A high temperature process for recycling spent nickel-metal hydride
rechargeable batteries has been recently developed at SINTEF/NTNU. The spent
battery modules were first frozen with liquid nitrogen for the de-activation
and brittle fracture treatment. The broken steel scraps and plastics were
then separated by the mechanical classification and magnetic separation. The
remaining positive and negative electrodes, together with the polymer
separator, were heated to 600-800oC in order to remove the organic components
and further separate the Ni-based negative electrode. XRF analyses indicate
that the heat-treated materials consist mainly of nickel, rare earth and
cobalt oxides. The valuable rare earth oxides were further recovered by the
high-temperature slagging treatment. The waste metallurgical slags, consist
mainly of SiO2 and CaO, were used as the rare earth oxide absorbent. After
the high temperature slagging treatment, over 98% of nickel and cobalt oxides
were reduced to the metal phase; meanwhile almost all rare earth oxides
remain in the molten slags. Furthermore, EPMA and XRF analyses of the slag
samples indicate that the rare earth oxides selectively precipitate in the
forms of solid xSiO2•yCaO•zRe2O3. The matrix of slag phase is Re2O3
deficient, typically being less than 5 wt%. This provides a sound basis to
further develop the high-temperature process of concentrating the Re2O3
oxides in slags.