Note: Descriptions are shown in the official language in which they were submitted.
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WET BASED FORMULATIONS FOR THE SELECTIVE REMOVAL OF NOBLE
METALS
FIELD
_
[0001] The present invention relates generally to processes for
recycling/reclaiming of noble metals,
such as ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, and
gold from source
materials.
DESCRIPTION OF THE RELATED ART
[0002] There are a number of sources of noble metals such as gold, silver and
platinum group metals
which offer the opportunity for economical recovery. For example, gold is
available from ores and
numerous scrap sources, including industrial wastes, gold plated electronic
circuit boards, and in
alloys with copper, zinc, silver or tin in the karat gold used in jewelry.
Silver is available from
photographic and x-ray film emulsions, scrap sterling, and numerous industrial
sources. Platinum
group metals are available from industrial sources, such as catalysts. There
are numerous instances in
which it is desirable to recover these metals from an aggregate material.
[0003] Platinum is a silvery, white, ductile metal which is insoluble in
mineral and organic acids, but
soluble in aqua regia. Platinum does not corrode or tarnish, and forms strong
complexes with halides
(i.e., chloride, bromide, fluoride and iodide). Platinum is used as a catalyst
(nitric acid, sulfuric acid,
and high-octane gasoline production; automobile exhaust gas converters), in
laboratory ware,
spinnerets for rayon and glass fiber manufacture, jewelry, dentistry,
electrical contacts,
thermocouples, surgical wire, bushings, electroplating, electric furnace
windings, chemical reaction
vessels, anti-cancer drugs and permanent magnets. Palladium is similarly a
silvery, white, ductile
metal which does not tarnish in air. It is the least noble (e.g., most
reactive) of the platinum group, is
insoluble in organic acids, but soluble in aqua regia and fused alkalies.
Palladium is used as a catalyst
for chemical processes including reforming cracked petroleum fractions and
hydrogenation, for
metallizing ceramics, as "white gold" in jewelry, in protective coatings, and
in hydrogen valves (in
hydrogen separation equipment). . Both platinum and palladium are good
electrical conductors and
are used in alloys for electrical relays in switching systems and
telecommunication equipment,
resistance wires and aircraft spark plugs. Further, platinum group metal
applications include
industrial radiography, catalysts, pen points, electrical contacts, jewelry,
coatings and headlight
reflectors.
[0004] Methods for the recovery of noble metals have taken many forms in the
prior art. The
conventional leaching of gold ores, for example, with alkaline cyanide
solutions, has been widely
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practiced on a commercial scale, but has known disadvantages including, for
example, slow leaching
rates, long contact times, and toxicity associated with the use of cyanide.
Other methods have
included the use of aqua regia or high temperature oxidative pressure
leaching. However, and in
addition to well known disadvantages, aqua regia has its limitations. For
example, aqua regia is
unable to dissolve some noble metals, e.g., silver.
[0005] Accordingly, there has remained a need for cost-effective methods and
compositions for the
recovery of noble metals from a variety of sources of such metals. Thus, while
prior art approaches
have been successful, these methods have typically suffered from one or more
disadvantages. The
present disclosure is directed to methods and processes that use halide-based
compositions at room
temperature to efficiently remove noble metals from the source comprising
same.
SUMMARY
[0006] The present invention relates generally to compositions and processes
for leaching noble
metals from sources comprising same including, but not limited to, ores,
jewelry, scraps comprising
said noble metals, waste materials, alloys, catalyst materials, and various
industrial sources. More
specifically, the compositions for leaching noble metals from sources are
acidic, halide-based
compositions that efficiently remove noble metals from the source at room
temperature.
[0007] In one aspect, a leaching composition is described, said composition
comprising at least one
oxidizing agent, at least one halide, at least one acid, and at least one
solvent.
[0008] In another aspect, a method of removing noble metals from a source is
described, said method
comprising contacting said source under conditions with the leaching
composition, wherein said noble
metals are dissolved or otherwise solubilized in the leaching composition, and
wherein the leaching
composition comprises at least one oxidizing agent, at least one halide, at
least one acid, and at least
one solvent.
[0009] Other aspects, features and advantages will be more fully apparent from
the ensuing
disclosure and appended claims.
DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS THEREOF
[0010] The present invention relates generally to compositions and processes
for leaching noble
metals from sources comprising same including, but not limited to, ores,
jewelry, scraps comprising
said noble metals, waste materials, alloys, catalyst materials, and various
industrial sources. More
specifically, the compositions for leaching noble metals from sources are
acidic, halide-based
compositions that efficiently remove noble metals from the source at low
temperatures.
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[0011] As used herein, "noble metals" refers to the group of metals including
gold, silver, the
platinum group metals, alloys comprising same, and combinations thereof The
"platinum group
metals" include ruthenium, osmium, rhodium, iridium, palladium and platinum.
[0012] As used herein, "base metals" corresponds to iron, nickel, zinc,
copper, aluminum, tungsten,
molybdenum, tantalum, magnesium, cobalt, bismuth, cadmium, titanium,
zirconium, antimony,
manganese, beryllium, chromium, germanium, vanadium, gallium, hafnium, indium,
niobium,
rhenium, thallium, alloys comprising same, and combinations thereof
[0013] "Substantially devoid" is defined herein as less than 2 wt. %,
preferably less than 1 wt. %,
more preferably less than 0.5 wt. %, and most preferably less than 0.1 wt. %.
"Devoid" corresponds
to 0 wt. %.
[0014] As used herein, "about" is intended to correspond to 5 % of the
stated value.
[0015] As used herein, "halide" corresponds to fluoride, chloride, bromide or
iodide-containing
species such as salts or acids.
[0016] As used herein, the "source" is a noble metal-containing material
including, but not limited to,
ores, jewelry, scraps comprising said noble metals, waste materials comprising
said noble metals
including electronic waste, alloys, catalyst materials, various industrial
sources, and combinations
thereof
[0017] As used herein, "to remove" noble metals from a source means that the
noble metal is
substantially dissolved or solubilized or the like in the leaching
composition, while base metals are
not substantially dissolved or solubilized or the like. "Substantially
dissolved" is defined herein more
than 95 wt. % of the material originally present is dissolved or solubilized
or the like, preferably more
than 98 wt. %, more preferably more than 99 wt. %, and most preferably more
than 99.9 wt. %. "Not
substantially dissolved" is defined herein less than 5 wt. % of the material
originally present is
dissolved or solubilized or the like, preferably less than 2 wt. %, more
preferably less than 1 wt. %,
and most preferably less than 0.1 wt. %.
[0018] As used herein, the term "leaches" or "leaching" corresponds to the
complete or partial
removal or extraction of the gold and/or other noble metals from the source
into the leaching
composition. The gold or other noble metal is dissolved or otherwise
solubilized in the leaching
composition, preferably dissolved.
[0019] As defined herein, "crushing" the source corresponds to any method that
substantially
exposes the gold and other noble metals of the source material to the leaching
composition, e.g.,
crushing, cracking, pulverizing, shredding, or grinding.
[0020] As defined herein, "agitation means" include, but are not limited to,
physical agitation such as
mixing, recirculation, turbulence, and combinations thereof
[0021] Compositions may be embodied in a wide variety of specific
formulations, as hereinafter
more fully described. In all such compositions, wherein specific constituents
of the composition are
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discussed in reference to weight percentage ranges including a zero lower
limit, it will be understood
that such constituents may be present or absent in various specific
embodiments of the composition,
and that in instances where such constituents are present, they may be present
at concentrations as low
as 0.001 weight percent, based on the total weight of the composition in which
such constituents are
employed.
[0022] In a first aspect, a method of removing noble metals from a source is
described, wherein said
noble metals are dissolved or otherwise solubilized in a leaching composition.
More specifically, the
method of removing noble metals from a source comprises contacting said source
with a leaching
composition, wherein said noble metals are dissolved or otherwise solubilized
in the leaching
composition. Preferably, noble metals are selectively removed relative to base
metals also present in
the source.
[0023] Advantageously, once a volume of a source has been processed and the
noble metals removed
(from the leaching composition), new volumes of the source can be added to the
leaching composition
and the process of removing the noble metals can be repeated again and again
until the leaching
composition is saturated with noble metals. Alternatively, a "feed and bleed"
process may be used
wherein clean leaching composition is periodically introduced to the working
leaching composition
with simultaneous withdrawal of some of the working leaching composition. The
leaching
composition comprising the noble metals can be processed to obtain useful
forms of said noble metals
(e.g., electrochemically, by electrowinning, or using reducing agents).
[0024] In removal applications, the leaching composition is contacted in any
suitable manner to the
source, e.g., by spraying the leaching composition on the source, by dipping
the source in a volume of
the leaching composition, by contacting the source with another material,
e.g., a pad, or fibrous
sorbent applicator element, that has the leaching composition absorbed
thereon, by contacting the
source with a recirculating composition, or by any other suitable means,
manner or technique, by
which the leaching composition is brought into contact with the source. It
should be appreciated that
the source (i.e., noble metal containing material) can be added to the
leaching composition as is,
pulverized into a powder, shredded into pieces, crushed, or in any other form
so long as the metals
contained in the source are readily exposed for removal from the source. The
leaching composition
and the source can be agitated such that the source is substantially exposed
to the leaching
composition.
[0025] In use of the leaching compositions described herein for removing noble
metals from a source
comprising same, the leaching composition typically is contacted with the
source for a time of from
about 1 min to about 120 minutes, preferably about 3 min to 60 at temperature
in a range of from
about 20 C to about 100 C, preferably in a range from about 20 C to about 60
C, more preferably
about 20 C to about 40 C, and most preferably about room temperature. Such
contacting times and
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temperatures are illustrative, and any other suitable time and temperature
conditions may be employed
that are efficacious to remove the noble metals from the source comprising
same.
[0026] In a second aspect, a leaching composition is described, said leaching
composition
comprising, consisting of, or consisting essentially of at least one oxidizing
agent, at least one halide,
at least one acid, and at least one solvent. In one embodiment, the leaching
composition comprises,
consists of, or consists essentially of at least one oxidizing agent, at least
one chloride salt, at least one
acid, and at least one solvent. In another embodiment, the leaching
composition comprises, consists
of, or consists essentially of at least one oxidizing agent, at least one
chloride salt, at least one sulfur-
containing acid, and at least one solvent. In still another embodiment, the
leaching composition
comprises, consists of, or consists essentially of at least one oxidizing
agent, at least one alkaline
chloride salt, at least one sulfur-containing acid, and at least one solvent.
In yet another embodiment,
the leaching composition comprises, consists of, or consists essentially of at
least one nitrate salt
oxidizing agent, at least one alkaline chloride salt, at least one sulfur-
containing acid, and at least one
solvent. The leaching composition is aqueous in nature and has a pH less than
about 2, more
preferably less than about 1.
[0027] In another embodiment, the leaching composition comprises, consists of,
or consists
essentially of at least one oxidizing agent, at least one halide salt, at
least one acid, and at least one
solvent, present in the following weight percentages, based on the total
weight of the composition:
component preferably more preferably most preferably
at least one oxidizing about 1 wt% to about about 1 wt% to about about 4 wt%
to about
agent 40 wt% 30 wt% 20 wt%
at least one halide about 1 wt% to about about 2 wt% to about about 3 wt%
to about
40 wt% 30 wt% 15 wt%
at least one acid about 1 wt % to about about 2 wt % to about about 7 wt %
to about
50 wt % 40 wt % 30 wt %
at least one solvent about 1 wt % to about about 1 wt % to about about 35
wt % to about
93 wt% 87 wt% 86 wt%
[0028] In still another embodiment, the leaching composition comprises,
consists of, or consists
essentially of at least one nitrate salt oxidizing agent, at least one
alkaline chloride salt, at least one
sulfur-containing acid, and at least one solvent, present in the following
weight percentages, based on
the total weight of the composition:
component preferably more preferably most preferably
at least one nitrate salt about 1 wt% to about about 1 wt% to about about 4
wt% to about
oxidizing agent 40 wt% 30 wt% 20 wt%
at least one alkaline about 1 wt% to about about 2 wt% to about about 3 wt% to
about
chloride 40 wt% 30 wt% 15 wt%
at least one sulfur- about 1 wt % to about about 2 wt % to about about 7 wt %
to about
containing acid 50 wt % 40 wt % 30 wt %
at least one solvent about 1 wt % to about about 1 wt % to about about 35
wt % to about
93 wt% 87 wt% 86 wt%
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[0029] Oxidizing agents are included in the composition to oxidize the metals
to be removed into an
ionic form and accumulate highly soluble salts of dissolved metals. Oxidizing
agents contemplated
herein include, but are not limited to, ozone, nitric acid (HNO3), bubbled
air, cyclohexylaminosulfonic
acidõ hydrogen peroxide (H202), oxone (potassium peroxymonosulfate,
2KHS05.KHSO4.K2SO4),
ammonium polyatomic salts (e.g., ammonium peroxomonosulfate, ammonium chlorite
(NH4C102),
ammonium chlorate (NH4C103), ammonium iodate (NH4I03), ammonium perborate
(NH4B03),
ammonium perchlorate (NH4C104), ammonium periodate (NH4I03), ammonium
persulfate
((NH4)2S208), ammonium hypochlorite (NH4C10)), sodium polyatomic salts (e.g.,
sodium persulfate
(Na2S208), sodium hypochlorite (NaC10)), potassium polyatomic salts (e.g.,
potassium iodate (KI03),
potassium permanganate (KMn04), potassium persulfate, potassium persulfate
(K2S208), potassium
hypochlorite (KC10)), tetramethylammonium polyatomic salts (e.g.,
tetramethylammonium chlorite
((N(CH3)4)C102), tetramethylammonium chlorate ((N(CH3)4)C103),
tetramethylammonium iodate
((N(CH3)4)103), tetramethylammonium perborate ((N(CH3)4)B03),
tetramethylammonium perchlorate
((N(CH3)4)C104), tetramethylammonium periodate ((N(CH3)4)104),
tetramethylammonium persulfate
((N(CH3)4)S208), tetramethylammonium nitrate), tetrabutylammonium polyatomic
salts (e.g.,
tetrabutylammonium peroxomonosulfate, tetrabutylammonium nitrate),
peroxomonosulfuric acid,
urea hydrogen peroxide ((CO(NH2)2)H202), peracetic acid (CH3(C0)00H), sodium
nitrate, potassium
nitrate, ammonium nitrate, and combinations thereof Most preferably, the
oxidizing agent comprises
a nitrate ion including, but not limited to, nitric acid, sodium nitrate,
potassium nitrate, ammonium
nitrate, tetraalkylammonium nitrate, and combinations thereof
[0030] The at least one halide is preferably a chloride-containing compound
including, but not
limited to, hydrochloric acid, and alkaline chlorides (e.g., sodium chloride,
potassium chloride,
rubidium chloride, cesium chloride, magnesium chloride, calcium chloride,
strontium chloride,
ammonium chloride, quaternary ammonium chloride salts), and combinations
thereof, with the
proviso that the chloride-containing compound cannot include copper chloride,
chlorine gas, or a
second, different halide. For example, the at least one halide is devoid of
compounds such as CuC12,
C12, and BrC12-. Preferably, the at least one halide comprises an alkaline
chloride, even more
preferably an alkali metal chloride such as sodium chloride. The at least one
halide can also include
salts and/or acids comprising bromide and iodide including, but not limited
to, sodium bromide,
sodium iodide, potassium bromide, potassium iodide, rubidium bromide, rubidium
iodide, cesium
bromide, cesium iodide, magnesium bromide, magnesium iodide, calcium bromide,
calcium iodide,
strontium bromide, strontium iodide, ammonium bromide, ammonium iodide,
quaternary ammonium
bromide salts, and quaternary ammonium bromide salts. The at least one halide
is preferably
substantially devoid of fluoride ions.
[0031] The at least one acid is preferably a sulfur-containing species such as
sulfuric acid, sulfate
salts (e.g., sodium sulfate, potassium sulfate, rubidium sulfate, cesium
sulfate, magnesium sulfate,
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calcium sulfate, strontium sulfate, barium sulfate), sulfonic acid, sulfonic
acid derivatives, and
combinations thereof Sulfonic acid derivatives contemplated include
methanesulfonic acid (MSA),
ethanesulfonic acid, 2-hydroxyethanesulfonic acid, n-propanesulfonic acid,
isopropanesulfonic acid,
isobutenesulfonic acid, n-butanesulfonic acid, n-octanesulfonic acid),
benzenesulfonic acid,
benzenesulfonic acid derivatives, and combinations thereof Preferably, the at
least one acid
comprises sulfuric acid, preferably concentrated sulfuric acid.
[0032] The at least one solvent includes, but is not limited to, water,
methanol, ethanol, isopropanol,
butanol, pentanol, hexanol, 2-ethyl-1 -hexanol, heptanol, octanol, ethylene
glycol, propylene glycol,
butylene glycol, tetrahydrofurfuryl alcohol (THFA), butylene carbonate,
ethylene carbonate,
propylene carbonate, dipropylene glycol, diethylene glycol monomethyl ether,
triethylene glycol
monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol
monoethyl ether, ethylene
glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol
monobutyl ether,
triethylene glycol monobutyl ether, ethylene glycol monohexyl ether,
diethylene glycol monohexyl
ether, ethylene glycol phenyl ether, propylene glycol methyl ether,
dipropylene glycol methyl ether
(DPGME), tripropylene glycol methyl ether (TPGME),dipropylene glycol dimethyl
ether, dipropylene
glycol ethyl ether, propylene glycol n-propyl ether, dipropylene glycol n-
propyl ether (DPGPE),
tripropylene glycol n-propyl ether, propylene glycol n-butyl ether,
dipropylene glycol n-butyl ether,
tripropylene glycol n-butyl ether, propylene glycol phenyl ether, 2,3-
dihydrodecafluoropentane, ethyl
perfluorobutylether, methyl perfluorobutylether, alkyl carbonates, alkylene
carbonates, 4-methy1-2-
pentanol, tetramethylene glycol dimethyl ether, and combinations thereof
Preferably, the at least one
solvent comprises water.
[0033] In another embodiment, the leaching composition further comprises a
corrosion inhibitor,
specifically a base metal corrosion inhibitor, so as to ensure that the
leaching composition selectively
removes noble metals from the source relative to base metals. Accordingly, the
leaching composition
can comprise, consist of, or consist essentially of at least one oxidizing
agent, at least one halide, at
least one acid, at least one solvent, and at least one corrosion inhibitor. In
one embodiment, the
leaching composition comprises, consists of, or consists essentially of at
least one oxidizing agent, at
least one chloride salt, at least one acid, at least one solvent, and at least
one corrosion inhibitor. In
another embodiment, the leaching composition comprises, consists of, or
consists essentially of at
least one oxidizing agent, at least one chloride salt, at least one sulfur-
containing acid, at least one
solvent, and at least one corrosion inhibitor.
Corrosion inhibitors for passivating the base metals
include, but are not limited to, ascorbic acid, adenosine, adenine, L(+)-
ascorbic acid, isoascorbic acid,
ascorbic acid derivatives, citric acid, ethylenediamine, gallic acid, oxalic
acid, tannic acid,
ethylenediaminetetraacetic acid (EDTA), uric acid, 1,2,4-triazole (TAZ),
triazole derivatives (e.g.,
benzotriazole (BTA), tolyltriazole, 5-phenyl-benzotriazole, 5-nitro-
benzotriazole, 3-amino-5-
mercapto- 1 ,2,4-triazo le, 1 -amino- 1 ,2,4-triazo le,
hydroxyb enzotriazo le, 245 -amino-p enty1)-
b enzotriazo le, 1 -amino-1,2,3 -triazo le, 1 -amino-5 -methyl-1,2,3 -triazo
le, 3 -amino- 1 ,2,4 -triazo le, 3 -
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mercapto-1,2,4-triazole, 3-isopropyl-1,2,4-triazole, 5-phenylthiol-
benzotriazole, halo-benzotriazoles
(halo = F, Cl, Br or I), naphthotriazole), 2-mercaptobenzimidazole (MBI), 2-
mercaptobenzothiazole,
4-methyl-2-phenylimidazole, 2-mercaptothiazoline, 5-aminotetrazole (ATA), 5-
amino-1,3,4-
thiadiazole-2-thiol, 2,4-diamino-6-methyl-1,3,5-triazine, thiazole, triazine,
methyltetrazole, 1,3-
dimethy1-2-imidazolidinone, 1,5-
pentamethylenetetrazole, 1 -phenyl-5 -mercaptotetrazo le,
diaminomethyltriazine, imidazoline thione, mercaptobenzimidazole, 4-methy1-4H-
1,2,4-triazole-3-
thiol, 5-amino-1,3,4-thiadiazole-2-thiol, benzothiazole, and combinations
thereof Most preferably,
the passivating agent comprises BTA, TAZ, triazole derivatives, or
combinations thereof
[0034] The leaching composition of the second aspect can further comprise
noble metal chelators,
surfactants, defoamers, and combinations thereof, as readily determined by the
person skilled in the
art.
[0035] In a particularly preferred embodiment, the leaching composition
comprises, consists of, or
consists essentially of sodium chloride, sulfuric acid, nitric acid, and
water, with the proviso that the
leaching composition is substantially devoid of hydrogen peroxide, copper (II)
chloride, chlorine gas,
BrC12-, fluoride-containing compounds, hydroxide-containing compounds, ferrous
ions, a sulfur
compound comprising a sulfur atom with an oxidation state in the range of -2
to +5, and cyanides.
[0036] It should be appreciated that when the leaching composition comprises a
nitrate such as nitric
acid, during the leaching of the noble metals from the source, NO gases can be
emitted.
Accordingly, preferably the leaching process is carried out in a system
comprising a condenser,
wherein the NO gases can be collected and converted back into nitric acid, as
readily known to the
person skilled in the art. As understood by the person skilled in the art,
"NO" corresponds to
mononitrogen oxides such as NO and NO2.
[0037] Advantageously, the leaching composition is easily recyclable and can
be employed in a
closed-loop process generating minimal waste. For example, once the leaching
composition has been
exposed to the source and noble metals have been removed from the source, the
resulting leaching
composition including the noble metals can be recycled by reclaiming the noble
metals. The recycled
leaching solution can be reused, with or without the addition of fresh
leaching composition chemistry.
When necessary to dispose of, the leaching composition is essentially non-
toxic once the noble metals
are reclaimed and the excess acidity neutralized.
[0038] The leaching compositions described herein are easily formulated by
simple addition of the
respective ingredients and mixing to homogeneous condition. Furthermore, the
leaching composition
may be readily formulated as single-package formulations or multi-part
formulations that are mixed at
or before the point of use, e.g., the individual parts of the multi-part
formulation may be mixed at the
tool or in a storage tank upstream of the tool. The concentrations of the
respective ingredients may be
widely varied in specific multiples of the composition, i.e., more dilute or
more concentrated, and it
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will be appreciated that the compositions described herein can variously and
alternatively comprise,
consist or consist essentially of any combination of ingredients consistent
with the disclosure herein.
[0039] Advantageously, the leaching composition described herein is capable of
substantially
removing noble metals from a source at room temperature without the use of
high temperatures (e.g.,
temperatures greater than about 100 C), high pressures (e.g., pressures
greater than atmospheric
pressure) or electrodes to maintain the voltage of the composition in a
specific range. Moreover, the
leaching composition is more environmentally friendly than the prior art
cyanide compositions and
more inexpensive than tri-iodide compositions. For example, the vessel that is
used to process the
source to remove the noble metals can comprise any material without any
concern of corrosion or
degradation.
[0040] The noble metals can be reclaimed from the leaching composition using a
number of methods
including, but not limited to, electrochemical techniques such as
electrowinning, and chemical
reduction processes. For example, a reducing agent can be added to the
leaching composition
containing noble metals to cause their precipitation. Depending on the noble
metal content, various
reducing agents can be applied to cause selective or non-selective
precipitation of noble metals.
Precipitation can be done in a manner to avoid the contamination of the
leaching composition, so that
the leaching composition can be regenerated and reused in the next leaching
cycle after the noble
metals have been removed. Preferably, the reducing agent is a so-called
environmentally friendly
chemical. Moreover, preferably the reduction occurs rapidly with minimal
heating requirements. For
example, precipitation with SO2 is known to be selective for gold, non-
contaminating to the leaching
composition and inexpensive. Gold is precipitated as a fine powder that is
separated from the
leaching solution by filtration. To facilitate filtration, a flocculating
agent can be added to the
solution at the same time as the reducing agent, if the reducing agent is in
liquid or gaseous form. If
the reducing agent is in the form of powder, a flocculating agent can be added
after complete
dissolution of the reducing agent to prevent collection of particles of the
reducing agent. For
separation of gold powder, commercially available MAGNAFLOK-351 (Ciba
Specialty Chemicals)
that is typically used for concentrating finely ground gold ores, can be used.
The use of a non-ionic
flocculating agent is preferred to avoid the possible undesirable recovery of
iodine from the
composition.
[0041] Alternatively, the reducing agents can include, but are not limited to,
sodium borohydride,
ascorbic acid, diethyl malonate, sodium metabisulfite, polyphenon 60 (P60,
green tea extract),
glucose, and sodium citrate. For example, as introduced in International
Patent Application No.
PCT/US11/48449 filed on August 19, 2011 and entitled "Sustainable Process for
Reclaiming Precious
Metals and Base Metals from e-Waste," which is hereby incorporated by
reference herein in its
entirety, ascorbic acid introduced to a composition comprising Au3+ ions at pH
1 produces highly pure
gold metal. Sodium metabisulfite (SMB) can be added to a composition
comprising Au3+ ions at pH 1
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or pH 7 and produce highly pure gold metal. Alternatively, the noble metal
ions can be converted to
noble metals via electrowinning or electrochemical techniques. Any suitable
means can be used to
remove the precipitated noble metals. Settling and decanting, filtering the
solution through a filter
press or centrifuging are convenient procedures for such removal.
[0042] After separation of the solid gold by filtering, centrifugation or any
other appropriate method,
the leaching composition may still include leached silver and palladium ions.
A selective reducing
agent may be added for precipitation of silver, such as hydroxylamine. The use
of a flocculating
agent is suggested to facilitate filtration. After separation of precipitated
silver, palladium can be
precipitated, for example, with the use of a stabilized alkali metal
borohydride and a flocculating
agent.
[0043] It should be appreciated that the source material subsequent to
leaching can be rinsed (e.g.,
with water) to further recover the residual leaching composition on the
surface of the source material,
which can contain very significant amounts of dissolved noble metals.
[0044] Electrowinning is a common way of gold recovery from solutions, but if
the rinse water
comprising dissolved gold is recovered, conventional electrowinning becomes
ineffective as gold is
present in rinse water in small concentrations. The removal of gold from rinse
water solutions can
become effective if high surface area (HSA) electrodes are used for
electrowinning. HSA
electrowinning may economically remove gold having a concentration greater
than 10 ppm down to
ppb level. Iodide can also be oxidized and recovered using the same process if
an undivided
electrowinning cell is used.
[0045] The features and advantages of the invention are more fully illustrated
by the following non-
limiting examples, wherein all parts and percentages are by weight, unless
otherwise expressly stated.
Example 1
[0046] 40 g of a leaching composition comprising 30 wt% water, 29 wt% sulfuric
acid (96%), 18
wt% nitric acid (70%) and 23 wt% saturated sodium chloride was prepared. The
leaching
composition was divided into four test tubes containing lOg each of the
leaching composition. Gold
fingers, pure Pd, pure Pt and pure Ag were added to each of the test tubes and
processed as indicated
and the pre- and post-weight of the noble metals determined, as summarized in
Table 1.
Au Ag Pd Pt
processed at 60 C for 60 minutes in 10 g leaching composition
pre-weight (g) 0.084 0.098 0.039 0.046
post-weight (g) 0 0.099 0.01 0.048
additional Au/Pd metals added to same solution and processed for 120 min at 60
C
pre-weight(g) 0.183 0.112
post-weight (g) 0 0
additional Au/Pd metals added to same solution and processed for 3 days at
room temperature
pre-weight(g) 0.102 0.052
CA 02943992 2016-09-26
WO 2015/130607 PCT/US2015/017088
post-weight (g) 0.057 0 0.041
total dissolved 0.312 0 0.203 0.005
metal (g)
[0047] It can be seen that the leaching composition effectively and
efficiently dissolved gold and
palladium and could be loaded with additional metal as more source is added to
said composition.
[0048] Although the invention has been variously disclosed herein with
reference to illustrative
embodiments and features, it will be appreciated that the embodiments and
features described
hereinabove are not intended to limit the invention, and that other
variations, modifications and other
embodiments will suggest themselves to those of ordinary skill in the art,
based on the disclosure
herein. The invention therefore is to be broadly construed, as encompassing
all such variations,
modifications and alternative embodiments within the spirit and scope of the
claims
hereafter set forth.
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