Falconbridge Limited in mid-1981 commissioned a copper smelter and refinery near Timmins, Ontario, to treat concentrate from its Kidd Mine. However, at the outset, the quality of the cathode copper produced in the Kidd refinery suffered from the presence of higher than usual concentrations of lead and selenium in the copper smelter’s anodes. Kidd cathode copper was not able to meet its customers’ specifications and obtaining product certification for the London Metal Exchange (“LME”) became a key focus.
After several process improvements were instigated, it was ultimately realised that the use of copper starter sheets was preventing the Kidd refinery meeting its cathode quality targets. Test work then began on the use of permanent stainless-steel cathodes. Preliminary tests using full-scale titanium blanks showed a reduction in the lead content of the cathode copper of a factor of four and a six-fold reduction in the selenium content, compared with the use of copper starter sheets.
The focus then shifted to developing a stripping machine, to develop stainless steel cathodes incorporating the existing header bars and evaluating edge-strip technology. The company’s board of directors gave approval for the conversion of the refinery to the Kidd technology in April 1985. The conversion was completed in 1986 and the Kidd refinery became the third to install permanent cathode and automated stripping technology.
Falconbridge began marketing the technology in 1992, after many requests from other refinery operators. Thus, the Kidd Process created competition between two suppliers of permanent cathode technology. The main differences between them were the cathode header bar, edge stripping and the stripping machine technology.
In contrast to the stainless steel header bar then used in the Isa Process cathode, the Kidd Process cathode used a solid copper header bar, which was welded onto the stainless steel sheet. This gave a lower voltage drop (by 8–10 millivolts) than the Isa Process cathode.
The Isa Process technology used the waxed edge at the bottom of the cathode plate to stop the copper depositing around the plate’s bottom to form a single mass of copper running from the top of one side of the cathode plate around the bottom to the top of the other side. The copper was stripped from the cathode plates as two separate sheets. The Kidd Process technology did not use wax, as it was thought that it could exacerbate the impurity problems with which the plant had been struggling. At Kidd, the stripping approach was to remove the copper from the cathode plate as a single V-shaped cathode product, akin to a taco shell.
The Kidd Process initially used a “carousel” stripping machine, but a linear installation was subsequently developed to provide machines with lower to medium stripping capacities for electrowinning plants and smaller refineries. The linear stripping machines, first installed in 1996, were more compact, less complex and had lower installation costs than the carousel machines.