Metal Reclamation from Spent Hydroprocessing Catalysts - Spent Hydroprocessing Catalysts - page 273

Toyabe et al. [621] developed an improved acid (H 2 SO 4 ) leaching process for the complete
extraction and recovery of all components (including Al) of the spent hydroprocessing catalyst
that contained Mo, V, Ni, Co in an alumina carrier. The process included the following steps:
(1) Roasting the waste catalyst at a temperature range of 400 ◦ C to1000 ◦ C to obtain a roasted
product.
(2) Preparing a reduction dissolution by dissolving the roasted product with sulfuric acid in
the presence of a metal (Al) as a dissolution catalyst.
(3) Separating a large part of the aluminum from the reduction dissolution solution and
recovering aluminum as ammonium aluminum sulfate from the solution, optionally after
subjecting the reduction dissolution solution to a treatment of removing iron.
(4) Extracting molybdenum as a molybdate by solvent extraction from the solution after
separating and recovering aluminum from the solution.
(5) Extracting vanadium as a vanadate by solvent extraction from the solution obtained as a
residue after extracting molybdenum.
(6) Recovering nickel and cobalt each as a hydroxide from the extraction residue after
recovering vanadium.
The use of H 2 SO 4 for extraction of metals and Al 2 O 3 present in spent hydroprocessing
catalysts was studied in detail by Inoue et al. [622,623] . The spent catalyst that contained coke,
Co, Mo, V, Ni, and Al 2 O 3 was first decoked and then treated with H 2 SO 4 (63%) and
evaporated to dryness. The evaporated mass containing the metals (Co, Mo, V, Ni, and Al) as
sulfates was dissolved in water. Individual metals, including Al, were then separated from the
solution by solvent extraction using different pH levels [624] . A series of extraction agents,
such as TR-83, PC-88A, Cyanex 272, Lix-63, and SYNEX DN-052, were used. The details of
these studies, as they apply to the separation of metals from solution by solvent extractions, are
given in a later section of this chapter.
In a process developed by the Hall Chemical Co (Ohio), hydrochloric acid was used for
leaching of metals from spent hydrotreating catalysts [625] . The spent catalyst was dissolved
completely in HCl and then molybdenum was precipitated first, as a sulfide, by adding H 2 S.
Next, vanadium was taken out by solvent extraction, reclaimed by adding caustic soda, and
precipitated as vanadium pentoxide. Nickel was removed by solvent extraction, and then
recovered as a sulfate by adding sulfuric acid. Cobalt was salvaged in a similar manner as
nickel.
High recoveries of Mo, Ni, and Al, i.e., 93, 98, and 96%, respectively using H 2 SO 4 were
reported by Siemens et al. [626] . Similarly, high recovery of Mo and Co, such as 92 and 97%,