IsaKidd refining technology

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 copper) 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. 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. 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. 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. The two technologies were brought together as the IsaKidd Technology in 2006, when Xstrata bought Falconbridge. This is about 60% of the estimated 2011 global refined copper production of 19.7 million tonnes. 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. 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. 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. The tendency to warp leads to frequent short-circuiting. The development of the Isa Process technology The development of the Isa Process tank house technology had its beginning in the zinc industry. MIM then developed a research program aimed at developing similar permanent cathode technology for copper refining. stitch-welded to a 304L stainless-steel hanger bar. 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. The process used involves leaching the copper from the material using an acidic chloride–sulfate solution, followed by solvent extraction to concentrate the leached copper and electrowinning. Electrowinning copper differs from electrorefining in that electrorefining uses a copper anode that is dissolved and redeposited on the cathode, while in electrowinning the copper is already in solution and is extracted from the solution by passing a current through the solution using an inert lead-alloy anode, and a cathode. The chloride in the leach solution at Port Pirie proved to be a problem for the stainless steel cathodes of the Isa Process. 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. 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. The groove weakens the structure of the copper growing at the bottom edge of the cathode plate because the copper crystals grow perpendicular to the cathode plate from opposite sides of the groove, causing them to intersect at right angles to each other. to US$37,216. Nickel is a key constituent of 316L stainless steel. The LDX 2101 alloy provides an alternative to the 316L stainless steel, The Isa Process technology continued to be developed and marketed by Xstrata Technology. Xstrata subsequently took over Falconbridge in 2006. The Kidd Process technology consequently became part of the Xstrata Technology tank house package and together they began to be marketed as IsaKidd, a name that represents the dual heritage of the technology. The result has been a technology package that combined what were mutually regarded as the best of both versions. This combination led to the development of new stripping systems and new cathode designs are in development. The variation in copper deposits on the cathode plates was one of the difficulties encountered with the earlier stripping machines. Areas of thin copper on the cathode plates, which are caused by short circuits, are difficult to separate from the stainless steel plate due to their lack of rigidity. Plates bearing such areas generally had to be rejected from the stripping machine and stripped manually. Similarly, sticky copper deposits (generally related to poor surface condition on the cathode plate, such as corroded surfaces or improper mechanical treatment), heavily nodulated cathode and laminated copper caused problems for stripping. Stripping machine development focussed on developing a device that could be seen as a more accommodating and universal stripping machine that could handle cathode plates with problem copper deposits without rejecting them or slowing the stripping rate. The result of this work was a new robotic cathode stripping machine. It incorporated the following features: • a stripping wedge that starts removing the copper from the top of the cathode plate and moves down to the bottom • guides to support the copper during the downwards motion to ensure that the copper does not strip prematurely • rollers designed to reduce the friction between the copper, the cathode plate and the wedge during the downward motion of the wedge • grippers that clamp the copper before it is pulled away from the cathode plate. The stripping wedges are mounted on two robotic arms, one for each side of the cathode plate. These arms strip the copper from the plate and lay the sheets of cathode copper onto conveyors for them to be taken away for bundling. ==Advantages of the IsaKidd Technology==

Advantages cited for the IsaKidd technology include: • long life – the operational life of the permanent cathodes without repair is said to be over seven years under correct operating conditions for electrowinning applications and over 15 years for electrorefining applications and the automation of cathode stripping. • no suspension loops – the suspension loops of starter sheets can corrode and thus cause cutting of the electrolytic cell liners. – due to the straight cathode plates, which eliminates short-circuiting, and other slimes compounds. • improved current efficiency – this arises both from eliminating short circuits caused by bent and irregular electrodes and from the shorter cathode cycles possible with the use of the reusable cathode plates. Current efficiencies of over 98% are claimed • increased refining intensity – this reduces the number of electrolytic cells needed in a refinery and its capital cost because the gap between the anodes and the cathodes can be narrower due to the lower risk of short circuits and because the current density can be increased, making the refining process faster. Refineries operating with the IsaKidd technology can achieve current densities of 330 amperes per square meter (“A/m2”) of cathode area, whereas a refinery using starter sheets can only operate at around 240 A/m2 • shorter cathode cycles – shorter cathode cycles are possible using the IsaKidd technology, which reduces the metal inventory and means that the refinery or SX–EW operator is paid more quickly • shorter anode cycles – the higher intensity of the refining also results in about a 12% reduction in anode cycle time, also reducing the metal inventory • uniform cathode copper sheets for ease of transport – the control over the dimensions of the copper sheets made possible by the IsaKidd technology, provides uniform cathode bundles that can be securely strapped and easily transported (see Figure 7) • improved safety – elimination of much of the manual handling leads to improved safety conditions in the workplace. Staff of the Cyprus Miami copper refinery wrote after their installation of the Isa Process technology that: “It is now well proven that tankhouses applying stainless steel cathode technology can consistently produce high quality cathodes while operating at higher cathode current density and at a lower cathode spacing than those used in conventional tankhouses.” ==References==