5,320,759
Jun. 14, 1994
[11]
[45]
111111.111111111111111111111111111111111111111111111111111111111111111111111
USOO5320759A
Patent Number:
Date of Patent:
United States Patent [19]
Coltrinari
32 Claims, No Drawings
A process for selectively recovering dissolved heavy
metals from a solution is disclosed that involves selectively
reacting a xanthate with such dissolved heavy
metals. Selective reaction of a xanthate with selected
dissolved hea'Vy metals is accomplished by conducting
the reaction under conditions such that only some of the
heavy metals react with the xanthate, to the exclusion of
reaction with other dissolved heavy metals. Selectivity
of the reaction is particularly influenced by the pH at
which the reaction occurs. Typically, the reaction
should occur at a pH below about 4.0. Xanthates, once
reacted, can be separated from the heavy metal xanthate
reaction product and recycled for use within the process.
Purified heavy metal product can be produced if
desired.
OTHER PUBLICATIONS
Takahashi et aI., "A Study on Removal of Cadmium
Ion from Mine Water by Flotation Method Utilizing
Xanthate as Selective Precipitant," Technology Reports,
Tohoku Univ., vol. 36, No.2, pp. 203-212 (Japan
1971).
Ohyama et aI., "Utilization of Xanthate as Selective
Precipitant for Nickel and Cobalt Ions," J. Min. Met.
Inst. Japan, 78 pp. 391-396 (Japan 1962).
Yamasaki et aI., "Utilization of Xanthate as a Selective
Precipitant for Nicle and Cobalt Ions, (2nd Report)-
Separation of Nickel from Cobalt," J. Min. Met. Inst.
Japan, 79, pp. 97-104 (Japan 1963).
"Heavy metal Removal from Wastewater with Starch
Xanthate" by R. E. Wing-Proceedings 29th Ind. Waste
Conf.-Perdue Univ. (May 1974).
"In Flotation" -F. Sebba pp. 88-89. Elsevier Publishing
House-1962.
Chemical Abstracts vol. 76, (1972) 131189k "Removal
of Cadmium Ion from Wastewater by a Flotation
Method Utilizing Xanthate as a Selective Precipitant".
Primary Examiner-Thomas M. Lithgow
Attorney, Agent, or Firm-Sheridan Ross & McIntosh
[54] SELECTIVE RECOVERY OF REAVY
METALS USING XANTHATES
[75] Inventor: Enzo Coltrinari, Golden, Colo.
[73] Assignee: Hazen Research, Inc., Golden, Colo.
[21] Appl. No.: 897,351
[22] Filed: Jun. 11, 1992
[51] Int. Cl.s C02F 1/54; C02F 1/56;
C02F 1/62; C02F 1/64
[52] U.S. Cl•.................................... 210/705; 210/710;
210/722; 210/724; 210/725;210/727; 210/728;
210/730; 210/731; 210/912; 210/913; 210/914;
423/43;423/26; 423/36; 423/37; 423/101;
423/140
[58] Field of Search 210/705, 706, 707, 912,
210/913,914,724,725,729,730,728,731,710,
722, 727; 423/42, 87, 89, 101, 140, 43, 26, 36,
37; 209/166, 167
[56] References Cited
U.S. PATENT DOCUMENTS
2,750,254 6/1956 Blake 209/167
3,054,746 9/1962 Gaden 209/166
3,203,968 8/1965 Sebba 209/167
3,800,024 3/1974 Forsell.
3,947,354 3/1976 Swanson.
3,979,286 9/1976 Wing 210/731
4,018,680 4/1977 Kupfer.
4,051,316 9/1977 Wing 2101731
4,054,516 10/1977 Izumi 209/167
4,083,783 4/1978 Wing 2101731
4,166,032 8/1979 Hanway 210/675
4,238,329 12/1980 Zievers 210/714
4,680,126 7/1987 Frankard.
4,844,873 7/1989 Lebon 210/705
4,986,970 1/1991 Haraidsen.
5,009,793 4/1991 Muller.
5,102,556 4/1992 Wong.
5,128,047 7/1992 Stewan 210/912
5,160,631 11/1992 Frost.
5,262,063 11/1993 Yen.
FOREIGN PATENT DOCUMENTS
4639544 11/1971 Japan 210/730
5009106 4/1975 Japan 210/705
[57] ABSTRACf
5,320,759
2
SUMMARY OF INVENTION
DETAILED DESCRIPTION OF THE
INVENTION
The present invention provides a process for selectively
recovering dissolved heavy metals from liquid
feed streams in which those heavy metals are dissolved,
Xanthates are reacted with dissolved heavy metals in
the solution under conditions, particularly with respect
to pH, at which some of the dissolved heavy metals
react with the xanthate to the exclusion of other dissolved
heavy metals. The heavy metals that selectively
react with the xanthate, in the form of a heavy metal
xanthate reaction product, can then be physically separated
from the solution by known solid-liquid separa-
1
FIELD OF THE INVENTION
BACKGROUND OF INVENTION
SELECITVE RECOVERY OF HEAVY METALS
USING XANTHATES The present invention involves selectively recovering
dissolved heavy metals from liquid feed streams in
5 which those selected heavy metals are dissolved. Selectively
recovering dissolved heavy metals according to
the invention comprises reacting a xanthate with selected
dissolved heavy metals under conditions, and
particularly with respect to pH, such that reaction of
10 xanthate with nonselected dissolved heavy metals is
excluded.
Liquid streams used in or generated by industrial The feed to the process can be any liquid containing
processes and drainage from mines, waste disposal sites dissolved heavy metals. Suitable sources of feed streams
and other industrial sites often contain dissolved heavy are varied, but include leach liquors, drainage from
metals that are toxic and, if not removed, will be dis- 15 mines or mining operations, drainage from waste discharged
into the environment causing serious pollution posal or industrial sites, effluent from industrial proproblems.
Also, many of these heavy metals are of sig- cesses, and brines from extractive industries. In one
nificant commercial value. A need exists to recover embodiment of the invention, the feed stream is a leach
these heavy metals to conserve valuable metals and to liquor resulting from leaching of a metal-containing ore
prevent environmental pollution. 20 or ore deposit, and preferably a leach liquor resulting
Heavy metals dissolved in waste and drainage liquids from heap-leaching of copper ore. In another embodiare
often present in low, yet toxic, concentrations. Cur- ment, valuable heavy metals, such as cobalt, nickel, and
rent techniques for recovering heavy metals at these copper are selectively recovered from such copper
low concentrations are either expensive or inefficient. heap-leach liquors after standard copper recovery tech-
Also, it is difficult to produce purified products of valu- 25 niques.
able heavy metals following heavy metal recovery tech- In one embodiment of the invention, selected disniques
that do not allow for selective recovery of heavy solved heavy metals are selectively recovered to the
metals. Selective recovery of heavy metals is desirable exclusion of dissolved iron(II) and/or dissolved zinc. In
so that revenue from sale of valuable metals recovered another embodiment, dissolved iron(III) is reduced to
can offset the cost of environmental clean-up of waste 30 iron(II) prior to reacting a xanthate with selected disand
drainage liquids and to conserve these valuable solved heavy metals.
metals, The process of the present invention can be practiced
The present invention involves the use ofxanthates to in on7 or in m';lltiple recovery. steps, each involving
selectively recover dissolved heavy metals from liquid selectIvely reactIng a xanthate wI~h sele?ted heavy metstreams.
Different affinities exhibited by different heavy 35 als. 1?e pr~cess of the present InventIon can al~o be
metals for reacting with xanthated sawdust have been combIned WIth o~her heavy mC?tal re~overy te~hniques.
reported by Flynn et aI., Absorption ofHeavy Metal Ions In one embodlme~t of the InVentIOn, a s.olid heavy
by Xanthated Sawdust, Bureau of Mines Report of Inves- metal xanthate reactIOn product ca~ be phys~cally sepatigating
Actions No. 8427, U.S. Department of the Inte- rated fr?m the feed stream follOWIng rea?tlo.n ~f xan-
n.or (1980). S0 IubI'll'tl'es 0 f heavy metal xanthates I.n 40 thate.W,Ithbselfelcted.he,avy metals.fiSucdh soltbdo-ldt'quld sepwater
are reported in Encyclopedia ofChemical Technol- aratlon IS y otatlOn In one pre erre ~m tment.
d't d b Ki k-Oth 3d Ed't' V I 24 648 Selected heavy metals can be chemIcally separated ogy, e ley r mer, I lon, o. , p. f h h I h t . od t if d
(1981) I . P bI' h N Y k NY rom t e eavy meta xant a e reactIOn pr uc, e-
, ntersclence u IS er, ~w or, . . sired. Individual heavy metals can be concentrated and
Use of xanthates t~ recover dIssolved heavy metals 45 purified heavy metal products can be produced.
has been repo:ted. WIng et aI., Rem,oval ofHeavy Metals Any xanthate salt capable of reacting with the sefrom
Industna! Waste Waters U~zng Insoluble Starch lected heavy metals can be used in the process of the
X,anthate, EnVIronmental Prot~ctlon Technology ~e- present invention. However, such xanthates are preferanes,
PB-283 792, U..S. EnVIronmental P~otectlon bly salts of sodium or potassium, and more preferably
Agency (May 1978), dIscusses the use of an Insoluble 50 salts of sodium. In one embodiment of the invention,
xanthated starch to recov~r heav~ m7~s from waste xanthates may be recycled in the process for further
waters generated by a pnnted CIrCUI.t Industry, lead reaction with dissolved heavy metals following chemibattery.
manufacturers, and a brass mIll. Flynn et al., cal separation of heavy metals from the heavy metal
AbsorptIOn of Heavy Metal Ions by Xanthated Sawdust, xanthate reaction product.
Bureau of Mines Report of Investigations No. 8427, 55
U.S. Department of the Interior (1980), discusses the
use of xanthated sawdust to recover dissolved heavy
metals from dilute aqueous solutions, mine-drainage
waters, and brines. In contrast to the present invention,
however, these references, disclose the use of certain 60
xanthates only as a means for nonselectively recovering
dissolved heavy metals. These references do not disclose
a process for selectively recovering dissolved
heavy metals using xanthates. The value of many heavy
metals can be realized only if selective recovery can be 65
achieved. Also, nonselective recovery of all heavy metals
is inefficient because some heavy metals may be
efficiently removed by less expensive processes.
The present invention relates to an improved process
for selectively recovering dissolved heavy metals from
solution.
5,320,759
3
tion processes, such as by flotation. Metal values can
then be chemicalIy separated from the heavy metal
xanthate reaction product by known processes, such as
by hydrometalIurgical techniques involving solvent
extraction folIowed by electrowinning to produce puri- 5
fied heavy metal products. The unreacted dissolved
heavy metals, remaining dissolved in the feed solution,
may then be recovered from the solution by subsequent
applications of the process of the present invention or
by other processes, if recovery of such remaining dis- 10
solved heavy metals is desired.
As used herein, the term heavy metals generally refers
to metals such as vanadium, chromium, manganese,
iron, cobalt, nickel, copper, zinc, arsenic, germanium,
molybdenum, gold, cadmium, tin, antinomy, platinum, 15
mercury, lead, bismuth and others, more preferably it
refers to iron, cobalt, nickel, copper, zinc, arsenic, germanium,
cadmium, antimony, and bismuth, and most
preferably it refers to iron, cobalt, nickel, copper, and
zinc. Heavy metals generalIy have a specific gravity in 20
excess of five. Many heavy metals such as lead, mercury,
copper, cadmium and others are known to be
toxic in low concentrations. Other heavy metals, such
as iron and zinc may be toxic at higher concentrations.
Many heavy metals, as for example, cobalt, nickel and 25
copper, are of significant commercial value.
Feed streams for the process of the present invention
include any liquids containing dissolved heavy metals,
preferably aqueous solutions, and more preferably
acidic aqueous solutions. Sources of feed streams are 30
varied. Such sources include leach liquors, drainage
from mines or mining operations, drainage from waste
disposal or industrial sites, effiuent from industrial processes
involving heavy metals, and brines from extractive
industries such as geothermal energy and petro- 3S
leum production. As used herein, leach liquor refers to
any liquid resulting from the treatment of any material
with a liquid to dissolve heavy metals present in that
material into the liquid in a leaching operation. Leach
liquor includes such liquid both before and after a pri- 40
mary or subsequent process for recovering dissolved
heavy metals from the leach liquor. The process of the
present invention is useful as a primary or as a secondary
or other subsidiary heavy metal recovery process.
A preferred feed stream is a leach liquor resulting 4S
from leaching of a metal-containing ore or ore deposit,
more preferably a leach liquor resulting from heapleaching
of copper ore, and most preferably a leach
liquor resulting from heap-leaching of copper ore
which leach liquor has already been subjected to stan- 50
dard copper recovery. In a copper heap-leach process,
an acidic solution, preferably an aqueous acidic solution,
more preferably an aqueous solution of sulfuric
acid, nitric acid or hydrochloric acid, and most preferably
an aqueous solution of sulfuric acid, is used to leach SS
copper from copper ore. One current industry practice
is to treat the resulting leach liquor by standard hydrometalIurgical
metal recovery techniques, such as by
solvent extraction followed by electrowinning, to produce
a purified copper product. Another current indus- 60
try practice is to remove copper from the resulting
leach liquor by cementation of metallic copper on iron,
which is often added as iron scrap. The cementation
product can then be processed using standard pyrometallurgical
techniques to produce a purified copper prod- 6S
uct. Low concentrations of copper, itself a valuable
heavy metal, and other heavy metals, some of significant
value such as cobalt and nickel, and particularly
4
cobalt, remain dissolved in the leach liquor folIowing
such standard copper recovery techniques. The process
ofthe present invention is useful for selectively recovering
heavy metals, including valuable copper, nickel, and
cobalt, remaining dissolved in such copper heap-leach
liquors.
According to the process of the present invention,
under appropriate process conditions, xanthates react
with some of the heavy metals dissolved in a suitable
feed stream, as previously described, to the exclusion of
reaction with other dissolved heavy metals, thereby
allowing selective recovery of selected heavy metals to
the exclusion of nonselected heavy metals. Although
total exclusion of any reaction between nonselected
dissolved heavy metals and a xanthate is usually preferred,
such total exclusion is not necessary according
to the process ofthe present invention. Partial exclusion
of nonselected heavy metals is often acceptable, and
depending upon the circumstances, may be preferred.
Selective recovery of selected dissolved heavy metals
according to the process of the present invention is
often advantageous even if minor quantities of nonselected
dissolved heavy metals also react with the xanthate.
An acceptable extent of reaction of nonselected
dissolved heavy metals depends. on particular conditions,
such as the nature of the specific embodiment and
economics. Factors such as the relative concentrations
of selected and nonselected heavy metals dissolved in
the feed stream and the relative amount of xanthate
reagent contacted with the feed stream can affect the
amount of reaction between a xanthate and nonselected
dissolved heavy metals.
Selective reaction of dissolved heavy metals can be
accomplished by controlIing process parameters, such
as temperature, pressure, the relative amount of xanthate
reagent contacted with the feed stream, and pH.
In a preferred embodiment, selectivity of the reaction is
accomplished by controlIing the pH of the solution. In
another preferred embodiment, the process of the present
invention is conducted at ambient temperature and
atmospheric pressure.
A preferred embodiment of the present invention
comprises selectively reacting a xanthate with heavy
metals dissolved in a feed stream at a solution pH such
that only selected dissolved heavy metals react with the
xanthate. In this embodiment, those heavy metals which
react are selectively recovered, to the exclusion of
heavy metals that do not react. The proper pH to effect
the desired selective recovery reaction can be determined
according to disclosures provided herein, or by
simple experimentation depending on makeup of the
feed stream and the selectivity desired. If the pH of a
feed stream is not at the desired reaction pH, then the
pH of the stream may be increased or decreased, such as
by the addition of base or acid, prior to reacting the
xanthate with the heavy metals dissolved in the feed
stream. The pH of the feed stream during the reaction
can likewise be controlIed by adding base or acid. Although
the optimum pH for reacting the xanthate with
selected heavy metals depends on process conditions
and the selectivity desired, the pH of reaction will typicalIy
be below about 4.0, preferably below about 3.5,
more preferably below about 3.3, and most preferably
below about 3.0.
In one embodiment, the process of the present invention
comprises contacting the feed stream containing
dissolved heavy metals with at least 50%, and preferably
in excess of 100%, of the stoichiometric quantity of
s
II
-o-c-s
Preferably, the anionic constituent of xanthate is of the
general formula
wherein R is any carbon-containing organic radical and
n is an integer of one or more indicating the number of
xanthate functional groups independently attached directly
to R. Preferably R is an alkyl or substituted alkyl,
more preferably R is ethyl, propyl, butyl, or pentyl, and
even more preferably, R is ethyl. IfR is a carbohydrate,
a substituted carbohydrate or a carbohydrate derivative,
then R is preferably cellulosic (such as with xanthated
sawdust), and preferably contains multiple xanthate
functional groups. If R is a polymerized carbohydrate
(such as a starch), a substituted polymerized carbohydrate,
or a derivative of a polymerized carbohydrate,
then R preferably contains multiple xanthate
functional groups.
Such xanthates are preferably salts of sodium or potassium,
more preferably salts of sodium, even more
preferably such xanthates are selected from the group
consisting of sodium ethylxanthate (NaC2HsOCS2),
potassium ethylxanthate (KC2HSOCS2), xanthated cellulosic
fibers (such as, for example, xanthated sawdust),
xanthated starches and combinations thereof, and most
preferably such xanthates are selected from the group
consisting of sodium ethylxanthate, potassium ethylxanthate,
and combinations thereof.
Methods for preparing xanthates are known in the
art. Xanthates are often unstable and should be used
soon enough following preparation to avoid significant
degradation. In one embodiment, a xanthate may be
prepared on site and used prior to degradation. In a
preferred embodiment, sodium ethylxanthate or potas-
5,320,759
5 6
xanthate relative to the amount of selected dissolved In a preferred embodiment of the invention, feed to
heavy metals assuming complete reaction with such the process is a leach liquor from a copper heap-leach
selected dissolved heavy metals. The xanthate is typi- process subsequent to traditional recovery of copper
cally of a quantity from about 50% to about 500% of from the leach liquor. Preferably, the dissolved heavy
such stoichiometric quantity, and preferably between 5 metals are present as sulfates. Preferably, dissolved
100% and 150% of such stoichiometric quantity. iron(III) is reduced to iron(II) prior to reacting a xan-
In one embodiment, the process of the present inven- thate with selected dissolved heavy metals, as prevition
comprises selectively recovering dissolved heavy ously described. Such reduction may be accomplished
metals in a feed stream, to the exclusion of dissolved using any suitable reducing agent as previously deiron(
II) and/or dissolved zinc. Dissolved iron is fre- 10 scribed. A xanthate is then reacted with selected disquently
present in suitable feed streams, often in high solved heavy metals under such conditions that the
concentrations relative to other dissolved heavy metals, xanthate reacts with dissolved cobalt, nickel and/or
and such dissolved iron can complicate the recovery of copper to the exclusion of zinc and/or iron(II). AIother
dissolved heavy metals or the subsequent produc- though the optimum pH for selectively reacting the
tion of purified valuable heavy metal products. Also, 15 xanthate with dissolved heavy metals to effect the dedissolved
iron can often be effectively removed from sired recovery of cobalt, nickel and copper will vary
feed streams by methods that are less expensive than the with the composition of the feed stream, the relative
process of the present invention. Likewise, dissolved amount of xanthate contacted with the feed stream, and
zinc can complicate recovery of other dissolved heavy other process conditions, the pH of reaction should
metals and subsequent production of purified valuable 20 generally be below about 4.0, preferably below about
heavy metal products, and is also often recoverable 3.5, more preferably below about 3.3, and most preferafrom
feed streams by methods t~at are. less expens!ve bly below about 3.0.
than the processes of the present mventlon. Accordmg As used herein the term xanthate includes all salts
to this embodiment, heavy metals such as iron(III), wherein the anio~ic constituent of such salt contains
copper, cobalt, nickel, bismuth, cadmium, arsenic, sil- 25 one or more of the xanthate functional group
ver, gold, mercury and lead are selectively reacted with
a xanthate to the exclusion of dissolved iron(II) and/or
dissolved zinc. To the extent that dissolved iron is present
as iron(II), complications and/or inefficiencies
caused by such dissolved iron can be reduced or 30
avoided by recovering other dissolved heavy metals to
the exclusion of iron(II). Likewise, complications and/
or ineffectiveness caused by dissolved zinc can be
reduced or avoided by recovering dissolved heavy
metals to the exclusion of zinc. Although the optimum 35
pH for reacting the xanthate with selected heavy metals
to effect the desired exclusion of reactions with zinc
and/or iron(II) will vary with the composition of the
feed solution, the relative amount of xanthate contacted
with the feed solution and other process conditions, the 40
reaction between the xanthate and the selected dissolved
heavy metals should generally occur at a pH
below about 4.0, preferably below about 3.5, more preferably
below about 3.3, and most preferably below
about 3.0. Although dissolved zinc and iron(lI) are 45
often both present in feed solutions, this embodiment
can also be used when only one of these constituents is
present in the feed stream.
Another embodiment of the invention comprises reducing
iron(III) dissolved in the feed stream to iron(lI) 50
prior to reacting a xanthate with selected dissolved
heavy metals. At low pH values suitable for selective
recovery herein, iron(III) has a higher affmity for reacting
with xanthates than iron(II). By reducing iron(III)
to iron(II), and thereafter reacting a xanthate with se- 55
lected dissolved heavy metals to the exclusion of iron(
II), complications and/or inefficiencies caused by recovering
dissolved iron can be limited. Such reduction
may be effected using any reducing agent suitable for
reducing iron(III) to iron(II), such as, for example, 60
elemental iron or metal sulfides. Metal sulfides used as
reductants are preferably sodium, potassium, or calcium
sulfides, and more 'preferably sodium hydrosulfide or
calcium sulfide. If the feed stream contains dissolved
copper, use ofa metal sulfide reductant can also result in 65
the precipitation of copper sulfide. Such precipitation of
copper sulfide may be advantageous if copper recovery
is desired.
5,320,759
Individual heavy metals can be concentrated and
purified heavy metal products produced, if desired,
using any suitable known hydrometallurgical technique
after chemically separating the heavy metal from the
heavy metal xanthate reaction product, as previously
described. In one embodiment of the invention, heavy
metals that have been chemically separated from the
heavy metal xanthate reaction product are dissolved in
an acidic aqueous solution, preferably an aqueous sulfuric
acid solution. Individual heavy metals can then be
concentrated and purified heavy metal products produced
by known hydrometallurgical methods. In a preferred
embodiment heavy metals comprising copper,
cobalt, and nickel are dissolved in an aqueous acid solution,
preferably an aqueous sulfuric acid solution, copper
is then extracted into an organic solvent, such as
di-2-ethylhexyl phosphoric acid (DEHPA). Cobalt is
then extracted into a second organic solvent, such as a
phosphinic acid, a commercial example of which is
Cyanex 272 by American Cyanamid Company. Nickel
8
solved heavy metals at one pH to recover the first selected
group of dissolved heavy metal constituents.
Xanthate may then be reacted with a second group of
selected heavy metals in a subsequent step at a different
S pH to effect recovery of the second selected group of
dissolved heavy metal constituents. Additional reactions
at additional pH's may be effected as desired.
Another embodiment comprises combining selectively
reacting xanthate with selected dissolved heavy
10 metals and other heavy' metal recovery techniques. For
example, as noted previously, copper dissolved in the
feed stream may be precipitated by adding a metal sulfide
prior to reacting other heavy metals with a xanthate.
Or, for example, following selective recovery of
15 some heavy metals using a xanthate, other heavy metals
may be removed by other methods in subsequent processes,
such as by precipitating such other heavy metals
using hydroxides or carbonates.
Following physical separation of heavy metal xanthate
reaction product from a feed stream, the selectively
reacted heavy metals can be chemically separated
from the heavy metal xanthate reaction product, if desired.
One embodiment of the present invention comprises
roasting the heavy metal xanthate reaction product
in the presence of oxygen to decompose the heavy
metal xanthate reaction product, preferably producing
oxides of the selectively recovered heavy metals. In
another embodiment, the heavy metal xanthate reaction
product is reacted with a non-heavy metal sulfide, preferably
a sodium or potassium sulfide, more preferably
sodium monosulfide or sodium hydrosulfide, and most
preferably sodium hydrosulfide, to produce reaction
products comprising heavy metal sulfides and a nonheavy
metal xanthate, preferably a sodium xanthate or a
potassium xanthate, more preferably sodium ethylxanthate
or potassium ethylxanthate, and most preferably
sodium ethylxanthate. The resulting non-heavy metal
xanthate may then be cycled in the process and contacted
with a feed stream to selectively react with additional
heavy metals. For example, when a heavy metal
xanthate reaction product is cobalt ethylxanthate, the
reaction with sodium monosulfide to chemically separate
the cobalt from the cobalt ethylxanthate, is assumed
to be as follows:
2NaC2H,OCS2+Co+2+S04-2-CO<C2.
H,OCS2n+2Na+ +S04-2
Suitable xanthates, as previously described, can be 20
present in a solid or liquid form prior to contacting the
xanthate with a feed solution to effect reaction between
a xanthate and selected heavy metals. Suitable xanthates
can be either soluble, insoluble or partially soluble in the
feed stream containing dissolved heavy metals. Con- 2S
tacting the xanthate and the feed stream to effect selective
reaction between the xanthate and dissolved heavy
metals can be accomplished using any suitable known
contacting technique. In the case of xanthates which are
soluble or partially soluble in aqueous solutions, such as, 30
for example, sodium ethylxanthate and potassium
ethylxanthate, such contacting may be effected by mixing
the xanthate and an aqueous feed stream to cause
dissolution of the xanthate into the feed stream. In the
case of insoluble xanthates, such as, for example, xan- 35
thated sawdust and insoluble xanthated starches, such
contacting may be effected by mixing the xanthate and
the feed stream or by passing the feed stream through a
process vessel, such as a packed tower, containing the
insoluble xanthate. Preferably, such contacting should 40
be for a time sufficient to allow the reaction between the
xanthate and selected dissolved heavy metals to reach
equilibrium. The process of the present invention can be
conducted in either a batch or continuous process.
The heavy metal xanthate reaction product will typi- 45
cally be a solid. Such heavy metal xanthate reaction
product can be physically separated from the feed
stream following reaction by any suitable solid-liquid
separation technique known in the art, such as by use of
gravity, filtration, cycloning, or flotation. In a preferred 50
embodiment, such solid-liquid separation is by flotation
of the heavy metal xanthate reaction product, which is
typically hydrophobic.
As noted above, in one embodiment of the invention,
the feed solution is a leach liquor. In such an embodi- 55
ment, subsequent to physical separation of the heavy
metal xanthate reaction product from the feed stream,
as described above, the resulting solution, free of heavy
metal xanthate reaction product, can be recycled to the
leaching process to dissolve additional heavy metals 60
from leached materials. Similar recycle processes can
also be practiced with other industrial processes involving
heavy metals.
In one embodiment of the present invention, dissolved
heavy metals are selectively recovered in multi- 65
pIe recovery steps, each involving selectively reacting a
xanthate with selected heavy metals. For example, xanthate
may be reacted with a first group of selected dis-
According to the process of the present invention,
when a suitable xanthate, as previously described, reacts
with a dissolved heavy metal, a heavy metal xanthate
reaction product is formed. For example, in the case of
sodium ethylxanthate reacting with dissolved cobalt in
a sulfate solution to form a heavy metal xanthate reaction
product ofcobalt ethylxanthate, the reaction would
be as follows:
7
sium ethylxanthate is prepared on site and used prior to
degradation. For example, sodium ethylxanthate can be
prepared from ethanol, sodium hydroxide and carbon
disulfide in an aqueous solution according to the following
reaction:
5,320,759
9
carbonate is then precipitated using a suitably reactive
carbonate, preferably sodium carbonate. In another
preferred embodiment, the copper: that has been extracted
into an organic solvent, as described previously,
is then stripped from the organic solvent and subjected 5
to electrowinning to produce a purified copper product.
In still another preferred embodiment, cobalt that has
been extracted into an organic solvent, as previously
described, is then stripped from the organic solvent and
subjected to electrowinning to produce a purified co- 10
balt product. Techniques for concentrating and recovering
cobalt and nickel products are generally discussed
by Jeffers, et al" Recovery of Cobalt from Spent Copper
Leach Solution Using A Continuous Ion Exchange, Bureau
of Mines Report of Investigations 9084, U.S. De- 15
10
examined to qualitatively determine the amounts of
heavy metals present.
Results of the three tests are summarized in Table 1.
Table 1 shows the selective reactivity of cobalt, nickel
and copper at a pH of 3.2 even when potassium ethylxanthate
is added in an amount significantly in excess of
the stoichiometric quantity required assuming complete
reaction with the copper, cobalt, and nickel. Table 1
also indicates that at a pH of 3.2, copper has a greater
affinity to react with the xanthate than cobalt, which
has a greater affmity than nickel. Dissolved iron(lI) and
zinc were relatively unreactive even when the xanthate
was added in an amount of 280% of that theoretically
required for reaction with the dissolved copper, cobalt,
and nickel.
TABLE 1
KC2H3OCS2 % of % of Dissolved Heavy Metals Recovered
Test No. Stoichiometric pH of Reaction Co Ni Cu Fe(lI) Zn
I 56 3.2 6 <10 91 <5 <10
2 110 3.2 91 63 98+ <5 <10
3 280 3.2 97+ 96+ 98+ 6 minor
90+ <5 90+
TABLE 2
% of Dissolved Heavy Metals Recovered
Cu Ge As .
EXAMPLE 2
2-2.3
pH of Reaction
4
Test
No.
EXAMPLE 3
This example illustrates chemical separation of selected
heavy metals from a heavy metal xanthate reaction
product and reuse of the xanthate to further react
with additional selected heavy metals. A 150 ml aqueous
feed solution containing d~ssolved heavy metals as
sulfates is prepared containing the following approximate
concentration in grams per liter of heavy metals:
0.26 copper, 0.16 cobalt, and 0.097 nickel. Approximately
0.40 grams of potassium ethylxanthate is dissolved
in 20 ml of water, which is then added dropwise
to the feed solution while stirring. The solution, at a
temperature of approximately 23° C., is maintained at
pH 2.7 during precipitation. After approximately 10
minutes, the solution is fIltered and the precipitate is
washed with water. Approximately 39 mg of copper, 23
mg of cobalt, and 11 mg of nickel precipitate from the
feed solution. The moist filter cake, weighing approxi-
This example illustrates selective recovery of dissolved
copper and arsenic to the exclusion of germanium.
In Test No.4, a 50 mI aqueous sulfate feed solution
is prepared containing the following concentrations
of heavy metals in grams per liter: 0.20 germanium,
0.20 copper, and 0.10 arsenic(III). The solution is
acidified with sulfuric acid to a pH of 1.5. A solution
containing 0.40 grams of potassium ethylxanthate dissolved
in 10 ml of water is added dropwise to the feed
35 solution while stirring. The pH of the solution is maintained
at between 2 and 2.3 by adding 0.5 mI of 10%
sulfuric acid solution. The reaction is conducted at a
temperature of 22° C. Following precipitation of the
heavy metal xanthate reaction product, the solution is
fIltered to remove the precipitate and then analyzed to
determine the concentration of dissolved heavy metals
remaining in the solution. Results of Test No. 4 are
shown in Table 2.
EXAMPLE I
This example illustrates the selective recovery. of
cobalt, nickel, and copper from a feed solution also
containing other heavy metals using varying relative
quantities of xanthate reagent. An aqueous feed stream 40
containing dissolved heavy metals as sulfates is prepared
containing the following approximate concentrations
in grams per liter of heavy metals: 0.035 cobalt,
0.027 nickel, 0.075 copper, 1.55 iron(II), 0.2 zinc, 3
aluminum, 5 magnesium, and 0.02 uranium. The pH of 45
the feed solution is 3.2. Three tests are performed, each
using a 50 ml sample of the feed solution. An aqueous
solution containing 20 grams per liter of potassium
ethylxanthate is prepared. In Test No.1, the feed solution
is treated with I ml of the potassium ethylxanthate 50
solution, containing 56% of the stoichiometric quantity
of potassium ethylxanthate assuming complete reaction
between the xanthate and dissolved cobalt, nickel and
copper in the feed solution. In Test No.2, the feed
solution is treated with 2 ml of the potassium ethylxan- 55
thate solution, containing 110% of the stoichiometric
quantity of potassium ethylxanthate. In Test No.3, the
feed solution is treated with 5 ml of the potassium
ethylxanthate solution, containing 280% of the stoichiometric
quantity of potassium ethylxanthate. All three 60
tests are conducted at 23° C. and a pH of 3.2. The solutions
are mixed for 15 minutes following addition of the
potassium ethylxanthate solution to the feed solution.
The solutions are filtered to remove the precipitate and
then analyzed to determine the concentration of cobalt, 65
nickel, copper, and iron(II) remaining dissolved in the
solution following precipitation of the heavy metal
xanthate reaction product. Also, the precipitates are
partment of the Interior; Ritcey, et aI., Development of 25
Solvent Extraction Process for the Separation of Cobalt
from Nickel. Extraction Metallurgy Division. Depanment
ofEnergy. Mines and Resources (Canada, Nov. 29, 1971);
and Ritcey, et aI., Solvent Extraction-Principles and
Applications of Metallurgy, Part II, Elsevier Scientific 30
Publishing Company (1979).
The following examples are provided for the purpose
ofillustrating the present invention and are not intended
to limit the scope of the invention.
5,320,759
12
droxide and combinations thereof and reacting said
xanthate with said dissolved first heavy metals before
degradation of said xanthate.
10. The process of claim 1, wherein said dissolved
second heavy metals comprise dissolved iron(lII), and
further comprising reducing at least a port of said dissolved
iron(III) to dissolved iron(lI) prior to reacting
said xanthate with said dissolved first heavy metals.
11. The process of claim 10, further comprising re-
10 ducing said iron(lII) to iron(lI) by contacting said solution
with a reducing agent selected from the group
consisting of elemental iron, calcium sulfide, sodium
hydrosulfide and combinations thereof.
12. The process of claim 1, wherein at least a portion
of said dissolved first heavy metals and said dissolved
second heavy metals are in the form of sulfates in said
solution.
13. The process of claim 1, wherein said solution
comprises dissolved copper, and further comprising
recovering at least a portion of said copper from said
solution prior to said reacting of said xanthate with said
dissolved first heavy metals.
14. The process of claim 13, wherein said step of
recovering said portion of said copper comprises reacting
said copper with a reactant selected from the group
consisting of calcium sulfide, sodium hydrosulfide and
combinations thereof.
15. The process of claim 1, wherein said reaction
product is a precipitate.
30 16. The process of claim 1, wherein said solution is
selected from a group consisting of drainage, leach
liquors and combinations thereof.
17. The process of claim 1, wherein said selectively
separating and recovering comprises physically separating
at least a portion of said reaction product from said
solution by means of flotation.
18. The process of claim 1, further comprising dissolving
at least a portion of first heavy metals present in
said reaction product in a second solution wherein first
heavy metals from said dissolved reaction product are
in the form of sulfates in said second solution.
19. The process of claim 18, further comprising selectively
extracting from said second solution at least a
port.ion of said first heavy metals dissolved in said second
solution into an organic solvent, stripping said extracted
first heavy metals from said organic solvent, and
subjecting said stripped first heavy metals to electrowinning
to produce a purified product of at least a portion
of said stripped first heavy metals.
50 20. The process of claim 1, further comprising roasting
in the presence of oxygen at least a portion of said
reaction product.
21. The process of claim 1, further comprising reacting
at least a portion of. said reaction product with a
metal sulfide.
22. The process of claim 21, wherein said metal sulfide
comprises a sulfide of sodium.
23. The process of claim 22, wherein said sulfide of
sodium comprises sodium hydrosulfide.
24. The process of claim 1, wherein said xanthate
comprises a product of chemically separating at least a
portion of first heavy metals from said reaction product.
25. A process for selectively recovering heavy metals
from a solution in which first heavy metals are dissolved,
said first heavy metals comprise heavy metals
selected from the group consisting of arsenic, bismuth,
antimony, lead and combinations thereof, said solution
also having second heavy metals dissolved therein, said
11
mately 0.7 grams and containing the washed precipitate,
is then mixed with 15 ml of an aqueous solution containing
8.6 grams per liter of sodium hydrosulfide. The
mixture is then mixed for approximately 35 minutes at a
temperature ranging between 40° C. and 53° C. The 5
resulting solids in the mixture are difficult to f1lter, and
therefore approximately one gram of sodium sulfate, 5
mg of a polyacrylamide flocculent (Percol 351), and 5
mg of a polyethylene oxide flocculent (Polyox 301) are
added to coagulate the fmes. The solution is then f1ltered,
resulting in 28 ml of f1ltrate.
Approximately 17 ml of the f1ltrate is then added to
and mixed with 90 ml of a second aqueous feed solution
containing dissolved heavy metals as sulfates in the
following approximate concentrations in grams per liter 15
of heavy metals: 0.26 copper, 0.16 cobalt, and 0.097
rlickel. The resulting solution is then mixed for 10 minutes
at a temperature of approximately 23° C. The solution
pH is maintained between 2.7 and 3.1 during precipitation.
The solution is then f1ltered and the precipi- 20
tate washed with water. Approximately 23 mg of copper,
7.1 mg of cobalt, and 0.8 mg of nickel precipitate
from the second feed solution.
While various embodiments of the present invention
have been described in detail, it is apparent that modifi- 25
cations of these embodiments will occur to those skilled
in the art. However, it is to be expressly understood that
such modifications and adaptions are within the scope
of the present invention, as set forth in the following
claims.
I claim:
1. A process for selectively recovering first heavy
metals comprising heavy metals selected from the
group consisting of arsenic, bismuth, antimony, lead and
mixtures thereof from a solution in which said first 35
heavy metals are dissolved, said solution also having
second heavy metals dissolved therein, said second
heavy metals being different than said first heavy metals,
the process comprising reacting a xanthate with at
least a portion of said dissolved first heavy metals to 40
form a reaction product at a pH of said solution at
which reaction of said dissolved second heavy metals
with said xanthate is excluded, and selectively separating
and recovering at least a portion of said reaction
product from said solution containing said dissolved 45
second heavy metal following said step of reacting.
2. The process of claim 1, wherein said solution comprises
an acidic aqueous solution.
3. The process of claim 1, wherein said pH of said
solution is below about 4.0.
4. The process of claim 1, wherein said pH of said
solution is below about 3.5.
5. The process of claim 1, wherein said pH of said
solution is below about 3.0.
6. The process of claim 1, wherein said dissolved 55
second heavy metals comprise heavy metals selected
from the group consisting of iron(II), zinc and combinations
thereof.
7. The process of claim 1, wherein said xanthate is
selected from the group consisting of sodium xanthate, 60
potassium xanthate and combinations thereof.
8. The process of claim 7, wherein said sodium xanthate
comprises sodium ethylxanthate and said potassium
xanthate comprises potassium ethylxanthate.
9. The process of claim 8, further comprising prepar- 65
ing said xanthate from reactants comprising ethanol, a
carbon sulfide, and a third reactant selected from the
group consisting of sodium hydroxide, potassium hy5,320,759
15
13
second heavy metals being different than said first
heavy metals, the process comprising reacting a xanthate
with at least a portion of said dissolved first heavy
metals to form a reaction product at a pH of said solution
at which reaction of said second dissolved heavy 5
metals with said xanthate is excluded, and selectively
separating and recovering at least a portion of said reaction
product from said solution containing said second
heavy metal dissolved therein following said step of 10
reacting.
26. The process of claim 25, wherein said solution
comprises an acidic aqueous solution.
27. The process of claim 25, wherein said pH of said
solution is below about 4.0.
14
28. The process of claim 25, wherein said pH of said
solution is below about 3.5.
29. The process of claim 25, wherein said pH of said
solution is below about 3.0.
30. The process of claim 25, wherein said second
heavy metals comprise heavy metals selected from the
group consisting of iron(II), zinc and combinations
thereof.
31. The process of claim 25, wherein said xanthate is
selected from the group consisting of sodium xanthate,
potassium xanthate and combinations thereof.
32. The process of claim 31, wherein said sodium
xanthate comprises sodium ethylxanthate and said potassium
xanthate comprises potassium ethylxanthate. .
• • • • •
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