Solvent extraction of metals from a Brazilian nickel lateritic liquor with D2EHPA and Cyanex 272

The solvent extraction of Fe (residual), Mn, and Co from a real sulfuric Ni lateritic liquor (initial pH = 3) containing Ca and Mg was evaluated using D2EHPA and Cyanex 272 as extractants (A/O ratio = 1, T = 50 °C, one contact stage). Fe was practically extracted by both extractants at pH > 3. While Mn was selectively separated from Co and Ni with D2EHPA (5% v/v) at pH 3 (βMn/Co = 167), it was co-extracted with Co with Cyanex 272, which in turns is much more effective than D2EHPA in separating Co and Ni (βCo/Ni = 697 with 15% v/v of Cyanex 272 at pH 4.5). In addition, D2EHPA presented high affinity to Ca at low pH conditions, while Cyanex 272 extracted Ca and Mg at similar extents but at a higher pH level. Therefore, two SX circuits at staged operations, the first with D2EHPA and the second with Cyanex 272, can produce Co and Ni rich-streams. It was verified that Fe, Mn, as well as Ca, and part of Mg may be removed from the liquor at pH 3 with D2EHPA (5% v/v), while Co and remaining Mg could be separated from Ni with Cyanex 272 (15% v/v) at pH 4.5. Subsequent stripping and raffinate treatment strategies were presented. Data fitting using the slope analysis method revealed that coordinate complexes of Mn with D2EHPA, as well as Mn and Co with Cyanex 272, has the exact same MR2(RH)2 molecular structure.