RI 5827 Recovery Of Zinc From Dross And Tin From Hardhead By Amalgam Electrolysis ? Summary

The principles and application of amalgam electrolysis to the recovery of zinc and tin from secondary products were studied; this Bureau of Mines project was one phase of investigating the development of more efficient methods for processing iron-bearing zinc and tin to produce both base metals of high purity. Zinc of 99-99-percent purity was recovered from galvanizer's dross with recovery efficiency of 98 percent. Tin of 99.9-to 99.99-percent purity was recovered from hardhead with recovery efficiency of 81 percent. Both materials were treated by the same method in separate systems. Mercury was used to leach zinc from dross and tin from hardhead to form amalgams of each metal, both of which were subsequently refined electrolytically to produce high-purity metal. Impurities that were contained in both secondary products behaved as theoretically predicted; impurities that were insoluble in mercury remained as sludge in the leaching column. Except for lead, the readily amalgamated impurities were prevented from fouling the electrolyte by the blocking action of the amalgam electrode. Lead impurity in the tin-refining system dissolved and immediately precipitated as the sulfate. The primary advantage of the amalgam refining method lies in direct recovery of the extremely pure base metal from highly contaminated secondary material.