Diagramme d'equilibre du systeme le calcium, le sulfate de sodium, l'oxygene, le sulfate d'arsenic, le sulfate d'antimoine par experimentation et modelisation et ses applications dans l'affinage du cuivre

Over the last century, basic fluxes such as sodium carbonate and lime have been widely used for removal of arsenic and antimony from blister copper. The use of soda-rich slag can result in several problems in a copper smelter, refractory corrosion being one. If would be beneficial to the industry to develop a refining system with low levels of sodium and the same chemical efficiency for As and Sb removal. During the early stage of this project, the candidate was involved in copper refining trials at the Noranda Technology Centre in order to identify promising low sodium systems. One potential system was the CaSO4-Na2SO4 system. This thesis is concerned with phase diagram determination and utilization of this system for copper refining.; A molten solution of calcium and sodium sulphates behave as an ionic liquid containing Na+, Ca2+//SO4 2-. This molten salt can readily absorb arsenic and antimony (AsO43- et SbO43- ) as well as oxygen (O2-). The ionic molten salt (including arsenic and antimony complexes, and oxygen) is composed of two cationic species and four anionic species (Na+, Ca2+ //SO42-, AsO43- , SbO43- and O2-). This system has not been studied in detail: no phase diagrams other than that of the CaSO4-Na2SO4 system were available. Solubility limits for O2-, AsO43- and SbO43- in CaSO4-Na 2SO4 molten salts were not known before the publication of the articles contained in this thesis.; In the first part of the experimental study, the CaO solubility in Na 2SO4-CaSO4 salts was investigated with an equilibration technique at 1100°C and 1200°C. The quasichemichal model was used to represent the thermodynamic properties of the reciprocal liquid salt solution (Na+, Ca2+//SO42-,O 2-). The Na2SO4 solid solution was modelled with the same formalism as an ionic solid solution (Na+,Ca 2+,Va0)2SO4 ((Va0) represent a cationic vacancy). Solid CaO and CaSO4 were considered as pure phases. After the modelling of the liquid and solid solutions, the liquidus projection of the Na2SO4-CaSO4-CaO was calculated. Lime solubility in pure Na2SO4 is less than 1 mol.% at 1100 and 1200°C, but the solubility increases rapidly with the CaSO4 concentration in Na2SO4-CaSO 4 solutions. At 1200°C, the maximal solubility of CaO in the liquid is obtained at double saturation (CaSO4 et CaO); at this point, the salt composition is approximately 0.14 Na2SO4, 0.10 CaO et 0.76 CaSO4 (molar fractions).; In the second part of the project, the common ion CaO-CaSO4-Ca 3(AsO4)2 ternary system was studied by differential thermal analysis and by an equilibration technique. A new solid phase was discovered close to the Ca5As2SO13 composition (CaO*CaSO4*Ca3(AsO4)2). The liquid region at 1200°C is very narrow in this system but expands considerably at 1300°C and 1400°C. Solid CaO, CaSO4, Ca5As 2SO13 and Ca4As2O9 were considered as stoichiometric compounds during the thernodynamic modelling. The liquid molten salt was modelled using the quasichemical formalism and the Ca3(AsO4)2 solid solution was modelled with the "compound energy formalism". The parameters from the solution models were optimized using available experimental data, and the CaO-CaSO4-Ca1.05AsO4 ternary liquidus projection was calculated from the models by Gibbs energy minimization. (Abstract shortened by UMI.)...