ENVIRONMANTALLY FRIENDLY AND PRODUCTIVE RECLAMATION OF
SCARCE METALS FROM SUPERALLOY SCRAP
Materials Technology
scrap. After that Re was separated from generated cake in a form of
soluble salt by environmentally friendly water leaching. Next
processing of the solution allows extracting Re in a form of
corresponding commercial product (Re2S7, NH4ReO4, LiReO4,
KReO4). The result of the preliminary trial is shown at the
flowchart (Fig. 2). The rest valuable elements (Nickel, Niobium,
Tantalum, Chromium, Molybdenum, Tungsten, Cobalt) are left in
the oxidized form as residue. They should be reclaimed by the
aluminothermic reduction process with liquid start. It has been
proved by us on the titanium containing oxides that this approach
provides high purity of the produced superalloys.
Innovative aspect and main advantages:
The technology anticipates application of the pyrometallurgical
approach that is sufficiently faster than hydrometallurgical one.
None hazardous waste is generated. At the same time the mostly
complete oxidation of Re in the scraps at the elevated temperatures
does not lead to formation of rhenium oxides in non-safety volatile
form. As an accessory advantage the rate of Re reclamation is
increased in terms of absence of non-desirable disorganized
sublimation of Re2O7.
The extraction of Re and the other scarce metals from the
superalloy scraps is environmentally sound ant cost efficient
operation.
be
introduced into the recycling
industry as a technology with
increase productivity. The main
advantage for the superalloy
industry is significant increase
of value of the generated scrap
in terms of Re reclamation.
should
It
Fig. 1. The Re-containing waste material
for
Current situation:
The Ni-base superalloys may contain additionally up to 19
elements that include Chromium, Cobalt, Hafnium, Niobium,
Rhenium, Tantalum, Molybdenum, Tungsten, and Titanium.
The majority of them are among scarce elements. The main
feature of the scarcity is demonstration of the regular great
surges in the metal market prices. The problem is currently so
pressing that a special purpose workshop is taking place at
R’07 World Congress that is the 8th event in the bi-annual
correspondent Congress series. One of its topics is “How can
recycling industry contribute to the prevention of metal
scarcities …â€.
Mostly hydrometallurgical methods are proposed for
extraction of the valuable elements from Ni-base superalloys.
They are based on decomposing of its fines with the acidic
chloride aqueous solutions saturated with chlorine gas or with
leach solutions. The electrochemical
the ammoniacal
methods should be also used
the operation of
decomposing. The decomposing of fines is followed by the
processing operations for extraction of the valuable elements
including Re. It is undoubtedly typical scarce metal with
fluctuant prices. The methods are efficient enough in many
cases. However
for
neutralization of the spent solutions. At the same time a lot of
the residues are generated at the neutralization operation. It is
difficult and expansive to get rid of the residues by their
following disposal, processing or recycling. The great
disadvantage of the above methods is still slow rate of the
decomposing operation although the several approaches for
its facilitation arranging interaction of scrap with Zn were
proposed.
sufficient efforts
requires
Currently there are several technologies in operation for
recycling the less complex Re-containing alloys. The general
pyrometallurgical approach of processing Re-W and Re –Mo
scrap is used at a plant of TOMA Group from Estonia. the
technology is based on calcining of the scrap. The generated
volatile Re2O7 is collected. Finally it is bounded by
ammoniac for production of NH4ReO4. The brief information
indicates that the Heraeus company processes Re-W(Mo)
alloys by salt fusion and Pt/Re spent catalyst by alkaline
pressure or sulfuric acid leach, The final Re powder is
produced by hydrogen
reduction. The correspondent
multistage
complex
reclamation of
including Re from
superalloy scrap is rather slow and very expensive.
the scarce metals
hydrometallurgical
process
the
of
Proposition:
The current proposition is just devoted to developing of a
novel approach in utilization of all scarce elements from the
superalloy scrap that is not directly reused in the new alloy
melts with or without preliminary refinement. The special
emphasis will be paid for Re extraction.
The main idea of the proposed process of Re extraction
from superalloy scrap is arranging the condition when the
metallic Re goes into solute non-volatile state during its
oxidation in a form of salts ReO4-anion without leaving the
reaction zone. So the Re-containing material (Fig. 1) is
processed by an oxidizer at the elevated temperatures. The
binding component is introduced for transferring of Re in
easily soluble non-volatile form. Drying of the product with
following its calcining provides complete oxidation of the
Fig. 2. Flowchart of the original process
Contact details:
Dr. Eugene Zhidkov
Head of Department
Physico-Technological Institute of
Metals and Alloys of NAS of Ukraine
34/1 Vernadsky Ave.Kiev-142, 03680, Ukraine
Phone: +38044- 424-6057
Fax: +38044- 424-1210
E-mail: vlads@visti.com
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