PJSC “MMC “Norilsk Nickel”, Polar Division, Norilsk, Russia:

E. V. Salimzhanova, Deputy Director, Center for Production Engineering Support
A. I. Devochkin, Deputy Director – Chief Engineer
E. V. Yudin, Control and Analytical Department, Chief Engineer
D. D. Karpushova, Leading Process Engineer, Center for Engineering Support of Production

Under the London Metal Exchange (LME) standard, the spiral elongation number (SEN) of the tested samples is to be at least 400 mm. The number allows to evaluate the difference in physical properties of copper of various purity. In the products of LME-listed foreign companies, the content of harmful impurities does not exceed 0.5–1 g/t (as to sulfur — 4 g/t). In addition to content of cathode metal impurities the major factor is their combination. The impurities with the most adverse effect on SEN value of Polar Division cathode copper are sulfur, selenium, tellurium, bismuth and lead. The main paths for harmful impurities to penetrate the cathode metal are as follows: inclusion of slime particles into growing deposit; entering of thiourea, its decomposition products or its complex copper compounds into cathode metal, ingress of electrolyte in form of sulfates into the deposit intercrystalline space. Special procedures were developed and implemented by the Polar Division of
Norilsk Nickel to ensure the cathode copper quality. New antistick coating for copper molds was introduced and the coating application method was refined diminishing antistick coating specific consumption approximately by factor of 5. Electrolyte filtration during electrolysis cells cleaning at the end of the anode cycle was implemented to reduce solid particles concentration in the electrolyte. Periodic control of surfactants concentration in the electrolyte was introduced in order to estimate their electrolyte activity. Finished cathodes washing procedure was optimized including washing machines sprayers modernization for uniform distribution of water on the cathode surface. Engineering and organizing actions were taken for maintenance of marketable copper quality. Essential equipment to apply European procedure EN 12893 for measurements of the cathode copper samples spiral elongation at the Polar Division was purchased and is being under assimilation. Copper cathode strapping line was modernized to provide cathode lots packing in accordance with the international standards. Decrease of electrolyte viscosity is another option to reduce the impurities content and maintain the cathode copper quality during intensive electrolysis. Optimal electrolyte composition was calculated in terms of the major components concentrations with regard to minimal electrolyte viscosity.

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