A novel strategy achieving enrichment of metal values from and into ammoniacal solutions

• A novel strategy was proposed to enrich metals from and into ammoniacal solutions.
• A special swing effect was found for metal extraction in ammoniacal solutions.
• The loaded organic phases can be effectively stripped by ammoniacal solutions.
• Rising temperature profits for stripping of zinc and nickel, but adverse for copper.

A novel strategy has been proposed to achieve enrichment of metal values from and into ammoniacal solutions through solvent extraction. The extraction equilibria of Cu(II), Ni(II) and Zn(II) in ammoniacal sulfate solution have been examined with β-diketone in the pH range of 6–12. The ammonia stripping behaviors of three metal ions have been studied by consideration of total ammonia, pH and temperature. The results indicate that a special swing phenomenon was found for both extraction and ammonia stripping processes. The loaded organic phases can be successfully stripped with ammoniacal solutions by adjusting total ammonia concentration and pH. Zinc and nickel are more easily stripped than copper. Increasing temperature is beneficial for the ammonia stripping of zinc and nickel but adverse for copper, thus potentially improving the Zn/Cu and Ni/Cu separation. The ammonia stripping isotherm shows that zinc can be efficiently enriched with two counter current stages. Moreover, there is no significant loss of organic phase during stripping. Therefore, direct enrichment of metal values through ammonia stripping has a good prospect for the integrated extraction and electrowinning circuit throughout ammoniacal systems.