Environmental Engineering Reference
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Figure 11.13: Recovering flow sheet of spent catalyst [From ref. 655 . Reprinted with permission].
precipitation, the sodium aluminate solution was purified and the carbonation decomposition
process was applied to produce Al(OH) 3. The Al(OH) 3 was then calcinated at 1200 Cto
produce
-alumina. The Ni and Co metals were recovered from the residue by leaching with
30% H 2 SO 4 . Recoveries of V, Mo, Ni, and CO were 95.8, 98.9, 98.2, and 98.5%, respectively.
Alumina recovery was 90.6% and the purity of alumina was 99.9%.
Karr et al. [657] conducted a series of experiments to optimize the operating conditions for
maximum recovery of Mo from spent hydrotreating catalysts by soda ash roasting process.
The spent catalyst used in this study contained 21 wt.% MoO 3 , 1.52 wt.% Co 3 O 4 , 0.85 wt.%
NiO, 60.4 wt.% Al 2 O 3 , and 4.67% SiO 2 . The effects of temperature, soda ash (Na 2 CO 3 )
concentration and roasting time on Mo recovery percentage, are shown in Figs 11.14a-c ,
respectively.
Under selected experimental conditions, i.e., roasting of the spent catalyst with 12 wt.% soda
ash at 600 C for 30min followed by leaching of the roasted mass with water, 92% Mo was
 
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