Separation of manganese, zinc and nickel from leaching solution of nickel-metal hydride spent batteries by solvent extraction

The paper is focused on the use of solvent extraction for purification of leach liquor solutions obtained by leaching of NiMH spent batteries: dissolved nickel is separated from manganese and zinc by liquid–liquid extraction using D2EHPA. Two extractants were investigated: D2EHPA and Cyanex 272 in n-dodecane, and the preliminary tests suggested that D2EHPA is more efficient to separate Mn and Zn from the leaching solutions. Under the optimized conditions it is observed that in extraction circuit a recovery > 99% of zinc and > 95% of manganese is archived. The experimental results suggested that two cross-flow liquid–liquid extraction steps are adequate to extract 100% of Zn and about 95% of Mn while the residual Ni was about 80% of its initial content. The extracted elements are stripped using a 4 M sulfuric acid solution and the stripping yields were very high, > 99% for Ni and Zn and about 98% for Mn. Finally, a possible process flowsheet to separate Mn and Zn from leach liquor of NiMH spent batteries by solvent extraction is proposed. The process includes two stages of extraction with 20% v/v of D2EHPA in n-dodecane (O/A = 1/1, room temperature, 30 min of contact, pH ≤ 2.5) and one stage of stripping with 4 M of H2SO4 (O/A = 1/0.5, room temperature, 15 min of contact). The raffinate rich in Ni has the following composition: 32 g/L of Ni, 0.87 g/L of Mn, and the aqueous liquid from the stripping step had the following concentrations: 9.86 g/L of Zn, 18 g/L of Mn and 7.33 g/L of Ni. The first solution could be treated to recover Ni, for example by precipitation, whereas the second liquid could be recycled in electrolytic section to recover metallic zinc and manganese oxide.