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The phrase "purification of copper refinery electrolyte " is misleading since typically, impurities are controlled by withdrawing a bleedstream of the circulating electrolyte. However, solvent extraction and ion exchange have also found some application in impurity control. This article describes conventional practice, including treatment of the bleedstream, and other attempts at electrolyte purification. Impurities to be discussed include Sb, Bi, As, Ni, Ca, ammonia, and organic fragments generated from hydrolysis of conventional cathode growth-modifying addition agents.
INTRODUCTION
In the production of copper, copperbearing sulfide concentrates are first smelted to copper matte. The molten matte is oxidized to blister copper by Peirce-Smith converting and the blister copper is fire refined and cast to copper anodes. The copper in these anodes is purified to high-purity copper cathodes by electrolysis in a solution of copper sulfate and sulfuric acid whose nominal composition is 40-45 g/L copper and 180-200 g/L sulfuric acid.
Although smelting, converting, and fire refining greatly reduce the concentration of impurities in copper concentrates, a small quantity of impurities remains in the copper anodes. The quantity of impurities varies depending upon the concentrate composition and the smelting, converting, and refining process. Typical values are shown in Table I. sec the sidebar for descriptions of impurities in anode copper.
CONTROL OF COPPER CONCENTRATION
In order to produce a cast anode that is dimensionally consistent and smooth-surfaced, some oxygen must be present in the molten anode copper. Typically, about 0.1-0.3% oxygen is present, for the most part as cuprous oxide (Cu^sub 2^O). During the electrorefi n ing process, contact of the Cu^sub 2^O with sulfuric acid in the electrolyte results in its partial dissolution:
Cu^sub 2^O + HO^sub 2^O^sub 4^ = CuSO^sub 4^ + H^sub 2^O + Cu
Because dissolution is chemical rather than electrochemical, this dissolved copper builds up in the electrolyte. In order to maintain a constant copper concentration in the electrolyte, a continuous electrolyte bleed is electrolyzed with insoluble anodes (i.e., an electrowinning process) to balance the quantity of copper dissolved chemically. In many copper refineries, the bleedstream is only partially decopperized then returned to the refinery. The bleedstream removed for impurity control is also decopperized. A portion of the copper recovered from the impurity bleedstream is quality cathodes; however, much is not. Although...