Solubility of some transition metal oxides in cryolite-alumina melts: Part II. Solubility of TiO2

Abstract

The solubility of TiO 2 in cryolite-alumina melts at 1020 ЊC was measured; it decreased with increasing alumina concentration up to ϳ3.5 wt pct total oxide and then increased at higher alumina concentrations. The solubility was found to be 3.1 wt pct Ti in cryolite, and 2.7 wt pct Ti in an aluminasaturated melt. Modeling indicated that the most probable titanium species are TiOF 2 and Na 2 TiO 3 , which coexist in the solution; the former dominates at low alumina concentrations and the latter at high alumina concentrations. Additional unknown amounts of fluoride may also be associated with these species. Determination of the solubility of TiO 2 in alumina-saturated melts as a function of temperature showed that the solubility increased from 1.9 wt pct Ti at 975 ЊC to 2.8 wt pct Ti at 1035 ЊC, the apparent partial molar enthalpy of dissolution of TiO 2 being 88 Ϯ 4 kJ mol Ϫ1 .

Development of a Novel Non-Consumable Anode for Electrowinning Primary Aluminum

“…(The previous authors (6) were not able to correlate their data to specific solutes.) Equilibrium constants and values of Cryolite ratio r Solubility of NiAl 2 O4 , mol ar fraction x10 5 Jentoftsen, et al, [6,7] This study…”

“…, mol % Jentoftsen et al [6,7] This study The same Trondheim group, Jentoftsen, Lorentsen, Dewing, Haarberg and Thonstad (7) also published an experimental study of the solubility of titanium oxide (TiO 2 ) in cryolite with an interpretation of solute identity using the simple log-log method. Figure 18 reproduces their experimentally determined data points, as well as a line 1 plotting their empirical function fitted to the entire data set, namely:…”

“…The specific (log-log) mode of thermodynamic modeling used by these authors (7) involves an implicit assumption that one Ti solute species is dominant over all others for a specific range of analysis. If this assumption were valid, the dominant TiO 2 solute in a given concentration range could be identified by a specific dependence of this solute activity upon the activity of another solute in the solution, in this case the dissolved alumina activity.…”

“…The effects of these additives on the alumina solubility in cryolite melts are of practical significance. The experimentally determined dependencies of alumina solubility on the additions of these fluorides are given as follows: (5) On the thermodynamic front, from experimental vapor pressures, emf's and/or Raman spectra, some authors have estimated changes in thermodynamic activities of NaF and AlF 3 in the "stoichiometric" cryolite melt (cryolite ratio r = 3) with small molar additions of LiF, CaF 2 and MgF 2 at temperatures close to 1300 K: Table 7 Literature data for interaction derivatives in "stoichiometric" cryolite melt (6,7) Addition LiF CaF2 MgF2…”

The Solubility of Some Transition Metal Oxides in Cryolite-Alumina Melts: Part III. Solubility of CuO and Cu2O

“…Previous papers in this series have described work on the solubility in cryolite-alumina melts of FeO and NiO, [2] and TiO 2 , [3] and related papers have given data on Fe 2 O 3 , [4] and shown how to handle the situation which arises when the solute element (Fe was the example considered) has more than one oxidation state. [5] The iron systems have two oxidation states (Fe(II) and Fe(III)), but each occurs in solution as only one species.…”