Recycling of the anode from spent Ni-MH batteries for synthesis of the lanthanide oxysulfide/oxysulfate compounds used in an oxygen storage and release system

• Recycling of rare earth metals from anodes of spent Ni-MH batteries.
• Rare earth oxysulfate/oxysulfide for oxygen storage and release system.
• Synthesis of the (La·Nd)2O2S·CeO2 and (La·Nd)2O2SO4CeO2 compounds.
• Thermal stability of rare earth oxysulfate/oxysulfide in different atmospheres.

In this work, lanthanide oxysulfide/oxysulfate compounds, denominated as an oxygen storage and release system, have been synthesized from the anode electrodes of spent Ni-MH batteries. The rare earth metals have recovered by means of chemical precipitation as a mixture of La2(SO4)3, Ce2(SO4)3, and Nd2(SO4)3. The synthesis of (La·Nd)O2S·CeO2 have been carried out by subjecting a mixture of La2(SO4)3, Ce2(SO4)3, and Nd2(SO4)3 to a heat treatment in a reducing atmosphere up to 1000 °C. The (La·Nd)O2SO4·CeO2 compounds have been obtained after thermal treatment of (La·Nd)O2S·CeO2 in a synthetic air atmosphere. The oxysulfide/oxysulfate compounds have been subjected to thermal cycles, respectively, in synthetic air as well as in an N2–CO atmosphere. The thermogravimetric plot (TG) for (La·Nd)2O2S·CeO2 shows a mass gain of 14.98% w/w in a temperature range of 300–550 °C, which is due to the oxidation of (La·Nd)2O2S·CeO2 to (La·Nd)2O2SO4CeO2, where 2 mol of O2 are added. Likewise, in the (La·Nd)2O2SO4CeO2 thermogravimetric plot, a mass loss of 17.16% w/w is observed in the range of 500–750 °C. This loss of mass can be associated with output of 2 mol of O2 forming again the (La·Nd)2O2S·CeO2. The transformation of the (La·Nd)2·O2S·CeO2 to (La·Nd)2O2SO4CeO2 causes an increase in the macropores.

Rare earth oxysulfate recovered from the anodes of the spent Ni-MH.Figure optionsDownload as PowerPoint slide