•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.

The dissolution mechanism of hemimorphite in NH3-(NH4)2SO4-H2O system at 298.15 K was investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis. The results show that hemimorphite is soluble in NH3-(NH4)2SO4-H2O system and its residue exists in the form of an amorphous SiO2 layer on the hemimorphite surface. The XPS data also indicate that the Si 2p3/2 and O 1s spectra of the hemimorphite are broadened and shift to higher binding energies and their binding energies are closer to silica with an increase of total ammonia and time. Solubility of hemimorphite in NH3-(NH4)2SO4-H2O system was measured by means of isothermal solution method at 298.15 K based on the study of the dissolution mechanism of hemimorphite. The results show that the solubility of zinc in solution increases firstly and then decreases with the increase of cT(NH3) (total ammonia concentration) at different NH3/NH4+ ratios. The solubility of silicon in solution decreases from 0.0334 mol/kg in cT(NH3)=4.1245 mol/kg NH3-(NH4)2SO4-H2O solution to 0.0046 mol/kg in cT(NH3)=7.6035 mol/kg NH3-(NH4)2SO4-H2O solution.

The solubility of 4-ethyl-1-phenyl-1,3-octadione in pure water, (NH4)2SO4, NH3 (aq), and (NH4)2SO4–NH3–H2O solutions was measured by means of isothermal solution method at 298.15 K. The investigated total ammonia concentration ranges of NH3, (NH4)2SO4, and (NH4)2SO4–NH3–H2O system were up to 1.8053 mol·L–1, 3.0135 mol·kg–1, and 6.4 mol·kg–1, respectively. The experimental results indicate that the solubility of 4-ethyl-1-phenyl-1,3-octadione in NH3 and (NH4)2SO4–NH3–H2O solutions increases with the increase of total ammonia concentration. In contrast, its solubility in (NH4)2SO4 solution decreases with the increase of the ammonium sulfate concentration. The Pitzer model was adopted to correlate the dependency of the solubility with the activity coefficients. The parameters obtained by the least-squares method can explain the salting effect phenomenon and can be used to calculate and predict the activity coefficients of 4-ethyl-1-phenyl-1,3-octadione in ammoniacal solutions by the Pitzer model.

The extraction behavior of nickel in ammoniacal sulfate solution using sterically hindered β-diketone (4-ethyl-1-phenyl-1,3-octadione, HA) was investigated systematically by consideration of various parameters, i.e. HA concentration, aqueous pH, total ammonia concentration, ionic strength and temperature. The results indicated that the nickel extraction is dependent not only on the pH, total ammonia concentration and temperature in the aqueous phase, but also on the nickel extract in the organic phase. It was found that the increase in the total ammonia concentration and pH depresses the nickel extraction in ammoniacal solutions. The overall extraction process is endothermic at pH 7.5 and exothermic at pH 8.5 and 9.5, respectively. This can be mainly attributed to the formation of nickel ammine species in the aqueous phase. Extraction of ammonia and water in the organic phase was studied in the presence and absence of nickel. And the structure of nickel extracts was examined by the UV–Vis and FT-IR spectroscopies. The results showed that ammonia molecule should be co-extracted by coordinating with nickel extracts (NiA2) as the form of NiA2⋅NH3. The water molecule is associated with β-diketone molecule by intermolecular hydrogen bonding in the absence of nickel, but extracted as the form of hydrated nickel extracts in the presence of nickel.Highlights► Nickel extraction from ammoniacal solution is sensitive to pH and total ammonia concentration. ► The formation of nickel ammine species in the aqueous phase depresses nickel extraction. ► The hydrated nickel extracts in the organic phase can decrease nickel extraction. ► Ammonia can be co-extracted in the form of NiA2·NH3 in the organic phase. ► Extraction reaction of nickel is endothermic at pH 7.5 but exothermic at pH 8.5 and 9.5.

The extraction behaviors of zinc by 1-(4′-dodecyl)-phenyl-3-tertiary butyl-1,3-octadione (HA) from ammoniacal solutions into ionic liquid (1-butyl-3-methyl-imidazolium hexafluorophosphate, [BMIM]PF6) and molecular organic solvent (nonane) were investigated. The effects of extractant concentration in the extracting organic phase, aqueous pH and total ammonia concentration in the aqueous phase were examined. The extraction efficiency of zinc in both extraction systems decrease with the increase of pH and total ammonia concentration. The extraction performance was evidently enhanced in the extraction system of [BMIM]PF6 with HA, especially at higher pH and total ammonia concentration. This can be attributed to the strong polarity environment of [BMIM]PF6. The extraction mechanism and the effect of zinc amine complexes on the extraction were discussed. The coordination environment of zinc ion in extracting phases were investigated by X-ray absorption spectra. The results showed that the different extraction behavior between nonane and [BMIM]PF6 is probably determinated by the hydration state of extracted zinc complex and the solvent polarity. Five extraction/stripping cycles were performed to examine the reusability of the extraction system and stripping characteristics.