Metal Reclamation from Spent Hydroprocessing Catalysts - Spent Hydroprocessing Catalysts - page 308

11.3.2 CRI-MET Process
CRI-MET's plant uses a two-stage caustic pressure leaching process to recover metals from
spent hydroprocessing catalysts [688,689] . In this process, spent catalysts are milled in a
solution of sodium aluminate and sodium hydroxide. The resulting slurry is fed into an
autoclave and leached under oxidizing conditions at elevated temperature and pressure to
convert the sulfur to sulfate, oxidize the organic compounds, and dissolve the molybdenum
and vanadium. The autoclaved material is thickened and filtered to separate the liquid from the
solids. The molybdenum from the first stage leach is separated from the vanadium as
molybdenum trisulfide, by H 2 S treatment. The molybdenum trisulfide is then converted to
low-grade molybdenum trioxide, which is then purified and calcined to pure molybdenum
trioxide. The vanadium solution is the feed for the vanadium hydroxide precipitation step with
soda ash. This hydroxide is water washed, dried, and calcined to form a vanadium oxide
product.
The solids from the first leach, containing alumina, cobalt, and nickel, are leached a second
time at high temperature and pressure with a strong caustic to solubilize aluminium. The
nickel-cobalt solids from the second leach are separated, washed, and dried, then shipped to
another plant to be calcined. The calcined nickel-cobalt material is then exported to a
nickel-cobalt refiner [689,690] . Sodium aluminate solution is treated further to produce an
alumina trihydrate product which is sold to producers of aluminium sulfate and sodium
aluminate.
11.3.3 EURECAT Process
Initially, EURECAT was using a combination of hydrometallurgical and pyrometallurgical
steps in its metal reclamation process [252,307,691] . The spent catalyst was heated in an
oxidizing environment to remove coke, part of the sulfur and other hydrocarbon impurities.
The decoked catalyst was then subjected to alkaline leaching with caustic soda. Mo, V and P,
and part of the Al present in the spent catalyst were converted to soluble sodium salts during
this treatment. The Ni, Co, Fe and most of the alumina were not leached out and remain in the
residual solid after filtration. The leaching efficiency was controlled by the parameters, such as
pH, concentration, liquid/solid ratio, residence time, etc. The process was continuous with a
counter current percolation using 12 tanks in series.
The filtrate contained Na salts of molybdate and/or tungstate, vanadate, and impurities, such as
arsenate and phosphate. The filtrate was purified to remove arsenate, and small amount of
aluminate before the separation of Mo and/or W and V. These impurities were removed by
precipitation. The ion exchange was used to separate Mo and V. Vanadyl sulfate and
ammonium molybdate were the final products. The filtrate cake containing between 2 and 4%
of Ni and/or Co was processed by pyrometallurgy to recover Ni and Co. The pyrometallurgical