Tellurium | EPFL Graph Search

Tellurium is a chemical element with the symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionally found in its native form as elemental crystals. Tellurium is far more common in the Universe as a whole than on Earth. Its extreme rarity in the Earth's crust, comparable to that of platinum, is due partly to its formation of a volatile hydride that caused tellurium to be lost to space as a gas during the hot nebular formation of Earth. Tellurium-bearing compounds were first discovered in 1782 in a gold mine in Kleinschlatten, Transylvania (now Zlatna, Romania) by Austrian mineralogist Franz-Joseph Müller von Reichenstein, although it was Martin Heinrich Klaproth who named the new element in 1798 after the Latin tellus 'earth'. Gold telluride minerals are the most notable natural gold compounds. However, they are not a commercially significant s

Speciation of aqueous tellurium(IV) in hydrothermal solutions and vapors, and the role of oxidized tellurium species in Te transport and gold deposition

Pascal Grundler, Lothar Helm, Yuan Tian

Despite the close association between tellurium (Te) and gold (Au) in many epithermal, orogenic, and intrusion-related hydrothermal ore deposits, the hydrothermal chemistry of Te remains poorly understood. We studied the protonation/ deprotonation and structure of tellurous acid ((H2TeO3)-O-IV) species in aqueous solutions and in water vapor as a function of pH from room-temperature to 505 degrees C using a number of methods: TeO2(s) solubility in solution and steam, potentiometry, NMR spectroscopy, and in situ XAS spectroscopy. The solubility of TeO2(s) increases by up to a factor 80 between ambient temperature and 200 degrees C. As the temperature increases, the pH range over which the neutral species H2TeO3(aq) dominates to the detriment of the ionic species H3TeO3+, HTeO3-and TeO32-expands. The structure of these species is a trigonal pyramid with the Te atom at its apex, indicating a stereochemically active electron pair. The Te-O bond lengths increase with increasing protonation (i.e., decreasing pH). Although hydrated tellurite species such as TeO2(H2O)(g) and TeO2(H2O)(2)(g) exist in significant concentrations in vapors equilibrated with TeO2(s), these species are unlikely to play a significant role in natural systems, because of the high solubility of Te(IV) in the liquid phase under these conditions. Solubility calculations conducted with the new and existing properties confirm the importance of reduced species for the vapor transport of Te, with a partitioning coefficient (Kd = Te concentration in vapor/Te concentration in liquid) up to >10(5) in favor of the vapor, and ppm concentrations of Te in reduced vapors at 300 degrees C. Thermodynamic calculations show that slightly basic, mildly reduced fluids that can transport Au efficiently as Au(HS)(2)(-) can also carry significant Te (e.g., similar to 100 ppb at 300 degrees C). The calculations also suggest that under magmatic hydrothermal conditions, large amounts of Te can be transported as Te(IV) complexes in oxidized fluids (coexisting with SO2(g)). Reduction of Te(IV) caused by processes such as fluid-rock interaction or fluid mixing will lead to a dramatic decrease in the solubilities of both Te and Au, and to the precipitation of telluride minerals. (C) 2013 Elsevier Ltd. All rights reserved.

Elsevier2013

Reactions directed towards Sb(OTeF5)-6 salts of new tellurium cations: formation, FT-Raman spectrum and X-ray crystal structure of [Cl3Te-F-TeCl3][Sb(OTeF5)6] containing the m-fluoro-bis[trichloro-tellurium(IV)] cation

Isabelle Dionne

The metathesis reaction of TeBr4 and AgSb(OTeF5)6 in SO2 led to [TeBr3][Sb(OTeF5)6] and AgBr, and that of 2AgSb(OTeF5)6 with 7Te:TeBr4 led to [Te4][Sb(OTeF5)6]2. The crystal structure of [Cl3Te-F-TeCl3][Sb(OTeF5)6] is reported, prepd. from Te, TeBr4 and AgSb(OTeF5)6 in SO2ClF. [Cl3Te-F-TeCl3][Sb(OTeF5)6] crystallizes in space group P.hivin.1 with a = 10.144(6), b = 10.462(2), c 9.023(4) .ANG., a 93.38(2), b 104.42(4), g 83.06(3) Deg, V = 920.3(5) .ANG.3 and Z = 2. The structure consists of isolated fluoride bridged [Cl3Te-F-TeCl3]+ cations and [Sb(OTeF5)6]- anions with some cation-anion interactions. The obsd. structure and FT-Raman spectrum of [Cl3Te-F-TeCl3]+ are in agreement with that predicted by theor. calcns. (B3PW91/3-21G*). [on SciFinder (R)]

2002

Tellurium speciation under hydrothermal conditions

Pascal Grundler, Lothar Helm

Tellurium is the only element which forms a variety of minerals with gold as principal component (e.g. calaverite AuTe2, krennerite (AuAg)Te2, petzite Ag3AuTe2 and sylvanite AgAuTe4). These minerals have been known for a long time and are of economic value in many deposits such as Cripple Creek (Colorado), Emperor (Fiji), and Săcărîmb (Romania), and “orogenic” gold deposits, including the giant Golden Mile deposit (Western Australia). However, knowledge the formation of these minerals is still incomplete.

2009

Speciation of aqueous tellurium(IV) in hydrothermal solutions and vapors, and the role of oxidized tellurium species in Te transport and gold deposition

Pascal Grundler, Lothar Helm, Yuan Tian

Elsevier2013