A Mineralogical overview of the behavior of nickel during copper electrorefining
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Occurrences of Nickel
Examples
solid solution in copper matrix
anode nos. 1 through 4
solid solution in copper matrix, NiO, trace NiFe204
anode no. 9
solid solution in copper matrix, kupferglimmer, trace NiFe204 solid solution in copper matrix, kupferglimmer, minor NiO, trace NiFe204 solid solution in copper matrix, more NiO, less kupferglimmer, trace NiFe204
anode no. 5 anode nos. 6 through 8
*Refs. 3 and 6.
along the copper grain boundaries. Because of the short 2-hour electrolysis time used, an extensive anode slimes layer has not yet developed on the face of this anode. The nickel in solid solution in the copper matrix dissolves along with the copper. Although most of the solubilized nickel remains in solution, a small percentage reprecipitates as crystals or masses of NiSOa.nH20 or (Cu, Ni)SO4-5H20 in the slimes layer attached to the anode face. Figure 6 shows the morphology of several NiSO4"nH20 crystals associated with C u S O 4 " 5 H 2 0 o n the surface of a corroded Kidd Creek copper anode (no. 1A). The nickel sulfate and copper sulfate crystals were on the anode face when the anode was removed from the electrolytic cell; that is, the crystals were formed during electrolysis. Electron microprobe analyses showed that many of the copper sulfate crystals were Ni-bearing. Most of the solubilized nickel accumulates in the electrolyte. The concentration of nickel in the electrolyte is largely a function of the nickel content of the anode, and this point is illustrated in Table V, which presents data for the three Canadian refineries as well as for two overseas operations. There is also an approximate correlation between the nickel concentration of the electrolyre and the nickel content of the cathode deposit, although
other factors also contribute to the nickel contamination of the copper cathode. Table H indicates that 80 to 100 pet of the nickel content of commercial anodes is in solid solution in the copper matrix. As only a very small amount (85 pct of the total nickel remains in solid solution in the copper matrix. If the anodes also contain >200 ppm Sb, kupferglimmer will be present; NiFe204 and Ni-bearing iron oxide phases will form depending on the iron content of the anode. The nickel present in solid solution in the copper metal matrix dissolves together with the copper, and the NiSOa accumulates in the electrolyte. Kupferglimmer, ideally Cu3Ni2_xSbO6-x with x = 0.1 to 0.3, occurs as euhedral crystals associated with other impurity phases at the grain boundaries of the copper anode; a small amount of Sn commonly substitutes for Sb in the structure. Nickel oxide and Ni-bearing iron oxide phases usually occur as euhedral crystals at the copper grain boundaries and preferentially concentrated near the top surface of the anodes; the NiO and Ni-bearing iron oxide phases are refractory and accumulate in the anode slimes. A trace amount of Cu-Ni silicate is present, and this phase also reports in the anode slimes. Although most of the dissolved nickel accumulates as nickel sulfate in the electrolyte
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