent sedimentological work has uncovered abundant iron silicate minerals in Archaean rocks. Here we quantify metal partitioning during the formation and subsequent diagenesis of an Fe(II) silicate mineral, a precursor to crystalline greenalite, in both seawater and hot hydrothermal fluids. Our data show that Fe(II) silicates could have precipitated rapidly in Archaean hydrothermal plumes, severely attenuating hydrothermal delivery of key nutrients, in particular copper, zinc and vanadium. These results provide a mechanistic explanation for metal availability patterns in Archaean oceans that is consistent with temporal patterns of metal utilization predicted from protein structures and comparative genomics. Further, our data suggest natural greenalite may provide an archive of metal availability in deep time.	Nov 2023
I18-Microfocus Spectroscopy	Geochemical investigations of noble metal-bearing ores: Synchrotron-based micro-analyses and microcosm bioleaching studies Loredana Brinza , Imad Ahmed , Carmen - Madalina Cismasiu , Ioan Ardelean , Iuliana Gabriela Breaban , Florica Doroftei , Konstantin Ignatyev , Cristina Moisescu , Mariana Neamtu Chemosphere DOI: 10.1016/j.chemosphere.2020.129388 Diamond Proposal Number(s): [20316] Show Abstract ▼ Abstract: Auriferous sulphide ores often incorporate micro-fine (or invisible) gold and silver particles in a manner making their extraction difficult. Nobel metals are lost in the tailings due to the refractory nature of these ores. Bioleaching is an environment-friendly alternative to the commonly used and toxic cyanidation protocols for gold extraction from refractory ores. In this paper, we investigate gold and silver bioleaching from porphyry and epithermal mineralisation systems, using iron-oxidizing bacteria Acidithiobacillus ferrooxidans. The invisible Au, sequestered in refractory ores, was characterised in situ by synchrotron micro X-Ray Fluorescence (SR-μ-XRF) and X-ray Absorption Spectroscopy (XAS), offering information on Au unaltered speciation at the atomistic level within the ore matrices and at a micro-scale spatial resolution. The SR-μ-XRF and XAS results showed that 10-20μm sized elemental Au(0) nuggets are sequestered in pyrite, chalcopyrite, arsenopyrite matrices and at the interface of a mixture of pyrite and chalcopyrite. Moreover, the preliminary bioleaching experiments of the two types of ores, showed that Acidithiobacillus ferrooxidans can catalyse the dissolution of natural heterogeneous Fe-rich geo-matrices, sequestering Au and Ag and releasing particulate phases or partially solubilising them within 60 days. These results provide an understanding of noble metal sequestration and speciation within natural ores and a demonstration of the application of synchrotron-based micro-analysis in characterizing economic trace metals in major mineral structures. This work is a contribution to the ongoing efforts towards finding feasible and greener solutions of noble metal extraction protocols.	Dec 2020
I22-Small angle scattering & Diffraction	Formation of green rust sulfate: a combined in situ time-resolved X-ray scattering and electrochemical study Imad A. M. Ahmed , Liane G. Benning , Gabriella Kakonyi , Aryani D. Sumoondur , Nick J. Terrill , Samuel Shaw Langmuir 26 (9) DOI: 10.1021/la903935j Diamond Proposal Number(s): [883] Show Abstract ▼ Abstract: The mechanism of green rust sulfate (GR-SO4) formation was determined using a novel in situ approach combining time-resolved synchrotron-based wide-angle X-ray scattering (WAXS) with highly controlled chemical synthesis and electrochemical (i.e., Eh and pH) monitoring of the reaction. Using this approach,GR-SO4 was synthesized under strictly anaerobic conditions by coprecipitation from solutions with known FeII/FeIII ratios (i.e., 1.28 and 2) via the controlled increase of pH. The reaction in both systems proceeded via a three-stage precipitation and transformation reaction. During the first stage,schwertmannite (Fe8O8(OH)4.5(SO4)1.75) precipitated directly from solution at pH 2.8?4.5. With increasing pH (>5), Fe2+ ions adsorb to the surface of schwertmannite and catalyze its transformation to goethite (?-FeOOH) during the second stage of the reaction. In the third stage, the hydrolysis of the adsorbed Fe2+ ions on goethite initiates its transformation to GR-SO4 at pH >7. The GR-SO4 then continues to crystallize up to pH ?8.5. These results suggest that with an FeII/FeIII ratio of ?2 in the initial solution the structural FeII/FeIII of the GR-SO4 will be close to that of the starting composition.	Feb 2010
NONE-No attached Diamond beamline	Coordination of Cd2+ ions in the internal pore system of zeolite-X: A combined EXAFS and isotopic exchange study S. D. Young , N. M. J. Crout , E. H. Bailey , J. F. W. Mosselmans , I. A. M. Ahmed Geochimica Et Cosmochimica Acta 73 (6), 1577-1587 DOI: 10.1016/j.gca.2008.12.018 Show Abstract ▼ Abstract: The effect of prolonged contact time (up to 130 days) on the immobilization of Cd by sorption to calcium exchanged zeolite-X (CaX), under environmentally relevant conditions, was studied using both isotopic exchange and extended X-ray absorption fine structure spectroscopy (EXAFS). Sorption and isotopic exchange measurements revealed time-dependent Cd sorption and indicated the movement of Cd2+ ions into less accessible sites due to ageing. EXAFS suggested progressive fixation of Cd in the double six-ring (D6R) unit of the CaX structure. Proportional allocation of the apparent Cd–Si bond distance to two ‘end-members’, across all contact times, indicated that the bond distance for labile Cd was 3.41 Å and for non-labile (or fixed) Cd was 3.47 Å.	Mar 2009

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