What Kind Of Lead Anode Is Good For Zinc Electrowinning?

Jul 28, 2022

What Kind of Lead Anode is Good for Zinc Electrowinning?

In electrowinning applications, lead and its alloys have been the preferred anode material for a long time. The anode material used in the electrowinning process should meet three requirements: electrical conductivity, electrocatalysis, stability, and certain resistance. Good electrical conductivity is essential for energy efficiency. Good electrocatalytic properties are essential to improve product yield. Long-term stability is also an important property because electrode wear and corrosion may cause product contamination, increasing energy consumption and material and labor costs due to the need for periodical maintenance. Also, the anode should have fine, uniform grains with little or no segregation of alloying elements to the grain boundary.

Pure lead is a weak material and it tends to creep and warp during use. Therefore, the lead must be alloyed in order to improve its mechanical properties. Lead has a relatively low melting point, which facilitates its casting, and it is also a very ductile material and can be machined with ease. In zinc electrowinning plants, lead-silver alloy has been widely used as an insoluble anode material. The lead-silver alloy anode in an acidic sulphate bath has the following favorable features, small amounts of Ag alloyed with lead decrease the oxygen overvoltage, and increase the corrosion resistance of material during electrolysis. A well established custom in most electrolytic zinc plants is to use Pb-Ag alloys containing 0.7-1.0 percent Ag as the anode material. The resulting benefits are a longer anode life and a lower Pb content in the cathodic zinc.

The lead-silver alloy anode in acidic sulphate bath has many favorable features, for example, alloying of silver in the alloys resulted in suppression of anodic oxidation of the materials, decrease in the anode potential, formation of dense oxide layer closely adhering to the electrode, and appearance of P-Pb02 in the anodic oxide layer, so the lead silver alloy anode has been employed in the electrolytic production of zinc for 50 years. Presently, most zinc plants use lead-silver alloys as anodes. The stability of the anodes is related to the cathode quality - the lead contamination level of the cathode deposits. To improve the performance of the lead anodes,  doping Ca or Sn in the Pb-Ag alloy and rolling lead anode plates to diminish the number of the holes, voids, and laps. However, there are some difficulties in their use that can create problems; one is concerned with the incorporation of lead corrosion products in cathode which decreases the purity. Also, the oxygen overpotential becomes relatively high which increases the cell voltage and decreases energy efficiency.