Precipitation and Characterization of Arsenate Phases from Ca(II)-Cu(II)- Fe(III)-AsO4-SO4 Hydrothermal Systems Mario Alberto Gomez Department of Mining and Materials Engineering McGill University Montreal, QC, Canada October 2010 A thesis submitted to McGill University in partial fulfillment of the requirements of the degree of Doctor of Philosophy © Mario Alberto Gomez, 2010 Abstract The scope of this thesis is the study of three Fe(III)-As(V) hydrothermal systems. The first one is the Fe(III)-AsO4-SO4 system and crystalline phases that are produced under high temperature (150-225°C); this was studied to clear up previous contradicting information on this system in relation to industrial arsenic products that are formed during the autoclave processing of arsenical sulphide gold feedstocks and asses their arsenic stability. The second system studied was Cu(II)-Fe(III)-AsO4-SO4 system at 150°C; this was investigated due to its relevance to industrial pressure leaching of copper concentrates. This system was studied in order to examine the possible effect of copper on the precipitation of scorodite. Finally, the structural and molecular examination of two members of the Ca(II)-Fe(III)-AsO4 system, namely yukonite (synthetic and natural and arseniosiderite was undertaken due to their relatively unknown nature and the potential role play in controlling arsenic release in tailings. In the first case, three arsenate phases were found to be produced at various conditions explored here, these were: sulfate containing-scorodite (Fe(AsO4)1-0.67x(SO4)x · 2H2O where 0.00≤x≤0.20), ferric arsenate sub-hydrate (FAsH; Fe(AsO4)0.998(SO4)0.01 · 0.72H2O), and basic ferric arsenate sulfate (BFAS; Fe(AsO4)1-x(SO4)x(OH)x · (1-x)H2O, where 0.3<x<0.7). Their domain of formation was determined in terms of temperature, acidity, Fe/As molar ratio and time. Our FAsH and BFAS produced phases were found to correspond to previously unrelated phases for this system. In addition to renaming these phases their unequivocal characterization (at the elemental, electronic, molecular and structural level) was established and their molecular formulae corrected. It is also shown that scorodite and BFAS exhibit metastability converting to FAsH upon extension of the reaction time. Finally, upon studying the long-term leachability of these phases as a function of pH it was determined scorodite and BFAS to be the least soluble (lowest arsenic release). In the second case, the presence of copper was not found to have any profound effect upon arsenic precipitation in the form of scorodite. The latter was found to be the only arsenate phase formed under all conditions tested (1-10 hrs reaction at 150 °C). However, the formation of a short lived intermediate in the form of a basic cupric ferric arsenate sulfate phase was observed for the first time in this system at shorter times (<1 hr) and lower i temperatures (< 150°C) before ultimately converting to the most stable phase (scorodite). These findings indicate that copper could coprecipitate at short retention times hence the importance of kinetics on the formation of scorodite. In the third system, the synthetic yukonite was found to be equivalent at the atomic, molecular and structural level to the natural yukonite. At the molecular level, arseniosiderite was found to have an H-bonding environment as in scorodite and exhibit extra protonated arsenate groups. In yukonite, in contrast, a wide diffuse H-bonding environment was observed with only arsenate groups present. At the electronic level yukonite and arseniosiderite were found to be identical, indicating that the local nature of the As, Fe and Ca atoms in these closely related but distinct phases is the same. Structural analysis of the materials showed that yukonite consists of nano and poorly crystalline domains while in the case of arseniosiderite micro-size single crystal domains exist. ii Resume La portée de cette thèse comprend l'étude de trois systèmes hydrothermiques Fe(III)- As(V). Le premier système est composé de Fe(III)-AsO4-SO4 et les phases cristallines qui sont produites a haute température (150-225°C) ; celle-ci a été étudié pour élucider l'information précédente contradictoire sur ce système par rapport aux produits arsenicaux industriels qui sont formés pendant le traitement en autoclave de minerais aurifère arsenicaux sulfuré et de la stabilité des produits arsenicaux. Le deuxième système étudié était de Cu(II)-Mg(II)-Fe(III)-AsO4-SO4 à 150°C. Ce système a été étudié due a son importance dan la lixiviation industrielle du cuivre et afin d’examiner l’effet du cuivre sur la précipitation de scorodite. Finalement, l'examen structural et moléculaire de deux membres de la famille des systèmes Ca(II)-Fe(III)-AsO4 et yukonite (synthétique, naturel et arseniosiderite), ont étés observés en raison de leur nature relativement inconnue et de leur potentiel pour contrôler le dégagement d’arsenic dans les résidus. Dans le premier cas, trois phases d'arsenate se sont avérées a être produites à diverses conditions; ceux-ci étaient : scorodite contenant de la sulfate (Fe(AsO4)1-0.67x(SO4)X · 2H2O ou 0.00≤x≤0.20), de l’arsenate de fer(III) sub-hydraté ; FAsH (Fe (AsO4)0.998(SO4)0.01 · 0.72H2O), et de la sulfate de fer d’arsenate basique ; BFAS (Fe(AsO4)1 x(SO4)X(OH)X · (1-x)H2O, ou 0.3<x<0.7). Leur domaine de formation a été déterminé en termes de température, acidité, proportion de Fe/As en concentration molaires et le temps. Nos phases de FAsH et de BFAS produites correspondent à des phases inconnues antérieurement pour ces system. En plus de renommer ces phases, leur caractérisation (au niveau élémentaire, électronique, moléculaire et structural) on étés établies et leur formules moléculaires corrigées. Il est également prouvé que les systèmes de scorodite et de BFAS éprouvent une métastabilité se convertissant en FAsH lors d’une réaction prolongée. En conclusion, en étudiant la lixiviation à long terme de ces phases en fonction du pH, il a été déterminé que la formation de scorodite et BFAS étaient favorisés (le plus bas dégagement d’arsenic). Dans le deuxième cas, la présence du cuivre ne s'est pas avérée a avoir un effet marqué sur la précipitation d’arsenic sous la forme de scorodite. Cependant cette phase arsenicale s'est avéré la seule à être formée sous toutes les conditions expérimentales (1-10 hrs réaction a 150 °C). Cependant, on a observé pour la première fois la formation d'une phase intermédiaire de courte durée sous iii forme de fer(III)-cuprique de sulfate d'arsenate basique dans ce système à des durées plus courtes (<1hr) et à de plus basses températures (< 150°C) ; avant de se transformer finalement en phase plus stable (scorodite). Les résultats de Therse indiquent que le cuivre pourrait co-précipiter à des durées de rétention plus courte donc l’importance kinétique pour la formation de scorodite. Dernièrement, le troisième système de yukonite synthétique s’est avéré équivalent au niveau atomique, moléculaire et structural au yukonite normal. Au niveau moléculaire, l'arseniosiderite s'est avéré a avoir un environnement de liaison-H comme dans le système de scorodite et comprends des groupes d’arsenate protonés. Dans le yukonite, on a observé un environnement étendu de liaison-H en présence seulement des groupes d'arséniate non-protonés. Les niveaux électroniques du yukonite et de l'arseniosiderite se sont avérés identique, indiquant que la nature locale des atomes de As, Fe et de Ca dans ces phases étroitement liées mais distinctes est identique. L'analyse structurale des matériaux a prouvé que le yukonite se compose de structures nano et médiocrement cristallines tandis que dans les systemes d'arseniosiderite des cristaux simple de taille micro existent. iv Acknowledgments I would like to first thank my official two supervisors: Professor George P. Demopoulos (Materials Engineering, McGill University) and Dr. Jeffrey N. Cutler (Canadian Light Source Inc) for their support, advice, patience and freedom to explore what I needed to in the pursuit of research. They offered me a chance to learn, study, use and combine two different disciplines together, i.e. the hydrometallurgical engineering field that produces the materials and the chemically based lab and synchrotron based analysis techniques that analyse the materials. Support for the work described in this thesis was received via a NSERC strategic project grant co-sponsored by Areva Resources, Barrick Gold, Cameco, Hatch and Teck Metals for which the author is thankful. In addition I would also like to thank some unofficial supervisors/colleagues that have been instrumental to guidance and direction of the author in the pursuit of research and learning. The first being Dr. L. Becze (Materials Engineering, McGill University), who reminded me and showed me how to work in a wet lab (particularly a hydrometallurgical lab) and was also always there to question the results gathered, something we had long discussions over in many projects but resulted in fruitful collaborations and numerous publications during the period of my time at McGill University. I would also like to thank Dr. Hassane Assaoudi (Chemistry Department, McGill University) who was the only person in Montréal when I came in 2007, that knew and could teach me how to do the correlation group analysis of vibrational spectra that also resulted in fruitful collaborations and publications together. I would also in this regard like to thank Dr. Samir Eluatik (Chemistry Department, University of Montréal) for showing me how to operate and provide the use of a state of the art Raman Microscope with 4 different wavelengths in addition to various vibrational tools. I would also like to acknowledge the different technicians and people that assisted me in this research presented herein.