Environmental Engineering Reference
In-Depth Information
Figure 11.14c: Effect of roasting time on molybdenum recovery [From ref.
657
. Reprinted with
permission].
5.06 wt.% SiO
2
. A flow diagram of the process is shown in
Fig. 11.16 [658]
. Under optimum
experimental conditions (i.e., roasting temperature at 900
◦
C, 20 wt.% addition of NaCl to the
feed, and a roasting period of 60min), it was possible to extract up to 90% of molybdenum
from the spent catalyst. Recovery of the other metals was not attempted in this study.
Recently, Chen et al.
[659]
investigated extraction of molybdenum and vanadium from a spent
catalyst (main chemical composition: 2.05% Mo, 0.42% V, 62% Al
2
O
3
, and 10.3% SiO
2
)by
roasting the residue with soda carbonate, followed by hydrometallurgical treatment of the
roasted products. In the roasting process, more than 91% of molybdenum and 90% of
vanadium could be extracted when a charge containing a sodium carbonate to spent catalyst
ratio of 0.15 was roasted at 75
◦
C for 45min and the roasted mass was leached with water
(liquid to solid ratio of 2) at 80-90
◦
C for 15min. After the purification of leach liquor, an
extraction solvent consisting of 20 vol.% trialkylamine and 10 vol.% secondary octyl alcohol
dissolved in sulfonated kerosene was used to extract molybdenum and vanadium in leach
liquor, 10 wt.% ammonia water was used as stripping agent. Adding 30 g/L NH
4
NO
3
to the
stripping solution and adjusting the pH to 7-8.5, over 99% of vanadium can be crystallized as
AMV. Over 98% of molybdenum can be crystallized as ammonium polymolybdate when pH
is between 1.5 and 2.5 (pH is adjusted by HNO
3
). AMV and ammonium polymolybdate were
calcinated at 500-550
◦
C, the purity of MoO
3
and V
2
O
5
was 99.08 and 98.06%, respectively.
The overall recoveries of Mo and V were 88.2 and 87.1%, respectively.
An integrated process for the recovery of all components of spent hydroprocessing catalysts
including the alumina as commercially marketable products without leaving any residue
material as solid waste has been reported by Llanos and Derering
[567,660,661]
. In this process
