Metal Reclamation from Spent Hydroprocessing Catalysts - Spent Hydroprocessing Catalysts - page 287

11.1.2.1 Roasting with Sodium Salts
Roasting of the spent catalysts with sodium salts (e.g. Na 2 CO 3 , NaCl, NaOH) followed by
leaching and separation of the metals has been reported in a number of studies. A detailed
description of the soda roasting process was presented by Sebenik and Ference [654] at the
ACS conference in 1982. The spent catalyst was first ground to approximately 100mesh and
roasted in air at 600 ◦ C in a rotary kiln or fluid bed calciner to remove carbon and sulfur
deposits. Then, the calcined material was mixed with soda ash (Na 2 CO 3 ) and the mix was
roasted again in air at 750 ◦ C to convert Mo and V oxides to Na 2 MoO 4 and NaVO 3 ,
respectively. The sodium carbonate roaster product was leached with water at 100 ◦ Cina
continuous stirred tank to solubilize Mo and V. Insoluble Co-Ni-Al 2 O 3 residue was readily
separated from the solution containing Na 2 MoO 4 and NaVO 3 by filtration. The
NaMoO 4 -NaVO 3 solution was treated with NH 4 C1 at 80 ◦ C to precipitate NH 4 VO 3 , which
was then filtered, dried and calcined at 500 ◦ CtoV 2 O 5 . The filtrate from the vanadium
precipitation tank was treated with calcium chloride or lime at ambient temperature to recover
the molybdenum as calcium molybdate. Mo and V recoveries ranging between 90 and 95%
were achieved in the process. The Co-Ni-Al 2 O 3 residue was digested with caustic soda in a
stirred pressure autoclave at approximately 250 ◦ C and 500 psi. The sodium aluminate solution
was filtered and then treated with CO 2 to precipitate sodium dawsonite (NaAl(OH) 2 CO 3 )
which could be used as a Bayer alumina feed. The insoluble NiO and CoO present in the
residue were subjected to further processing to recover Ni and Co.
Wang et al. [655] studied recovery of Mo, Co, and alumina from spent CoMo/Al 2 O 3
hydrotreating catalyst using caustic roasting followed by ammonia and acid leaching
treatments. The spent catalyst was first decoked and then roasted with caustic soda. The
roasted material was leached by concentrated ammonia to obtain the solution containing
mainly molybdenum and a solid containing essentially alumina and cobalt. Then, the solution
was treated with nitric acid and concentrated ammonia to obtain highly pure ammonium
molybdate. The residue was dissolved by sulphuric acid, and aluminum sulfate in the solution
was crystallized with ammonium sulfate to form ammonium alum. Cobalt was converted into
a complex ion by excess ammonia and then recovered as highly pure metal cobalt powder by
replacing with zinc powder. The recovery rate for molybdenum, aluminum, and cobalt were
higher than 90, 85, and 90%, respectively.
Chen et al. [656] used alkali (NaOH) roasting for recovering metals from the spent
hydroprocessing catalyst that contained V, Mo, Ni, Co, and Al 2 O 3 . A schematic flow diagram
of the process is shown in Fig. 11.13 . Roasting of spent catalyst with NaOH (mole ratio of
Na 2 O:Al 2 O 3 = 1:2) was carried out at 750 ◦ C for 30min. The roasted product was leached with
water. Vanadium and molybdenum were dissolved in sodium aluminate solution in the
leaching process leaving Ni and Co as residue. Barium hydroxide and barium aluminate were
added to the solution to recover V and Mo, respectively. After the recovery of V and Mo by