Environmental Engineering Reference
In-Depth Information
A and X-type zeolites by hydrothermal synthesis using spent FCC catalysts as raw material
has been reported in some recent studies
[562,563]
. The prepared zeolite material (4A type)
exhibited a crystallinity exceeding 90% and had an ion exchange capacity resembling that of
commercial products used for water treatment.
For similar applications in water treatment, spent hydroprocessing catalysts would have to be
used in a non-decoked form to inhibit leaching of metals. However, in combination with
activated sludge unwanted leaching could be minimized. There are also numerous options to
minimize the leachability of the metals from spent hydroprocessing catalysts using various
methods for the metals immobilization. Therefore, the water treatment applications, as a
potential outlet for spent hydroprocessing catalysts, deserve a thorough evaluation.
9.4.3 Other Materials
Although the use of spent hydroprocessing catalyst in cement/concrete production and water
treatment appears to be restricted because of its hazardous nature, there are many other useful
materials such as fused alumina, synthetic aggregates, anorthite glass-ceramics, refractory
cement, and refractory brick, which have been prepared from spent hydroprocessing catalysts.
These materials are listed
Table 9.9 [22]
.
9.4.3.1 Abrasives and Alloys
A process for the preparation of abrasive material from spent hydrotreating catalysts (e.g.
Co-Mo-Al
2
O
3
and Ni-Mo-Al
2
O
3
) was developed by Zeiringer
[564]
. The basic steps
involved in the process are:
(1) Melting the spent catalyst in presence of a reducing agent such as coke or aluminium
metal (powder).
(2) Cooling the melt at a suitable rate to obtain the abrasive material with desired crystallite
size.
(3) Mechanically separating the catalyst metal components (Co-Mo, or Co-Mo-Ni-V)
accumulating as an alloy residue before or after solidification of the abrasive material
containing mainly alumina as corundum crystallites.
The solid product containing alumina as corundum crystallite is an excellent abrasive.
Depending on the type and amount of additives as well as the crystallite size, these abrasives
may be used for various purposes. The catalyst component metals accumulating as an alloy at
the bottom of the melting vessel are separated from the alumina melt before solidification or
permitted to solidify therewith in a block. Depending on the type of the catalyst, the alloy is
comprised primarily of Mo-Co, W, Ni, Mo-Co-Ni-V and various impurities such as sulphur,
carbon, silicon, iron, or titanium. After the alloy has been mechanically separated from the
