Acid Molarity of the Aqueous Phase:
In order to demonstrate the utility of the variation in extraction with the changing molarity of the acid for the separation of metal ions, we will use the data of extraction in Cyanex 923 and HMWA (sub-Sec. 3.3.2).
We will confine the discussion to binary separations. But before proposing conditions for separations, the stripping agents for back extracting metal ions remaining in the organic phase of Cyanex 923, may be mentioned. The 0.5 M oxalic acid is able to recover all the metal ions from the organic phase. However, 0.1 M H2SO4 can also be used to strip all the metal ions except Ga (III). Washing the organic layer with less than 0.01 M HCl or H2SO4 can bring about quantitative recovery of Cu (II), Zn (II) and Cd (II) free from Fe (III). Water is also an effective reagent for the recovery of Cu (II), Zn (II) and Cd (II). In all the above cases, two volume wash of the stripping agent is required for the quantitative recovery of the metal ion from the organic phase.
The data on the extraction in Cyanex 923 have been used for a variety of binary separations involving 3d transition metal ions. These separations along with the conditions of separation and recovery are listed in Tables 3.1 (a) and (b).
Most of these separations have been achieved by selective extraction of a metal ion at an appropriate acidity. Ti (IV) / V (IV) was separated from Fe (III) / Ga (III) / Zn (II) / Cd (II) by selective extraction of the latter from 2 M HCl; however, for the separation of Ti (IV) / V (IV) from Ai (III) / Mg (II), the former was extracted from 10 M HCl solution.
For obtaining mutual separation of Ti (IV) and V (IV), both the metal ions were first extracted from 10 M HCl solution followed by stripping of V (IV) using 10 M H2SO4.
The data on the extraction in Cyanex 923 have been used for a variety of binary separations involving 3d transition metal ions. These separations along with the conditions of separation and recovery are listed in Tables 3.1 (a) and (b).
Most of these separations have been achieved by selective extraction of a metal ion at an appropriate acidity. Ti (IV) / V (IV) was separated from Fe (III) / Ga (III) / Zn (II) / Cd (II) by selective extraction of the latter from 2 M HCl; however, for the separation of Ti (IV) / V (IV) from Al (III) / Mg (II), the former was extracted from 10 M HCl solution. For obtaining mutual separation of Ti (IV) and V (IV), both the metal ions were first extracted from 10 M HCl solution followed by stripping of V (IV) using 10 M H2SO4 and that of Ti (IV) employing 2 M HCl. In between the washings by the two stripping agents, the organic layer was washed with water. Cr (III) can be separated from Fe (III) / Co (II) / Cu (II) / Zn (II) by extracting the latter at an appropriate molarity of HCl.