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Extractive Metallurgy of Rhenium: A Review

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 SPECIAL RARE-EARTH MINERALS ISSUE

Extractive metallurgy of rhenium:

a review
C.D. Anderson, P.R. Taylor and C.G. Anderson
PhD student, professor and professor, respectively, Kroll Institute for Extractive Metallurgy
Colorado School of Mines, Golden, CO

Abstract
A variety of processing technologies exist for recovery from both primary and secondary sources of rhenium.
Currently, there are no known primary rhenium deposits; thus, the method in which primary rhenium is produced
is dependent on the commodity of which it is a byproduct, e.g., copper, molybdenum, uranium, etc. In addition,
focus on the recovery of rhenium from secondary sources, such as alloy scraps and catalysts, is continually growing.
This paper presents a review of both primary and secondary processing technologies for the recovery of rhenium.
Minerals & Metallurgical Processing, 2013, Vol. 30, No. 1, pp. 59-73.
An official publication of the Society for Mining, Metallurgy, and Exploration, Inc.

Key words: Rare-earth minerals, Rhenium, Ammonium perrhenate, Extractive metallurgy

Introduction lar, Chile’s Molibdenos y Metales S.A. (Molymet), is the largest

In recent times, the aerospace and petrochemical molybdenum and rhenium producer in the world (Whittaker,
industries have come to rely on a silver-white transition 2012). The 2011 geographic breakdown of worldwide rhenium
metal, with a specific gravity of 21 and the second- reserves and production quantities are shown in Table 1.
highest melting point (3,180° C) of any metal in the Rhenium is typically sold on long-term contracts between
periodic table. This metal is rhenium (Re), the last consumers and producers. Unfortunately, data available on
natural element to be discovered, in 1925, by Mr. and historical rhenium prices is mostly based on free market pric-
Mrs. Walter Noddack and Professor Otto Berg. The ing and, thus, may not reflect the actual pricing of the rhenium
element was named after the Rhine River of their na- market to the desired extent. Nevertheless, Fig. 1 illustrates
tive Germany (Millensifer, 2010). Rhenium’s unique a combination of historical free market rhenium prices from
properties have made it a vital part of the superalloy a variety of sources, which demonstrate price fluctuations in
industry, most prominently in nickel superalloys used the market. Some of the major fluctuations may be attributed
in both aerospace and industrial gas-fired turbines. Its to the following historical events (Polyak, 2011; Naumov,
second largest application is in the catalyst industry for 2007; Blossom, 1998):
the production of unleaded gasoline (Polyak, 2011).
The concentration of rhenium in the earth’s crust • 1970: Use of rhenium in petrochemical catalysts begins.
is rather small, at approximately 0.7-1.0 parts per • 1980: Amount of rhenium used in petrochemical cata-
billion (Millensifer, 2010), although there is specu- lysts doubles.
lation that this number may be as high as 10 ppb • 1991: Dissolution of U.S.S.R. leads to an increased sup-
(Fleischer, 1959). The only documented occurrence ply of rhenium in the market.
of rhenium as a mineral, rheniite (ReS2), was found • 1999, 2003, 2006: Appearance of new generation turbine
near the Russian Kudryavyi volcano (Korzhinsky blades containing rhenium.
et al., 1994; Tessalina et al., 2008). Other than this
specific occurrence, rhenium is typically associated As of 2011, the U.S. Geological Survey (USGS) reported that
with molybdenum-copper porphyry deposits in con- the free market price for 99.99% pure rhenium metal powder
centrations of up to 0.2% (Woolf, 1961). Currently, is approximately $2,000/kg (Polyak, 2011).
there are no producers of primary rhenium, and almost Due to the lack of primary rhenium deposits, the method
all rhenium, with few exceptions, is produced as a with which it is processed is directly related to the method
byproduct of the molybdenum and copper industries. with which the minerals it is associated with are produced,
In 2011, Chile produced the most rhenium (~25,000 typically copper and molybdenum. Characteristically, rhenium
kg) and contained the world’s largest rhenium reserve found in mixed copper/molybdenum deposits is first separated
(~1.3 M kg) (Polyak, 2011). One processor in particu- with the molybdenum from the copper, using conventional

Paper number MMP-12-077. Original manuscript submitted November 2012. Revised manuscript accepted for publication
December 2012. Discussion of this peer-reviewed and approved paper is invited and must be submitted to SME Publications
Dept. prior to August 31, 2013. Copyright 2013, Society for Mining, Metallurgy, and Exploration, Inc.

MINERALS & METALLURGICAL PROCESSING 59 Vol. 30 No. 1 • February 2013

Figure 1 — Historical rhenium metal power price from 1952-2012 (year 2012: Metal Pages 2012; years 2007-2011: Polyak,
2011; years 1999-2006: Naumov, 2007; years 1952-1998: Blossom, 1998).

Table 1 — Worldwide rhenium reserves and production by

country. Source: Polyak, 2011. 2ReS2 +7.5O2(g) = Re2O7(g)+ 4SO2(g)
Country Reserves (kg) Production (kg) (ΔG°298K = - 406.5 kcal) (1)
Chile 1,300,000 25,000 It should be noted that rhenium heptmoxide is extremely
United States 390,000 6,000 volatile (Pvap = 711 mmHg at 633K); thus, at the temperatures
used for molybdenum roasting (900-950 K) it is likely that
Russia 310,000 1,500
nearly all of the rhenium present is volatilized. This volatile
Kazakhstan 190,000 2,500 product exits the furnace with the flue gases and is subsequently
Armenia 95,000 400 recovered as perrhenic acid (HReO4) after being scrubbed with
Peru 45,000 5,000 water via the following reaction.
Canada 32,000 1,800 Re2O7(g) + H2O = 2HReO4(aq)
Poland NA‡ 4,500 (ΔG°298K = -15.16 kcal) (2)
Other countries 91,000 1,500 After scrubbing, the aqueous rhenium is typically recovered
World total (rounded) 48,000 2,500,000 using solvent extraction or ion-exchange processes. Gener-
‡NA = not available ally, the end precursor product produced by these methods is
ammonium perrhenate (NH4ReO4) via crystallization (Mil-
lensifer, 2010).
In the following subsections, rhenium recovery methods
concentration technologies, typically froth flotation. After that rely on the pyrometallurgical volatilization of rhenium
this, rhenium is recovered as a byproduct from molybdenum and production of an ammonium perrhenate as an intermediate
processing (Naumov, 2007). product are discussed and broken into their respective branches
The principal molybdenum end product, molybdenum tri- of concentration technology.
oxide (MoO3), is the basic raw material for most commercially
used products of molybdenum. Therefore, the method in which Ion exchange processes. The original Kennecott Process
rhenium is produced is dependent on the production method of for the recovery of rhenium involves the previously mentioned
MoO3. Molybdenum trioxide is produced via pyrometallurgi- scrubbing process, in which the exhaust gases of the molyb-
cal roasting or hydrometallurgical pressure oxidation (Gupta, denum roasting circuit are washed with water to produce per-
1992; Ketcham et al., 2000). rhenic acid. The pregnant solution is continually recirculated
In addition to being produced as a byproduct of the mo- through the scrubber circuit until the rhenium concentration
lybdenum/copper industry, focus on the recovery of rhenium reaches approximately 100 mg/L. After this, the solution is
from secondary sources, such as alloy scraps and catalysts, is conditioned for 24 hours with caustic soda, soda ash and
continually growing. oxidized with calcium hypochlorite. The pH of this solution
Accordingly, the following sections are broken into both is brought up to 10 to precipitate any contaminants (primar-
the methods by which rhenium is recovered as a byproduct of ily iron) remaining in solution and allow them to settle. The
primary processing, as well as from secondary sources. solution is filtered and sent to an ion exchange circuit, where
the anionic resin preferentially adsorbs the aqueous rhenium
Rhenium recovery from pyrometallurgical from the alkaline solution. After the loading stage is finished,
effluent streams the rhenium is stripped by the addition of hydrochloric acid.
In pyrometallurgical roasting of molybdenum concentrates A caustic soda solution is then used to remove the remaining
containing rhenium, rhenium present in the molybdenum adsorbed molybdenum, which is subsequently recovered as
concentrate is oxidized to rhenium heptoxide (Re2O7) via the calcium molybdate. Perchloric acid and hydrogen sulfide are
following simplified reaction. then added to this solution to precipitate rhenium as rhenium

February 2013 • Vol. 30 No. 1 60 MINERALS & METALLURGICAL PROCESSING

 Figure 2 — The original Kennecott Process (Sutulov, 1965).

sulfide (Re2S7). This precipitate is then redissolved in a solution solution is then sent to a series of ion exchange columns, where
of ammonia and hydrogen peroxide, from which it crystallizes rhenium is selectively adsorbed on the weakly basic anionic
as ammonium perrhenate (NH4ReO4). Figure 2 illustrates the resin as the perrhenate anion (ReO4-). After the loading phase,
flowsheet for the original Kennecott Process. the rhenium is eluted using an ammonia solution. The loaded
Currently, KGHM’s Glogow smelting facility (Glogow, Po- eluent is the sent to vacuum crystallization, where ammonium
land) is utilizing ion exchange technology (the Ecoren process) perrhenate is produced. Typically, repeated recrystallization is
for the recovery of aqueous rhenium, from copper concentrate necessary to produce a high-grade (99.95% pure) ammonium
smelter flue gas. In this process, the rhenium within the copper perrhenate product. The Glogow smelter facility has the ca-
concentrate is volatilized as rhenium heptoxide and reports to pability to produce 4-5 t of ammonium perrhenate per year.
the sulfuric acid scrubbing plant. Like the Kennecott Process, The Ecoren process flowsheet is shown in Fig. 3 (Chmielarz
the rhenium heptoxide is scrubbed using water, and brought and Litwinionek, 2010).
into solution along with various other impurities, including
molybdate, sulfate and sulfite salts. The typical rhenium con- Solvent extraction processes. Some of the richest rhenium-
centration in this solution is 0.02 g/L. This solution is sent containing deposits in the world are found in Kazakhstan. In
to a closed polypropylene filter press to remove any residual the Zhezkhazgan deposit, copper concentrates produced can
silicon prior to being sent to the ion exchange columns. The contain up to 30 g/t of rhenium. Abisheva et al. have proposed

MINERALS & METALLURGICAL PROCESSING 61 Vol. 30 No. 1 • February 2013

 Figure 3 — KGHM Ecoren rhenium recovery at the Glogow smelter (Chmielarz and Litwinionek, 2010).

a process in which the copper concentrate is electrosmelted, firmed by Singh et al., who ran a 250-L rhenium extraction
and the rhenium present is volatilized, as rhenium heptoxide pilot plant using it. Results showed that 98% of the aqueous
(Re2O7), and scrubbed with water/dilute sulfuric acid to form rhenium was recoverable, and allowed for the production of a
perrhenic acid (HReO4) in concentrations of up to 0.25 g/L. 98% pure rhenium precursor product using solvent extraction
The aqueous rhenium solution is sent to a solvent extraction (Singh et al., 1982).
step for the selective separation of rhenium from the impurity As an alternative to the conventional method of ammonium
elements present. The extractant used in this technology is tri- perrhenate precipitation, the USBM developed a solvent-
alklamine organic compound (TAA) in a kerosene diluent. The extraction/electrowinning process for rhenium recovery from
loaded organic phase is stripped using ammonium hydroxide molybdenite roasting. Once more, rhenium heptoxide present
to produce ammonium perrhenate. The barren organic phase in the flue gas was scrubbed using water. The aqueous rhenium
is then recycled for further use in solvent extraction, and the was oxidized using sodium chlorate and the pH of the solu-
impure ammonium perrhenate is continually dissolved and tion was brought to 12 by caustic soda addition. Prior to the
recrystallized to produce a 98.5% pure ammonium perrhenate solvent extraction step, the solution was filtered to remove any
product (Abisheva et al., 2011). A flowsheet of this process precipitates that formed during pH adjustment. The pregnant
is shown in Fig. 4. solution was then sent to a six-stage extraction circuit, which
The use of a tertiary amine rhenium extractant was con- used a combination of: 5% aliquat 336, 5% primary decyl

February 2013 • Vol. 30 No. 1 62 MINERALS & METALLURGICAL PROCESSING

Figure 4 — Flowsheet for the recovery of rhenium from sulfuric acid scrubbing solution (Abisheva et al., 2011).

alcohol (PDA) and 90% kerosene as the extractant

phase. The loaded organic was then stripped using a
1-M perchloric acid/ammonium sulfate solution. After
stripping, the rhenium-rich electrolyte was sent for
electrowinning using a current density of 360 A/m2.
Results from the pilot plant experimentation show that
rhenium metal can be prepared from dilute impure so-
lutions containing aqueous rhenium and molybdenum
(Churchward and Rosenbaum, 1963). An illustration
of the flowsheet for this process is shown in Fig. 5.

Alternative methods for rhenium recovery

In addition to the use of conventional ion exchange
or solvent extraction processes, there are a number of
processes that involve novel methods for the extraction
and production of rhenium. The following section
will describe each of these in their respective context.

Recovery from Mo/Cu ores. As an alternative

to traditional roasting technology, Rio Tinto’s Ken-
necott facility at Bingham Canyon, UT has patented
(US# 6149883) an alkaline pressure oxidation process
for the recovery of molybdenum and rhenium from
molybdenite concentrates (molybdenum autoclave
process or MAP). In this process, the molybdenite
flotation concentrate is leached with either sodium
or potassium hydroxide at elevated temperature (150-
200° C) and pressure (517 - 1,400 kPa or 75-200 psig)
to form soluble molybdate (MoO42-).The aqueous
molybdate is then recovered using solvent extraction
and is stripped with an ammonium hydroxide eluent.
The rhenium present in the molybdenite concentrate
is primarily recovered in the solvent extraction step,
in the loaded strip solution. After this, it is recovered
using a selective ion exchange resin, which typically
contains quaternary amine functional groups (Ketcham
Figure 5 —USBM SX/EW process flowsheet for rhenium recovery et al., 2000).
(Churchward and Rosenbaum, 1963). In 2009, Freeport-McMoRan applied for a patent

MINERALS & METALLURGICAL PROCESSING 63 Vol. 30 No. 1 • February 2013

 Figure 6 — Freeport pressure oxidation rhenium recovery process (Waterman et al., 2009).

(US# 0263490A1) for a proprietary method of recovering patent (AUS# 2011229125) to Alexander Mining Plc. for the
rhenium as a byproduct of copper leaching/molybdenum oxi- MoReLeach process (Sutcliffe et al., 2012). Officially titled
dation. The application states that, “the rhenium rich PLS can “Method of oxidative leaching of molybdenum-rhenium sul-
originate from an active copper leach, stockpile copper leach, fide ores and/or concentrates,” the process involves leaching
acid blowdown stream, or a leach of molybdenite roaster flue a molybdenum/rhenium concentrate in a closed reactor vessel
fumes and dusts.” This loaded stream is sent to an activated at atmospheric temperature and pressure. The lixiviant used is
carbon column circuit for adsorption of the aqueous rhenium. an “aqueous solution of chlorine-based oxidizing species,” in
After adsorption, the loaded rhenium is stripped using an elu- which the predominant chlorine-based oxidizing species are
ent solution containing approximately 2.5% sodium hydroxide hypochlorite (ClO-) ions. The molybdenum sulfide is oxidized
and 2.5% ammonium hydroxide at a pH of 7, and an operat- to the soluble molybdate anion (MoO42-), and the rhenium
ing temperature of 80-110° C. After elution, the rhenium-rich present is oxidized to the perrhenate anion (ReO4-) via the
stream is sent for rhenium recovery to produce a pure rhenium following proposed reactions (Gupta, 1992). Note: the second
product, and a rhenium lean eluate solution for optional reuse reaction is proposed by the author.
in the circuit (Waterman et al., 2009). An example of Freeport’s MoS2 + 9NaClO + 3H2O = MoO42-(aq) + 9NaCl +
proposed rhenium recovery circuit is shown in Fig. 6.
In October 2012, the Australian Patent Office granted a 2SO42-(aq) + 6H+ (ΔG°298K = -506.9 kcal) (3)

February 2013 • Vol. 30 No. 1 64 MINERALS & METALLURGICAL PROCESSING

Figure 7 — MoRe leach process (Sutcliffe et al., 2012).

ReS2+ 9.5NaClO + 2.5H2O = ReO4-(aq) + 9.5NaCl + sorbant, activated charcoal in the gold industry. But, in this
2SO42-(aq) + 5H+ (ΔG°298K = -535.7 kcal) (4) process, an ion exchange resin is added to a solution that has
already undergone leaching. Thus, after perrhenic acid is
After dissolution, the pregnant solution is separated from produced by scrubbing with water, the ion exchange resin is
the undissolved residue and sent for a metal separation stage added to selectively remove the rhenium and molybdenum
such as solvent extraction, ion exchange, etc. Additionally, the from solution, via adsorption onto the resin. Experimental
proposed process allows for the regeneration of hypochlorite results show that by using a strong basic anionic exchange
for subsequent reuse as a reagent. A flowsheet of the proposed resin, rhenium can be selectively adsorbed from solution. Ad-
process is illustrated in Fig. 7. ditionally, elution results have shown that molybdenum can be
In the mid-1990s, after discovering rheniite (ReS2) at the selectively eluted from the resin by using ammonium chloride
Russian Kudryavyi volcano, Russian researchers found that the (NH4Cl) as the eluent, leaving rhenium adsorbed. After this,
high-temperature fumarole gases exiting the volcano contained rhenium can then be stripped from the resin using dilute nitric
considerable (0.5-2.5 g/t) of rhenium in the form of gaseous acid (Lan et al., 2006).
rhenium chlorides (ReCl5) and fluorides (ReF5). Currently, In 1947, Melaven and Bacon, of the University of Tennes-
researchers are working on using zeolites as the adsorption see, patented (US# 2,414,965) a technology for the recovery of
medium for the rhenium rich fumarole gases. As of 2007, re- rhenium from molybdenite roasting flue dust. In their process,
searchers are operating this process on a pilot scale, although cyclone flue dust was recovered, and rhenium was leached
this process may prove rather difficult, due to the inherent with water and compressed air. After lixiviation, potassium
danger of the natural environment and lack of infrastructure chloride was added to the solution to recover rhenium as a pure
within the area (Naumov, 2007; Sinegribov et al., 2007). potassium perrhenate (KReO4) precipitate. Metallic rhenium
Lan et al. have proposed a novel process for the recovery of was then produced by roasting the potassium perrhenate in
rhenium-containing flue dusts, using an application commonly a silver tube under a hydrogen atmosphere at 350° C. After
used in gold hydrometallurgy, known as the “resin-in-pulp” roasting, the residue is washed with hot distilled water, leav-
process. The resin-in-pulp process relies on the addition of a ing a pure metallic rhenium product (Melaven and Bacon,

MINERALS & METALLURGICAL PROCESSING 65 Vol. 30 No. 1 • February 2013

 Figure 8 —The Melaven process (Melaven and Bacon, 1947).

1947; Sutulov, 1965). The flowsheet for the Melaven process The proposed flowsheet for this process is shown in Fig. 9.
is shown in Fig. 8. In another case where rhenium is found in uranium leach-
Recovery from uranium leach liquors. After finding ing solutions, Chekmarev et al. have proposed the recovery
rhenium adsorbed on their uranium ion-exchange columns in of rhenium using complexation and ultrafiltration methods
Palangana, TX, efforts were made for the recovery of rhenium with the aid of water-soluble polyelectrolytes. Rhenium in the
as rhenium sulfide. Rhenium was present in the ammonium pregnant leach solution is complexed using VA-type cationic
carbonate leach liquor as the perrhenate anion, ReO4-, which polyelectrolytes containing quaternary ammonium base groups.
is selectively adsorbed on the anionic exchange resin. The These complexes are sent through ultrafiltration to selectively
proposed process calls for the elution of this anion by way of remove the high molecular weight rhenium complex, leaving
ammonium nitrate and precipitation of rhenium sulfide (Re2S7) a wash solution ready for subsequent rhenium processing
with the addition of hydrogen sulfide gas (Goddard, 1996). (Chekmarev et al., 2004).

February 2013 • Vol. 30 No. 1 66 MINERALS & METALLURGICAL PROCESSING

 Figure 9 — Recovery of rhenium sulfide (Goddard, 1996).

Recycling of rhenium high temperature properties of tungsten and rhenium, it is not

In addition to being produced as a byproduct of molybde- uncommon to find these metals in alloys together. Thus, W-Re
num, it is possible to recycle rhenium during processing, and scrap may be recycled via an oxidative pyrometallurgical
after its use within the industry. The following subsections will roasting technique. Initially, the scrap is roasted at 1,000° C,
illustrate a number of the current and proposed technologies under an oxidizing atmosphere to produce rhenium heptoxide
that might be used to recover rhenium from secondary sources. (Re2O7), which is subsequently condensed in the cooler part
of the tube furnace (Fig. 10).
Recycling from superalloys and alloy scraps. Due to the This material is then sent for digestion in water. The aque-

Figure 10 — Schematic of the W-Re tube furnace (Heshmatpour and McDonald, 1982).

MINERALS & METALLURGICAL PROCESSING 67 Vol. 30 No. 1 • February 2013

 Figure 11 — The H.C. Starck process for superalloy recycling (Olbrich et al., 2009).

ous rhenium (ReO4-) is subsequently precipitated as potassium Co, Ni, Fe, Mn and Cr from the leach liquor. Magnetic sepa-
perrhenate upon the addition of potassium chloride via the ration is then applied to the insoluble components for further
following reaction. separation and concentration. The pregnant leach solution is
sent to an ion exchange step, where the aqueous rhenium is
KCl + ReO4- = KReO4 + Cl-(aq)
selectively adsorbed and can be recovered using the methods
(ΔG°298K = -6.133 kcal) (5) described in the previous sections (Olbrich et al., 2009). An
example of the flowsheet for this process is shown in Fig. 11.
The potassium perrhenate is filtered and further purified Through the use of electrolytic decomposition of rhenium
via continued dissolution and recrystallization. After purifica- superalloys, Stoller et al. have patented (US# 0110767) a
tion, the salt is dried and sent for reduction under a hydrogen process that involves the use of titanium baskets as electrodes.
atmosphere at approximately 350° C. Experimental results The baskets containing the superalloy scrap are fed to a poly-
show that 93.1% of the rhenium was recovered to produce a propylene electrolysis cell containing a 18% HCl solution.
99.98% pure Re° product (Heshmatpour and McDonald, 1982). The electrolytic dissolution is carried out for 25 hours at a
H.C. Starck has applied for a patent (US # 0255372 A1) for frequency of 0.5 Hz, current of 50 amps, voltage of 3-4 V and
a process for the elevated temperature digestion and recycling a temperature of 70° C. The remaining scrap is then filtered
of rhenium-containing superalloys. Initially, the superalloys from the pregnant solution and sent for further dissolution in
are digested in a molten salt melt containing NaOH, Na2CO3, sodium hydroxide/peroxide solution. After completion, this
and Na2SO4 at temperatures of 850-1,100° C in a directly fired filtrate is sent to ion exchange for the recovery of rhenium and
rotary kiln. In addition to this, oxidizing agents such as nitrates molybdenum. Rhenium is recovered using the ion exchange
and peroxides of the alkali metals are added. The melt from this processes discussed previously (Stoller et al., 2008). An il-
process is then cooled and sent to a comminution process for lustration of this process is shown in Fig. 12.
size reduction. The material is then leached using water as the
lixiviant to dissolve the 6 and 7th group elements present in the Recycling of spent Pt-Re catalysts
superalloy. This slurry is then filtered to separate the insoluble Petroleum-reforming catalysts containing rhenium and plati-

February 2013 • Vol. 30 No. 1 68 MINERALS & METALLURGICAL PROCESSING

Figure 12 — Electrochemical method for recycling of superalloys (Stoller et al., 2008).

num on an alumina substrate are used in the refining industry solution, and cooled to allow for crystallization of ammonium
for the improvement of the octane level of fuels. After being perrhenate. After continued redissolution and recrystallization,
deactivated, an effective method for the recovery or rhenium a high-purity ammonium perrhenate precipitate is produced
and other PGM metals is necessary. There are two basic meth- (El Guindy, 1997). The flowsheet for this process is shown
ods by which this is achieved (Kasikov and Petrova, 2009): in Fig. 13.
As an alternative to sulfuric acid, sodium bicarbonate may
1. Complete dissolution of the alumina substrate. also be used as a lixiviant. The proposed advantage of this
2. Selective dissolution and recovery of rhenium and process is the complete removal of the ion exchange circuit
platinum. shown in Fig. 14. Experiments were performed on crushed
and uncrushed catalysts in both packed columns and agitated
The following summaries will present examples of both of leach vessels. Experimental results showed that that rhenium
these technologies; for further information, refer to Kasikov’s is preferentially leached in the sodium bicarbonate solution.
literature review “Processing of deactivated platinum-rhenium Rhenium recovery reached 97% for crushed catalysts, and 87%
catalysts” (Kasikov and Petrova, 2009). for uncrushed catalyst samples. After dissolution, the aque-
ous rhenium is crystallized via evaporative crystallization as
Complete dissolution of the alumina substrate. During an ammonium perrhenate intermediate product (Angelidis et
complete dissolution of the alumina substrate, sulfuric acid al., 1999). The flowsheet for this process is shown in Fig. 14.
may be used for dissolution of alumina, rhenium and, to some
extent, platinum. The rhenium-rich solution is separated from Selective leaching of rhenium and platinum. The methods
the platinum-containing residue and aqueous aluminum us- used to selectively recover platinum and rhenium from spent
ing ion exchange. Rhenium is eluted from the organic amine catalysts without completely dissolving the alumina substrate
resin by way of hydrochloric acid addition. After elution, the vary from calcination of the catalysts to selective leaching in
rhenium-rich eluate is neutralized using ammonium hydrox- alkaline or acid conditions at ambient and elevated temperatures
ide. This solution is then evaporated to form a super-saturated (Kasikov and Petrova, 2009).

MINERALS & METALLURGICAL PROCESSING 69 Vol. 30 No. 1 • February 2013

 Figure 13 — Method for rhenium recovery from spent reforming catalysts (El Guindy, 1997).

February 2013 • Vol. 30 No. 1 70 MINERALS & METALLURGICAL PROCESSING

 Figure 14 - Rhenium recovery using sodium bicarbonate (Angelidis et al., 1999).

By calcining the catalyst at temperatures up to 1,150° C, the iodide or bromide and oxygen to selectively leach Pt and Re,
γ-Al2O3 undergoes a phase transition to the chemically stable while leaving behind the alumina substrate. At 160° C and an
α-Al2O3 phase, lowering the dissolution of the alumina catalyst. oxygen overpressure of 800 kPa (116 psig), the authors report
The platinum and rhenium can then be selectively leached a rhenium recovery of 98% (Han and Meng, 1996).
in concentrated (5 mol/L) sulfuric acid solutions containing
sodium chloride and a potassium persulfate oxidant (K2S2O8). Production of metallic rhenium
Kpumaneva reports that rhenium and platinum recoveries are as Generally, metallic rhenium is not produced at the facility
high as 95.5% and 97%, respectively (Kpumaneva et al., 2001). at which it is concentrated and separated from other elements.
Additionally, a U.S. patent (US#: 5542957) has been granted Instead, it is produced from ammonium perrhenate (APR)
involving the selective leaching of platinum and rhenium at using methods similar to those used in the molybdenum and
elevated temperatures (50-300° C) and pressures (207-9,000 kPa tungsten industries; i.e., a reductant such as carbon monoxide
or 30-1,300 psig). In this process, a dilute solution of sulfuric or hydrogen is used. Although APR is the typical precursor
acid (0.001-1.0 mol/L) is used in the presence of ammonium material that is reduced, potassium perrhenate may also be

MINERALS & METALLURGICAL PROCESSING 71 Vol. 30 No. 1 • February 2013

 Figure 15 — Production of rhenium from ammonium perrhenate (Millensifer, 2010).

used (Sutulov, 1965). two hours, and then the temperature is raised to 500° C for
The two primary methods for the production of metallic an additional two hours. The reduction product is then cooled
rhenium are: slowly in an inert atmosphere to prevent oxidation and washed
with water to remove any residual alkaline material (Hurd
1. The reduction of ammonium perrhenate (NH4ReO4). and Brimm, 1939). The proposed reaction for this technique
2. The reduction of potassium perrhenate (KReO4). is shown below.

Ammonium perrhenate (NH4ReO4) is the typical precursor 2KReO4 + 7H2 = 2Re° + 2KOH + 6H2O
product used in the production of metallic rhenium and rhenium (ΔG°298K = -16.07 kcal) (7)
compounds, including metallic rhenium powder and perrhenic
acid. Metallic rhenium is produced by being reduced by hy- Conclusion
drogen gas at elevated temperature, T = 1,000° C (Hurd and Most of the processes involved in the production of primary
Brimm, 1939). Ammonium perrhenate (APR) is placed in boats and secondary rhenium involve the use of either elevated
and subjected to countercurrent hydrogen gas flow. Depending temperatures, elevated pressures, large amounts of reagents
on the particle size of metallic rhenium powder product, the or a combination of the three. Thus, it is imperative that the
reduction may be completed in single or multiple stages and extraction and recovery of rhenium is as efficient as economi-
the APR may be ground prior to reduction (Millensifer, 2010). cally possible. Some possible research opportunities for the
The proposed reaction for this process is shown below. Figure development of higher efficiency processes are suggested in
15 illustrates the typical production steps in making metallic the following paragraphs.
rhenium from ammonium perrhenate. The roasting of molybdenum concentrates containing
2NH4ReO4(s) + 7H2 = 2Re° + 2NH3 + 8H2O rhenium is an elevated-temperature, exothermic process that
requires temperatures of 900-950 K. Early scrubbing attempts
(ΔG°298K = -37.16 kcal) (6)
of flue gases were relatively inefficient, capturing roughly 25%
In Hurd and Brimm’s process for the commercial reduction of the rhenium present. Through innovation in the scrubbing
of potassium perrhenate, the feed material is crushed to ap- equipment used, recoveries have now increased to approxi-
proximately 60 US mesh and dried at 175° C. The material is mately 80% (Millensifer, 2010). Thus, increasing the recovery
then placed in a silver boat inside of a refractory tube furnace. of rhenium from roasting flue dusts presents itself as a viable
The boat is heated to 250° C under a hydrogen atmosphere for research opportunity.

February 2013 • Vol. 30 No. 1 72 MINERALS & METALLURGICAL PROCESSING

 Conversely, another option for increased rhenium recovery B.D. Bryskin, ed., February 9-13, 1997, Orlando, FL, TMS, pp 89-97.
may involve the use of hydrometallurgical pressure oxidation Fleischer, M., 1959, “The geochemistry of rhenium, with special reference to
its occurrence in molybdenite,” Economic Geology, Vol. 54, pp. 1406-1413.
of molybdenum concentrates. Although this process involves Goddard, J.B., 1984, “Recovery of rhenium from uranium in-situ leach liquor,”
the use of elevated temperatures/pressures and additional re- Society of Mining Engineers Transactions of AIME, Vol. 274, pp 1996-2000.
agents, the enhanced recoveries inherent to the process may Gupta, C.K., 1992, Extractive Metallurgy of Molybdenum, 1st Edition, CRC
Press, pp 164-165.
make this a viable alternative to traditional roasting processes. Han, K.N., and Meng, X., 1996, “Recovery of platinum group metals and rhe-
Research of this technique, and other technologies involving nium from materials using halogen reagents,” US Patent No. 5,542,957,
the use of low temperature hydrometallurgical oxidation is Washington, D.C., U.S. Patent and Trademark Office.

currently ongoing in industry.

Heshmatpour, B., and McDonald, R.E., 1982, “Recovery and refining of rhenium,
tungsten and molybdenum from W-Re, Mo-Re and other alloy scraps,”
As a complementary process to both roasting and pressure Journal of the Less Common Metals, Vol. 86, pp 121-128.
oxidation, the need for efficient separation of aqueous rhenium Hurd, L., and Brimm, E., 1939, “Metallic rhenium,” Inorganic Syntheses, Vol.
from the process stream is essential. A variety of techniques
1, pp 175-178.
Kasikov, L., and Petrova, A., 2009, “Processing of deactivated platinum-rhenium
have been the subject of investigation, including ion exchange, catalysts,” Theoretical Foundations of Chemical Engineering, Vol. 43, No.4,
solvent extraction and activated carbon. With the continual pp 544-552.
development of higher selectivity resins and extractants used Ketcham, V.J., Coltrinari, E.J., and Hazen, W.W., 2000, “Pressure oxidation
process for the production of molybdenum trioxide from molybdenite,” US
in both ion exchange and solvent extraction, the area presents Patent No. 6,149,883, Washington, D.C., U.S. Patent and Trademark Office.
itself worthy of further research and development. Korzhinsky, M.A., Tkachenko, S.I., Shmulovich, K.I., Taran, Y.A., and Steinberg,
Relatively new to the rhenium industry is the processing of G.S., 1994, “Discovery of a pure rhenium mineral at Kudriavy volcano,”
Nature, Vol. 369, No. 6475, pp 51-52.
rhenium-laden manufacturing scrap and end-of-life materials, Kpumaneva,, E., Rtveadze, V., and Igumnov, S., 2001, “Platinum and rhenium
such as catalysts and super alloys. Since this is such a new extraction with base material dilution,” Khimicheskaya Technologiya, Vol.
faction of the rhenium industry, the research possibilities are 5, pp 12-17.
Lan, X., Liang, S., and Song, Y., 2006, “Recovery of rhenium from molybdenite
almost endless, but should definitely include the utilization of calcine by a resin-in-pulp process,” Hydrometallurgy, Vol. 82, No. 3-4, pp.
primary processing techniques, as well as the implementation 133-136.
of end-of-life recycling programs. Melaven, A.D., and Bacon, J.A., 1947, “Process for recovering rhenium,” US
As rhenium sources are depleted, the need for efficient and
Patent No. 2,414,965, Washington, D.C., U.S. Patent and Trademark Office.
Millensifer, T.A., 2010, “Rhenium and rhenium compounds,” Kirk Othmer Ency-
economical extraction from both primary and secondary sources clopedia of Chemical Technology, John Wiley and Sons, pp. 1-21.
is essential in maintaining the rhenium supply. This paper has Naumov, A., 2007, “Rhythms of rhenium,” Russian Journal of Non-Ferrous
presented a review of both the current and former technolo- Metals, Vol. 48, No. 6, pp. 418-423.
Olbrich, A., Meese-Marktscheffel, J., Jahn, M., Zertani, R., Stoller, V., Erb, M.,
gies used in the extractive metallurgy of rhenium, as well as Heine, K.H., and Kutzler, U., 2009, “Recycling of superalloys with the aid of
provided some areas for potential technological development. an alkali metal salt bath,” US Patent Application No. 0255372 A1,Washington,
D.C., U.S. Patent and Trademark Office.
Polyak, D.E., 2011, USGS Mineral Commodity Summary: Rhenium, Reston, VA:
Acknowledgments U.S. Geological Survey.
Special recognition is due to Tom Millensifer for his assis- Sinegribov, V., Sotskov, K., and Yudin. A., 2007, “Recovery of valuable elements
tance with this paper; in addition, the authors thank the Office from fumarole gases,” Theoretical Foundations of Chemical Engineering,
Vol. 41, No. 5, pp. 593-598.
of Naval Research for the financial support that allowed this Singh, H., Rao, M.S., Rao, G.V., and Reddy, M.V., 1982, “Development of a sol-
research to occur. vent extraction process for recovery of rhenium from impure scrub liquors,”
SME Preprint, No. 82-99.
Stoller, V., Olbrich, A., Meese-Marktscheffel, J., Mathy, W., Erb, M., Nietfeld,
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