Abstract
This work focused on purifying copper electrolytes from a bismuth impurity on a laboratory scale. The electrolyte came from Polish copper electrorefineries with the content of main components, g/dm3: 49.6 Cu, 160 H2SO4. The electrolyte was enriched in bismuth by Bi2O3 addition. Purification of bismuth contamination was carried out using selected agents with adsorbing effects, such as barium hydroxide octahydrate, strontium carbonate, barium carbonate, barium and lead sulfates. The trials were performed until achieving the Bi level—below 0.1 g/dm3. During the experiments, it was noticed that electrolyte purification degree depends on initial Bi concentration in electrolyte, time and temperature, as well as on the type and amount of the bismuth-lowering agent. The most satisfactory results of Bi impurity removal were with additions of barium hydroxide octahydrate, strontium carbonate and barium carbonate to electrolyte at 60 °C for 1 h. These parameters revealed the highest electrolyte purification degree. Bismuth is not removed effectively from electrolytes by barium sulfate or lead sulfate addition. The efficiency of the purification process is much higher when the agents are added to the solution in the form of carbonates or hydroxides. Extending the electrolyte purification process time may cause dissolution of bismuth from the resulting precipitate and increase of bismuth concentration in electrolytes.
Highlights
Bismuth is one of the most problematic impurities in copper electrorefining
The literature data show that bismuth electrolyte concentrations below ~0.1 g/dm3 have no negative impact on the produced copper cathode in the electrorefining process, and bismuth will not interfere with the electrolysis [5]
It can be concluded that: (1) The electrolyte purification degree depends on the initial Bi concentration in copper electrolyte, on time and temperature as well as on the type and amount of the bismuthlowering agent
Summary
Bismuth is one of the most problematic impurities in copper electrorefining. Its elevated concentration in the electrolyte can contribute to contamination of the produced copper cathode, so the bismuth level in the electrolyte must be controlled [1,2]. In many publications, techniques of copper electrolyte purification from impurities have been proposed, due to increased Bi content [1,6] These methods include: ion exchange using selected ion exchange resins (Unicellex UR-3300, Duolite C-467, Lewatit TP 260) [1,7,8,9], solvent extraction using selected extractants (DEHPA, MEHPA, Kelex 100, DS 5834, LIX 1104, REX-1, REX-2, TDA) [1,10,11,12,13], molecular recognition technology (MRT) using specially designed organic chelating agents or ligands [14,15,16,17,18,19].
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