United States Patent
Coltrinari et ale
[ 19] [ II ]
[45]
4,011,146
Mar. 8, 1977
OTHER PUBLICATIONS
lonidas, "The Dry Chlorination of Complex Ores",
Mining and Scientific Press, vol. 112, pp. 781-789,
May 1916.
Primary Examiner-G. L. Kaplan
Assistant Examiner-Aaron Weisstuch
[54] PROCESS FOR SEPARATION AND
RECOVERY OF METAL VALUES FROM
SULFIDE ORE CONCENTRATES
[75] Inventors: Enzo L. Coltrinari, Arvada; James E.
Reynolds, Golden, both of Colo.
[73] Assignee: Cyprus Metallurgical Processes
Corporation, Los Angeles, Calif.
[22] Filed: Nov. 13, 1975
[21] Appl. No.: 631,700
Related U.S. Application Data
[63] Continuation-in-part of Ser. No. 516,450, Oct. 21,
1974, abandoned.
[52] U.S. Cl. _ 204/66; 75/112;
75/113; 75/118 R; 75/120; 204/98; 204/99;
204/109; 204/111; 204/114; 204/115;
204/117; 204/118; 204/128; 204/129;
423/38; 423/39; 423/40; 423/46; 423/94;
423/98; 423/99; 423/103; 423/109; 423/494;
23/270 R
[51] Int. Cl.2 COlG 5/00; COlG 21/16;
C2SC 3/34
[58] Field of Search 204/66,98,99, 109,
204/111,114,115,117,118,128,129;
423/38-40,46,94,98,99,103,109,494;
75/111-114,118,120
[56] References Cited
UNITED STATES PATENTS
26 Claims, 2 DraWIng Figures
[57] ABSTRACT
An improvement in conventional processes for recovering
metal values from sulfide ores containing lead,
zinc and silver sulfides in which process the metal sulfides
are converted to chlorides by chlorination followed
by solubilization of the chlorides with a sodium
chloride leach and subsequent recovery of the metals
from their chlorides in accordance with a conventional
flow sheet including crystallization, cementation, precipitation,
fused salt electrolysis, etc., with chlorine
being recovered for reuse by electrolysis of the sodium
chloride leach solution substantially depleted of lead,
silver and zinc, the improvement being a pollution-free
process which comprises:
I. recycling the sodiumchloriide solution depleted of a
major percentage of lead and silver to the sodium
chloride or brine l~aching step; and
2. controlling the concentration of zinc and other impurities
in the sodium chloride or brine leaching solution
by bleeding a portion from the recyc!e stream of
(1) above, removing lead, zinc and other metal impurities
from the bleed stream, electrolyzing the bleed
streaVl to produce chlorine, sodium hydroxide and a
weak sodium chloride solution followed by recycle of
the chlorine to the dry chlorination step and weak
sodium chloride solution, after concentration, to the
leach solution to control the concentration of zinc
chloride and other impurities in the leach solution. A
further improvement is the use of an alternate dry chlorination
procedure for the sulfide ores and, particularly,
ores such as the tetrahedrite-tennantite series
which are more satisfactorily.chloridized by dry chlorination
than by wet chlorination. Another improvement
is use of a flow sheet by which no impurities are removed
from the process in the form of chlorides so that
no chlorine is lost from the system.
Baker et al. 423/46
Hirt 423/46
Avery 423/98
Christensen 204/11 X
9/1903
4/1921
1/1922
5/1925
739,374
1,375,002
1,402,732
1,539,713
~
~
(1) a
.c:
.C/i
COg
I
~
~
H.,O _
00
~
......
\0
......:I
......:I
f
1
NoOH
r CARBONATION
..------l SOLID / LIQUID
SEPARATION
NoCI
...-.I'J'---=-----1 ELECTROLYSfS
~WEAKNoCI
.....J I '---'
Na2C03 ~ INEUTRALIZATION I i
*
}
I SILVER I IMPURITIES I flRODUCT CARBONATES
STREAM t.
I Pb I
CEMENTATION ---r- Fe
~
Fe=:j Ag I ~ CEMENTATION
,---,---l L1QUID/ SOLID J-SEPARATION
Pb SOLID I LIQUID
SPONGE SEPARATION i~
~ + +-+---i EVAPORATOR I ..~- ;J>
t
t
r GALENA 1
CONCENTRATES
i
[CHLORINATION I- I
~
IBRIN E LEACH I
r PbCI2 ·1
ICRYSTALLIZATION
~
PbCI2
~ SOLID / L1QUID-l
II SEPARATION
I I SOLID / LIQUID I SEPARATION
i
CI2
j.J.q:. J
J--l.
~
0\
~
--o
J--l.
J--l.
--
CI2
-----S-W-EE-P-G-AS--(N-2)---,
rII
I
-J
T.J.q= 2
rr--II
Sb COMPOUND
l!::_~~=========="",=:=J;;
CONCENTRATES .'.',..: , "':" : :,'..; ,: , '.',:.:.,.,.,:.,.:,. '.':-.: ..+:<.: , .. :,;.:...';.:.: , :::::..:,:,
ZONvE I I '- --Z-O~N"E~2--/
CHLORINATION OCCURRING IN ZONE I CHLORINATED
FORWARD SWEEP OF S2CI2 IN ZONE 2 CONCENTRATES
1
LEAD
I r PRODUCT ELEMENTAL S
a RESIDUE
BACKGROUND OF THE INVENTION AND PRIOR
ART
This application is a continuation-in-part of our application
Ser. No. 516,450 filed Oct. 21, 1974, now
abandoned.
PROCESS FOR SEPARATION AND RECOVERY OF
METAL VALUES FROM SULFIDE ORE
CONCENTRATES
CROSS-REFERENCES TO RELATED
APPLiCATIONS
4,011,146
1 2
The tetrahedrite-tennantite polymorphic series of
metal sulfide minerals is discussed at page 181 of
Dana's "Manual of Mineralogy," 15th Edition, published
by John Wiley and Son~, New York, New York.
5 The formula for tetrahedrite is given as (Cu,Fe,Zn,
Agh2Sb4S13' Arsenic may take the place of antimony
in the pure arsenicend member, tennantite.
These minerals are extremely refractory to chemical
leaching.As an illustration of the difficulty of leaching
10 them, it is disclosed at page 72 ofthe book entitled The
Chemistry of Hydrometallurgical Processes by Alfred
Richard Burkin that tetrahedrite was leached with concentrated
sodium sulfide solution. This is an extreme
The invention comprises chlorinating sulfide ore procedure.
concentrates to convert the metal sulfides therein to 15 The minerals are known to occur with other minerals
chlorides from which the metals are subsequently re- such as, galena, and the amount of lead in the comcovered
in accordance with a flow sheet to be de- . bined minerals has always contributed to the economic
scribed. The invention includes the flow sheet irrespec- feasibility of processing this me to recover principally
tive of the chlorination procedure, and the combina- lead and silver. The present high price of silver makes
tion of the flow sheet with the chlorination step. Lead 20 it economically attractive to recover the silver from the
and silver are the principal metals which' can be eco- tetrahedrite-tennantite minerals irrespective of
nomically recovered from the ores. A further feature of whether other minerals are associated with them. It is
the invention is the use of dry chlorination procedure known that in some.galena-tetrahedrite ore, some silver
which is particularly effective on the tetrahedrite-ten- sulfide is in the galena while the remainder of the silver
nantite series of sulfide ores. 25 is locked in the lattice of the tetrahedrite crystals from
Conversion of metallic sulfides into chlorides in which it is very difficult to release so that it is available
metal recovery processes is not broadly new. Aqueous for conversion to the soluble chloride froni which the
chlorination of metal sulfide concentrates, with ferric silver is readily recoverable by cementation or other
chloride and chlorine gas in a sodium chloride or cal- conventional means.
cium chloride solution has been performed. U.S. Pat. 30 It has been conventional to recover lead and silver
No. 1,736,659 to Mitchell discloses a process exempli- from galena-tetrahedrite ores by pyrometallurgical
fying this mode of recovery of metal values from sul- processes with conversion of the sulfur present to sulfur
fide ores using a wet chlorination process. The process dioxide which was released to the atmosphere with its
ofthis patent does not include recycle ofleach solution polluting effect. In view of comparatively recent reor
sodium chloride solution, includes a roasting step 35 strictions on the permissible sulfur dioxide content of
with consequent air pollution, includ~s removal of the atmosphere there is a demand for non-pollution
chloride from the system in the lead chloride, removal processes for recovering silver and other metals from
of iron from the system as the hydroxide rather than the tetrahedrite-tennantite senes of minerals alone or
carbonate, and differs in other aspects from the flow . in combination with other minerals.
sheet of this invention.. . .. .. .' 40 The difficulty of breaking down the minerals to make
An()ther-piibiication-of interesds the artIcle enilfIed the sulfide components thereof available for chlorina-
"The Dry Chlorination of Complex Ores" by Ionidas in tion is not solved by the use of conventional processes
Mining and Scientific Press, Volume 112, May 27, used on ores other than tetrahedrite-tennantite miner-
1916. This article discloses partially dry chlorinating als ofsomewhat similar composition. For example, U.S.
concentrates of metal sulfides, including lead, zinc and 45 Pat. No. 1,736,659, mentioned above, discloses a prosilver
sulfides, with chlorine gas with final chlorination cess for recovering metals from sulfide ores including
being accomplished in a roasting step in the presence of the metals lead and silver in which the metal sulfides
air in which the ferric chloride formed in the chlorina- are converted to chlorides by wet chlorination with
tion step is decomposed to produce chlorine which calcium chloride solution. As the test results hereinafcompletes
the chlorination of the metal sulfides. The 50 ter presented show, wet chlorination is not effective to
process is directed chiefly to the production and elec- convert the metals of the tetrahedrite-tennantite series
trolysis of zinc chloride and is not a pollution-free pro- to chlorides without use of an excessive amount of
cess as sulfur dioxide is produced in the roasting step chlorine, excessive process time and without reduced
and released to the atmosphere. The procedure for yields of metals.
recovering metal from the chlorides in this process 55 A dry chlorination technique for ores containing
lacks the features which the process of the Mitchell lead, zinc and silver is disclosed in the article menpatent
lacks as outlined above and differs in other re- tioned above entitled "The Dry Chlorination of Comspects
from the flow sheet of the present invention. plex Ores" by C. A. Ionidas, dated May 27, 1916, pub-
It has been found that when the chlorination product Iished in Volume 112 of Mining and Scientific Press.
of this invention is treated with sodium chloride to 60 The process was developed fior processing complex
solubilize the metal chlorides, an undesirable build-up sulfide ores containing zinc which could not be treated
of impurities, particularly zinc chloride, in the brine profitably by other means and us directed essentially to
leach solution occurs which adversely affects the ability the recovery of zinc by fused bath electrolysis, "the
of the solution after a period of time to solubilize silver most vital step in the whole process...." The process is
and lead chlorides from the chlorinated ore product. 65 used on ores having a high content of iron so that only
The present process provides a means for overcoming a partial chlorination is performed followed bya roastthis
problem and obtaining high recoveries of silver and ing step "in the presence of air'" to regenerate chlorine
lead. consumed in the initial formation of ferric chloride.
4
BRIEF DESCRIPTION OF THE ORAWINGS
DETAILED DESCRIPTION OF THE PROCESS AND
SPECIFIC EXAMPLES
(t is an important feature of the process that the
separation of the prescribed amount of bleed stream
from the recycled sodium chloride leach solution, and
the subsequent recycling thereof to the sodium chlor-
5 ide leach after removal of zinc and other metal impurities
therefrom, results in zinc chloride being removed
from the brine leach solution substantially at the rate it
is being added to thereby prevent its build-up in the
brine leach solution with resultant inhibition of the
10 solubilization of lead chloride. Another important feature
of the invention is the conservation of chlorine
feature in which no chlorine leaves the system as chloride
in impurities or otherwise but any removal of chlo-
15 rine is as chlorine gas through electrolysis so that it can
be recycled to the dry chlorination step without any
substantial loss of any chlorine introduced into the
system either for dry or wet chlorination. A distinct
advantage of the process is that it is pollution-free with
20 no chlorine or lead vapors or compounds being released
to the atmosphere and substantially all of the
sulfide sulfur being converted to elemental sulfur
rather than to sulfur dioxide as in the prior pyrometallurgical
processes.
The present process will now be described with reference
to the annexed drawings, wherein:
FIG. 1 is a generalized flow sheet illustrating the
30 process of the present invention performed as a continuous
process.
FIG. 2 is a diagrammatic illustration of a rotary kiln
for conducting the gaslsolid dry chlorination step of the
process of the invention countercurrently when dry
chlorination is used.
4,011,146
BRIEF STATEMENT OF THE INVENTION
3
The present dry chlorination procedure cannot be conducted
in the presence of oxygen, either contained in
air or otherwise if a pOllution-free process is desired,
because the sulfur released is immediately oxidized to
sulfur dioxide in the presence of oxygen. The article
discloses a process performed on an ore not containing
arsenic or antimony differing widely from tetrahedritetennantite
ores. The statement on page 787 postulating
that the process is effective on ores containing arsenic
and antimony obviously does not include ores of the
tetrahedrite-tennantite series. Certainly, a pollutionfree
process was not. contemplated in view of the roasting
step performed in the presence of air.
The invention is an improvement in processes for
treating sulfide ore concentrates containing lead, silver
and zinc sulfides to recover principally silver and lead,
part of the improvement comprising conducting the
recovery of the metals from their chlorides resulting
from the chlorination step in a manner to prevent
build-up of impurities, including zinc chloride, in the
sodium chloride leach solution used to solubilize the
metal chlorides formed in the chlorination step. The
process includes as an alternate to wet chlorination of 25
the sulfides a dry chlorination procedure using dry
chlorine gas to convert the sulfides to chlorides, the
.sulfide sulfur to elemental sulfur, and volatilize the
chlorides of arsenic and antimony if these metals are
present followed by solubilizing the chlorides with sodium
chloride solution. Although the dry chlorination
step can be performed above the melting point of sulfur,
the preferred temperature range is between 50° C
and the melting point of sulfur with the most preferred 35
temperature range being 80° C to about the melting
point of sulfur. During the dry chlorination step, the
sulfur chlorides formed are contacted by means of an
iriert sweep gas with ore to convert them to metal
chloride and elemental sulfur so that substantially no The present invention will be illustrated with respect
sulfur chlorides are released to the atmosphere. The 40 to a galena/tetrahedrite concentrate on which a dry
dry chlorination procedure is particularly effective on chlorination procedure was used. It is to be understood
sulfides of the tetrahedrite-tennantite series alone or that this process is applicable to other ores containing
combined with some other mineral, such as galena. the sulfides of lead, silver and zinc and that chlorina-
After chlorination of the sulfides by whatever tion is not restricted to dry chlorination as wet chlorimethod
the metal chlorides are separated from the 45 nation can be used. The dry chlorination procedure will
resulting solution and the metals lead and silver, which be described in connection with illustrative examples
are of principal interest, recovered from the separated before descrip~ion of the process for recovering metals
aqueous chlorides. Lead chloride is crystallized out of from the chlondes. . ..
the solution by cooling and lead recovered from the 50 . In order to comp.are .the effectiveness of dry chlo~malead
chloride by fused salt electrolysis with the chlorine tlon and wet chlormatlon p~ocesses based on the s~lver
produced being recycled to the chlorination step. The extracted, amo~nts of chl~n.ne used, a~d process tm~e,
silver is removed from the lead chloride-depleted solu- a sample of r~sldue contammg c.ryst~lhne tetrahednte
tion by cementation. The lead and silver-depleted solu- was treated w.lth ~oth a wet chlon~at~on pr?cedu.re and
tion, from which a bleed stream is separated, is recy- 55 the dry c~lonnatIon pro~ess of ~hIS mvention wIth the
cled to the sodium chloride brine leach. The bleed comparative results obtamed bemg set forth below.
stream after final removal of lead and silver therefrom In order to obtain the sample of tetrahedrite from the
by iron cementation is neutralized with sodium carbon- available galena-tetrahedrite concentrate, the latter
ate to remove zinc and other metal impurities there- was treated as described below to remove most of the
from as carbonates follov.:,ed by electrolysis of the re- 60 lead sulfide.
suiting solution to produce chlorine which is recycled Commercial galena-tetrahedrite concentrates were
to chlorination, with some of the weak sodium chloride leached in acidic 450 gil CaCl2+30 gil Fe+3 solution at
electrolyte, after concentration, being recycled to the 90° C maintaining EMF. at 400-450 mv by injecting
sodium chloride brine leach solution, the procedure gaseous Cl2 into slurry for 1.5 hours. The term "EMF"
preventing build-up of zinc and other impurities therein 65 refers to oxidation-reduction potential of an indicator
in the continuous process, and sodium hydroxide from electrode versus a reference electrode. The residue was
the electrolysis being carbonated and recycled to the filtered, washed well with hot 450 gil CaCl2 solution,
neutralization step. then H20, and dried at 60° C.
5
4,011,146
6
The difference between the total sulfur and the elemental
sulfur is the combined sulfur in the metal sulfides,
the elemental sulfur resulting from the conversion of
lead sulfide tolead chloride.
The wet chlQrination process was performed on the
tetrahedrite-sulfur residue as described in the following
example with results in chlorine consumption, process
time and silver extracted being given:
EXAMPLE I
EXAMPLE I
Assay of Residue
*Total sulfur
"Elemental sulfur
%
Ag .58
Pb 1.2
·S' 64
··So 51
Zn 14
Sb 1.9
Cu 2.1
Fe 4.7
%
with ore entering the reaction zone where the sulfur
chlorides are reacted with the sulfide ore to form metal
chlorides and elemental sulfur with the result that sulfur
chlorides are not products of the reaction as in the
5 process of U.S. Pat. No. 739,374. The length of the kiln
is divided into two zones comprising the reaction zone,
the zone approaching the discharge end preferably
operating at a temperature of approximately 1150 C
and the upper end of the tube preferably operating at a
10 temperature of from 800_1150 Cwith the upper temperature
range being below the melting point of sulfur.
Chlorination occurs primarily in zone 1, and evolution
of sulfur chlorides occurs in zone 2. The off-gases containing
volatilized antimony pentachloride (SbCI5 ) are
15 removed in a scrubber and antimony recovered therefrom.
If a pollution-free process is desired, substantially
no oxygen is admitted to the reaction area.
To avoid excessive stickinessduring the reaction, the
temperature within the kiln· should be maintained
Aqueous Chlorination
Conditions:
Results:
Pulp Density
Leach Solution
EMF.
Temperature
Time
Ag extracted
Chlorine consumed
39 g residue/lOoo ml solution
45J(.0I CaCl•• 58 gil Zn.
31 Fe+++. 6 gil Cu.
2 IHCL
Maintained at 780--800 mvby
injecting CI. into slurry
in closed system under 2 psig
pressure.
94°
8.2 hours
88%
4285 lb. CI.tton feed residue
S.ct. + 2H.O = 2HCl + SO. + Ift.S (or polythionic
acids)
The following example was performed in accordance
with the dry chlorination process· described immediately
above with results being shown in amount of chlorine
consumed, process time, and silver recovered.
EXAMPLE II
below the melting point of sulfur. It is an important
35 feature of the dry chlorination step that it is performed
at the relatively low temperatures specified with the
conversion of the sulfide sulfur to elemental sulfur so
that the disadvantages due to the presence of melted
sulfur are eliminated and the :sulfur is removed in the
40 solid form rather than as a vapor as in the processes of
U.S. Pat. Nos. 846,657 and 1,917,233. In zone 2, heat
is applied in order to increase the vapor pressures of
sulfur chlorides so that they can be swept forward by
the sweep gas, nitrogen:
In addition to the necessity of preventing the escape
to the atmosphere of substantial amounts of sulfur
chlorides, it is desirable to have a minimum amount of
sulfur chlorides in the chlorina~ed product to avoid· an
hydrolysis in the subsequent sodium chloride leach
50 performed to dissolve silver chloride. Such a reaction
with S2C12, for example, is represented as follows:
Dry chlorination of the tetrahedrite-sulfur residue
was performed as described below.
The general reactions occuring in the dry chlorination
step are:
I. MS +CI2 -> MCI2+ 'h S2; where M= Pb, Zn, Cu,
Fe, Ag, etc.
2. S2 + CI2 -+ S2CI2
3. MS + S2CI2 -+ MCI2+ 3/2 S2
4. Sb2S3 + 5CI2 -+ 2SbCI5 + 3/2 S2
In order to most efficiently utilize the chlorine,
contact of the pulverized concentrate with chlorine gas
should be done in a counter-current system as shown in 45
FIG. 2., which is operated to prevent the presence of
very little, if any, oxygen entering the reaction area, as
the illustrative process is a pollution~free process.
As shown in FIG. 2 of the drawing, the concentrate in
finely divided form (ground to - 65 mesh) enters the
upper end ofa rot~ry kiln and chlorine gas is introduced
at the discharge end of the kiln so that most
highly concentrated chlorine gas contacts the more
nearly completely chlorinated concentrate. The kiln is
an indirect fired kiln; however, since this reaction is 55
exothermic, little, if any, applied heat is required. An
inert sweep gas, for example, nitrogen gas, is recirculated
along with the chlorine to contact sulfur chlorides
Dry Chlorination
Conditions:
Results:
Apparatus Rotary Glass Kiln
Charge 50 g
Chlorine Addition 14 g over 70 min. period
Temperature 75° C
Time 70 minutes
The chlorinated product was leached in 450 gil
CaCI.+ 30. gil Fe+3 + 5 gil Hel solution for
I hour at ~no C.
Ag Extracted 94%
Dry Chlorination
7
EXAMPLE II-continued
4,011,146
8
illustrates the dry chlorination of lead sulfide concentrates
and subsequent solubilization of the resultant
metal chlorides with sodium chloride in accordance
10 with the flow sheet of the invention.
EXAMPLE III
Chlorination Conditions
Apparatus 3 Compartment Rotary Kiln
15
Zone I Reaction:
CI2 Addition 58~00 Ib/ton PbS ore
Inert Gas Nitrogen
N2 :CI2 = 1:1 Vol. Ratio
Temperature 80° C
Time 2 Hr.
Zone 2 Reaction:
20
Inert Gas Nitrogen
Temperature 110-115°C
Time 1.5 Hr.
Leach Conditions
Pulp DensIty 50 g Chlorinated Product
per liter Leach Solution
Leach Solution 290t NaC!. pH 1.5
25
Temperature 95°
Time 1.5 to 3 Hrs.
Results
Chlorine Consumed 550 lb. CI,/ton feed residue
The results show that 6% more silver was extracted in
the dry chlorination process using less than 1/7 the
amount of chlorine and 1/7 the chlorination time. Substantially
all the sulfide sulfur in the metal sulfides was
converted to elemental sulfur while in the wet chlorination
process a substantial amount of sulfide sulfur was
converted to sulfate. The results illustrate the effectiveness
in terms of chlorine consumption, silver recovery,
and process time of the dry chlorination process on
tetrahedrite-tennantite type concentrates alone. The
same type results have been obtained on this type concentrate
associated with galena, and, obviously, the ore
or concentrate with which the tetrahedrite-tennantite
mineral is associated will have little effect on its reaction
or breakdown under dry and wet chlorination
treatment.
The feature of the invention relating to the recovery
of metals from the chlorinated products of the chlorination
step will now be described in conjunction with
the illustrative example.
The concentrate used in the illustrative example had
the following analysis:
30
Silver 0.30% - 0.35% Ag
Lead 68% - 70% Pb
Antimony 0.80% - 1.4% Sb
Sulfur (Total) 14% - 17% Zn
Zinc 4% - 6% Fe
Iron 2% - 4% 35 Cu
CI
pbS
Concentrates
100 g
0.34
70
1.2
4.5
2.7
:94
<.1
AssaY. %
0.28
58
.41
3.7
2.3
.80
23
Leached
Residue
18.6 g
.012
.12
.098
16
7.9
.18
% Sb Volatilized During Chlorination = 59
% Extracted During NaCI Leach - Ag = 99.3
Pb = 99.9
Sb =96
Zn = 33
Fe =47
Cu =97
The ore concentrate was ground before chlorination to
-65 mesh. The ground concentrate was dried as the dry
chlorination procedure was used and the dried concen- 40
trate subjected to dry chlorination.
Chlorination of the ore was performed with dry chlorine
gas in the kiln illustrated in FIG. 2 in accordance
with the counter-current system described above. A The results of the example show that more than 99
definite amount of chlorine gas per ton of concentrate 45 percent of the lead and silver content of the concenis
metered into the kiln to substantially convert the lead trate was converted to the chloride and extracted durand
silver values to the chlorides in the continuous ing the brine leach. In addition a substantial amount of
process. Since the reaction between the lead sulfide the antimony was recovered. Substantially all of the
(PbS) and chlorine is quite exothermic, some cooling sulfide sulfur was converted to elemental sulfur in the
may have to be done in Zone I, or, alternatively, addi- 50 dry chlorination step.
tion of inert materials, such as sand, recycled product, It was found by using dry chlorination and the flow
or the like, as a diluent for the concentrate can be used. sheet of FIG. 1 that low temperature (80°-115° C) dry
In Zone 2, as stated above, heat may be applied in chlorination with controlled chlorine addition
order to increase the vapor pressures of sulfur chlorides (580-620 Ibs. of chlorine per ton of concentrate) folso
that they can be swept forward by the sweep gas, 55 lowed by a sodium chloride leach at 90°_95° C for an
nitrogen. hour extracted 99% of the silver, 99.9% of the lead,
The amount of chlorine gas required for chlorination 33% of the zinc, 47% of the iron, 97% of the copper
depends upon the composition of the concentrates. For and 96% of the antimony. During chlorination, antithe
galena/tetrahedrite concentrates, most of the chlo- mony was volatilized, probably as SbCIs, and recovered
rine is used to chlorinate the galena (PbS). These con- 60 from the off-gases of the chlorination step. Arsenic, if
centrates assay approximately 70% lead, and the theo- present, can also be recovered in this manner. As stated
retical requirements of chlorine for the reaction PbS + above, substantially all of the sulfide sulfur in the metal
CI2 = PbCI2 + S per ton of concentrate is 480 Ibs. of sulfides was converted to elemental sulfur. This is an
chlorine. The remaining 100-140 Ibs. of chlorine (the improvement over pyrometallurgical processes in
total chlorine addition being from 580-620 Ibs. of chlo- 65 which the sulfur is released as polluting sulfur dioxide,
rine per ton of concentrate), chlorinates the tetrahe- sulfur chlorides or as sulfur vapor.
drite and some of the sulfides of other metals such as The invention will now be further described with
zinc, iron, copper and others. The following example reference to the flow sheet of FIG. 1.
S
320
320
18.8
18.8
Sb Zn Fe Cu
24.0 90.0 54.0
36
24.00 90.00 90.00
pb
1400
1400
Ag
1385
6.70 5 9 5 18
14 ±IO
0.10 8 I 60 29 .8 ±31O
2 30 56
6.80 1400 24 90 90 18.8 ±320
6.80
6.80
ESTIMATED MATERIAL BALANCE FOR
GALENAnETRAHEDRITE
Lb.non Concentrates
Input
Pbs
Concentrates
4,011,146
9 10
The leaching referred to in the example is peformed about 50°_80° Cto precipitate zinc, iron and other
as follows. Irrespective of whether dry or wet chlorina- metal impurities as carbonates in a readily filterable
tion is used, the flow sheet of FIG. 1 is followed beyond form. Sodium· carbonate is used here because its reacthe
chlorination step. The chlorinated product is tion with zinc chloride produces sodium chloride which
leached in the brine leach with sodium chloride solu- 5 is subsequently submitted to electrolysis so that no
tion to solubilize the lead and silver chlorides, and chlorine is lost from the system in the removal of zinc
other metal chloride impurities. After start-up, the and other impurities.
brine leach solution is supplemented with recycled The bleed solution after solids removal is subjected
sodium chloride in the continuous process, as shown. to electrolysis to produce chlorine gas, sodium hydrox-
The leach solution for the tetrahedrite/galena concen- 10 ide, and a weak sodium chloride solution. The prior
trate during operation ordinarily contains from removal of zinc and other impurities from the solution
260-280 grams per liter of sodium chloride, approxi- greatly facilitates the electrolysis as the electrolysis is
mately 40 grams per liter oflead, about 0.15 grams per almost physically impossible with zinc and the other
liter of silver, 15-30 grams per liter of zinc, 15-30 impurities present in the electrolyte. The sodium hygrams
per liter of ferrous iron, and lesser amounts of 15 droxide is carbonated to produce sodium carbonate
copper, antimony, calcium, magnesium, manganese, which is recycled to the neutralization step. The chloaluminum,
etc. The leaching step, irrespective of the rine gas is recycled to the chlorination step and the
concentrate being processed, is preferably performed impurity depleted sodium chloride bleed solution after
at a temperature of from about 80°-100° C. The leach concentration is recycled to the leach step to prevent
slurry is filtered hot and the residue discarded or pro- 20 zinc build-up in the leach solution as explained above.
cessed to recover the elemental sulfur, if desired. The process can, of course, be performed both con-
The next step, as appears from the annexed. flow tinuous or batch.
sheet of FIG. 1, is the recovery of lead. The solubilized Based on the results obtained with the process using
lead chloride is crystallized from the sodium chloride a dry chlorination procedure a material balance for a
leach solution by cooling from 80°-100° C to approxi- 25 typical commercially available [ead sulfide concentrate
mately 15°_20° C. The crystalline lead chloride is sepa- (galena/tetrahedrite) is as follows:
rated from the solution by centrifuging, dried, and
electrolyzed in a fused salt cell to produce product
lead, and chlorine gas which is recycled to the chlorination
step. 30
The next step is the recovery of silver. The silver is
precipitated from the lead chloride-depleted sodium
chloride leach solution by cementation with metallic
iron or lead to produce an impure silver sponge con- Iron Powder
taining some copper, lead, iron and other trace impuri- 35
ties. This sponge must be refined to produce a pure
silverproduct. The lead and silver-depleted leach solu- Products
tion minus a bleed stream is recycled to brine leach as Leasd
h Ag pon~e
sown. Sb Chlonde
About 5-15% of the recycled leach solution is bled 40 Lea~h
off from the main stream as a bleed stream. The main re~~ri;'
purpose of this is to treat this amount of the main C~bon~~~s
stream as described below to remove impurities, especially
zinc chloride, and recycle the impurity-depleted
bleed stream to the brine leach, all for the purpose of 45 All the chlorine gas added is used internally.
controlling the concentration of zinc chloride and
other impurities in the leach solution. Zinc chloride is All the chlorine gas added is used internally.
known to appreciably decrease the solubility of lead The Material Balance Table shows that theoretically
chloride in sodium chloride solutions. Accordingly, in all of the lead and silver can be recovered by the proorder
to maintain maximum dissolution of lead chlor- 50 cess with the loss of no chlorine from the system. After
ide, the zinc chloride and other impurities are removed start-up virtually no chloride addition to the continuous
through the bleed stream at substantially the same rate process is needed subject to ordinary losses due to
at which they are introduced from the chlorination mechanical operations, such as, filtration, concentrastep.
tion, etc.
Another purpose of the bleed stream and its treat- 55 While the invention has been illustrated by its appliment
is to permit removal of the impurities in a form cation to lead, silver and zinc containing tetrahedrite/-
other than chlorides with consequent loss of chlorine galena concentrate and the use of a dry chlorination
from the system, and to recover chlorine as gas so that procedure, it is by no means limited to this ore and
it can be recycled to the chlorination step without any technique. The invention includes the use of dry or wet
loss of chlorine from the system. 60 chlorination techniques on ores in general containing
As shown in the flow diagram, lead remainingin the lead, zinc and silver, the flow sheet beyond the chloribleed
stream is removed by cementation with metallic nation step being applicable irrespective of the method
iron and the resultant sponge lead recycled to the silver of chlorination.. The flow sheet can be used to recover
cementation step. Any silver cemented out will be recy- metals from their chlorides produced by wet chlorinacledlikewise.
The lead in solution in the bleed stream 65 tion of their sulfides with results comparable to those
is decreased from about 15 grams to 0.2 grams per liter. produced in the example.
The bleed stream is next neutralized with sodium It is seen from the above description of the invention
carbonate at a pH of about 8.5 and at a temperature of that a process has been providled for the recovery of
45
4,011,146
12
9. The process of claim 7 in which the temperature of
dry chlorination is from about 500 C to 1500 C.
10. The process of claim 7 in which the sodium chloride
leach solution contains from about 250 to 300
5 grams per liter of solution of sodium chloride.
11. The process of claim 7 in which the concentrate
is galena/tetrahedrite ore.
12. The process of claim 1 in which the leaching step
(b) is carried out at about 800 C to 1000 C.
10 13. The process of claim 1 in which the sodium chloride
leach solution in step (c) is cooled to about 200 C to
precipitate lead chloride.
14. The process of claim 1 in which the silver is recovered
in step (d) by cementation with metallic iron.
15 15. The process of claim 1 in which the concentrate
is chlorinated in step (a) by a wet chlorination step.
16. A process for treating a galena/tetrahedrite ore
concentrate including lead, silver, antimony and zinc
sulfides comprising the steps of: .
20 a. dry chlorinating the pulverized concentrate with
chlorine gas to convert the sulfides to chlorides,
volatilize the antimony chloride, and convert the
sulfide sulfur to elemental sulfur, said chlorination
being carried out at a temperature of from about
500 C to 1500 C;
b. leaching at a temperature of about 800 C to 1000 C,
the residue from step (a) with an aqueous sodium
chloride solution containing about 250 to 300
grams/liter of sodium chloride to dissolve lead
chloride and silver chloride to extract these chlorides
from the remaining solids;
c. cooling the sodium chloride leach solution from
step (b) to about 200 C to precipitate substantially
all of the lead chloride and separating the lead
chloride therefrom;
d. fusing the lead chloride from step (c) and electrolyzing
the fused salt to produce chlorine gas and
lead;
e. recycling the chlorine gas from step (d) to step (a);
40 f. recovering the silver from the lead chloride depleted
leach solution remaining from step (c) by
cementation with metallic iron;
g. removing from about 5% to 15% by weight of the
silver and lead depleted leach solution from step
(f) as a bleed stream and recycling the remainder
of the solution to the leach solution of step (b);
h. removing any lead and silver remaining in the
bleed stream by iron cementation;
i. precipitating zinc and other impurities from the
bleed stream with sodium carbonate;
j. regenerating chlorine gas from sodium chloride in
the bleed solution by electrolysis;
k. recycling the chlorine gas from step (j) to the dry
chlorination step of step (a);
55 I. carbonating the sodium hydroxide formed in step
(j) to form sodium carbonate and recycling the
sodium carbonate to precipitation step (i); and
m. recycling sodium chloride solution from step (j) to
the leaching step (b).
60 17. The process of claim 16 in which the concentrate
includes arsenic sulfide and the arsenic is volatilized in
dry chlorination step (a).
18. In the process of recovering metals from sulfide
ores containing at least the sulfides of lead, silver and
65 zinc in which the sulfides are converted to elemental
sulfur and chlorides by chlorination, the chlorides solubilized
in sodium chloride, lead chloride removed from
the leach solution by crystallization for recovery of
11
metals from their sulfide ores by chlorination of the
sulfides to chlorides and elemental sulfur followed by
solubilization of the chlorides with sodium chloride and
subsequent recovery of the metals from the chlorides,
in which process substantially all of the sulfide sulfur in
the ore 'is converted to elemental sulfur, build-up of
zinc chloride and other impurities in the sodium chloride
leach solution is prevented, no chlorine is lost from
the system by removal of any impurities as chlorides,
the chlorine of the metal chlorides from which metals
are recovered being recovered as a gas for recycle to
chlorination, and in which there is no appreciable loss
of chloride from the system. The invention includes the
combination with the chlorination step of the recovery
of all chlorine as a gas so that the recovered gas can be
reused in the chlorination step. The process has the
overall advantage that it is pollution-free with no chlorine
gas escaping from the system and no lead or sulfur
compounds or vapors being released to the atmosphere.
What is claimed is:
1. A process for recovering metals from a sulfide ore
concentrate containing lead, silver and zinc sulfides
comprising the steps of:
a. chlorinating the concentrate to convert the metal 25
sulfides to metal chlorides and convert the sulfide
sulfur in the ore to elemental sulfur;
b. leaching the residue of step (a) with aqueous sodium
chloride to dissolve lead and silver chlorides
and remove these chlorides from the remaining 30
solids;
c. cooling the sodium chloride leach solution to precipitate
substantially all of the lead chloride followed
by separating it from the leach solution;
d. recovering the silver from the lead chloride de- 35
pleted leach solution remaining from step (c);
e. removing a bleed stream from the solution remaining
from step (d) and recycling the remainder of
the solution to the leach solution of step (b);
f. removing substantially all of the zinc and other
impurities from the bleed stream;
g. subjecting the bleed stream to electrolysis to produce
chlorine gas;
h. recycling the purified bleed stream to leaching step
(b); and
i. recycling the chlorine gas to the chlorination step
(a).
2. The process of claim 1 performed continuously.
3. The process of claim 1 in which any lead and silver
remaining in the bleed stream of step (e) is removed by 50
iron cementation before removal of zinc' in step (f).
4. The process of claim 1 in which zinc is removed
from the bleed stream of step(f) by neutralizing the
bleed stream with sodium carbonate to form sodium
chloride and zinc carbonate.
5. The process of claim 4 in which sodium hydroxide
formed in the electrolysis ofsodium chloride in step (g)
is carbonated to form sodium carbonate which is recycled
to the neutralization step.
6. The process of claim J in which the bleed stream
of step (h) is concentrated before recycling to leaching
step (b).
7. The process of claim 1 in which the concentrate is
chlorinated in step (a) by dry chlorination with dry
chlorine gas.
8. The process of claim 7 in which the dry chlorination
is carried out at a temperature below the melting
point of elemental sulfur.
* * * * *
14
ture between about 500 C and the melting point of
sulfur to convert substantially all of the sulfide
sulfur to elemental sulfur in solid form and to effect
conversion of the metal compounds to metal chlorides,
and recovering metal from the chlorides.
22. The process of claim 21 in which chlorination is
performed at a temperature between about 800 C and
the melting point of sulfur.
23. The process of claim 2] in which the minerals
10 contain silver.
24. The process of claim 23 in which the silver containing
mineral is tetrahedrite.
25. The process of claim 21 in which sulfur chlorides
formed during dry chlorination are reacted with the
15 metal sulfides to form metal chlorides and elemental
sulfur.
26. The process of claim 25 in which the process is
performed by introducing the metal sulfides and dry
chlorine gas countercurrently into the reaction zone
20 and an inert sweep gas is introduced into the reaction
zone to bring sulfur chlorides formed during the dry
chlorination into contact with metal sulfides entering
the reaction zone.
4,011,146
13
lead, silver recovered from the leach solution by cementation,
the leach solution after removal of lead and
silver therefrom recycled to the sodium chloride leaching
step, the improvement comprising preventing the
build-up of zinc in the leach solution in the leaching 5
step by removing a bleed stream from the lead and
silver depleted leach solution, removing zinc from the
bleed stream and recycling the bleed stream to the
leaching solution in the leaching step.
19. The process of claim 18 including subjecting the
bleed stream to electrolysis after removal of zinc therefrom
to produce chlorine gas and recycling the chlorine
gas to the dry chlorination step.
20. The process of claim 19 in which the zinc is removed
by precipitating it as zinc carbonate by the addition
of sodium carbonate, the sodium hydroxide produced
in the electrolyis is carbonated to sodium carbonate
and the sodium carbonate recycled to the zinc
precipitation step.
21. The process of recovering metal values from
minerals of the polymorphic series of complex metal
sulfides tetrahedrite-tennantite comprising:
a. subjecting the minerals to dry chlorination with
chlorine gas in the absence of oxygen at a tempera-
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55
60
65