Environmental Engineering Reference
In-Depth Information
Figure 11.7: Electrolytic recoveries of Mo, Ni and V (a) and potential of cell anode and cathode
versus time (b) [From ref.
629
. Reprinted with permission].
efficiency for leaching all four metals, e.g., 47% V, 59% Mo, 60% Co, and 56% Ni were
leached by 1 wt.% oxalic acid solution. The effect of reagent concentration and other
conditions of leaching were not investigated and optimized in this study.
Marafi et al.
[480,488,490]
used organic acids, such as oxalic acid, citric acid, and tartaric
acid, for selective leaching of metal contaminants, such as V and Ni, present in spent residue
hydroprocessing catalysts. Although the objective of these studies was rejuvenation of catalyst
for reuse, they are briefly summarized here, because of their relevance to metal reclamation.
Decoked (oxidic) and coked (sulfidic) form of the catalysts were used in leaching experiments.
The selectivity for removal of the major metal foulant (V) was higher for the catalyst leached
prior to decoking. However, the addition of an oxidizing agent, such as Fe(NO
3
)
3
, Al(NO
3
),
H
2
O
2
, was found necessary to improve the leaching efficiency of organic acids when the spent
catalyst with coke (i.e. prior to decoking) was used
[475,477,488]
. Vanadium, which is the
