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

Abstract

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 4M 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, 30min of contact, pH≤2.5) and one stage of stripping with 4M of H2SO4 (O/A=1/0.5, room temperature, 15min of contact). The raffinate rich in Ni has the following composition: 32g/L of Ni, 0.87g/L of Mn, and the aqueous liquid from the stripping step had the following concentrations: 9.86g/L of Zn, 18g/L of Mn and 7.33g/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.