RECOVERY OF METALS FROM ELECTROACTIVE COMPONENTS OF SPENT Ni-MH BATTERIES AFTER LEACHING WITH FORMIC ACID

Abstract

this work describes a route for recovering nickel, cobalt, iron, zinc and lanthanides from spent nickel-metal hydride batteries. Formic acid was used as leachant. Experiments were run at 25-50°C for 1-4 h. Under the best conditions leaching yields surpassed 99 wt.%, except for iron. The insoluble matter contains almost solely iron as iron(III) basic formate. The leachate went through six separation procedures, combining solvent extraction with D2EHPA as extractant, and precipitation reactions. Fe2+ and Zn2+ were extracted together (> 99 wt.%) from the original leachate (pH ~1.5). Yttrium and lanthanides were precipitated as oxalates directly from the raffinate (> 99.9 wt.%) upon addition of sodium oxalate. In the next steps, Mn2+ and Co2+ were extracted with D2EHPA at buffered pH (3 and ~4.8, respectively), after adding NaOHaq. About 10 wt.% of leached Ni2+ was coextracted with Co2+. The remaining Ni2+ was precipitated from the raffinate after addition of aqueous sodium oxalate at pH 6. After precipitation of Al3+ upon addition of NaOHaq. until pH ~8, sodium formate was recovered after slow evaporation of the final aqueous solution at 60oC. It contains ~90 wt.% of the formate present in the leachant.

Elution of Divalent Cations from Iron Ore Mining Waste in an Indirect Aqueous Mineral Carbonation for Carbon Capture and Storage

“…Halli et al [55] conducted an elution study using electric arc furnace dust and found up to 14% of Fe 2+ elution using 0.27 M formic acid in 168 h, which was a longer reaction time. Lower elution reactivity of Fe 2+ was also observed in other studies using formic acid as an extraction agent [56,57]. The Ca 2+ elution showed better results with maximum elution of 30% using 1.5 M solution at 12 min and 25 min steadily, followed by 23.6% using 1.0 M solution within 12 min, demonstrating a rapid initial rate of elution.…”