Single Crystal Raman Spectroscopy of Selected Arsenite, Antimonite and Hydroxyantimonate Minerals
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SINGLE CRYSTAL RAMAN SPECTROSCOPY OF SELECTED ARSENITE, ANTIMONITE AND HYDROXYANTIMONATE MINERALS Silmarilly Bahfenne B.App.Sci (Chem.) Chemistry Discipline This thesis is submitted as part of the assessment requirements of Master of Applied Science Degree at QUT February 2011 KEYWORDS Raman, infrared, IR, spectroscopy, synthesis, synthetic, natural, X-ray diffraction, XRD, scanning electron microscopy, SEM, arsenite, antimonate, hydroxyantimonate, hydrated antimonate, minerals, crystal, point group, factor group, symmetry, leiteite, schafarzikite, apuanite, trippkeite, paulmooreite, finnemanite. i ii ABSTRACT This thesis concentrates on the characterisation of selected arsenite, antimonite, and hydroxyantimonate minerals based on their vibrational spectra. A number of natural arsenite and antimonite minerals were studied by single crystal Raman spectroscopy in order to determine the contribution of bridging and terminal oxygen atoms to the vibrational spectra. A series of natural hydrated antimonate minerals was also compared and contrasted using single crystal Raman spectroscopy to determine the contribution of the isolated antimonate ion. The single crystal data allows each band in the spectrum to be assigned to a symmetry species. The contribution of bridging and terminal oxygen atoms in the case of the arsenite and antimonite minerals was determined by factor group analysis, the results of which are correlated with the observed symmetry species. In certain cases, synthetic analogues of a mineral and/or synthetic compounds isostructural or related to the mineral of interest were also prepared. These synthetic compounds are studied by non-oriented Raman spectroscopy to further aid band assignments of the minerals of interest. Other characterisation techniques include IR spectroscopy, SEM and XRD. From the single crystal data, it was found that good separation between different symmetry species is observed for the minerals studied. iii iv TABLE OF CONTENTS KEYWORDS ············································································ I ABSTRACT ············································································ III TABLE OF CONTENTS ···························································· V LIST OF FIGURES ······························································· VIII LIST OF TABLES ····································································· X LIST OF APPENDICES ···························································· XI LIST OF PUBLICATIONS ······················································· XII STATEMENT OF ORIGINALITY ··········································· XIII ACKNOWLEDGMENTS ························································ XIV 1 CHAPTER 1 ······································································ 1 1.1 INTRODUCTION ······················································· 3 1.2 GENERAL DESCRIPTION OF COMMON MINERALS ········ 4 1.2.1 Arsenic Trioxide ··················································· 4 1.2.2 Antimony Trioxide ················································ 6 1.2.3 Antimony Pentoxide ·············································· 7 1.3 STRUCTURAL STUDIES OF MINERALS ························ 8 1.3.1 Arsenite ····························································· 8 1.3.2 Antimonite ·························································· 9 1.3.3 Hydroxyantimonate ··············································· 9 1.4 VIBRATIONAL SPECTROSCOPY ································· 10 1.4.1 Arsenic Trioxide ················································· 11 1.4.2 Raman Investigations into Arsenite Speciation in Aqueous Solutions ·············································· 13 1.4.3 Existence of Polymeric Species in Aqueous Solutions ···· 16 1.4.4 Vibrational Spectroscopy of Arsenite Minerals ············· 19 1.4.5 Antimony Trioxide ·············································· 20 1.4.6 Raman Investigations of Antimony Speciation in Aqueous Solutions ·············································· 23 1.4.7 Vibrational Spectroscopy of Antimonite Minerals ········· 23 1.5 SYNTHETIC ARSENITES ·········································· 24 1.5.1 Preparation of Arsenites ········································ 24 1.5.2 Vibrational Spectroscopy of Synthetic Arsenites ··········· 25 1.6 SYNTHETIC ANTIMONITES ······································ 25 1.6.1 Preparation of Antimonites ···································· 25 1.6.2 Vibrational Spectroscopy of Synthetic Antimonites ······· 26 1.7 SYNTHETIC HYDROXYANTIMONATES ······················ 27 1.7.1 Preparation of Hydroxyantimonates ·························· 27 1.7.2 Vibrational Spectroscopy of Synthetic Hydroxyantimonates ············································ 28 1.8 PROJECT AIMS ······················································· 29 2 CHAPTER 2 ···································································· 31 2.1 INTRODUCTION ····················································· 33 2.2 SYNTHETIC PROCEDURES ······································· 33 2.2.1 Wet Chemistry Method ········································· 33 2.2.2 Hydrothermal Method ·········································· 34 2.3 INSTRUMENTAL TECHNIQUES ································· 35 v 2.3.1 Raman Microscopy ·············································· 36 2.3.2 Infrared Spectroscopy ··········································· 37 2.3.3 Scanning Electron Microscopy ································ 37 2.3.4 X-Ray Diffraction ··············································· 38 2.4 SPECTRAL MANIPULATION ····································· 38 3 CHAPTER 3 ···································································· 39 3.1 INTRODUCTION ····················································· 41 3.2 EXPERIMENTAL ····················································· 42 3.2.1 Mineral ···························································· 42 3.2.2 Synthetic Procedures ············································ 42 3.2.3 Raman Microscopy ·············································· 43 3.2.4 DFT Calculations ················································ 43 3.3 DESCRIPTION OF CRYSTAL STRUCTURE ··················· 43 3.4 RESULTS ································································ 44 3.4.1 X-ray Diffraction ················································ 44 3.4.2 Raman Microscopy ·············································· 46 3.4.2.1 Factor Group Analysis ······································· 46 3.4.2.2 Raman Spectra of Finnemanite ····························· 47 3.5 DISCUSSION ·························································· 51 3.6 CONCLUSION ························································· 56 4 CHAPTER 4 ···································································· 59 4.1 INTRODUCTION ····················································· 61 4.2 EXPERIMENTAL ····················································· 62 4.2.1 Minerals ··························································· 62 4.2.2 Synthetic Procedures ············································ 62 4.2.3 Raman Microscopy ·············································· 63 4.2.4 Hartree-Fock Calculations ····································· 63 4.3 DESCRIPTION OF CRYSTAL STRUCTURE ··················· 64 4.4 RESULTS ······························································· 65 4.4.1 Results of X-ray Diffraction ··································· 65 4.4.2 Scanning Electron Microscopy ································ 69 4.4.3 Raman Microscopy ·············································· 69 4.4.3.1 Factor Group Analysis ······································· 69 4.4.3.2 Raman Spectra of Paulmooreite ···························· 71 4.5 DISCUSSION ·························································· 76 4.6 CONCLUSION ························································· 82 5 CHAPTER 5 ···································································· 83 5.1 INTRODUCTION ····················································· 85 5.2 EXPERIMENTAL ····················································· 86 5.2.1 Minerals ··························································· 86 5.2.2 Synthesis of Leiteite ············································ 86 5.2.3 Raman Microscopy ·············································· 87 5.3 DESCRIPTION OF CRYSTAL STRUCTURE ··················· 87 5.4 RESULTS ······························································· 88 5.4.1 X-ray Diffraction ················································ 88 5.4.2 Scanning Electron Microscopy ································ 89 5.4.3 Raman Microscopy ·············································· 89 vi 5.4.3.1 Factor Group Analysis ······································· 89 5.4.3.2 Raman Spectra of Leiteite ···································· 91 5.5 DISCUSSION ·························································· 97 5.6 CONCLUSION ························································ 101 6 CHAPTER 6 ··································································· 101 6.1 INTRODUCTION ···················································· 103 6.2 EXPERIMENTAL ···················································· 104 6.2.1 Mineral ··························································· 104 6.2.2 Synthesis of ZnSb2O4 ·········································· 104 6.2.3 Synthesis of Trippkeite CuAs2O4 ···························· 105 6.2.4 Raman Microscopy ·············································