All Zinc, All OK

No Aluminium, No Zinc

Around 90 % of the zinc produced worldwide by smelting is obtained wet-chemically using the hydrometallurgical process. In this process, aluminium and lead sheets are immersed in a sulfuric acid solution (electrolyte), which, depending on the smelter, may also contain recycled zinc. The lead sheet acts as the anode and the cold-rolled aluminium sheet as the cathode. Depending on the smelting process, a zinc layer of sufficient thickness for further process steps is deposited on the surface of the aluminium cathode over a period of 24 to 48 hours by electrochemical processes.

The elementary zinc adhering to the aluminium sheet is mechanically removed from the cathode in a process known as stripping; it is then cleaned, re-melted in smelting furnaces and cast for further use, usually in ingot form. The aluminium cathode sheets then go back into the electrolyte solution and are used again for zinc production. A single cathode sheet can thus be reused hundreds of times over the course of its service life, which can be several years.

Apart from its corrosion resistance and electrical conductivity, aluminium is used as a cathode sheet because of its favorable effect on hydrogen overvoltage, which makes the extraction of zinc by hydrometallurgy possible in the first place.

The Advantages of AMAG PROCATH®

• Optimal conductivity The electrical conductivity of cathodes is a crucial factor in a successful zinc smelting process. AMAG therefore uses only pure aluminium such as EN-AW1050, EN AW1070 or EN-AW1200 for the cathode sheets. Customer-specific variants are also possible, depending on the requirements of their specific smelters.
• Increased Strength AMAG cathode sheets undergo additional cold rolling. This provides improved thickness tolerance as well as increased strength. This improves the mechanical resistance of the sheets in the subsequent stripping process at the end customer, and thus increases service life.
• Excellent Form Tolerances AMAG PROCATH® provides excellent flatness and low residual stress, especially in the stress-relieved tempers H34 and H36. This prevents possible warping at the end customer, when welding support rods to cathode sheet.
• Patented Edge Strip Technology With Unmatched Quality Plastic strips are applied to the edges of the cathode sheet to prevent the zinc deposited on the cathode surfaces from growing laterally towards the electrolyte tank where it cannot be removed by the stripping process, thus possibly creating a short circuit. The advantage of AMAG’s specific method of application is the absence of adhesive media such as silicone, or mechanical fixation. It relies on a combination of chemical interaction between the special chemical composition of the edge strip and the aluminium surface. The resulting bond is a perfect seal that is resistant to electrolytes. This prevents the electrolyte from infiltrating the edge strip, thereby preventing premature failure of the elements and extending the service life.
• Extremely Tight Form Tolerance The excellent flatness of AMAG's cold-rolled cathode sheets enables smelters worldwide to achieve minimum spacing between the cathodes and anodes, which increases yields. This not only optimizes the use of space in the electrolyte bath, but also ensures the most efficient use of resources.

One of AMAG's two cathode edge coating plants was recently upgraded to ensure that it will continue to supply the vital and versatile metal in the accustomed quality in future. In particular, the pressing station – in which the cathode sheets are fitted with edge strips in a process patented by AMAG – was completely upgraded to the latest state of the art. This conversion now makes it possible, as with the second plant of this type, to fit the edge strips in a fully automated process and always with the same high quality that is typical of AMAG edge strips. In-house formulas with defined production parameters for each individual end customer eliminate the need for operators to manually control the system parameters. This automation step not only significantly reduces downtimes during a product changeover at the plant; it also builds plant redundancy, which creates fallback options for theoretical failure scenarios, thus making AMAG an even more reliable partner.