BACKGROUND
This invention relates to a method for recovering platinum group elements from
an article containing at least one platinum group element.
Modern gas or combustion turbines must satisfy the highest demands with
respect to reliability, weight, power, economy, and operating service life. In the
development of such turbines, the material selection, the search for new suitable
materials, as well as the search for new production methods, among other things, play
an important role in meeting standards and satisfying the demand.
The platinum group metals (PGM) or PGMs (platinum, palladium, rhodium,
iridium, osmium, and ruthenium) are becoming increasingly important to the global
economy. The aviation industry uses precious metals in the manufacture of aircraft
engines. Gold and silver, as well as palladium and platinum, are used in the
manufacture of different types of aircraft engines. Typically, an aircraft engine has up
to 23 parts that contain precious metals. Various aircraft engine parts that use precious
metals include vanes, stators, blades, fuel nozzles, fuel manifolds, tobi ducts, and heat
exchangers. Whereas parts of an aircraft's engine turbine system and avionics system
use gold and silver, the aircraft blades use platinum. This invention relates to the
recovery of platinum from used aviation components.
2
•
After the life of an aircraft engine is over, the aviation industry can still recover
precious metal from aircraft engines and their parts. Until recently, platinum group
metals (PGM) were recovered by classical precipitation procedures, which involved
many repeated precipitation/redissolution stages in order to obtain metal of the desired
purity. These processes are extremely tedious and time-consuming, with metal being
tied-up in process often for many months.
Yet, recovery of precious metals can account for up to 50 percent of an aircraft
engine's recycling value. As such, there is a need for new and improved methods for
recovering platinum group elements from an article containing at least one platinum
group element, including for example new and improved methods for recovering
platinum from engine turbine blades.
SUMMARY
Aspects of the present disclosure provide for the recovery of platinum from gas
turbine engine components that are being discarded or in conjunction with the removal
ofplatinum-containing coatings therefrom during repair and reworking.
One aspect of the present disclosure is a method for recovering platinum from an
gas engine component, comprising: contacting the engine component with a chemical
comprising an acid; stripping the engine component, wherein said stripping comprises
removing the thermal barrier control and platinum aluminide from the engine
component; dissolving soluble metals out of the engine component; separating the
thermal barrier control, platinum aluminide and soluble metals from the engine
3
•
component; revealing a platinum-rich layer as part of the engine component;
mechanically separating the platinum-rich layer from the engine component;
centrifuging the platinum-rich layer; and recovering the platinum from the gas engine
component.
In another aspect, the present disclosure is a method for recovering platinum
from a gas engine component, comprising: contacting the engine component with a
chemical comprising an acid; dissolving at least a portion of a thermal barrier coating
and platinum aluminide on said engine component to expose a platinum rich layer;
separating the platinum-containing layer from the thermal barrier coating and platinum
aluminide; mechanically removing the platinum-containing layer from the engine
component; and recovering the platinum from the platinum-containing layer by
centrifugation.
In one embodiment, the gas engine component is a turbine blade. The
separating the platinum-rich layer step or mechanically removing step can be
accomplished by high ultrasonic treatment of the component, tumbling of the
component, vibratory finishing of the component, dry ice blasting of the component, or
a combination thereof. In one example, the separating the platinum.-rich layer step or
mechanically removing step is selected from the group consisting of hand brushing,
high pressure water blasting, ultrasonic cleaning, tumbling, vibratory finishing, or a
combination thereof. In another embodiment, the component is first treated in a
ultrasonic bath and subsequently the component undergoes a tumbling step, vibratory
finishing, or a combination thereof. This sequential approach can effectively remove
any residual platinum.
4
In one embodiment, the separating the platinum-rich layer step or
mechanically removing step is accomplished by high ultrasonic treatment of the
component for a period of at least 3 hours. In another embodiment, the separating the
platinum-rich layer step or mechanically removing step is accomplished by treatment of
the component in an ultrasonic environment, and wherein the platinum-rich layer is
dislodged from the component and a slurry is formed comprising the platinum-rich
residue in water.
In one embodiment, the separating the platinum-rich layer step or
mechanically removing step is accomplished by tumbling treatment of the component
for a period of at least 45 minutes. In another embodiment, the separating the
platinum-rich layer step or mechanically removing step is accomplished by treatment of
the component in a tumbling environment, and wherein the platinum-rich layer is
dislodged from the component and a slurry is formed comprising the platinum-rich
residue in water.
In one aspect, the present disclosure is a method for recovering platinum
from a turbine blade, comprising: dipping the turbine blade into a chemical comprising
an acid; dissolving at least 50% of a thermal barrier coating or platinum aluminide on
said turbine blade; exposing a platinum rich layer on said turbine blade; mechanically
separating the platinum-rich layer from the turbine blade; and recovering the platinum
from the platinum-rich layer by centrifugation.
These and other aspects, features, and advantages of this disclosure will
become apparent from the following detailed description of the various aspects of the
5
disclosure taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE FIGURES
The subject matter, which is regarded as the invention, is particularly
pointed out and distinctly claimed in the claims at the conclusion of the specification.
The foregoing and other features and advantages of the disclosure will be readily
understood from the following detailed description of aspects of the invention taken in
conjunction with the accompanying drawings.
Figure I shows a table, indicating the amount of platinum-rich smut
removed from a turbine blade stripped using GRC chemistry.
Figure 2 shows a graphic of one aspect of the platinum recovery process.
Figure 3a and 3b recite the steps for recovering platinum from an gas
engine component, and Figure 3c recites the steps for recovering platinum from a
turbine blade.
DETAILED DESCRIPTION
In an aircraft gas turbine (jet) engine, air is drawn into the front of the
engine, compressed by a shaft-mounted compressor, and mixed with fuel. The mixture
is combusted, and the resulting hot combustion gases are passed through a turbine
mounted on the same shaft. The flow of gas turns the turbine by contacting an airfoil
portion of the turbine blade, which turns the shaft and provides power to the
6
compressor. The hot exhaust gases flow from the back of the engine, driving it and the
aircraft forwardly.
During operation of gas turbine engines, the temperatures of combustion
gases may exceed 3,000° F, considerably higher than the melting temperatures of the
metal parts of the engine, which are in contact with these gases. The metal parts that
are particularly subject to high temperatures, and thus require particular attention with
respect to cooling, are the hot section components exposed to the combustion gases,
such as blades and vanes used to direct the flow of the hot gases, as well as other
components such as shrouds and combustors.
The hotter the turbine gases, the more efficient is the operation of the jet
engine. There is thus an incentive to raise the turbine operating temperature. However,
the maximum temperature of the turbine gases is normally limited by the materials used
to fabricate the turbine vanes and turbine blades of the turbine. Many approaches have
been used to increase the operating temperature limits and operating lives of the airfoils
of the turbine blades and vanes.
The metal temperatures can be maintained below melting levels with
current cooling techniques by using a combination of improved cooling designs and
thermal barrier coatings. In one approach, a protective layer is applied to the airfoil of
the turbine blade or turbine vane component, which acts as a substrate. Among the
currently known diffusional protective layers are aluminide and platinum aluminide
layers. The protective layer protects the substrate against environmental damage from
the hot, highly corrosive combustion gases. This protective layer, with no overlying
7
ceramic layer, is useful in intennediate-temperature applications. For higher
temperature applications, a ceramic thennal barrier coating layer may be applied
overlying the protective layer, to fonn a thennal barrier coating (TBC) system.
Thennal barrier coatings (TBCs) are well-known ceramic coatings, for
example, yttrium stabilized zirconia. Ceramic thennal barrier coatings usually do not
adhere optimally directly to the superalloys used in the substrates. Therefore, an
additional metallic layer called a bond coat is placed for example, by chemical vapor
deposition (CVD), between the substrate and the TBC to improve adhesion of the TBC
to the underlying component. In one fonn, the bond coat is made of a diffusion nickel
aluminide or platinum aluminide, whose surface oxidizes to fonn a protective
aluminum oxide scale in addition to improving adherence of the ceramic TBC.
Even with the use of these protective techniques, there remain problems
to overcome in extending the operating service temperatures and operating lives of the
turbine blade components. There is a large cost to replacing these turbine blade
components, especially because of the expensive components used to manufacture such
components. As a result, it is beneficial to extract particular needed components from
used parts for future use in the manufacture of new parts. For example, platinum group
metals (PGM) are often employed in the aviation industry. Because platinum group
metals are relatively expensive and are often obtained from sources outside the United
States, it is advantageous to recover platinum group metals from parts used in airplanes.
Many advanced gas turbine engine components, especially turbine
blades, are coated with platinum modified diffusion aluminide coatings (PtAl). These
8
coatings offer superior environmental protection in oxidation and Type I hot corrosion
conditions within a turbine engine. As outlined above, these coatings are also
employed as bond coatings beneath physically vapor deposited (PVD) thermal barrier
coatings.
The Pt present in PtAl coatings is most often deposited by electroplating.
To develop the required PtAl chemistry and structure, about 0.5-0.8 grams of Pt are
electroplated onto relatively smaller turbine blades, while up to on the order of 1.5
grams of Pt may be electroplated onto larger blades. After plating, the Pt is
incorporated into the coating by diffusion, with the final composition of the
predominant coating phase being (Ni,Pt)Al.
A PtAl coating may be removed from a blade if the coating itself or
some other feature of the blade does not meet the engineering or quality requirements
for the part. In such a case, the coating is stripped, the part reworked and then recoated
with PtAl. Turbine blades are also stripped of PtAI coatings after engine operation to
enable inspection and repair of the turbine blades.
Stripping of PtAl coatings is accomplished in a variety of manners.
Stripping of PtAl coatings can be accomplished by acid stripping using mineral acids
such as hydrochloric, phosphoric, nitric, and mixtures of these acids. The acids react
with the coating and dissolve some of the coating constituents, especially Ni. After the
reaction, a thin, loosely adherent, black film residue comprising Pt, aluminum oxides
and heavy metal oxides of various elements from the substrate material is left behind on
the blade. After stripping a number of parts, the stripping solutions become ineffective
9
and are discarded. Most often the acids are neutralized, the metals chemically
precipitated out, and the precipitate filtered from the solution. The precipitate, although
it contains minor amounts of Pt, is disposed of as solid waste.
The platinum rich residue was removed from stripped turbine blades by
mechanical methods such as ultrasonic treatment or vibratory finishing. Traditionally a
"cutting" type media has been used in vibratory finishing machines to remove residue.
Cutting media consist of abrasive aluminum oxide particles in a soft binder. The binder
breaks down, releasing aluminum oxide particles into the vibratory finish machine.
Large volumes of sludge are produced. The residue is thus contaminated and diluted
by the abrasive media as it breaks down, such that the Pt is no longer economically
recoverable. Overflow from wet blast or vibratory finishing machines used to clean
blades is treated in a wastewater system, and the solids, although they contain Pt, are
disposed of as waste.
One aspect of the present disclosure is a method for recovering platinum
from a gas engine component, comprising: contacting the engine component with a
chemical comprising an acid; stripping the engine component, wherein said stripping
comprises removing the thermal barrier control and platinum aluminide from the
engine component; dissolving soluble metals out of the engine component; separating
the thermal barrier control, platinum a1uminide and soluble metals from the engine
component; revealing a platinum-rich layer as part of the engine component;
mechanically separating the platinum-rich layer from the engine component;
centrifuging the platinum-rich layer; and recovering the platinum from the gas engine
component.
10
The gas engine component can be a turbine blade. The separating the
platinum-rich layer step or mechanically removing step can be accomplished by high
ultrasonic treatment of the component, tumbling of the component, vibratory finishing
of the component, dry ice blasting of the component, or a combination thereof. In one
example, the separating the platinum-rich layer step or mechanically removing step is
selected from the group consisting of hand brushing, high pressure water blasting,
ultrasonic cleaning, tumbling, vibratory finishing, or a combination thereof. In another
embodiment, the component is first treated in a ultrasonic bath and subsequently the
component undergoes a tumbling step, vibratory finishing, or a combination thereof.
This sequential approach can effectively remove any residual platinum.
The high ultrasonic treatment of the component can be for a period of at
least 3 hours. In one embodiment, the ultrasonic treatment of the component is for a
period of between 3 hours to 8 hours. In another embodiment, the ultrasonic treatment
of the component is for about 12 hours. In another embodiment, the separating the
platinum-rich layer step or mechanically removing step is accomplished by treatment of
the component in an ultrasonic environment, and wherein the platinum-rich layer is
dislodged from the component and a slurry is formed comprising the platinum-rich
residue in water.
The tumbling treatment of the component can be for a period of at least
45 minutes. In one embodiment, the tumbling treatment is for a period between 30
minutes and 300 minutes. In one embodiment, the tumbling treatment is for a period
between 60 minutes and 180 minutes. In another embodiment, the tumbling treatment
is for about 120 minutes. In one embodiment, the separating the platinum-rich layer
11
step or mechanically removing step is accomplished by treatment of the component in a
tumbling environment, and wherein the platinum-rich layer is dislodged from the
component and a slurry is formed comprising the platinum-rich residue in water.
A PtAI coating may be removed from a blade if the coating itself or
some other feature of the blade does not meet the engineering or quality requirements
for the part. In such a case, the coating is stripped, the part reworked and then recoated
with PtAI. Turbine blades are also routinely stripped of PtAI coatings after engine
operation to enable inspection and repair of the turbine blades.
In situations where PtAI coatings are removed mechanically by abrasive
grit blasting, rather than chemically, Pt-bearing debris from grit blasting is filtered from
the process air and is disposed of as solid waste. By one of the above processes, the Pt
from the PtAl stripping operation finds its way into the final waste stream of a turbine
blade repair plant. Many high volume operations feed into the final waste stream in a
manufacturing plant and dilute the concentration of Pt in the solid waste to the point
where it is not economically viable to recover the precious metal.
In certain embodiments, the PtAI bondcoat is removed from the turbine
blade by means of a chemical stripping process. This process dissolves aluminum and
other metals from the PtAl coating, leaving behind a platinum-rich smut. In one
embodiment, the disclosure describes a new and improved method for mechanically
removing this smut, including ultrasonics, vibrations, and dry-ice blasting, and
recovering the smut quantitatively by means of centrifugation. The presently disclosed
method is also applicable to end-of-life parts.
12
In one aspect, the present disclosure is a method for recovering platinum
from a gas engine component, comprising: contacting the engine component with a
chemical comprising an acid; dissolving at least a portion of a thermal barrier coating
and platinum aluminide on said engine component to expose a platinum rich layer;
separating the platinum-containing layer from the thermal barrier coating and platinum
aluminide; mechanically removing the platinum-containing layer from the engine
component; and recovering the platinum from the platinum-containing layer by
centrifugation.
In one embodiment, different chemicals are used for leaching aluminum.
In another embodiment, different methods are used for mechanically removing the smut
and/or recovering the fine powdered platinum-rich smut. Prior to the teachings of the
present disclosure, removal of the platinum-rich smut was carried out by means of
aluminum oxide grit blasting to provide a clean airfoil surface. In this process the
platinum was incorporated into the spent grit blasting material and significantly diluted.
This spent grit was then classified as hazardous waste and had to be disposed of
accordingly at great expense.
Applicants have identified a chemical stripping process to leach out the
soluble metals (primarily aluminum) while leaving behind a platinum-rich "smut."
Further, Applicants' disclosure teaches a new and improved method by which this
platinum-rich smut can be removed without contamination of the smut by foreign
materials. In one embodiment, a vibratory tumbler with ceramic media and water
results in complete, satisfactory removal of the smut and the formation of a fine
suspension of platinum smut in water. This water is then introduced into a continuous
13
high speed centrifuge (CEPA) which separates the smut from the water to provide a
product that is >45 wfIlo platinum. In one embodiment, the disclosed process allows for
the recovery ofthe platinum from the coatings quantitatively.
Prior attempts to recover platinum have involved dissolving the
platinum in very strong acids, then neutralizing the acid to precipitate platinum salts,
which were highly contaminated; this process is not particularly viable for commercial
use. In contrast, in one aspect, the present disclosure is a method for recovering
platinum from a turbine blade, comprising: dipping the turbine blade into a chemical
comprising an acid; dissolving at least 50% of a thermal barrier coating or platinum
aluminide on said turbine blade; exposing a platinum rich layer on said turbine blade;
mechanically separating the platinum-rich layer from the turbine blade; and recovering
the platinum from the platinum-rich layer by centrifugation. U.S. Patent Numbers
6,494,960, 5,976,265, and 5,486,135 and application numbers 2003/005020,
2002/010309, and 2002/0072306 provide additional alternatives and are incorporated
herein.
In one embodiment, the disclosure is directed to mechanical removal of
platinum-rich smut from airfoils that have been treated using chemical stripping
methods. Applicants teach that these mechanical methods include an ultrasonic bath,
tumbling with media, vibratory finishing, water jets, brushes, compressed air, dry-ice
blasting and the like. In another embodiment, the present disclosure is directed to
recovery of the fine platinum power by filtration, centrifugation, settling, decanting, or
a combination thereof.
14
The advantages of the present disclosure include the reduced loss of
valuable platinum metal and the avoidance of the cost of disposal of used grit blasting
media that is contaminated with platinum and other metals. In addition, in order to
practice the present disclosure, in one embodiment, conventional chemical stripping
processes already in place and approved by the FAA can be used. Moreover, as
mentioned supra, by practicing the presently disclosed method, the cost of disposal of
spent grit blast media as hazardous waste is avoided and valuable platinum metal is
recovered and can be recycled.
Grit blasting is a common method to clean dirt and remove coatings.
Unfortunately, grit blasting does not clean dirty or blocked internal passageways. Grit
blasting can damage the base alloy thereby thinning airfoil walls. Chemical solutions
are used for cleaning dirt and stripping coatings from gas turbine components.
A first class of stripping compositions (composition (i)) comprises
aliphatic or aromatic sulfonic acids. Examples of suitable aliphatic sulfonic acids are
methanesulfonic acid (MSA) and ethanesulfonic acid, with methanesulfonic acid being
preferred. Illustrative aromatic sulfonic acids are benzene sulfonic acid, toluene
sulfonic acid, and naphthalene sulfonic acid. In a particular embodiment, stripping of
the turbine blade is performed by using a composition comprising an aliphatic sulfonic
acid such as MSA, ethanesulfonic acid, methanesulfonic acid, or a combination thereof.
A second class of stripping compositions (i.e., composition (ii)) includes
a solution of an inorganic acid and an organic solvent. Examples of the inorganic acid
for this class of compositions are hydrochloric acid, nitric acid, and perchloric acid.
15
In certain embodiments, the solvent is one which reduces the activity
and increases the wetting capability of the inorganic acid relative to the substrate. (The
chemical interaction between an acid and a hydrocarbon solvent will often differ from
the interaction between the acid and a solvent like water). It has been found that the
combination of the inorganic acid and the organic solvent removes substantially all of
the aluminide coating material without adversely affecting the substrate.
Examples of organic solvents for use in combination with the inorganic
acid include aliphatic alcohols, aromatic alcohols, chlorinated alcohols, ketones, nitrilebased
solvents, nitrated hydrocarbon solvents, nitrated aromatic solvents such as
nitrobenzene; chlorinated hydrocarbons, amines, and mixtures of any of the foregoing.
Several specific examples of the aliphatic alcohols are methanol, ethanol, and
isopropanol. Mixtures of alcohols may be used as well. Specific examples of the
aromatic alcohols are phenols and substituted phenols.
A third stripping composition for this invention (composition (iii))
comprises sulfuric acid or an aqueous solution of sulfuric acid. For the aqueous
solution, the ratio of acid to water is usually in the range of about 10:90 to about 65:35.
In certain embodiments, the ratio is in the range of about 15:85 to about 40:0.
Moreover, a wetting agent is usually used in this type of stripping composition, as
described below.
For end use applications in which minimal pitting of the substrate if any
is preferred, a different stripping composition could be employed. For example,
methanesulfonic acid is effective at removing aluminide material from the substrate,
16
although the rate of removal is not as high as in the case of ReI-alcohol. A distinct
advantage of methanesulfonic acid is that it does not adversely affect the substrate to
any substantial degree, beyond uniform corrosion. As used herein, "uniform corrosion"
refers to the removal of a thin layer of the substrate - usually less than about 2 microns
in thickness.
In some embodiments, the stripping composition further includes a
wetting agent. The wetting agent reduces the surface tension of the composition,
permitting better contact with the substrate and the aluminide-based coating.
Illustrative wetting agents are polyalkylene glycols, glycerol, fatty acids, soaps,
emulsifiers, and surfactants. The wetting agent is usually present at a level in the range
of about 0.1% by weight to about 5% by weight, based on the total weight of the
composition.
Other additives are sometimes used in the stripping composition. For
example, inhibitors are sometimes employed to lower the proton concentration, and
thereby lower the activity of the acid in the composition. The lowered activity in tum
decreases the potential for pitting of the substrate surface. An exemplary inhibitor is a
solution of sodium sulfate in sulfuric acid, or a solution of sodium chloride in
hydrochloric acid. The level of inhibitor used is usually about 1% by weight to about
15% by weight, based on the weight of the entire stripping composition. Moreover,
oxidizing agents are sometimes used in the stripping composition to prevent the
formation of a reducing environment. Examples include peroxides (e.g., hydrogen
peroxide), chlorates, perchlorates, nitrates, permanganates, chromates, and osmates
(e.g., osmium tetroxide). The level of oxidizing agent used is usually about 0.01% by
17
weight to about 5% by weight, based on the weight of the entire stripping composition.
In one embodiment, the oxidizing agent is used with acids that are reducing agents, e.g.
hydrochloric acid.
The particular stripping composition may be applied to the substrate in a
variety of ways. For example, it can be brushed or sprayed onto the surface. Very
often, immersion of the substrate in a bath of the stripping composition is the most
practical technique. The bath can be maintained at a temperature below about 1700 F.
(770 C.) while the substrate is immersed therein. In a particular embodiment, the bath
is maintained at a temperature below about 1300 F. (540 C.). The process could be
carried out at room temperature, although a higher temperature range would usually be
maintained to ensure process consistency if the room temperature is variable. Higher
temperatures (within the boundaries set forth above) sometimes result in more rapid
removal of the aluminide coating.
The baths containing the stripping compositions are often stirred or
otherwise agitated while the process is carried out, to permit maximum contact between
the stripping agent and the coating being removed. A variety of known techniques
could be used for this purpose, such as the use of impellers, ultrasonic agitation,
magnetic agitation, gas bubbling, or circulation-pumping. Immersion time in the bath
will vary, based on many of the factors discussed above. On a commercial scale, the
immersion time will usually range from about 15 minutes to about 400 minutes. In
some embodiments, the immersion time will be a period less than about 150 minutes.
In particular embodiments, the immersion time will be a period less than about 75
minutes. Exposure to the stripping composition causes the aluminide coating on the
18
surface of the substrate to become degraded.
In some embodiments of the present disclosure, the substrate surface is
contacted with two stripping compositions, in sequence. The first composition is one
which very quickly begins to remove the aluminide materials. A specific example is
the mixture of the inorganic acid and the solvent which reduces the activity of the
inorganic acid relative to the substrate, as described previously. Illustrative
compositions of this type are hydrochloric acid with an alcohol such as ethanol; and
sulfuric acid with water.
The second stripping composition is one which is capable of removing
the aluminide material more slowly, and with no pitting or attack on the substrate,
except for the possible occurrence of uniform corrosion, as discussed previously. One
example is the stripping composition based on an alkane sulfonic acid, such as
methanesulfonic acid.
Typically, each stripping composition is used in the form of a bath in
which the substrate can be immersed. Contact times and bath temperatures will vary,
based on many of the factors described previously, e.g., type and amount of aluminide
material requiring removal. Usually, the first bath will be maintained at a temperature
in the range of about 0° C. to about 40° C., with an immersion time between about 5
minutes and about 30 minutes. The second bath will typically be maintained at a
temperature in the range of about 40° C. to about 60° C., with an immersion time
between about 30 minutes and about 300 minutes. As in previous embodiments, the
surface can then be subjected to a gentle abrasion step (or similar technique) to remove
19
the degraded coating, e.g., by light grit-blasting.
The present disclosure relates generally to platinum recovery and
methods for recovering platinum from aviation components, including engine
turbine blades.
EXAMPLES
The disclosure, having been generally described, may be more readily
understood by reference to the following examples, which are included merely for
purposes of illustration of certain aspects and embodiments of the present disclosure,
and are not intended to limit the disclosure in any way.
Figure I is a table, showing platinum-rich smut removed from a turbine
blade stripped using GRC chemistry. The CFM56-7 blade was stripped using GRC
chemistry, the smut was removed in an ultrasonic bath, and filtered through Whatman
#4 fluted filter. The isolated yield was 1.5g.
Figure 2 shows a graphic of one aspect ofthe platinum recovery process.
As shown in Figure 3a, the method for recovering platinum from an gas
engine component, comprises contacting the engine component with a chemical
comprising an acid (305). The engine component is stripped, removing the thermal
barrier control and platinum alurninide from the component (310). Having dissolved
the soluble metals out of the engine component (315), the thermal barrier control,
platinum aluminide and soluble metals are separated from the engine component (320),
20
revealing a platinum-rich layer as part of the engine component (325). The platinumrich
layer is then mechanically separated from the engine component (330), centrifuged
(335) and the platinum is recovered from the engine component (340).
In another example, shown in Figure 3b, the method for recovering
platinum from a gas engine component, comprises contacting the engine component
with a chemical comprising an acid (350). At least a portion of a thermal barrier
coating and platinum aluminide that is on said engine component is dissolved to expose
a platinum rich layer (355). This platinum-rich layer is separated from the thermal
barrier coating and platinum aluminide (360). Having mechanically removed the
platinum-rich layer from the engine component (365), the platinum is recovered from
the platinum-rich layer by spinning down the slurry (370).
In another embodiment, shown in Figure 3c, the method for recovering
platinum from a turbine blade comprises dipping the turbine blade into a chemical
comprising an acid (375), and dissolving at least 50% of a thermal barrier coating or
platinum aluminide that is on the turbine blade (380). Once the platinum-rich layer is
exposed on the turbine blade (385), it is then mechanically separated from the turbine
blade (390), and the platinum-rich layer is recovered by centrifuging the slurry
containing the platinum-rich layer (395).
In a first example, lab-scale experiments were conducted to
determine whether platinum could be recovered in the form of "smut" that
remains on stripped blades after PtAI-coated airfoils have been run through the
chemical stripping process. Applicants conceived that platinum can be recoverable
21
after this stripping step because the stripping chemicals function by dissolving
aluminum from the PtAI, leaving behind a loosely-adherent platinum "smut."
Individual blades were stripped in the laboratory using two different
stripping chemistries, one of which being using the MSA. The stripped blades
were then desmutted in a lab-scale ultrasonic bath and the resultant suspension was
filtered via gravity through filter paper. A CFM56-7 stage 1 blade afforded 1.5 g
of recovered material that was submitted for ICP analysis. CFM56-7 blades were
used because they are representative of a type of blade that has PtAI coating and are
commonly repaired. The results of this analysis are shown in Figure 1 and indicate
that the smut consisted of 47-49% platinum.
A 5 g sample of this material was analyzed and found that the
material contained ">40%" platinum, far exceeding the 25% limit for customers'
favorable processing costs.
A full-scale study on a set of 24 blades was conducted. The
turbine blades were stripped using the conventional MSA stripping bath.
Subsequently, two different methods of platinum rich smut removal were
performed in place of grit blasting: an ultrasonic bath and tumbling (see Figure 2).
Although it appears that tumbling or vibratory finishing provide
more complete removal of smut, the method suffers from the drawback that the
recovered smut is contaminated (>80%) with ceramic particulate caused by
abrasion of the ceramic tumbling media. The smut recovered from the ultrasonic
22
desmutting operation was uncontaminated by tumbling media.
Thus, not all methods for desmutting the turbine blades provide
similar results. Applicants have discovered, in part, that there is an advantage to
using ultrasonic desmutting as compared to other removal methods. Further,
Applicants discovered that more vigorous ultrasonic desmutting provides for
better platinum recovery and in a shorter period of time. A variety of methods for
smut removal are available. Ultrasonic bath, tumbling and vibratory finishing all can
be used, either alone or in combination. If tumbling or vibratory finishing are used, the
resultant product can be contaminated with ceramic media material that is abraded
away during the process. The method selected is dependent upon the purity
requirements of the subsequent purification steps. Ultrasonic baths typically produce
the purest product, but some residual platinum may adhere to the airfoils. This residual
platinum can be effectively removed in a subsequent tumbling or vibratory finishing
step.
In a second experiment, modifications to the configuration of the
ultrasonic bath were made to enhance smut removal. This resulted in ca. 80%
removal of smut (based upon visual estimation). The ultrasonic bath used for Pt
smut removal was one of a variety of commercially-available ultrasonic baths using a
varying, sweeping frequency. Higher ultrasonic bath energy and a higher bath volume
to part surface area ratio results in shorter cycle times; lower bath energy with a lower
bath volume to part surface area ratio requires longer cycle times. Desmutting cycles
can range from a few minutes to 45 minutes, depending on bath volume, number of
parts and ultrasonic energy. The resultant suspension was filtered via gravity using a
23
fluted Whatman filter paper of medium porosity. Higher porosity (faster) results in
shorter cycle and lower yield, while lower porosity (slower) results in higher yield and
longer cycle time.
Closer examination of the filtration recovery method revealed that the
smut became embedded in the bag, making ultimate recovery challenging. As a
result, Applicants identified alternative methods to recover fine particulates
dispersed in a relatively large volume of liquid. Applicants identified a method
that provides smut free of contamination. This method employs the CEPA highspeed
continuous centrifuge, providing quantitative recovery of platinum smut that
is ca. 50% platinum by weight.
Applicants also considered alternatives to ultrasonic desmutting
followed by continuous centrifuging. In one embodiment, Applicants identified
dry-ice blasting as an alternative. Dry-ice blasting is a process whereby dry-ice (solid
carbon dioxide) is ejected at high velocity from a nozzle and used to remove the smut
from the blades. A wide range of velocities, particle sizes and particle velocities may
be used. In general, a higher energy particle can more effectively remove smut, but at
higher cost. The advantage of this method is that it might be possible to
combine the smut removal and recovery processes. This method may require the
design and construction of a dry-ice blasting booth that would be connected to a
dust collector that would trap the smut that was removed. Applicants have
established that either method of recovery (ultrasonic desmutting followed by
continuous centrifugation or dry-ice blasting with dust collection) would efficiently
remove platinum smut.
24
•
The advantages of the presently taught disclosure is that it provides
for improved methods for recovering the value of the recovered platinum, 0.5 - 1.5
g Ptlblade (depending on engine). Platinum spot price is approximately $1600/oz;
value per blade is therefore about $25 - $100. Since the present assignee produces
tens of thousands of blades per, there is a significant value in the present discovery
of new and improved processes for the recovery of platinum from used aviation
parts, including engine turbine blades.
It is to be understood that the above description is intended to be
illustrative, and not restrictive. For example, the above-described embodiments (and/or
aspects thereof) may be used in combination with each other. In addition, many
modifications may be made to adapt a particular situation or material to the teachings of
the various embodiments without departing from their scope. While the dimensions
and types of materials described herein are intended to define the parameters of the
various embodiments, they are by no means limiting and are merely exemplary. Many
other embodiments will be apparent to those of skill in the art upon reviewing the
above description. The scope of the various embodiments should, therefore, be
determined with reference to the appended claims, along with the full scope of
equivalents to which such claims are entitled. In the appended claims, the terms
"including" and "in which" are used as the plain-English equivalents of the respective
terms "comprising" and "wherein." Moreover, in the following claims, the terms
"first," "second," and "third," etc. are used merely as labels, and are not intended to
impose numerical requirements on their objects. Further, the limitations of the
following claims are not written in means-plus-function format and are not intended to
25
be interpreted based on 35 U.S.C. § 112, sixth paragraph, unless and until such claim
limitations expressly use the phrase "means for" followed by a statement of function
void of further structure. It is to be understood that not necessarily all such objects or
advantages described above may be achieved in accordance with any particular
embodiment. Thus, for example, those skilled in the art will recognize that the systems
and techniques described herein may be embodied or carried out in a manner that
achieves or optimizes one advantage or group of advantages as taught herein without
necessarily achieving other objects or advantages as may be taught or suggested herein.
All publications, patents, and patent applications mentioned herein are
hereby incorporated by reference in their entirety as if each individual publication or
patent was specifically and individually indicated to be incorporated by reference. In
case of conflict, the present application, including any definitions herein, will control.
While the invention has been described in detail in connection with only a limited
number of embodiments, it should be readily understood that the invention is not
limited to such disclosed embodiments. Rather, the invention can be modified to
incorporate any number of variations, alterations, substitutions or equivalent
arrangements not heretofore described, but which are commensurate with the spirit and
scope of the invention. Additionally, while various embodiments of the invention have
been described, it is to be understood that aspects of the disclosure may include only
some of the described embodiments. Accordingly, the invention is not to be seen as
limited by the foregoing description, but is only limited by the scope of the appended
claims.
This written description uses examples to disclose the invention,
26
including the best mode, and also to enable any person skilled in the art to practice the
invention, including making and using any devices or systems and performing any
incorporated methods. The patentable scope of the invention is defined by the claims,
and may include other examples that occur to those skilled in the art. Such other
examples are intended to be within the scope of the claims if they have structural
elements that do not differ from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from the literal language of
the claims.
* * * * *

WECLAIM:
1. A method for recovering platinum from an gas engine component, said method
comprising:
contacting the engine component with a chemical comprising an acid;
stripping the engine component, wherein said stripping comprises removing the
thermal barrier control and platinum aluminide from the engine component;
dissolving soluble metals out of the engine component;
separating the thermal barrier control, platinum aluminide and soluble metals
from the engine component;
revealing a platinum-rich layer as part of the engine component;
mechanically separating the platinum-rich layer from the engine component;
centrifuging the platinum-rich layer; and
recovering the platinum from the gas engine component.
2. The method of claim 1, wherein said gas engine component is a turbine blade.
3. The method of claim I, wherein the separating the platinum-rich layer step is
accomplished by high ultrasonic treatment of the component, tumbling of the
component, dry ice blasting of the component, or a combination thereof.
4. The method of claim I, wherein the separating the platinum-rich layer step is
selected from the group consisting of hand brushing, high pressure water blasting,
ultrasonic cleaning, vibratory finishing, or a combination thereof.
5. The method of claim I, wherein the separating the platinum-rich layer step is
28
accomplished by high ultrasonic treatment of the component for a period of at least 3
hours.
6. The method of claim 1, wherein the separating the platinum-rich layer step is
accomplished by treatment of the component in an ultrasonic environment, and wherein
the platinum-rich layer is dislodged from the component and a slurry is formed
comprising the platinum-rich residue.
7. The method of claim I, wherein the separating the platinum-rich layer step is
accomplished by tumbling treatment of the component for a period of at least 45
minutes.
8. The method of claim 1, wherein the separating the platinum-rich layer step is
accomplished by treatment of the component in a tumbling environment, and wherein
the platinum-rich layer is dislodged from the component and a slurry is formed
comprising the platinum-rich residue.
9. A method for recovering platinum from a gas engine component, said method
comprising:
contacting the engine component with a chemical comprising an acid;
dissolving at least a portion of a thermal barrier coating and platinum aluminide
on said engine component to expose a platinum rich layer;
separating the platinum-containing layer from the thermal barrier coating and
platinum aluminide;
mechanically removing the platinum-containing layer from the engine
29
component; and
recovering the platinum from the platinum-containing layer by centrifugation.
10. The method of claim 9, wherein said gas engine component is a turbine blade.
11. The method of claim 9, wherein the mechanically removing step IS
accomplished by high ultrasonic treatment of the component, tumbling of the
component, dry ice blasting of the component, or a combination thereof.
12. The method of claim 9, wherein the mechanically removing step is selected
from the group consisting of hand brushing, high pressure water blasting, ultrasonic
cleaning, vibratory finishing, or a combination thereof.
13. The method of claim 9, wherein the mechanically removing step is
accomplished by high ultrasonic treatment of the component for a period of at least 3
hours.
14. The method of claim 9, wherein the mechanically removing step is
accomplished by treatment of the component in an ultrasonic environment, and wherein
the platinum-rich layer is dislodged from the component and a slurry is formed
comprising the platinum-rich residue in water.
15. The method of claim 9, wherein the mechanically removing step is
accomplished by tumbling treatment of the component for a period of at least 45
minutes.
30
16. The method of claim 9, wherein the mechanically removing step is
accomplished by treatment of the component in a tumbling environment, and wherein
the platinum-rich layer is dislodged from the component and a slurry is formed
comprising the platinum-rich residue in water.
17. A method for recovering platinum from a turbine blade, said method
comprising:
dipping the turbine blade into a chemical comprising an acid;
dissolving at least 50% of a thermal barrier coating or platinum aluminide on
said turbine blade;
exposing a platinum rich layer on said turbine blade;
mechanically separating the platinum-rich layer from the turbine blade; and
recovering the platinum from the platinum-rich layer by centrifugation.
18. The method of claim 17, wherein said gas engine component is a turbine blade.
19. The method of claim 17, wherein the separating the platinum-rich layer step is
accomplished by high ultrasonic treatment of the component, tumbling of the
component, dry ice blasting of the component, or a combination thereof.
20. The method of claim 17, wherein the separating the platinum-rich layer step is
selected from the group consisting of hand brushing, high pressure water blasting,
ultrasonic cleaning, vibratory finishing, or a combination thereof.
21. The method of claim 17, wherein the separating the platinum-rich layer step is
accomplished by high ultrasonic treatment of the component for a period of at least 3
31
hours.
22. The method of claim 17, wherein the separating the platinum-rich layer step is
accomplished by treatment of the component in an ultrasonic environment, and wherein
the platinum-rich layer is dislodged from the component and a slurry is formed
comprising the platinum-rich residue in water.
23. The method of claim 17, wherein the separating the platinum-rich layer step is
accomplished by tumbling treatment of the component for a period of at least 45
minutes.
24. The method of claim 17, wherein the separating the platinum-rich layer step is
accomplished by treatment of the component in a tumbling environment, and wherein
the platinum-rich layer is dislodged from the component and a slurry is formed
comprising the platinum-rich residue in water.
~ -t-kio -th.e- Z. ,~~ dO ~ NO~~J U,,1-
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MANISHA Sl~ t N~jlA-7401
Agent for the App lean
LEXORBIS .
1Property Practice
Intellectua
7091710, Tolstoy House,
15-17, Tolstoy Marg,
New Delhi-ll OOOl