Environmental Engineering Reference
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Figure 11.14a: Effect of temperature on molybdenum recovery.
extracted as sodium molybdate. The sodium molybdate solution was treated with HCl to adjust
the pH to 2 and then purified by adsorption on activated charcoal with ammonia and the
solution was heated at 90 C to produce ammonium polymolybdate which on calcination at
450 C produced highly pure (99.9%) MoO 3 . A schematic diagram of the overall process is
shown in Fig. 11.15 [657] .
In another related study published recently by Karr et al. [658] , roasting of spent catalyst with
NaCl was also found to be effective for Mo recovery from a spent hydrorefining catalyst that
contained 21.8 wt.% MoO 3 , 4.97 wt.% NiO, 1.54 wt.% Co 3 O 4 , 60.4 wt.% Al 2 O 3 , and
Figure 11.14b: Effect of soda ash addition on recovery of molybdenum.
 
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