Metal Reclamation from Spent Hydroprocessing Catalysts - Spent Hydroprocessing Catalysts - page 267

Table 11.1: Typical compounds recovered from spent hydroprocessing catalysts [From ref. 608 .
Reprinted with permission].

Alumina trihydrate Alumina-silica aggregate

Calcium tungstate Ammonium molybdate

Chromium oxide Ammonium vanadate

Molybdenum oxide Nickel-cobalt concentrate

Molybdenum trisulfide Sodium vanadate

Vanadium hydroxide wet cake Sodium molybdate

Vanadium pentoxide Ferro molybdenum

Ferro vanadium

metals in water may also be enhanced by roasting spent catalysts with compounds containing
alkali metals, such as sodium and potassium. Two-stage processes may employ both leaching
and roasting. The volatilization and/or dissolution of metals of interest can be enhanced by
chlorination. Attempts have been made to develop novel methods which could be competitive
with conventional methods for metal reclamation.

Once in the solution, the metals can be isolated in a pure form using established methods
based on selective precipitation. There have been decades of experience with metals separation
from various solutions using extracting agents of organic origin. In this case, a high selectivity
of extraction can be achieved by merely adjusting the pH of the solution containing an
extracting agent. The structures of several extracting agents which have been used
commercially are shown in Fig. 11.1 [622] .

11.1.1 Leaching Studies

Aqueous solutions of ammonia and ammonium salts, various concentrations of inorganic acids
(e.g., HCl, H 2 SO 4 , and HNO 3 ) and alkalis have been used as leaching solutions. Among
organic agents, water-soluble organic acids have been attracting most of the attention.
Compared with inorganic acids and ammonia salts solutions, aqueous solutions of organic
acids ensure an environment requiring much less safety precautions. A wide range of
microorganisms and fungi have been tested for their suitability and selectivity for bioleaching.

11.1.1.1 Leaching with Ammonia and Ammonium Salt Solutions

Ammonia and ammonium salt solutions have been used by many researchers to extract metals,
such as Mo, V, Co, and Ni, from spent catalysts. In the patented process, Gutinikov [609] used
ammonium carbonate solution for leaching of metals from spent catalysts and recovered more
than 90% of Mo and V, and 60-70% of Ni. A similar process was reported by Millsap and
Reisler [610] for extracting metal values from the spent Ni-Mo/Al 2 O 3 catalyst. The catalyst