High-pressure behavior and P-induced phase transition of CaB3O4(OH)3·H2O (colemanite)

Colemanite (ideally CaB3O4(OH)3\ub7H2O, space group P21/a, unit-cell parameters: a ~ 8.74, b ~ 11.26, c ~ 6.10 \uc5, \u3b2 ~ 110.1\ub0) is one of the principal mineralogical components of borate deposits and the most important mineral commodity of boron. Its high-pressure behavior is here described, for the first time, by means of in situ single-crystal synchrotron X-ray diffraction with a diamond anvil cell up to 24 GPa (and 293 K). Colemanite is stable, in its ambient-conditions polymorph, up to 13.95 GPa. Between 13.95 and 14.91 GPa, an iso-symmetric first-order single-crystal to single-crystal phase transition (reconstructive in character) toward a denser polymorph (colemanite-II) occurs, with: aCOL-II=3\ub7aCOL, bCOL-II=bCOL, and cCOL-II=2\ub7cCOL. Up to 13.95 GPa, the bulk compression of colemanite is accommodated by the Ca-polyhedron compression and the tilting of the rigid three-membered rings of boron polyhedra. The phase transition leads to an increase in the average coordination number of both the B and Ca sites. A detailed description of the crystal structure of the high-P polymorph, compared to the ambient-conditions colemanite, is given. The elastic behaviors of colemanite and of its high-P polymorph are described by means of III- and II-order Birch-Murnaghan equations of state, respectively, yielding the following refined parameters: KV0=67(4) GPa and KV\u2032=5.5(7) [\u3b2V0=0.0149(9) GPa-1] for colemanite; KV0=50(8) GPa [\u3b2V0=0.020(3) GPa-1] for its high-P polymorph

Thermal stability and high-temperature behavior of the natural borate colemanite: An aggregate in radiation-shielding concretes

Colemanite is a natural borate that can be used as an aggregate in neutron-radiation shielding concretes. In this study, we report its thermal behavior, up to 500 degrees C, by describing: 1) its dehydration mechanisms and 2) its thermo-elastic parameters. The thermal expansion of colemanite is significantly anisotropic. The refined volume thermal expansion coefficient at ambient conditions is: alpha(V0) = 4.50(10).10(-5) K-1. The loss of structural H2O occurs at least from similar to 240 degrees C, and at T > 325 degrees C an irreversible amorphization occurs, followed by a complete dehydration. The potential implications on the use of colemanite as concrete-aggregate are discussed. (C) 2019 Elsevier Ltd. All rights reserved

Crystal chemistry and temperature behavior of the natural hydrous borate colemanite, a mineral commodity of boron

Colemanite, CaB3O4(OH)3*H2O, is the most common hydrous Ca-borate, as well as a major mineral commodity of boron. In this study, we report a thorough chemical analysis and the low-temperature behavior of a natural sample of colemanite by means of a multi-methodological approach. From the chemical point of view, the investigated sample resulted to be relatively pure, its composition being very close to the ideal one, with only a minor substitution of Sr2+for Ca2+. At about 270.5 K, a displacive phase transition from the centrosymmetric P21/a to the acentric P21 space group occurs. On the basis of in situ single-crystal synchrotron X-ray (down to 104 K) and neutron diffraction (at 20 K) data, the hydrogen-bonding configuration of both the polymorphs and the structural modifications at the atomic scale at varying temperatures are described. The asymmetric distribution of ionic charges along the [010] axis, allowed by the loss of the inversion center, is likely responsible for the reported ferroelectric behavior of colemanite below the phase transition temperature

Acid Mine Drainage and PTE distribution in a volcanic sulfur mine: the Thiorichia Mine, Milos Island, Greece

Acid Mine Drainage is a major environmental concern in sulfur-rich ore deposits and is widely studied in different geological contexts and for a variety of sulfide ore deposits. Milos volcanic sulfur mine represents in this picture a type of ore deposit whose acid mine drainage concern is little studied. Milos Island is an active volcano of the Hellenic volcanic arc, with a main caldera collapse structure and a widespread secondary activity. The island hosts seven active mines that exploit bentonite (with the biggest mine in Europe), perlite and pozzolan deposits and several abandoned sulfur, kaolin, barite and manganese mines. Such intense mining activity in a 160 km2 highly touristic island increases the importance of environmental studies for the sustainability of the island economy. Sulfur mining at Milos started in V century BC, but the first modern mining concession dates back to 1862 and led to the opening of the Thiorichia Mine on the Eastern shore of the island. The mining site comprised several tunnels, sulfur purification facilities and other buildings for workers accommodation and administration. Sulfur purification was gained firstly with the Calcaroni method and later with Gill four chambers furnace. Extraction declined in the second half of last century and the mine was definitely closed in 1981. During the field survey three different earthen materials were sampled: sands from the adjacent beach, stream sediments downstream from the purification plant and dumped material, close to the purification plant and uphill on the road leading to the mine. Beach samples are coarser (sandy gravels) due to wave erosion while both sediments and wastes fall in the range of sands and gravely sands. Acid Mine Drainage potential was assessed with ABA procedure and results show that beach sands have no acid potential due to complete leaching of sulfur while sediments and wastes have variable acid potential closely related to the degree of sulfur oxidation. Whole rock ICP analyses show that the highest environmental hazard for PTE is related to the high mercury content of stream sediments and wastes. XRD-powder diffraction analyses show that quartz represents the overwhelming mineral phase in all the samples analysed. Minor phases as alunite-like minerals, micas, elemental sulfur, opal and kaolinite-like minerals have also been detected. The present work shows that Acid Mine drainage and PTE concern studies in sulfur deposits are particularly difficult due to the complete decoupling between the acid potential production, strictly related to the elemental sulfur content of the materials, and the potential release of PTE in the environment, probably associated to secondary clay and alunite-like minerals

High-pressure behavior and phase transition in colemanite, an industrially relevant inoborate

Colemanite, CaB3O4(OH)3 x H2O, is a common constituent of natural borate deposits and a relevant mineral commodity, for its applications in the B-extraction processes and in the production of lightweight cements and ceramics [1,2]. Its crystal structure is monoclinic (P21/a, a = 8.712 \uc5, b = 11.247 \uc5, c = 6.091 \uc5, \u3b2 = 110.12\ub0, V = 560.4 \uc53), characterized by infinite chains of Bpolyhedra based on a fundamental ring-unit made by one triangular BO3 and two B(O,OH)4 tetrahedra. These chains are alternated with chains of Ca-polyhedra (coordination number, CN =8), giving rise to sheets parallel to (010). Adjacent sheets are mainly interconnected through an H-bonding system involving hydroxyl groups and H2O molecules. The links among structural polyhedra, both B and Ca, are all corner sharing in type [3]. Despite its relevance in industrial applications, the behavior of colemanite at high pressure has never been investigated. In this work, we have characterized the elastic behavior, the phase stability, the phase transition and the structural evolution with pressure of a natural colemanite single crystal based on an in-situ synchrotron X-ray diffraction study, performed at the P02.2 beamline of PETRA-III, Hamburg, Germany. Colemanite, in its ambient conditions polymorph, is found to be stable up to 13.95 GPa. A IIIorder Birch-Murnaghan (III-BM) EoS fit leads to a refined bulk modulus (at ambient conditions) (KV0) of 76(8) GPa [K\uf0a2 = 4.4(10)]. Comparative structure analysis, based on the refinements of the structure model at different pressures, shows that the B-polyhedra act as quasi-rigid units and the bulk compression is mainly accommodated by the compression of Ca-polyhedra and by polyhedral tilting. Between 13.95 and 14.91 GPa, colemanite undergoes a reconstructive phase transition toward a monoclinic polymorph (P21/n, a = 11.726(11) \uc5, b = 10.206(1) \uc5, c = 23.45(3) \uc5, \u3b2 = 95.07(9)\ub0, V = 2796(4) \uc53, at 14.91 GPa). The average coordination number of boron is found to increase: of the 18 independent B sites, 3 are triangularly coordinated and 15 are tetrahedra. Two independent infinite chains of B-polyhedra are alternated with two independent chains of Capolyhedra (CN = 8 or 9), by means of corner- and edge-sharing links. A II-BM EoS fit leads to a refined KV0 of 60(6) GPa for the high-P polymorph of colemanite. X-ray diffraction patterns collected during P-release show that the phase transition is completely reversible and colemanite fully recovers its starting structural features. [1] K. Okuno Radiat. Prot. Dosim. 2005, 115, 258-261. [2] A. Christogerou, T. Kavas, Y. Pontikes, S. Koyas, Y. Tabak, G.N. Angelopoulos Ceram. Int. 2009, 35, 447-452. [3] P.C. Burns, F.C. Hawthorne Can. Mineral. 1993, 31, 297-304

High-pressure behavior and phase transition in colemanite, an inoborate

Colemanite, CaB3O4(OH)3 x H2O, is a common constituent of natural borate deposits and a relevant mineral commodity, for its applications in the B-extraction processes and in the production of lightweight cements and ceramics [1,2]. Its crystal structure is monoclinic (P21/a, a = 8.712 Å, b = 11.247 Å, c = 6.091 Å, β = 110.12°, V = 560.4 Å3), characterized by infinite chains of Bpolyhedra based on a fundamental ring-unit made by one triangular BO3 and two B(O,OH)4 tetrahedra. These chains are alternated with chains of Ca-polyhedra (coordination number, CN =8), giving rise to sheets parallel to (010). Adjacent sheets are mainly interconnected through an H-bonding system involving hydroxyl groups and H2O molecules. The links among structural polyhedra, both B and Ca, are all corner sharing in type [3]. Despite its relevance in industrial applications, the behavior of colemanite at high pressure has never been investigated. In this work, we have characterized the elastic behavior, the phase stability, the phase transition and the structural evolution with pressure of a natural colemanite single crystal based on an in-situ synchrotron X-ray diffraction study, performed at the P02.2 beamline of PETRA-III, Hamburg, Germany. Colemanite, in its ambient conditions polymorph, is found to be stable up to 13.95 GPa. A IIIorder Birch-Murnaghan (III-BM) EoS fit leads to a refined bulk modulus (at ambient conditions) (KV0) of 76(8) GPa [K = 4.4(10)]. Comparative structure analysis, based on the refinements of the structure model at different pressures, shows that the B-polyhedra act as quasi-rigid units and the bulk compression is mainly accommodated by the compression of Ca-polyhedra and by polyhedral tilting. Between 13.95 and 14.91 GPa, colemanite undergoes a reconstructive phase transition toward a monoclinic polymorph (P21/n, a = 11.726(11) Å, b = 10.206(1) Å, c = 23.45(3) Å, β = 95.07(9)°, V = 2796(4) Å3, at 14.91 GPa). The average coordination number of boron is found to increase: of the 18 independent B sites, 3 are triangularly coordinated and 15 are tetrahedra. Two independent infinite chains of B-polyhedra are alternated with two independent chains of Capolyhedra (CN = 8 or 9), by means of corner- and edge-sharing links. A II-BM EoS fit leads to a refined KV0 of 60(6) GPa for the high-P polymorph of colemanite. X-ray diffraction patterns collected during P-release show that the phase transition is completely reversible and colemanite fully recovers its starting structural features. [1] K. Okuno Radiat. Prot. Dosim. 2005, 115, 258-261. [2] A. Christogerou, T. Kavas, Y. Pontikes, S. Koyas, Y. Tabak, G.N. Angelopoulos Ceram. Int. 2009, 35, 447-452. [3] P.C. Burns, F.C. Hawthorne Can. Mineral. 1993, 31, 297-304

From Nature to materials science: (Cs,K)Al4Be5B11O28(Cs,K)Al_{4}Be_{5}B_{11}O_{28} (londonite) as a super-hard material

Londonite is a rare Cs-bearing mineral with ideal chemical formula (Cs,K)Al4Be4(B,Be)12O28 (with Cs > K). The building block units of the structure of londonite are represented by clusters of four edge-sharing Al-octahedra linked to B- and Be-tetrahedra. Gatta et al. (2011) investigated the phase stability and the elastic behavior of londonite up to 4.85(5) GPa (at room-T) and up to 1000°C (at room-P) by in situ X-ray powder diffraction data, but no structure refinements were possible. Whether no phase transition was observed within the pressure-range investigated, londonite proved to have an extremely high bulk modulus: KP0 = 280(12) GPa, similar to those of carbides (e.g., B4C with KP0 ~ 245-306 GPa; Lazzari et al., 1999; Fujii et al., 2010). Considering the thermo-elastic properties and the significantly high fraction of boron (B2O3 ~50 wt%), the synthetic counterparts of londonite could be considered a potential inorganic host for 10B in composite neutron-absorbing materials. Furthermore the high content of Cs makes londonite-type materials potential host for nuclear waste. However, to date, because of the absence of structural data at high pressure and to the modest P-range investigated by Gatta et al. (2011), a comprehensive description of the P-induced deformation mechanisms at the atomic scale is still missing. In this study, the isothermal compressional behaviour of londonite is studied by in situ single-crystal synchrotron X-ray diffraction experiment with a diamond anvil cell up to 25 GPa. The compressional behavior and the deformation mechanisms at the atomic scale are described. Londonite does not experience any phase transition or change of the compressional behavior within the P-range investigated.Fujii, T., Mori, Y., Hyodo, H., Kimura, K. (2010): X-ray diffraction study of B4C under high pressure. J. Phys. Conf. Ser., 215, 012011. Gatta, G.D., Vignola, P., Lee, Y. (2011): Stability of (Cs,K)Al4Be5B11O28 (londonite) at high pressure and high temperature: a potential neutron absorber material. Phys. Chem. Miner., 38, 429-434. Lazzari, R., Vast, N., Besson, J.M., Baroni, S., Dal Corso, A. (1999): Atomic structure and vibrational properties of icosahedral B4C boron carbide. Phys. Rev. Letters, 83, 3230-3233

Wardite (NaAl3(PO4)(2)(OH)(4)Greek ano teleia2H(2)O) at High Pressure: Compressional Behavior and Structure Evolution

International audienceThe high-pressure behavior of wardite, NaAl3(PO4)(2)(OH)(4)center dot 2H(2)O (a = 7.0673(2) angstrom, c = 19.193(9) angstrom, Sp. Gr. P4(1)2(1)2), has been investigated by in-situ single-crystal synchrotron diffraction experiments up to 9 GPa, using a diamond anvil cell under quasi-hydrostatic conditions. This phosphate does not experience any pressure-induced phase transition, or anomalous compressional behavior, within the pressure-range investigated: its compressional behavior is fully elastic and all the deformation mechanisms, at the atomic scale, are reversible upon decompression. A second-order Birch-Murnaghan Equation of State was fitted to the experimental data, weighted by their uncertainty in pressure (P) and volume (V), with the following refined parameters: V-0 = 957.8(2) angstrom(3) and K-V0 = -V-0( partial differential P/ partial differential V)(P0),(T0) = 85.8(4) GPa (beta(V0) = 1/K-V0 = 0.01166(5) GPa(-1)). Axial bulk moduli were also calculated, with: K-0(a) = 98(3) GPa (beta(0(a)) = 0.0034(1) GPa(-1)) and K-0(c) = 64(1) GPa (beta(0(c)) = 0.0052(1) GPa(-1)). The anisotropic compressional scheme is: K-0(a):K-0(c) = 1.53:1. A series of structure refinements were performed on the basis of the intensity data collected in compression and decompression. The mechanisms at the atomic scale, responsible for the structure anisotropy of wardite, are discussed