The Performance of Lead Tin Calcium (PbSnCa) Anodes in Metal Electrowinning

The Performance of Lead Tin Calcium (PbSnCa) Anodes in Metal Electrowinning

The PbSnCa alloy anode was introduced in the 1980s for the first time. Each of the used alloying elements has special effects on the properties of lead. Calcium is used to improve mechanical properties rather than corrosion performance. It has been shown that the optimum calcium content of 0.07-0.09 wt.% results in the maximum yield strength of Pb-Ca alloy. On the negative side, calcium weakens the corrosion resistance of the lead anodes. The presence of calcium in the lead causes the precipitation of Pb3Ca, which reduces the grain size and increases the intercrystalline area of the corrosion layer. Consequently, intergranular corrosion is promoted in the PbCa alloys.

The addition of tin to the PbCa decreases the amount of the Pb3Ca phase at the grain boundaries through the formation of the Sn3Ca phase that is more stable. Therefore, tin reduces the intergranular corrosion in the PbCa anodes. Moreover, the presence of tin in the anodic layer causes higher conductivity of the layer and inhibits the anode passivation problem. The mechanical properties of lead alloys can also be improved by the tin alloying element. Since tin might be trapped in the large (Pb1-xSnx)3Ca precipitations in PbSnCa alloys, its effective amount depends on the amount of calcium in the lead alloy. PbCaSn alloys are the most popular lead-based anodes in the copper electrowinning process.