A sulfidation Process for Recovering Ni from an Acidic Spent Catalyst, and the Chemical Characterization of the Sulfide Precipitates.

This study proposed a sulfidation process as a practical approach for recovering Ni from the acidic spent catalyst. Ni can be obtained by a precipitate as NiS particle by adding Na₂S in the acidic media (pH 3). In the presence of chelate agents, 2,2'-bipyridine (bpy), the percentage value of Ni recovery by a hydroxylation process was only 46%, and the recovery value improved to 88% by the sulfidation. XAFS analyses for the precipitates showed that more than 60% of NiS from chelate-free media was oxidized to NiSO₄; while about 80% of Ni remained as NiS when it was generated in the bpy-containing condition. However, Ni was also bound with bpy in the NiS particle, revealed by FT-IR spectra. From these results,, in the spent catalyst, Ni would be precipitated as an S-Ni-bpy cluster by the sulfidation process. [ABSTRACT FROM AUTHOR]