The IsaKidd Technology is a copper electrorefining and electrowinning technology that was developed independently by Copper Refineries Proprietary Limited (“CRL”), a Townsville, Queensland, subsidiary of MIM Holdings (which is now part of Glencore, and at the Falconbridge Nickel Mines now-dismantled Kidd Creek refinery that was at Timmins, Ontario. It is based around the use of reusable cathode starter sheets for copper electrorefining and the automated stripping of the deposited “cathode copper” from them.J C Jenkins, “Copper tank house technology reviewed and assessed,” in: The Aus.I.M.M. North Queensland Branch, Smelting and Refining Operators Symposium, May 1985 (The Australasian Institute of Mining and Metallurgy: Melbourne, 1985), 195–204.
Overview
The old way of electrorefining copper (pre-1978) The usual process of electrorefining copper consists of placing a copper anode (about 99.5–99.7% pure copperT Robinson, “Electrolytic refining,” in: Extractive Metallurgy of Copper, Fourth Edition, Eds W G Davenport, M King, M Schlesinger and A K Biswas (Elsevier Science Limited: Kidlington, Oxford, England, 2002) 265–288.) in sulfuric acid (H2SO4) bath of copper electrolyte, together with a cathode, and passing a current between the anode and cathode through an external circuit. At the applied electropotential, copper and less noble elements dissolve in the electrolyte, while elements more noble than copper, such as gold (Au) and silver (Ag), do not. Under the influence of the applied electrical potential, copper ions migrate from the anode and deposit on the cathode, forming cathode copper.
The current IsaKidd technology represents the merger of the copper refining technologies developed by the two different organisations. The initial Isa Process development in the late 1970s, with its reusable stainless-steel cathode starter sheets, represented an advance on the previous technology of single-use starter sheets of pure copper, the production of which was a labour-intensive process.
The production of the single-use starter sheets involved laying down a sheet of copper by electrolysis on each side of a “mother plate”. Generating the sheet took a day, and thousands of sheets could be needed every day. Originally, the copper starter sheets were separated from the mother plate manually, but over time the process was automated.O Nakai, H Sato, K Kugiyama and K Baba, “A new starting sheet plant at the Toyo copper refinery and productivity improvements,” in: Proceedings of Copper 99–Cobre 99 International Conference, Volume III—Electrorefining and Electrowinning of Copper, Eds J E Dutrizac, J Ji and V Ramachandran (The Minerals, Metals and Materials Society: Warrendale, Pennsylvania, 1999), 279–289. In addition, limitations associated with the use of copper starter sheets meant that it was difficult to meet the purity specifications of some new copper applications that were, in the 1970s and 1980s, demanding higher quality copper.
IsaKidd process The development of the Isa Process tank house technology at CRL eliminated the whole process and cost of producing the starter sheets by using stainless-steel permanent cathodes. It also included substantial automation of the process of inserting the permanent cathodes into the electrolytic cells and their subsequent removal and stripping of the sheets of deposited cathode copper. The labour force required to operate a refinery using the IsaKidd technology has been estimated at 60–70% less of that required for refineries using starter sheets.W Armstrong, “The Isa Process and its contribution to electrolytic copper,” paper presented at the Rautomead Conference, Scotland, August 1999.W R Hopkins and I E Lewis, “Recent innovations in SX/EW plants to reduce capital and operating costs,” Minerals & Metallurgical Processing, February 1990, 1–8.
MIM Holdings began marketing the Isa Process technology in 1980, as a result of demand from other refinery operators.
Falconbridge subsequently independently developed a similar process to improve operations at its Kidd Creek copper refinery, near Timmins, Ontario.“About ISAKIDD Technology.” Accessed 20 June 2013. The initial development of permanent cathodes was for internal use, but marketing of the Kidd Process was initiated in 1992 after requests from other refinery operators.P E Donaldson and P J Murphy, “Kidd Process permanent cathode technology advancements,” in: Proceedings of [sic] Copper 99–Cobre 99 International Conference. Volume III—Electrorefining and Electrowinning of Copper, Eds J E Dutrizac, J Ji and V Ramachandran (The Minerals, Metals and Materials Society: Warrendale, Pennsylvania, 1999) 301–310.
The two technologies were brought together as the IsaKidd Technology in 2006, when Xstrata bought Falconbridge.
The IsaKidd Technology now dominates global copper refining. It has been licensed to 102 users and Xstrata Technology, which markets the technology, reports on its website a total installed capacity of some 12 million tonnes per year (“t/y”) of copper production, as of October 2011.List of IsaKidd installations. Accessed 20 June 2013. This is about 60% of the estimated 2011 global refined copper production of 19.7 million tonnes.The World Copper Factbook 2012, International Copper Study Group. Accessed 29 June 2013.
The development of the IsaKidd technology allowed increased productivity, reduced operating costs and the production of consistent, high-quality cathode copper.
History
Electrolytic refining of copper was first patented in England by James Elkington in 1865 and the first electrolytic copper refinery was built by Elkington in Burry Port, South Wales in 1869.
There were teething problems with the new technology. For example, the early refineries had trouble producing firm deposits on the cathodes. As a result, there was much secrecy between refinery operators as each strove to maintain a competitive edge.
The nature of the cathode used to collect the copper is a critical part of the technology. The properties of copper are highly susceptible to impurities. For example, an arsenic content of 0.1% can reduce the conductivity of copper by 23% and a bismuth content of just 0.001% makes copper brittle.D C Lynch, S Akagi and W G Davenport, “Thermochemical nature of minor elements in copper smelting mattes,” Metallurgical Transactions B, 22B, October 1991, 677–688. The material used in the cathode must not contaminate the copper being deposited, or it will not meet the required specifications.
The current efficiency of the refining process depends, in part, on how close the anodes and cathodes can be placed in the electrolytic cell. This, in turn, depends on the straightness of both the anode and the cathode. Bumps and bends in either can lead to short-circuiting or otherwise affect the current distribution and also the quality of the cathode copper.
Prior to the development of the Isa Process technology, the standard approach was to use a starter sheet of high-purity copper as the initial cathode. These starter sheets are produced in special electrolytic cells by electrodeposition of copper for 24 hours onto a plate made of copper coated with oil (or treated with other similar face-separation materials) or of titanium. Thousands of sheets could be needed every day, and the original method of separating the starter sheet from the “mother plate” (referred to as “stripping”) was entirely manual.
Starter sheets are usually quite light. For example, the starter sheets used in the CRL refinery weighed 10 pounds (4.53 kilograms).J C Jenkins and J C Saint-Smith, “Townsville copper refinery,” Proceedings of the Aus.I.M.M., No. 197, 1961, 239–260. Thus, they are thin and need to be handled carefully to avoid bending.
Over time, the formation of starter sheets was improved by mechanisation, but there was still a high labour input.
Once the starter sheets were formed, they had to be flattened, to reduce the likelihood of short circuits, and then cut, formed and punched to make loops from which the starter sheets are hung from conductive copper hanger bars in the electrolytic cells (see Figure 1).
The starter sheets are inserted in the refining cells and dissolved copper electrodeposits on them to produce the cathode copper product (see Figure 2). Because of the manufacturing cost of the starter sheets, refineries using them tend to keep them in the cells as long as possible, usually 12–14 days. On the other hand, the anodes normally reside in the cells for 24–28 days, meaning that there are two cathodes produced from each anode.
The starter sheets have a tendency to warp, due to the mechanical stresses they encounter and often need to be removed from the refining cells after about two days to be straightened in presses before being returned to the cells.M E Schlesinger, M J King, K C Sole and W G Davenport, Extractive Metallurgy of Copper, Fifth Edition (Elsevier: 2011), 259. The tendency to warp leads to frequent short-circuiting.
Due to their limitations, it is difficult for copper produced on starter sheets to meet modern specifications for the highest-purity copper.P E Donaldson and J J Detulleo, “Falconbridge’s Kidd Copper Refinery – birthplace of the Kidd Process: an update on the refinery and the latest developments in the Kidd Process”, in: Copper 2003–Cobre 2003. Volume V — Copper Electrorefining and Electrowinning, Santiago, Chile, 30 November–3 December 2003, Eds: J E Dutrizac and C G Clement (Canadian Institute of Mining, Metallurgy and Petroleum: Montreal, 2003), 165–174.
The development of the Isa Process technology
The development of the Isa Process tank house technology had its beginning in the zinc industry. During the mid-1970s, MIM Holdings Limited (“MIM”) was considering building a zinc refinery in Townsville to treat the zinc concentrate produced by its Mount Isa operations. As a result, MIM staff visited the zinc smelters using the best-practice technology and found that modern electrolytic zinc smelters had adopted permanent cathode plate and mechanised stripping technology.
MIM recognised that the performance of traditional copper refineries was constrained by the poor cathode geometry inherent in using copper starter sheets.N J Aslin, D Stone and W Webb, “Current distribution in modern copper refining,” in: Proceedings of the International Symposium on Computational Analysis, Eds M J Dry and D G Dixon (Canadian Institute of Mining, Metallurgy and Petroleum: 2005). Accessed 23 May 2013.
MIM then developed a research program aimed at developing similar permanent cathode technology for copper refining. CRL had been operating in Townsville since 1959, using conventional starter-sheet technology and treating blister copper produced in the Mount Isa Mines Limited copper smelter at Mount Isa in Queensland. CRL incorporated the permanent cathode technology in its 1978 refinery modernisation project. The material initially selected was 316L stainless steel,N J Aslin, O Eriksson, G J Heferen and G Sue Yek, “Developments in cathode stripping machines – an integrated approach for improved efficiency,” in: Proceedings of Cu 2010, Hamburg, Germany, 6–10 June 2010. Accessed 23 May 2013. stitch-welded to a 304L stainless-steel hanger bar.W Webb and J Weston, “The development of a “lower resistance” permanent cathode (ISA Cathode BR),” Minera Chilena, March–April 2003. Accessed 28 June 2013. The hanger-bar assembly was then electroplated with copper to a thickness of 1.3 millimeters (“mm”) (later increased to 2.5 mm and then 3.0 mm to improve the corrosion resistance of the hanger bar) to approximately 15 mm down onto the blade, which provided sufficient electrical conductivity and gave the assembly some corrosion resistance.