Note: Descriptions are shown in the official language in which they were submitted.
2~
PC-213~
The invention is directed to a process for
recovering silver from intermediate materials containing
silvex along with other valuable metals includi~g metals of
the platinum groupu
It is known that many base metal ores such as
those of copper, nickel, zinc, l.eadt etc~ also cGntain
metals of the platinum group together with silver, gold,
selenium, tellurium~ etc~ 5uch ores form important sources
of the valuable metals which are k~own colloquially as
I'precious metals"O
These metals occur in the various metal ore~ in
small amounts and become concentrated during the working up
o~ ~he b~se mfltals in the form of:~ariou~ inter~ediates
including anode sludges, leach residues, cements, etc.
~ccordingly, t~le compositions of these precious metals-
contain.ing materials vary widely depending upon the nature
of the ore containing th~ sameO Despite ~he differences in
composition these materials tend to lend themse~ves to a
more or less common scheme of treakment and tend to contain
~he same ingredients to a great extent although the propor-
tions of valuable metals therein can vary. Thus r me~als
which may be present in the precious metals intermediate
pro~ucts include all six members of the platinum group,
gold, ~ilvery selenium, te].lurium, lead, arsenic, antimony~
tin, bismutht copper, nickel, zinc, iron and sulur. Once
the material.5 are concentrated in the form Qf anode sludges,
leach residues, etc. it then becomes important to recover
the metal values as completely as possible and to produce
metal concentrates oE respectable purltyO One known method r
for example, can involve decopperizing of the preciou~ metal
sz~
intermediate by leaching with sulfuric acid and then
smelting in a Dor~ furnace in which silver may be recovered
in the form of Dore metal. Such a procedure i5 expensive
and can produce harmful emissions of ~elenium, arsenic, lead
and other heavy metals.
It is known also to recover precious metal from
intermediate products by dissolution in hydrochloric acid
with chloxination followed by ammonia extraction o silver
~rom the resulting residues and recovery of platinum ~roup
metals~ selenium, and tellurium from the leach liquor. It
iS al50 known from the photographic art that thiosulfate
solutions can be employed ~o dissolve silver from light
unaffected por ions of film which is employed for photo-
graphic purposes. Ammonium thiosulfate leaching of gold and
silver from ammoniacal leach residues in ~he presence o
~upric ion and free ammonia is al~o known.
R~levant publications which can be cited in
respect o~ the subject matter include _v ~ Metal
1963, ~ol. 36, No. 11, pages 85-86; and U.S. Patents No.
~o 3,658,510; No. 4~070,182; 4,269,622 and No. 4,2~9,~70.
~ t is desirable that a hydrometallurgical method
be provided for working up precious metal intermediate
materials which will provide for selec~ive and ef.ficien~
separation of silver therefrom.
S~MMARY OF THE INVENTION
Silver containing precious metal intermediate
materials to be treated for the recovery of silver are first
slurried with water and are leached with chlorine to
dissolve essentially all of the precious metals and to
~o produce a leach residue containing the silver largely as
silver chloride. Thereafter, the leach residue and the
5~;~
supernatant liquor containing dissolved chlorides are
separated and the residue is contacted with an aqueous solu-
tion of thio~ulfate to dissolve the silver. The thiosulfate
solution is then worked up to recover silver therefromO
DETAILED DESCRIPTION OF_THE_INVENTION
Silver~containing precious metal intermediates to
be treated in accordance with the invention are slurried
with wat~r in the proportion of about 5 to about SO~ by
: weight solidsO The resulting slurry is then chlorlnated for
a time sufficient to convert the silver content to ~ilver
chloride and to chlorinate most of the remaining metal
values a~ chlorides. In the course of the chlorination a
substantial quantity of hydrochloric acid can be formed by
reactions between chlorine and elements such as sulfur,
~elenium, tellurium, arsenic, etc., or compou~ds thereof~
Chlorination is usually exothermic. Accordingly,
cooling of the solution may sometimes be required. The
addition rate of chlorine will be controlled ~o avoid
possible overheating and/or excessive chlorine consumption.
A convenient temperature range for chlorination is about
60C to about 80DC.
After completion of the chlorine leach, the
silver-containing residue is separat~d from the supernatant
solution, which now contains the precious metals.
The silver-containing residue can then be leached,
preferably at ambient temperature, with a thiosulfate
solution e.g., sodium thiosulfate, to dissolve silver selec-
tively with regard to impurities such as silica and ferrites
which may be co~present in the silver-con~aining residue.
The thiosulfate leach may be conducted at a temperature of
about 10 to about 80C. When lead i5 present ln the
chlorine leach residue to an extent requiring selective
removal of the silver, the pH of the thiosulfate leach solu-
tion should be at least 7 and more preferably pH 9 or pH 10.
When the thiosulfate solution is sufficiently basic, the
thiosulfate leach is highly selective or silver as compared
to lead in the precipitate being di.ssolved. ~hiosulfate is
used in approximately the proportions of two to four mols o
thiosulfate ~or each mol o~ silver to be leached~ A further
advantage of maintaining a thiosulfa~e ~olution basic has ~o
do with the fact ~hat s~abili~y of the solutions is ~hereby
increased. Small amounts of a sulfite, e.g. sodium sulfite
added to the thiosulfake leach solution will also improve
stability.
The thiosulfate leach solution containing silver
from the residue may be readily treated to recover the
silver in a variety of ways. For example, cementation with
metals 5uch as iron, zinc or magnesium at amb.;ent
temperature produces cements analyzing on ~he order of 90%
silver. Or~anic reducing agents, such as fructose, dextrose
and lactose can be used to produc~ silver precipitates of
high purity~ i.eL at least about 90% in silver, Electro-
lytic recovery means may also be used.
As noted hereinbefore, the composition of the
silver-containing precious metal intermedlates to be treated
in accordance with the invention~ can vary widely depending
upon the ore from which the intermediates are obtaine~. It
may be convenient in connection with the working up/ ~or
~xample, of copper refinery sludges to recover silver, to
subject the sludge to a decopperizing leach in sulfuric acid
prior to treatment in accord2nce to the invention,
Similarly, a lead removal step may be employed prior to
35~
treatment of ~he interme~iate in accordance w:ith the inven~
tion.
Some e~amples will now be givenO
EXAMPL~S
66.2 kg of a precious metals-containing feed,
analyzing (%) 1~5 Pt~ 1.6 PdJ 0.40 Au, 0.16 Rh~ 0.09 Ru~ 7.6
Ag, 7~1 Pb~ 5.6 Se, 0.67 Tel 0~34 Cu was slurried in water
at a solids density of ~450 9 solids per liter oE slurry and
heated to 60C. Gaseous chlorine was sparged into the
agitated slur~y ~or a ~otal of 4 h a~ a flowrate of
100Q/min. A~ter ~iltra~ion of ~he leached slurry about 4~.5
kg of leach res.idue was obtained, which was found to analyze
(%) 0.035 Pt, 0.016 Pd, 0~005 Au, 10.1 Ag, 3O2 Pb. The
~ollowing metal extractions were obtained (~O 98 Pt, 99.3
Pd, 99.1 Au/ ~1 Ag.
The thiosulfate leach was conductecl as follows:
33.8Q of water was added to 15.5 kg of the above chlorine
leach residue (39~ moisture). NaOH was added to the
agitated slurry to bring the p~ to 10.0 at 22C. Then 3.75
kg oE ~2S23 was added (3.9 kg Na2S2O3/k~ Ag) and the
slurry was agitated ~or 30 minutes at a pH of 10 (22C)~
The residue was filtered off and washed with one cake
disp:lacement of water. Since the leach re~idue contained a
large quantity oE filter-aid, which tends to trap large
amounts o~ leach liquor~ the wet residue was su~jécted to a
repulp leach using llQ o~ water and 0.4 kg of Na2S2O3~
Leaching was again conducted for 30 minutes at 22C ~pH 10).
~inally, the leach residue was separated f~om the solution
by filtra~ion. The leach residue analyzed 0.11~ Ag and 5~2~
Pb. 99.1% of the silver was extracted w~-th only 0~8% of the
: lead.
The thiosulfake leach liquor and the repulp leach
li~uor were combined, resulting in a solution analyzing
(g/l) 18.0 Ag and 0~07 Pba Sulfuric acid was added to the
solution to reach a p~ of 4.0 at ~2S. Then iron powder w~9
added to cement the contained silver values. The pH was
held at 4 by simul~aneous addition of sulfu~ic acid. When a
redox potential of -400 mV(SCE~ was reached, the slurry was
~: 10 filtered. The silver cemen~ analyzed (%3 87.1 Ag, gO3 ~e,
~ 0.38 Pb, 1 r 4 S. More than 99.9% of the silver had been
; cemented and the barren solution analyzed 10 mg/l Ag.
!~
170 9 of a moist (39.4~ H20) precious metals
containing ~eed analyzing (%) 1073 P~ 65 Pd, 0.33 ~u,
2.00 Ag, 3.43 Pb and 52.0% SiO2 was slurried with water and
various amounts of hydrochloric acid, as shown in Table lo
The resulting slurries ~30-35% solids) were agitated and
heated to 80Co Gaseous chlorine was bubbled into the
slurry at a flowrate of ~1 9/l slurry-min for a total of 4
h. The slurry~ was then f iltered and the leach residue and
the leach liquor were analyzed.
As shown in Table 1, it was found ~hat the extrac-
tion of the precious metals Pt, Pd and Au was essentlally
una~fected by the init:ial acidity. ~Iowever, much less
silver was extracted (only 002~) in the test where the feed
was slurried with water. Thus, a be~ter separation of
silver from Pt, Pd and Au was achieved.
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Exam~le 3
A chlorine leach residue analyzing~ in weight
percent, 17.3 Ag and 9O9 Pb was subjected to a number of
thiosulfate leach ~ests at p~ values between 2 and 12. The
leach conditions were si.milar as .in Example 1 and are listed
in Table 2, t~gether with the results of duplicate tests.
The extraction of silver w~s lowest (~97%) at a p~ of 2.0,
and was generally g9~ or higher between p~ 4 and 12. The
dissolution o lead was strongly influenced by the pH. At
10pH 6 and below~ more than 75% of the Pb was dissolved~
whereas at pH 8 less than 20~ Pb was extracted and at a pH
of 10 the dissolu~ion of Pb was only
. TABLE 2
; LEACHING OF CHLORTNE LEAC~I
ESIDUE WI.~ GorluM tYIOSU~-~T,
eed Assa~ 17~3 Ag, 9.9 Pb
Conditions: Leaching of 102 g C12 leach res.idue at
20~ solids in water, 3.85 g Na2S2O3/g
Ag t 30 min. at 22C. ~epulp in 15 g/1
Ma2S~O3 solu~.ion (30 min at 22C) at ~he
sam~ pH.
RESIDUE ASSAY~%~ L
Aq Pb Aq Pb
2.~ 0.gl 2.~0 96.2 33.2
2.0 0.~g 2.2~ 97.2 8~,9
4O0 0522 2~60 9~.0 83.7
4.0 ~.22 2561 99.1 ~2.9
6.0 0.13 3.40 99.5 77.6
6.0 0.20 3.44 9~.~ 77~1
8~0 0~16 10.8 g~.3 19.5
8.0 Q.09 10.8 99~5 ~7.9
1~.0 0.20 12.8 ~9.1 1.1
1~.0 0.25 13.4 98.9 0.8
1:;!.0 0~16 12~8 g9~3 lol
1250 0 r 30 13.1 98.7 ~.6
5~;~
Example 4
A thiosulfate leach liquo~ OQ) analyzing ~g/l)
18~4 Ag and 68 S203- at pH 10 was acidified to pH 4, and 3.3
g of Mg granules (70-80 mesh) was added over 2 h with simul-
taneous addition o 151.5 ml of 50 g/l ~I2So4 solution ~o
maintain pH 4. During this period the temperature rose from
22 to 31C and the redox potential of the solution decreased
rom +70 m~ to ~250 m~ (Pt v~ SCE). After filtration and
drying~ the solids ~20014 g~ analyzed (%)~ 90.9 Ag, 106 Mg
and 3.15 S. The filtrate (1.085Q) contained 0~042 g/l AgO
Thus, 99.7% of the silver was recovered in the 501ids
Example 5
A thiosulfate leach liquor (l.OQ) analyzing (g/l)
18.5 Ag, 0.11 Pb and 69 S~03= at pH 10 wa~ heated to 80~C
and 14.3 g of D-fruc~ose was added. The solution W~5
maintained at p~ 10 by addition of 72.9 ml of a lSO g/l NaO~I
solution. After 15 minutes the redox potential o~ the solu-
tion had ~ecreased from O mV to -660 mV (Pt vs SCE) and the
sil~er mirror~ originall.y plated on the sides of the beaker,
disappeared leaving a flocculant precipitate (18023 g) which
analyzed (%~: :97.5 ~g~ 0.55 Pb, and 0.66 S. The filtrate
(1.044~) a~aly~ed <5 mg/l ~9. ~hus, 99~97% of the sil~er
was recovered in the solids.
Example_6
~ thiosulfate leach liquor tl.OQ) analyzing (g,~l)
17.9 Ag, 0.10 Pb, and 67 S203= at pH 10 was heated to 80~C
a~ld 14.3 g of ~-glucose was addedO The solution was
maintained at pH 10 by addition of 265 ml of a 38 g/l NaOH
solution. After 30 minutes the redox potenkial of the solu-
tion had decreased from +30 mV to -660 mV (Pt vs SCE) and
the silver mirror, originally plated on the sides oE the
~ 5 ~ ~
beaker, disappeared leaving ~ 10cculant precipitate (17.45
9~ whlch analyzed (%) 97.9 Ag, 0.52 Pb, and 0.56 S. The
filtrate ~1.26Q~ contained 40 mg/l ~g. Thus, 9~.7~ of the
silver was .recovered in the solid 5 .
~xam~le 7
A thiosulfate leach liguor (l.OQ~ containing 17.9
g~l Ag and 67 g/l S~03- was adjusted to p~l 13 at 24C by
adding 1~ 9 NaO~. Then 14.3 g of D-fructose was added.
After 2 hours the redox potential had decreased from +ÇO mV
to -225 mV (Pt vs SCE) and 8.85 g of precipitate was
filtered off. After standing overnight, an additional 8.30
g of precipitate was recovered. The combined precipitates
analyzed 99.6~ Ag while the solution contained only 70 mg/l
Ag. Thus, 99.6~ of the silver was recovered in the solids.
xample 8
The compositions of ive other precious metal~
containing mater ials susceptible to treatment in accordance
with the invention are shown in Table 3. Each of these
mater.ials was chlorine leached under the conditiorls and for
the times shown ;n Table 4. It will be seen from Table 4
that excellent extractions of platinum-group metals and gold
were achieved with all the materials treated although the
compositions thereof varied widely. On the other hand,
extractions of silver were low. The compositions, in weight
percent, of the chlorine leach residues are shown in Tahle
5. ~11 oE the chlorine leach residues were susceptib.le to
thiosulfate leaching to di~solve silver~
~ 10 -
352~
TABLE 3
PM CONTAINING FEEDS TO CHLQRINE-WATER LEACHING
-- ASS~YS (%~ V
Feed ~lo. 1 2 3_ _ 4 5
S::u ().09 0.75 1042 1.8~ 38~6
N i 0 . 2 û 5 . 6 53 ~ 9 0 1 D 3 0 1 3 . 7
Fe - -- 0-74 0.13 4O45
S ~ -- ---- 19 . 4
S~ Oog6 8.40 -- 1600 10E~6
Te 0~14 0.60 -- ~.oo 0~14
Pb 3.7 5.90 11.8 2.75 3O08
Sb 0.05 0.03 -- 0.05 0.15
Sn (1 . 39 0 . 75 -- 0 O 3n o . 2~
Bi 0.04 0.15 -- 0.13 0.07
As 0.73 0.75 -- D.25 0.26
P~ 2.32 1.1~ 8.0 0.21 ~.04
Pd 12 1,81 8.0 0O52 2.22
~u 0.47 0.36 2.70 0.25 0.5S
Rh 0.29 0.17 1.55 0.06 0.40
Ru 0.13 0.10 0.30 0.10 0~14
Ir 0.1 0.05 -- O~t)3 OolO
Ag 2,5 9,.S 34.3 13.1 7.32
SiO2 67 41.û
- 11 ~
:
8~2~
TABLE 4
CHLORINE-WATER LE:ACHING OF PM FEEDS
Conditions: Pulp density 250-400 g/Q in water
1.0 2 .S g ~ 12/minQ slurry
Feed 1 2 3 4 5
Leach
Temperature 60 60 80 80 80
(C)
I,each Time
(h~ 6 6 5 6 5
gXTRACTIONS (~3
. . _. .,
Cu 78 75 g9 96 ~99 ~ 9
2~i 7 15 99.2 89 99.
Fe ~ 21 99
S ~
Se 95 99 . 5 -- 99 . 7 80
Te 99 . 9 99 -- 99, 7 93, 3
Pb 60 98 89 93 99
2 0 .Sb 23 59 ~- 72 94
Sn 4 49 -~ 82 9~
Bi 72 94 -- 94 92
As 88 72 -- 88 99
Pt 99 . 2 99 . 2 99 . ~ 9g . 3 98 . 8
Pd 99.,9 99.4 99.6 99.8 g~.6
Au 99v9 98.2 98.9 99,û 99~4
Rh 99 . 7 97 96 98 97
Ru --- 98 97 g9 . 4 96
Ir 99 . 7 97 -- 96 88
Ag 0.6 1.7 ~ 3.3
S.iO2<0.2 0.0~ ---- _ __
-- 12 -- -
~8~
T~BLE 5
CHLORINE-WATER LEACH RESIDUE ASSA~S (~)
. . . ~
1 2 3 4 5
Cu 0.02 0~37 a.o3s o.~ 0.05
Ni a.~g 6.35 0.065 0.~1o.n8
Fe -- -- -- 0.250018
S ~ 50.5
Se 0~07 0.07 -- 0.152.43
TeI OoOl OoOl ~~ 0~03~0~01
Pb 1.8 0.17 2090 0~53 . 0.08
Sb 0.06 0.04 -- 0~4 0O05
Sn 0,.51 0~46 ~ OolSO~OS
Bi 0.01 0.01 -- 0.020.04
As 0.11 0.28 -- 0.110.02
Pt 0.002 0O013 0.1~ 0~0050.14
Pd 00002 0~013 0~075 0~0040.051
Au<0~001 0.010 0~064 0~00700018
Rh<0.001 0.007 0.14 0.0040.057
Ru -- 0.004 0.020 0.0~20.033
Ir~0.001 0~003 -- 0~0030~0~7
Ag 3~43 12~0 74~0 30~6 33~8
SiO274.6 57.0
Although the present invention has been de~cribed
in conjunction with preferred embodiments, it is to be
understood that modi~ications and variations may be resorted
to wikhout departing from the spirit and scope of the inven-
tion, as those skilled in the art will readily understand.
Such modifications and variations are considered to be
within the purview and scope of the invention and appended
claimS.
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