Zinc recovery from dilute ammoniacal media using an integrated solvent extraction and electrolysis process

Abstract

Zinc(II) was recovered from dilute ammoniacal media through an integrated process combining solvent extraction and electrolysis with ammonia stripping. Zinc ions were firstly enriched into organic phase at pH 7.56 through synergistic extraction between β-diketone and TBP or Cyanex 923. The concentration of extracted zinc(II) increased at pH < 7.56, but clearly decreased at pH 7.56–9.98. The extracted zinc species could be effectively stripped from the loaded organic phase using ammoniacal liquor at pH 9.5, because the ammonia stripping process followed an trend opposite to the extraction process. The extraction and ammonia stripping isotherms verified that Zn(II) concentration can be increased from 1.3 g/L to >56 g/L by using β-diketone and Cyanex 923. Metallic zinc can be obtained by direct electrolysis from the ammoniacal stripping solution. The presence of small amounts of the dissolved extractant molecules can improve the crystallization of zinc deposits. A gelatin additive was used to smoothen the morphology of zinc deposits and refine their crystalline structure. These results indicate that the proposed integrated process will facilitate the recovery of various zinc-bearing primary and secondary resources in ammoniacal media.