U.S. patent application number 15/121622 was filed with the patent office on 2016-12-15 for wet based formulations for the selective removal of noble metals.
The applicant listed for this patent is ENTEGRIS, INC.. Invention is credited to Tianniu CHEN, Ping JIANG, Michael B. KORZENSKI.
Application Number | 20160362804 15/121622 |
Document ID | / |
Family ID | 54009528 |
Filed Date | 2016-12-15 |
United States Patent
Application |
20160362804 |
Kind Code |
A1 |
CHEN; Tianniu ; et
al. |
December 15, 2016 |
WET BASED FORMULATIONS FOR THE SELECTIVE REMOVAL OF NOBLE
METALS
Abstract
Compositions and processes for leaching noble metals from
materials comprising said noble metals. Advantageously, the
halide-based composition is environmentally friendly and
effectively removes noble metals at room temperature without the
need for high pressures and electrodes.
Inventors: |
CHEN; Tianniu; (Westford,
MA) ; JIANG; Ping; (Danbury, CT) ; KORZENSKI;
Michael B.; (Bethel, CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ENTEGRIS, INC. |
BILLERICA |
MA |
US |
|
|
Family ID: |
54009528 |
Appl. No.: |
15/121622 |
Filed: |
February 23, 2015 |
PCT Filed: |
February 23, 2015 |
PCT NO: |
PCT/US15/17088 |
371 Date: |
August 25, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61944366 |
Feb 25, 2014 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22B 11/04 20130101;
C22B 3/08 20130101; C22B 3/44 20130101; C22B 11/042 20130101; C23F
1/30 20130101; C25C 1/20 20130101; Y02P 10/20 20151101; C22B 3/065
20130101; C22B 3/22 20130101 |
International
Class: |
C25C 1/20 20060101
C25C001/20; C22B 3/22 20060101 C22B003/22; C22B 3/08 20060101
C22B003/08; C22B 3/00 20060101 C22B003/00; C22B 3/06 20060101
C22B003/06 |
Claims
1. A leaching composition comprising, at least one oxidizing agent,
at least one halide, at least one acid, and at least one
solvent.
2. The leaching composition of claim 1, wherein the composition
includes a pH of less than about 2.
3. The leaching composition of claim 1, wherein the at least one
oxidizing agent comprises at least one species selected from the
group consisting of ozone, nitric acid (HNO.sub.3), bubbled air,
cyclohexylaminosulfonic acid, hydrogen peroxide (H.sub.2O.sub.2),
oxone, ammonium peroxomonosulfate, ammonium chlorite
(NH.sub.4ClO.sub.2), ammonium chlorate (NH.sub.4ClO.sub.3),
ammonium iodate (NH.sub.4IO.sub.3), ammonium perborate
(NH.sub.4BO.sub.3), ammonium perchlorate (NH.sub.4ClO.sub.4),
ammonium periodate (NH.sub.4IO.sub.3), ammonium persulfate
((NH.sub.4).sub.2S.sub.2O.sub.8), ammonium hypochlorite
(NH.sub.4ClO), sodium persulfate (Na.sub.2S.sub.2O.sub.8), sodium
hypochlorite (NaClO)), potassium polyatomic salts (e.g., potassium
iodate (KIO.sub.3), potassium permanganate (KMnO.sub.4), potassium
persulfate, potassium persulfate (K.sub.2S.sub.2O.sub.8), potassium
hypochlorite (KClO), tetramethylammonium chlorite
((N(CH.sub.3).sub.4)ClO.sub.2), tetramethylammonium chlorate
((N(CH.sub.3).sub.4)ClO.sub.3), tetramethylammonium iodate
((N(CH.sub.3).sub.4)IO.sub.3), tetramethylammonium perborate
((N(CH.sub.3).sub.4)BO.sub.3), tetramethylammonium perchlorate
((N(CH.sub.3).sub.4)ClO.sub.4), tetramethylammonium periodate
((N(CH.sub.3).sub.4)IO.sub.4), tetramethylammonium persulfate
((N(CH.sub.3).sub.4)S.sub.2O.sub.8), tetrabutylammonium
peroxomonosulfate, peroxomonosulfuric acid, urea hydrogen peroxide
((CO(NH.sub.2).sub.2)H.sub.2O.sub.2), peracetic acid
(CH.sub.3(CO)OOH), sodium nitrate, potassium nitrate, ammonium
nitrate, and combinations thereof.
4. The leaching composition of claim 1, wherein the at least one
oxidizing agent comprises a nitrate salt selected from the group
consisting of nitric acid, sodium nitrate, potassium nitrate,
ammonium nitrate, tetraalkylammonium nitrate, and combinations
thereof, preferably nitric acid.
5. The leaching composition of claim 1, wherein the at least one
halide comprises an alkaline chloride.
6. The leaching composition of claim 1, wherein the at least one
halide comprises a chloride species selected from the group
consisting of hydrochloric acid, 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 species cannot include copper chloride, chlorine
gas, or a second, different halide in the compound, preferably
sodium chloride.
7. The leaching composition of claim 1, wherein the at least one
acid is a sulfur-containing acid, selected from the group
consisting of sulfuric acid, sodium sulfate, potassium sulfate,
rubidium sulfate, cesium sulfate, magnesium sulfate, calcium
sulfate, strontium sulfate, barium sulfate, sulfonic acid, sulfonic
acid derivatives, and combinations thereof.
8. (canceled)
9. The leaching composition of claim 1, wherein the composition
further comprises at least one of surfactants, defoamers, and
combinations thereof.
10. The leaching composition of claim 1, wherein the composition
comprises nitric acid, sodium chloride, sulfuric acid, and
water.
11. The leaching composition of claim 1, wherein the composition
further comprises at least one corrosion inhibitor.
12. The leaching composition of claim 1, wherein the leaching
composition is substantially devoid of hydrogen peroxide,
fluoride-containing compounds, CuCl.sub.2, Cl.sub.2,
BrCl.sub.2.sup.-, 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.
13. A method of removing noble metals from a source, said method
comprising contacting said source under conditions with a leaching
composition, wherein said noble metals are dissolved or otherwise
solubilized in the leaching composition, wherein said leaching
composition comprises at least one oxidizing agent, at least one
halide, at least one acid, and at least one solvent.
14. (canceled)
15. The method of claim 13, wherein the source is selected from the
group consisting of ores, jewelry, scraps comprising noble metals,
waste materials comprising noble metals, electronic waste materials
comprising noble metals, alloys, catalyst materials, and industrial
sources.
16. The method of claim 13, wherein the source is crushed, cracked,
pulverized, shredded, or ground to expose the noble metals.
17. The method of claim 13, wherein the leaching composition and
source are agitated such that the source is substantially exposed
to the leaching composition.
18. The method of claim 13, wherein the conditions are selected
from the group consisting of time of from about 1 min to about 120
minutes, temperature in a range of from about 20.degree. C. to
about 100.degree. C., and combinations thereof.
19. (canceled)
20. The method of claim 13, further comprising reclaiming the noble
metals from the leaching composition by electrochemical techniques
such as electrowinning, or chemical reduction processes.
21. The method of claim 13, wherein the removal of noble metals
from the source is effectuated at temperatures less than about
100.degree. C., pressures not greater than atmospheric pressure,
and without the use of electrodes.
22. The method of claim 13, wherein the noble metals comprise a
species selected from the group consisting of gold, silver,
ruthenium, osmium, rhodium, iridium, palladium, platinum, alloys
comprising same, and combinations thereof.
23. (canceled)
Description
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 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.
[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
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.degree. C. to about
100.degree. C., preferably in a range from about 20.degree. C. to
about 60.degree. C., more preferably about 20.degree. C. to about
40.degree. C., and most preferably about room temperature. Such
contacting times and 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:
TABLE-US-00001 component preferably more preferably most preferably
at least one about 1 wt % to about 1 wt % to about 4 wt % to
oxidizing agent about 40 wt % about 30 wt % about 20 wt % at least
one about 1 wt % to about 2 wt % to about 3 wt % to halide about 40
wt % about 30 wt % about 15 wt % at least one about 1 wt % to about
2 wt % to about 7 wt % to acid about 50 wt % about 40 wt % about 30
wt % at least one about 1 wt % to about 1 wt % to about 35 wt % to
solvent about 93 wt % about 87 wt % about 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:
TABLE-US-00002 component preferably more preferably most preferably
at least one about 1 wt % to about 1 wt % to about 4 wt % to
nitrate salt about 40 wt % about 30 wt % about 20 wt % oxidizing
agent at least one about 1 wt % to about 2 wt % to about 3 wt % to
alkaline about 40 wt % about 30 wt % about 15 wt % chloride at
least one about 1 wt % to about 2 wt % to about 7 wt % to sulfur-
about 50 wt % about 40 wt % about 30 wt % containing acid at least
one about 1 wt % to about 1 wt % to about 35 wt % to solvent about
93 wt % about 87 wt % about 86 wt %
[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
(HNO.sub.3), bubbled air, cyclohexylaminosulfonic acid, hydrogen
peroxide (H.sub.2O.sub.2), oxone (potassium peroxymonosulfate,
2KHSO.sub.5.KHSO.sub.4.K.sub.2SO.sub.4), ammonium polyatomic salts
(e.g., ammonium peroxomonosulfate, ammonium chlorite
(NH.sub.4ClO.sub.2), ammonium chlorate (NH.sub.4ClO.sub.3),
ammonium iodate (NH.sub.4IO.sub.3), ammonium perborate
(NH.sub.4BO.sub.3), ammonium perchlorate (NH.sub.4ClO.sub.4),
ammonium periodate (NH.sub.4IO.sub.3), ammonium persulfate
((NH.sub.4).sub.2S.sub.2O.sub.8), ammonium hypochlorite
(NH.sub.4ClO)), sodium polyatomic salts (e.g., sodium persulfate
(Na.sub.2S.sub.2O.sub.8), sodium hypochlorite (NaClO)), potassium
polyatomic salts (e.g., potassium iodate (KIO.sub.3), potassium
permanganate (KMnO.sub.4), potassium persulfate, potassium
persulfate (K.sub.2S.sub.2O.sub.8), potassium hypochlorite (KClO)),
tetramethylammonium polyatomic salts (e.g., tetramethylammonium
chlorite ((N(CH.sub.3).sub.4)ClO.sub.2), tetramethylammonium
chlorate ((N(CH.sub.3).sub.4)ClO.sub.3), tetramethylammonium iodate
((N(CH.sub.3).sub.4)IO.sub.3), tetramethylammonium perborate
((N(CH.sub.3).sub.4)BO.sub.3), tetramethylammonium perchlorate
((N(CH.sub.3).sub.4)ClO.sub.4), tetramethylammonium periodate
((N(CH.sub.3).sub.4)IO.sub.4), tetramethylammonium persulfate
((N(CH.sub.3).sub.4)S.sub.2O.sub.8), tetramethylammonium nitrate),
tetrabutylammonium polyatomic salts (e.g., tetrabutylammonium
peroxomonosulfate, tetrabutylammonium nitrate), peroxomonosulfuric
acid, urea hydrogen peroxide ((CO(NH.sub.2).sub.2)H.sub.2O.sub.2),
peracetic acid (CH.sub.3(CO)OOH), 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 CuCl.sub.2,
Cl.sub.2, and BrCl.sub.2.sup.-. 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, 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-methyl-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-triazole, 1-amino-1,2,4-triazole,
hydroxybenzotriazole, 2-(5-amino-pentyl)-benzotriazole,
1-amino-1,2,3-triazole, 1-amino-5-methyl-1,2,3 -triazole,
3-amino-1,2,4-triazole, 3-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-dimethyl-2-imidazolidinone,
1,5-pentamethylenetetrazole, 1-phenyl-5-mercaptotetrazole,
diaminomethyltriazine, imidazoline thione, mercaptobenzimidazole,
4-methyl-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,
BrCl.sub.2.sup.-, 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.sub.x gases can be emitted.
Accordingly, preferably the leaching process is carried out in a
system comprising a condenser, wherein the NO.sub.x 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.sub.x" corresponds to mononitrogen oxides such as
NO and NO.sub.2.
[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 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.degree. 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 SO.sub.2 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 Aug.
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 Au.sup.3+ ions at pH 1 produces highly pure
gold metal. Sodium metabisulfite (SMB) can be added to a
composition comprising Au.sup.3+ ions at pH 1 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 10 g 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.
TABLE-US-00003 Au Ag Pd Pt processed at 60.degree. 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.degree. 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 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.
* * * * *