RECOVERY OF ZINC FROM ZINC WASTE GALVANIC SLUDGES WITH INCREASED COPPER AND NICKEL CONTENT

摘要

Neutralizing sludges generated by the Czech plating industry are disposed of as a hazardous waste. However, these sludges could be considered as a secondary raw material to recover valuable metals such as Cu, Ni and Zn. Applications of existing modem technologies are not economical in the Czech Republic, where the production of Cu, Ni or Zn galvanic waste corresponds to several tens of tons of pure metal. The amount of zinc sludges formed in the Czech Republic is several times higher then that of other neutralizing sludges. For this reason, a simple method of processing zinc waste galvanic sludge containing 26.4% Zn, 4.1%Cu and 2.0%Ni was developed and verified in this study on a laboratory scale. We consider that this method based on caustic leaching of the sludge, should be economical under pilot scale conditions for processing smaller amounts of zinc sludges with increased copper and nickel content. To establish optimum parameters of the proposed method, the sludge was leached in concentrated NaOH solutions at elevated temperatures and different liquid-to-solid ratios. The subsequent electrowinning process was performed with refined zinc caustic leach liquors, which were purified using cementation technique. Effects of operational variables on Zn electrowinning have been studied using the conventional plate-plate electrowinning cell.