A Fundamental Study on Vacuum Lift Refining of Molten Copper

Abstract

Experiments of vacuum lift refining of molten blister copper have been carried out using a copper sample of about 600 g for a concurrent elimination of residual oxygen, sulphur and impurities.
The volume of liberated SO₂ gas was measured by the pressure change in five vacuum reservior tanks connected in turn with the vacuum vessel of about 1.6 cm ID made of a transparent quartz tube.
An oxygen concentration cell using a calcia stabilized zirconia or a small crystal microphone was equipped inside the vacuum vessel so as to permit the continuous measurement of oxygen potential or the detection of evolution of gas bubbles in the lifted melt.
The present process of overblowing of blister copper in a converter and of the subsequent reduction to refined blister copper in a refining furnace and the vacuum refining process of blister copper were discussed and compared in terms of an equilibrium diagram representing the functional relation among dissolved oxygen, log (% O), dissolved sulphur, log (% S), and the partial pressure of SO₂.
Initial concentrations of oxygen and sulphur, 0.130 and 0.107%, were decreased to 0.030% for oxygen and 0.006% for sulphur after vacuum lifts of 4 times each at an average pressure of about 2 mmHg. Other impurities in synthetic blister copper were also removed: 40 to 70% of Sb, 30 to 60% of Pb, and about 10% of As for initial concentrations of 0.4, 0.25 and 0.4% at reduced pressures of a few mmHg, respectively.