Electrowinning

Electrowinning
In this final step, the rich electrolyte is pumped through a series of tanks or "cells" in the electrowinning tankhouse. Hanging in the tanks are insoluble lead plates, alternating with sheets of thin copper or stainless steel. Each lead plate serves as the anode pole of an electric circuit. The thin copper sheets, called starter sheets, or the stainless steel sheets, called blanks, serve as the cathode pole. A direct current passes from the anode through the electrolyte to the starter sheet or blank, causing the copper ions in the electrolyte solution to plate (attach) onto the starter sheet or blank. After six to seven days in the tankhouse, 100- to 300-pound copper cathodes that are 99.999 percent pure and ready for market are harvested. The electrolyte that has passed through the tankhouse, now depleted of its copper, is returned as "lean electrolyte" to the stripping step of the process to begin that cycle again.

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