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

摘要

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 La_2(SO_4)_3, Ce_2(SO_4)_3, and Nd_2(SO_4)_3. The synthesis of (La • Nd)O_2S • CeO_2 have been carried out by subjecting a mixture of La_2(SO_4)_3, Ce_2(SO_4)_3, and Nd_2(SO_4)_3 to a heat treatment in a reducing atmosphere up to 1000 ℃. The (La • Nd)O_2SO_4 CeO_2 compounds have been obtained after thermal treatment of (La • Nd )O_2S • CeO_2 in a synthetic air atmosphere. The oxysulfide/oxysulfate compounds have been subjected to thermal cycles, respectively, in synthetic air as well as in an N_2-CO atmosphere. The thermogravimetric plot (TG) for (La • Nd)_2O_2S • CeO_2 shows a mass gain of 14.98% w/w in a temperature range of 300-550 ℃, which is due to the oxidation of (La•Nd)_2O_2S•CeO_2 to (La • Nd)_2O_2SO_4CeO_2, where 2 mol of O_2 are added. Likewise, in the (La•Nd)_2O_2SO_4CeO_2 thermogravimetric plot, a mass loss of 17.16% w/w is observed in the range of 500-750 ℃. This loss of mass can be associated with output of 2 mol of O_2 forming again the (La•Nd)_2O_2S•CeO_2. The transformation of the (La•Nd)_2•O_2S•CeO_2 to (La•Nd)_2O_2SO_4CeO_2 causes an increase in the macropores.