Electronic applications require electrolytic copper (99.99% pure or higher).

Xstrata, the world’s fourth largest copper producer, as well as the fifth largest diversified metals and mining company, is known for more than its metal output: the Group subsidiary Xstrata Technology develops technologies for sale, both to in-house operations and to other metals and mining companies worldwide. The Xstrata Technology flagship, based in Townsville in northern Australia, is the Tankhouse Group selling the ISA and KIDD PROCESS™ technologies – copper production technology applied to both electrolytic refining and electrowinning plants. The ISA and KIDD technologies account for approximately 60 percent of the world cathode copper production (more than 99.99% pure copper).

A key feature of Xstrata’s technology is the use of permanent stainless steel cathode plates in lieu of conventional copper starter sheets. Stainless cathode plates, 3.25mm thick and in grade EN 1.4404 / ASTM 316L, have a lifetime of 10-15 years when operated to specification. A single plate, weighing about 30kg, can produce up to 6,000kg of pure copper per year.

Specification demands on the stainless steel sheet used to manufacture the cathode plates are strict: the sheet must have perfect flatness to achieve superior precision in cathode straightness. Flatness is also important to enable optimal plate alignment and even copper growth in the tankhouse. The sheet surface finish must be close to perfect so there are no crevices where copper can adhere, locking the copper onto the plate and affecting stripping.

For many years Xstrata Technology has sourced unique cathode-plate stainless steel in grade EN 1.4404 / ASTM 316L from the Outokumpu Nyby coil products plant in Torshälla, Sweden. The sheet, produced to customized flatness and surface-finish specifications, is a result of long-term cooperation and joint product development between the coil plant and Xstrata Technology. The plant operates a combination of processes that can achieve extraordinarily high levels of flatness.

Recent development work together has focused on identifying alternative stainless steel materials with improved durability and greater cost effectiveness. The pressure on this development work has increased with the recent very high and variable costs of key stainless steel constituents such as nickel.

Ken Hayes of Outokumpu’s Australian sales company, the account manager of the Outokumpu-Xstrata partnership, was instrumental in introducing Xstrata Technology engineers to Outokumpu’s proprietary duplex stainless steel grade LDX 2101® (EN 1.4162). This grade offers a number of major benefits over the conventional austenitic grade. The high mechanical strength of LDX 2101®, similar to that of all duplex grades, allows for significant weight reductions and consequent cost savings. Owing to its very low nickel content, LDX 2101® offers excellent price stability and, at times of soaring nickel prices, a lower raw material price in absolute terms than austenitic grades.

The many benefits of LDX 2101® appealed to the Xstrata engineers, but its use in the demanding application was not without complications that needed to be overcome. The high strength of LDX 2101® makes it harder to flatten than austenitic grades, and LDX 2101® did not at first promise an adequate surface finish.

Outokumpu specialists from research & development and cold rolling operations went to work with Xstrata engineers, and together they managed to solve the challenges. In close partnership, they developed an LDX 2101® sheet product that met Xstrata Technology’s requirements. Xstrata Technology tested the LDX 2101® plates, first in house, then in some of their customers’ plants to prove the concept.

Xstrata Technology first put in an order for LDX 2101® sheet to manufacture a few hundred cathode plates. Xstrata’s confidence in LDX 2101® has grown as their experience in the grade has accrued, and the Outokumpu Australian sales company booked the first large order in August 2007. This order was for 667 tons of LDX 2101® sheet to manufacture 20,000 plates for the solvent-extraction-electrowinning process of the Tenke copper project in the Democratic Republic of Congo.

At around the same time, the sales company booked an order from Xstrata Technology for 1,555 tons of grade EN 1.4404 / ASTM 316L sheet, also to manufacture permanent cathode plates, demonstrating the success of the business relationship and the premium products that have been developed together over many years.

Mr. Hayes comments on the potential that LDX 2101® offers for mining companies: “The price stability of LDX 2101® gives more credibility to feasibility studies with assurance that the price of stainless steel will remain stable. Sudden and sharp increases in stainless steel prices due to nickel price fluctuation can easily make a feasibility study outdated, causing the mining company extra costs and delays in launching new projects. In extreme cases, LDX 2101® could even be the deciding factor that makes a project viable.”

For more information, please contact:
Ken Hayes
Regional Manager
Outokumpu's Australian sales company
Phone +61 3 9369 3344
E-mail: ken.hayes(at)outokumpu.com

In (1) electrorefining and (2) electrowinning, a current is used (1) to dissolve copper from an anode (a plate of copper containing impurities) into a conducting solution, or (2) to extract copper from a solution into which it has been leached from ore. Pure copper is deposited onto a cathode plate. Photo courtesy of Xstrata Technology