Refining of Low-Grade Copper by Electrolysis in Sulfamic Acid Media

Abstract

Refining of low-grade copper alloy by electrolysis in sulfamic acid media was investigated. Binary Cu-1 mass％X (X＝Ni, Pb, Sb, Bi, As, Se, Ag, Au) alloys and a low-grade copper alloy assaying 70 mass％ Cu containing Ni, Pb, Sb, Bi, As, Sn, Se, Ag, and Au were synthesized and served as anode material. Galvanostatic electrolysis at 300 A · m⁻² was carried out using pure copper anode and Cu-1 mass％X alloy anodes in 1.63 mol · L⁻¹ H₂SO₄-0.63 mol · L⁻¹ Cu(II) aq. at 40 °C and 1.03 mol · L⁻¹ HSO₃NH₂-0.63 mol · L⁻¹ Cu(II) aq. at 25 °C, where the solubility of the copper salts in their corresponding media was almost same. Pure copper was passivated in the sulfuric acid media likely due to the formation CuSO₄ · 5H₂O in 23 hours. Impurities such as Ni, Se, Ag, and Au promoted passivation. On the other hand, all anodes tested in the sulfamic acid media were not passivated in 24 hours. The refining of the low-grade copper alloy was examined in 0.51 m o l · L⁻¹ HSO₃NH₂-0.63 mol · L⁻¹ Cu(II) aq. at 25 °C by galvanostatic electrolysis at 200 A · m⁻². As a result, dense copper cathode of 99.99 mass％ purity was obtained. The current efficiency was approximately 98.5 ％. During electrolysis, the terminal voltage periodically increased to 2.0 V and then returned to its initial value. However, the anode was not completely passivated. The energy loss due to such an increase and decrease of the terminal voltage was evaluated to be approximately 13 ％. The mechanism of the fluctuation of the terminal voltage was considered.