Thermodynamics of oxygen in dilute liquid silver- lead-tellurium alloys

J. Nyk1 and B. Onderka1

1AGH University of Science and Technology, Poland

Keywords: oxygen activity, coulometric titration, silver production, galvanic cell, thermodynamics
property: oxygen activity
material: liquid Ag-Pb-Te-O alloys

The anode slimes, the by-product of the electrolytic refining of copper, is a valuable source of silver, gold, platinum group metals, lead and tellurium. Due to their various technological applications pure silver and its alloys are very important materials. Tellurium, selenium and lead are redundant admixtures in silver and have to be removed during metallurgical refining processes. The processing of slimes usually involves many technological steps of removing Cu, Pb, Te, etc., and to leave pure Ag, Au, Pt-group metals as doré alloy. Conventional processing by smelting of slimes in converters with addition of fluxes and oxidizing agents and with injection of oxygen into molten bath reduces the amount of Cu, Se, Te, Pb. The distribution coefficient of tellurium between metal and slag depends on the oxygen activity in liquid metal. Thus, the knowledge of oxygen interaction in Ag-Te-Pb-O liquid alloys is a key parameter in Ag purification process.

Using solid oxide galvanic cells with the solid YSZ zirconia electrolyte:

Kanthal+Ir, O in Ag-Te-Pb | O2- | air, Pt

oxygen activities in liquid dilute Pb and Te solutions in silver were measured in the temperature range from 1285 to 1385 K. Oxygen activity coefficient was determined in liquid Ag-Te-Pb-O alloys for variable XPb and XTe content (from 0.1 to 0.4 for XPb and from 0.02 to 0.05 for XTe). From the obtained results interaction coefficients εOPb and εOTe as a function of temperature were derived and they take the forms:

εOPb = -74653/T + 32.760

εOTe = -16806/T + 7.244

Additionally, the oxygen interaction coefficient in liquid silver-lead-tellurium dilute solutions, εOPb,Te, as the function of temperature was obtained.

Because of nonexistence of silver oxides in elevated temperatures it is impossible to quench the solutions of oxygen in Ag in order to analyze it. The electrochemical coulometric titration method seems to be the only one to study thermodynamics of oxygen in liquid silver and its alloys in a wide range of oxygen partial pressures.

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