Thomas A. O'Donnell

Production of Ultra Clean Coal, Part I – Dissolution behaviour of mineral matter in black coal toward hydrochloric and hydrofluoric acids

The mineral matter in an Australian black coal has been isolated using a low-temperature ashing (LTA) procedure. This LTA procedure is a modification of the Australian Standard for LTA at 370 degrees C, and alleviates adverse effects to thr: minerals caused by the heat of combustion. The leaching behaviour of the mineral matter towards aqueous HCl and hydrofluoric acid (HF) is presented. HCl can dissolve simple compounds such as phosphates and carbonates, yet it cannot completely dissolve the clays. HF resets with almost every mineral in the mineral matter, except pyrite, and most of the reaction products are water soluble. However, at HF concentrations greater than that required to dissolve the aluminosilicate compounds in the mineral matter, insoluble compounds form. These compounds include CaF2, MgF2 and a compound containing Na, which is believed to be NaAlF4. It is proposed that HF reacts preferentially with the aluminosilicates in the mineral matter to form largely AlF2+, AlF3 and SiF4, and that the concentrations of free fluoride (F-) and AlF4- are not high enough to complex cations such as Ca2+, Mg2+ and Na+. When the mineral matter is treated with HF concentrations greater than that required to dissolve all of the aluminosilicates, AlF3, AlF4- and SiF62- form, the concentration of F- is high enough to complex Ca2+ and Mg2+ and form insoluble CaF2 and MgF2, and the concentration of AlF4- is high enough to complex Na+ and form insoluble NaAlF4. This work has application toward the development of a process for producing Ultra Clean Coal with less than 0.1% by weight mineral matter

Production of Ultra Clean Coal: Part II—Ionic equilibria in solution when mineral matter from black coal is treated with aqueous hydrofluoric acid

A model fur determination of the concentration of fluoride complexed aluminium and silicon species, free fluoride (F-), II+ ions and molecular HF in solution when aluminosilicate compounds are treated with aqueous HF is presented. The model elucidates chemical mechanisms governing both the dissolution behaviour of the mineral matter in coal towards aqueous HF, and the unwanted precipitation of various fluoride compounds, such as CaF2, MgF2 and NaAIF(4). The controlling parameter for the precipitation of fluoride compounds is the free F- concentration in solution. The model has application toward the development of chemical strategies for dissolving virtually all of the mineral matter from coal and avoiding the unwanted precipitation of fluoride compounds. The model also has application toward the development of a strategy for recovering fluoride from spent leaching solutions. Ultimately, this work will assist in the development of a process for the production of Ultra Clean Coal (UCC) containing less than 0.1% by weight mineral matter.

Production of ultra clean coal: Part III. Effect of coal's carbonaceous matrix on the dissolution of mineral matter using hydrofluoric acid

An Australian bituminous coal was treated with increasing concentrations of hydrofluoric acid (HF), and the extraction levels of Al, Si, Fe, Ti, K, Na, Ca and Mg were determined. These extraction levels were compared to those obtained when the mineral matter alone, produced by ashing the coal at a low temperature, was treated with HF, in order to quantify the extent that the carbonaceous matrix inhibits extraction. The carbonaceous matrix inhibits the dissolution of Ti to a large extent. Si and Fe are the next most inhibited elements. It is proposed that the Ti is present as extremely small particles, of possibly less than 1 mum in length, which are finely disseminated throughout the coal.

A specific method for the preparation of many transition metal and actinide oxide tetrafluorides

Abstract A general method for the preparation of many transition metal and actinide oxide tetrafluorides by oxygen-fluorine exchange of their respective hexafluorides using boric oxides is described. This simple procedure affords the preparation of MoOF 4 , WOF 4 , ReOF 4 , OsOF 4 and UOF 4 in high yield while reaction of boric oxide with IrF 6 and RuF 6 leads to the preparation of lower fluorides of these elements. The preparation of oxide tetrafluorides by reaction of their oxide tetrachlorides with anhydrous HF has also been investigated, as well as a study of some halogen-exchange reactions of the oxide tetrafluorides.

On the acidity of hydrogen fluoride

Abstract An explanation is proposed for the rapid increase in acidity in progressing from dilute solutions of HF in H2O to solutions of greater concentration ( ca. 10M). Anhydrous HF has been shown to be more acidic than generally believed and to require very small adventitious concentrations of F− to become quite basic. Oxidation of I2 is used to demonstrate the dependence of the nature of species in HF solution on the acidity or basicity of the medium.

The structures of barium hexafluorosilicate and cesium hexafluororhenate(V)

Abstract The crystal structure of CsReF 6 , together with a reinvestigation of that of BaSiF 6 , is reported. Both have been determined from single crystal three-dimensional X-ray diffraction data. The structure of BaSiF 6 has been found to conform to the initially assigned space group R 3 m , contrary to the suggestions of other workers. The unit cell of BaSiF 6 has the dimensiona a hex 7.189(1), c hex 7.015(1) A; Z = 3. Refinement by a least squares method gave R 0.0079 and R w 0.0077. Crystals of CsReF 6 belong to the lower symmetry rhombohedral space group R 3 . The unit cell has the dimensions a hex 7.853(1), c hex 8.140(1) A; Z = 3. Refinement gave R 0.031 and R w 0.030. The lowering of symmetry is caused by rotation of the ReF 6 − octahedra about the 3-fold axis through each Re atom, causing CsReF 6 to have the KOsF 6 structure.

Arsenic pentafluoride equilibria in anhydrous hydrogen fluoride

Abstract Earlier work has indicated that arsenic pentafluoride when dissolved in anhydrous HF is present largely as the anion As 2 F 11 - , particularly temperatures much below ambient. Raman spectra and conductance measurements are used here to show that, at and near room temperature, there are significant concentrations of molecular AsF 5 , AsF 6 - and As 2 F 11 - in equilibrium and that on reduction of temperature, As 2 F 11 - is formed at the expense of AsF 5 and AsF 6 - . The implications of the Lewis acid and oxidant strengths of AsF 5 are discussed as affecting synthetic procedures in anhydrous HF.

The vibronic and raman spectra of the uranyl ion in anhydrous hydrogen fluoride

The vibronic spectrum of the UO22+ cation in HF-AsF5 solution has been recorded in the range 340–450 nm and is much better resolved than corresponding aqueous spectra.

Halogen-exchange reactions of the hexafluorides of osmium, iridium and ruthenium - preparation and characterization of Ir2F3Cl6, Os2Br4F5 and Ir2Br4F5

Abstract Halogen-exchange reactions of the hexafluorides of osmium, iridium and ruthenium with a selected number of halogen-exchange reagents (BCl3, BBr3, BI3 and CCl4) have been studied. In every case mixed halides of these elements were formed. Stoichiometric mixed valence compounds of empirical formulae Ir2F3Cl6, Os2Br4F5 and Ir2Br4F5 have been isolated and characterized by infrared and UV-visible spectroscopy, X-ray methods, magnetic measurements and other physical procedures. All three have been shown to be polymeric in nature. The compound of related stoichiometry, Mo2Cl3F6, which is formulated as (Mo3Cl93+)(MoF6−)3, has been further studied by the above techniques and is contrasted with the mixed halides of osmium and iridium. Stoichiometric mixed halides could not be isolated from the ruthenium hexafluoride reactions.

A simple multigram synthesis of β-UF5 - reduction of UF6 by PF3

Abstract Controlled low-temperature reduction of UF6 with commercially-available PF3 in a standard metal vacuum system provides a convenient multigram synthesis of β-UF5. A comparison is made with reduction reactions of UF6 reported earlier and with the corresponding NpF6 and PuF6 reactions.