Anezka Radkova, Heather Jamieson Application of synchrotron radiation-based techniques on study of mine waste mineralogy Anezka Radkova, Heather Jamieson AESRC, 2015 http://www.esrf.eu/

Outline Introduction to synchrotron related analytical techniques - µXRF, µXAFS, µXRD Why is the study of tailings mineralogy important? Arsenic (As) rich tailings Nova Scotia Antimony (Sb) secondary minerals in tetrahedrite rich waste rock: Slovakia Conclusions

Synchrotron light source High brilliance (many orders of magnitude more than with X-rays produced in conventional X-ray tubes) Highly focused light Tunable energy http://www.esrf.eu/

Experimental techniques: 1) µXRF (X-ray fluorescence spectroscopy) spot analyses and mapping Characteristic X-ray emission lines Determining elemental compositions   Resolving elements distribution Micro-focusing techniques - studies of the spatial element distribution on a micrometric scale (chemical zoning and impurity distributions) Combination with other techniques: XRD, XANES, EXAFS elemental analysis can be combined with other microanalysis techniques  μ-XRF - selecting sample areas before applying other microanalysis techniques Secondary oxides mixture 50 µm SbLa FeKa CuKa AsKa BiLa Sb Fe Cu As Bi

Experimental techniques: 1) microXRD Structural information of crystalline compounds - high brilliance enable to detect nanoparticulate crystals Detection of low-abundance crystalline phases Environmental materials characterization as a heterogeneous multi-phase systems of generally poor crystallinity

Experimental techniques: 1) XAFS (X-ray absorption spectroscopy) and µXAFS XANES Oxidation state Coordination chemistry 2.32Å 2.46Å 3.43 Å 2.90 Å Fe2O3 EXAFS Quantitative Local Structure. information on the atoms organisation and chemical bonding around an absorbing atom XANES = X-ray Absorption Near-Edge Spectroscopy EXAFS = Extended X-ray Absorption Fine-Structure Pacheco and Bargar, 2011

Application of mine waste mineralogy study: What questions can we answer? What is the dominant form of contaminant of interest? Is the contaminant present in toxic or bioaccessible form? Molecular- level speciation of trace environmental contaminants are necessary for understanding their behavior. Will the contaminant remain stable or is it likely to get mobilized? Prediction of contaminant behaviour when selecting the remediation technique for particular site

ARSENIC BIOACCESSIBILITY IN THE NOVA SCOTIA GOLD MINING DISTRICTS Arsenic-bearing gold ore mining – As rich tailings Close distance to residential areas, at times used for racing off-road vehicles Inhalation or ingestion of As-bearing tailings- risk to human health In case of some samples no As phases confirmed by field observation or conventional XRD, even though most of these samples contain As concentrations in the wt% range (>10,000 ppm) Photo: Catherine Craigen Walker et al., 2009

Ferric arsenates (scorodite, amorphous Fe arsenate, kaňkite) Heterogenous near surface tailings containing arsenopyrite and its oxidation products: Ferric arsenates (scorodite, amorphous Fe arsenate, kaňkite) Ca-Fe arsenates (yukonite and an amorphous form) Remediation challenge: mix of oxidized and reduced As species BIOACESSIBILITY Walker et al., 2009

Behavior of antimony during the weathering of the tetrahedrite-tennantite [Cu12(Sb,As)4S13] minerals in abandoned waste rock piles Photo: Martin Chovan

A B C Sb hosts: Mixture of nanocrysctalline romeite group mineral with pyrochlore structure and tripuhyite (FeSbO4), lower wt% of Sb in amorphous phases Amorphous phases tetrahedrite BSE Amorphous phases high Tripuhyite and pyrochlore low

Metals and metalloids distribution in tetrahedrite oxidation products wt%

Conclusions Synchrotron techniques effective for mine tailings and waste rock mineralogy study: XRF – identification chemical associations XRD – identification mineral species XAFS – information about structural form and oxidation state of metals at molecular level bulk XANES – proportions of metal species these methods can be effectively used to characterize host minerals of contaminants such as As and Sb in mine waste identification of mine waste compounds helps to predict further behaviour of contaminants

Acknowledgements EMPA assistance: Brian Joy APS assistance: Robert Gordon, Zoe Finfrock EMPA assistance: Brian Joy