United States Patent
Goens et al.
[ 19) [ 11]
[45]
3,973,949
Aug. 10, 1976
[52) U.S. CI. 75/112; 75/114;
75/120; 204/60; 204/128; 423/92; 423/100;
423/105; 423/109; 423/419
[51] Int. Cl,2 C22B 3/00; COIG 9/00
[58] Field of Search 423/109, 99, 150, 139,
423/105,491, 100,419,92; 204/128,39;
75/101 BE, 120, 112, 114
[54] ZINC RECOVERY BY CHLORINATION
LEACH
[75] Inventors: Duane N. Goens; James E. Reynolds,
both of Golden, Colo.
[73] Assignee: Cyprus Metallurgical Processes
Corporation, Los Angeles, Calif.
[22] Filed: Feb. 13, 1975
[21] Appl. No.: 549,728 .
[56] References Cited
UNITED STATES PATENTS
1,736,659 11/1929 Mitchell 423/36
2,045,092 6/1936 MitchelL 423/109
2,094,277 9/1937 Mitchell 423/109
2,187,750 1/1940 Marvin 75/101 R
3,206,276 9/1965 Burwell et al... 23/312 ME
3,206,277 9/1965 Burwell et al... 23/312 ME
3,251,646 5/1966 Alon et al.. 75/101 BE
3,649,220 3/1972 Powell et al. 423/99
FOREIGN PATENTS OR APPLICATIONS
44-4647 1969 Japan 423/109
IRON HYt)ROxrOE
COPPER SILVER
ARSENIC lEAD BISMUTH
Primary Examiner-Oscar R. Vertiz
Assistant Examiner-Wayne A. Langel
Attorney, Agent, or Firm-Sheridan, Ross & Fields
[57] ABSTRACT
A pollution-free process for the recovery of high purity
zinc from zinc containing material including sulfide
ores which provides for maximum conservation
and re-use of reagents, the process consisting of chlorinating
the materials either with ferric chloride or
chlorine gas followed by selective removal of metals
other than zinc by standard procedures, such as, lead
chloride crystallization, cementation, etc. to produce a
solution containing essentially only zinc chloride and
ferrous chloride. To enhance the purity of the zinc
end product zinc chloride is separated from the ferrous
chloride solution with a zinc selective extraction
agent from which the zinc chloride is stripped with sodium
chloride solution in a sodium chloride stripping
circuit followed by precipitation of zinc as the carbonate.
The sodium chloride formed in precipitating zinc
carbonate with sodium carbonate goes to an electrolytic
cell to produce chlorine and sodium hydroxide by
electrolysis which latter is carbonated to sodium" carbonate
for circulation to the zinc carbonate precipitation.
The sodium chloride stripping circuit includes
the electrolytic cell where excess chlorine is removed
from the stripping solution. The ferrous chloride raffinate
from the zinc chloride extraction step is sent to a
chlorination and hydrolysis step where ferric chloride
leaching agent is regenerated and iron removed.
Chloride from the electrolysis step is used for the
chlorination step. The process results in very little loss
of reagents from the system.
27 Claims, 3 Drawing Figures
Cl2 NoGI
ZINC PROOUCT
u.s. Patent Aug. 10, 1976 Sheet 1 of 2 3,973,949
ZINC RECOVERY BY CHLORINATION LEACH
FEED OF ZINC
CONTAINING
MATERIAL
T FERRIC
CHLORIDE
LEACH
IRON COPPER SILVER
CEMENTATION ARSENIC LEAD BISMUTH
TAILS
LEAD CHLORI DE
ELECTROLYSIS
ZnCI2 LOADED ORGANIC
ZnCI2
ZnO----" ' NoCI
ZINC CHLORIDE
,.-------~ STRIPPING
WITH NoCI
CHL~RINE J
IRON HYDROLYSIS ~-- p~6~BcT ZINC CHLORIDE
AND/OR SOLVENT
~C:!:H~LOe:R~I~N~A.:!:.TO~1 ~NU---FeCI2-----LJE~X~T!R~A~C.!T.!.SIO~NW
STRI~PED
ORGIi\NIC
IRON
RECOVERY
NoCI
IRON ~IRON HYDROXIDE
PRECIPITATION
ZINC DUST~ ZINC DUST TRACE METAL
PURIFICATION IMPURITIES LOAD
CADMIUM ETC.
CALCINE ZINC
CARBONATE
-NoCI- ZINC
CARBONATE .r,:;; PRECIPITATION
No2C03 T
ZnC03
NoCI
ELECTROLYSIS
CARBONATION ~----'
TO No2C03
ZINC PRODUCT
ISOTHERMS FOR SOLVENT EXTRACTION OF ZINC
FROM FERROUS CHLORIDE SOLUTIONS WITH TBP
No
....,
N
t/)
:n:r
n-
-p-~
0\
~
a
w..\0
oq"J
W ..
':f
\C
~
c..c.n
30
-,-.J.q: 3
5 10 15 20 25
SOLVENT PHASE. g/I ZINC
u~401 I I I ---JI~/~7'i-ia-it_I"i-w;-f I
N
., I I I I 1/
ISOTHERMS FOR STRIPPING ZINC FROM
75% TRtBUTYl PHOSPHATE SOLVENT
Sa iii iii
I I' I I ..°.........3. 21 I I ...V. >I-, , I
:C:: .[/' I I aX.. 24' I ~.,-»f I I
o . ,
o:::) I I , III I I ~ 161 rr~7 I I
o
C
10
I..'l.q: 2
10 20 30 40 - !SO eo
AQUEOUS PHASE. gIl ZINC
• V
! ~1S% Tep
l o-
J
/
I ..to% 364
//~
/ , V / v<2!,% TB p
4
°0
32
36
°z28
N
~..24 III en
~;W
Q.
.....
wz 16
~
o
en 8
3,973,949
BRIEF DESCRIPTION OFTHE DRAWINGS
FIG. 1 is a flow diagram of the process of the invention,
FlG. 2 is a graph of a loading curve of zinc chloride
on a tributylphosphate extractant, and
FlG. 3 is a graph of a stripping curve showing the
effectiveness of stripping zinc chloride from a tributylphosphate
extractant.
DESCRIPTION OF THE PREFERRED
EMBODIMENT
2
also regenerating the stripping agent by removing chlorine
gas at the anode which is sent with the rest of the
chlorine to the iron chlorination step, sodium hydroxide
formed in the electrolysis step being converted to
5 sodium carbonate which is sent to the zinc carbonate
precipitation step. Part of the sodium hydroxide may be
included in the stripping agent when the tertiary amine
is used as an extractant to control the acidity of the
amine extractant. Zinc is recovered from the precipi-
10 tated zinc carbonate by calcination and the carbon
dioxide formed is sent to the sodium hydroxide carbonation
step. Chlorine from the electrolysis step is sent to
the iron chlorination step in one modification of the
invention while in an alternative modification in which
15 chlorine gas is used for the chlorination step it is sent to
the gas chlorination step.
, An alternative procedure is the precipitation of zinc,
as zinc hydroxide with sodium hydroxide from the cell
thus eliminating the step of carbonating sodium hy20
droxide when the zinc is precipitated as the carbonate.
Reference will now be made to the flow diagram of
FIG. 1 for a description of the process of the invention.
35 The flow diagram and its description does not include
the conventional equipment used in the various steps,
such as, thickeners, filters, centrifuges, dechlorinaters,
evaporaters, etc.
The feed can be any material which contains zinc,
40 usually, a chlorinatable ore of zinc. The process can be
used to recover zinc from scrap alloys of zinc. The
invention is illustrated by its application to the recovery
of zinc and other metals from a sulfide ore; however, it
is by no means limited to this application as zinc can be
45 recovered from various zinc containing starting materials.
If the zinc is being recovered from an ore the latter
will first be ground and concentrated. For this purpose
of illustrating the operation of the invention as depicted
in the flow diagram of FIG. 1 an example was selected
50 in which the feed material was a concentrate ofzinc ore
which contained 24.4% zinc, 15.6% iron, 15.8% lead,
27.6% sulfur and 4.1 ounces of silver per ton, the example
being described below.
One and two-stage leaches were performed by contacting
varying amounts of the concentrate with 500 cc
of ferric chloride lixiviant in conventional 1000 cc
3-neck flasks provided with paddle stirrers, reflexing
condensers and heating mantles.
The lixiviant in all tests contained approximately 100
60 gil ferric iron and 30 gil ferrous iron. In the I-stage
leaches the amount of concentrate was varied so that 1,
50 and 200 per cent of stiochiometric ferric iron was
available to react with the lead and zinc sulfides. It was
found that ferrous chloride serves the function of hold-
65 ing the lead chloride in solution. The preferred concentration
of ferrous chloride in the leach solution for
holding all of the lead chloride in solution is in excess of
about one molar. The leaches were performed at 100°C
1
SUMMARY OF THE INVENTION
ZINC RECOVERY BY CHLORINATION LEACH
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention lies in the field of recovering metals
from their ores and other metal containing material by
first chlorinating the metals followed by final recovery
of the metals from their chlorides.
2. Description of the Prior Art
Competition, the increasing necessity of using lower
and lower grade ores, the requirement that metal recovery
processes be essentially non-polluting, and
other factors have created a demand for a reduction of
the costs for recovering metals from their ores and
other materials for the pollution-free processes. Conservation
and re-use of reagents appears to be the most
feasible area for reduction of costs.
U.S. Pat. No.1 ,736,659, Mitchell, discloses a process
for the recovery of metals from their sulfide ores in
which the metals are first chlorinated and then selectively
separated. In this process iron is separated from
the desired zinc chloride by precipitation of the iron
before the zinc recovery step. The disadvantage of this
procedure is that substantial zinc losses will occur in 25
the voluminous iron hydroxide precipitate. Further,
Mitchell precipitates the zinc product from the original
dissolution solution after various attempts at removing
impurities from it. Such a system inevitably results in an
impure zinc product. The present invention uses a zinc 30
selective extractant by which the zinc is effectively
cleanly separated from the dissolving solution without
the necessity of prior precipitation of all other impurities.
The present process thereby permits a higher recovery
of higher purity zinc.
In the Mitchell process an electrolytic cell is used to
generate from sodium chloride formed in the zinc precipitation
step the base required to precipitate zinc. In
the present process the electrolytic cell is used not only
for this purpose but primarily to regenerate the sodium
chloride stripping agent used to remove the zinc from
the extractant so that additional reagent need not be
added for stripping. Using sodium chloride regenerated
in the process as the stripping agent and including the
electrolytic cell in the stripping circuit to remove excess
chlorine ions picked up by the stripping solution in
stripping obviates the necessity for an additional stripping
reagent and an external procedure for removing
excess chlorine ions.
A process is disclosed for recovering zinc from materials
in which it is contained in which zinc and other
metals in the material are first chlorinated to form a
leach solution of chlorides of the metals followed by 55
recovery of lead chloride by crystallization, removal of
trace metals such as copper, silver, arsenic, lead and
bismuth, etc., by cementation, separation of the zinc
chloride from the remaining ferrous chloride solution
by tertiary amine or tributylphosphate extraction
agents for the zinc chloride with the ferrous chloride
being sent to an iron hydrolysis and chlorination step,
the zinc chloride being stripped from the agent with an
electrotyzed sodium chloride solution followed by the
precipitation of zinc from the strip solution with sodium
carbonate with the regeneration of sodium chloride
which goes to a sodium chloride electrolytic cell for
formation of chlorine and sodium hydroxide, the cell
3,973,949
4
system. The use of an extractant containing 75% by
volume of tributylphosphate to the organic solvent
gives the best results. The organic solvent used was
kerosene; however, other conventional organic sol-
5 vents may be used as solvents for the extraction agents.
A preferred range is from about 25 to 85 volume per
cent of tributylphosphate to the organic. The isotherm
shows that solvent loadings in excess of 30 Ilg zinc were
found to be possible and nearly complete extraction of
the zinc can be achieved by using a number of extraction
stages.
Zinc chloride was stripped from the loaded tributylphosphate
and tertiary amine extractants with sodium
chloride brine solution which is generated in the electrolytic
cell as discussed hereinafter. Conventional
stripping techniques were used. Other alkali metal
chlorides can be used as stripping agents, such as, potassium
chloride, by adjusting the system accordingly.
FIG. 3 is a comparative stripping isotherm made from
results obtained by stripping zinc from 75% tributylphosphate
solvent with various concentrations of sodium
chloride solution and water. As the isotherm
shows, strip solutions containing 30 gil of zinc were
obtained using 2-3 molar sodium chloride solution for
stripping.
The ferric iron that is entrained or otherwise extracted
with the solvent will strip and contaminate the
zinc solution. Accordingly, it is important to conduct
the leaching so that substantially all of the iron is in the
ferrous state or if this is not done to reduce as much
iron as possible to the ferrous state and remove any
remaining ferric iron as well as any bismuth, silver or
cadmium before the IQading step. The extractants do
ont appreciably load 'ferrous iron. Any iron that is entrained
in the stripping solution can be oxidized with
chlorine and will precipitate with ferric hydroxide upon
raising the pH to 3-4 with sodium carbonate. Only
minute amounts of antimony, arsenic and lead will
extract.
It was found that the teritary amines were effective as
loading agents and can be stripped of zinc chloride with
the sodium chloride strip solution coming from the
electrolytic cell. When the amines are used as extractants
the flow diagram is altered to use some of the
sodium hydroxide from the cell to control the acidity of
the amines for providing the best stripping efficiency.
As seen from the flow diagram, the ferrous chloride
from which the zinc chloride was separated with the
extraction agent is sent to iron hydrolysis and chlorination.
By hydrolyzing part of the raffinate from the solvent
extraction step exchange iron oxide is formed
from the iron added for cementation and can be removed
from this system. The remainder of the raffinate
is chlorinated with chlorine from the electrolysis cell
discussed below to ferric chloride which is returned to
the leaching step. This permits use of the iron originally
in the starting material as ferric chloride.
The solution from stripping contains essentially zinc
chloride and sodium chloride. After further removal of
iron by precipitation as ferrous hydroxide and cementing
out trace impurities, such as, minute amounts of
lead, cadmium etc. by zinc cementation with zinc dust
the zinc chloride is sent to a zinc carbonate precipitation
step where zinc is precipitated with sodium car-
65 bonate formed by carbonating sodium hydroxide produced
in the electrolytic cell. After filtration zinc carbonate
is calcined and otherwise treated to produce a
high purity zinc product, some of which can be recy-
3
for one half to four hours. The leaching resulted in
conversion to the chlorides of 97.6% zinc, over 95%
lead, 35-50% iron and 96% silver with the sulfur being
converted to elemental sulfur which was removed in
the tails.
An alternative procedure is the use of chlorine gas
either alone or with some ferric chloride for the chlorination
step. Following chlorination with the gas the
remainder of the flowsheet is carried out. Chlorine gas
from the anode is recycled to the gas chlorination step. IO
The next step in the flow diagram, after required
filtration, is the recovery of lead chloride from the
leach solution by crystallization. Lead chloride crystals
were recovered from the 2-stage leach filtrate by cooling
from the initial 80°C to about 10°C. The crystals 15
contained 73.9% lead. Lead is recovered from the crystallized
lead chloride by fused salt electrolysis to produce
metallic lead and chlorine which latter is cycled to
the iron chlorination step.
The filtrate from the lead chloride crystallization 20
contained as impurities 1.09 gil copper, 0.018 gil antimony,
0.038 gil arsenic and 1.52 gil lead as well as the
original silver content. These metal impurities were
removed by conventional cementation procedures with
metallic iron. The removal efficiency of the metal im- 25
purities by cementation was found to be 99.8% copper,
85% arsenic, 33% antimony and 9% lead. The treatment
with metallic iron serves the additional purpose of
reducing all of the iron in the solution to ferrous iron.
Other metals than iron may be used for cementation of 30
the trace metals and other means for removing them
may be used. Other means for reducing the iron to the
ferrous state or insuring that it is in the ferrous state
and may be used. It is important that the solution which
is contacted with the extraction agent later to remove 35
zinc chloride be substantially free of ferric iron as the
agents extract ferric iron which would contaminate the
zinc product. One way to insure there is substantially
no ferric iron in the metal depleted leach solution contacted
by the zinc chloride selective extraction agent is 40
to reduce the ferric iron with metallic iron or other
reducing agent. However, the ferric chloride leach of
the starting material can be readily conducted so that
substantially no ferric iron exists in it.
The filtrate from the cementation step contained 45
essentially ferrous chloride and zinc chloride with a
minor amount of the metal impurities mentioned
above. The next step is the separation of zinc chloride
from the ferrous chloride with an extractant which is
selective for the zinc chloride. Successful extractants 50
for zinc chloride were found to be tributylphosphate
and a tertiary amine (TriCa-C1 amine) sold under the
tradename "Agoden 364". Other tertiary amines can
be used as extractants, such as, tri-Iaurylamine, triisooctylamine
and tridecly amine. Other alkyl phos- 55
phates can be used, such as, the lower trialkylphosphates,
including tripropylphosphate, dibutylphosphate
and trioctylphosphate. By reference herein to zinc
chloride in connection with loading and stripping from
the agent is meant either molecular zinc chloride or an 60
anionic zinc complex. The zinc complex as well as
molecular zinc chloride can be stripped from the
loaded extractant with water or sodium chloride solution.
Conventional countercurrent extraction procedures
were used.
Extraction isotherms were made for various extraction
systems, FIG. 2 being a graph of an isotherm for
two tributylphosphate systems and one Adogen 364
3,973,949
5 6
cled to the zinc dust cementation step. As stated previ- The overall result of the process is that there, is a
ously, an alternative proce<:lure for the final recovery of maximum. conservation and reuse of reagents wth very
zinc is to precipitate it as zinc hydroxide with sodium little addition of reagents required after startup.
hydroxide from the cell and avoid the sodium hydrox- What is claimed is:
ide carbonation step. 5 1. In the process for treatment of materials contain-
The sodium chloride formed in the precipitation of ing zinc and other metals including lead, copper, silver,
zinc and that coming from the stripping step goes to the iron and tra~e metals in which the zinc and other metelectrolytic
cell where some of it is electrolyzed, to als are first converted to chlorides including ferric
produce chlorine at the anode and sodium hydroxide chloride either by wet chlorination with ferric chloride
while some of it has its chlorine content reduced and 10 leaching or dry chlorination followed by separation of
then is recycled to the stripping step. The chlorine lead from the resulting leach solution by crystallization
formed at the anode is sent to the iron chlorinatipn steP of lead chloride and further separation of copper, silfor
chlorinating ferrous chloride to ferric chloride. vel', and trace, metals, reducing substantially all of the
The cell used is commonly known as a chlorine-alkali ferric iron in the leach solution to ferrous iron, ulticell
or "Chloro"Alkali" cell and is of the type used for 15 mately precipitating zinc as zinc carbonate with an
the commerical production of chlorine from sodium alkali· metal carbonate and electrolyzing the alkali
chloride. An anion ion exchange diaphragm which metal chloride formed by the zinc carbonate precipitaprevents
the mixing of sodium chloride and sodium tion in an electrolytic cell to produce chlorine gas
hydroxide in the-cell is used. When sodium chloride is which is cycled to the chlorinationstep and alkali metal
used to strip zinc chloride from the agents it was found 20 hydroxide which is converted to alkali metal carbonate
that it picks up, chlorine ion in increasing concentra- for the zinc carbonate precipitation step, the improvetions
as it is recycled. Unless chlorine ion is continu- ment which comprises: separating the zinc chloride
ously removed during recycling its concentration in- from the ferrous chloride in the metal depleted leach
creases, to the,point were the soilltiondoes not effec-, solution with an extraction. agent selective for zinc
tively strip zinc chloride. Cycling the sodium chloride 25 chloride ,dissolved.in all immiscible organic solvent,
stripping solution' through the cell where chlorine is stripping the zinc chloride from the ,extraction agent
continuously removed solves the problem, prior to the .zinc carbonate precipitation step with an
Analyses showed that the process described is effec- alkali metal chloride stripping solution from the elective
to recover 98% or more of the zinc .contained in trolytic celJ through which the alkali metal chloride
the starting materials as l,l high purity product. ' , 3.0 from the zinc carbonate precipitation step, is continu-
, The ,signific,ant advantages of the invention as re- ously cycled for removal from it of excess chlorine ion
picked up, in the stripping. .
spects conservation of reag~ntsareapparent from the 2. The process of claim lin which the extraction
above description and theaccompanying flow diagram, agent is a I11ember selected from the group consisting of
First of all, all of the cblorine introduced into the sys- 3.5 lower alkyl phosphates and teritary amines.
tern either byferric' chloride chlorination'or gas chlorination
is conserved and reused. None of it is eliminated 3. Ute process of claim 2 in which the concentration
" , ' of the extraction agent is about 20-85% byv,olume in
from the system by, the removal of imy of the metal the organic solvent.. ," ,,' "
impurities. ,The chlorine in, the lead chloride is recov- 4. The process of claim 3 in which the ,conC:l::ntration
ered. in ,the lead chlorine fused bath electrolysis and 40 of the extraction agent is about 75% by volu~epf the
cycled to the irpn.chlorination step to regenerate ferric organic solvent.' ,
chloride. The chlorine i~ th~ metal chloride impurities 5. The process of,claim 2 in which the alkali metal
is converted to ferrous chloride in the iron cementation compounds are sodium compounds.
step. The chlorine in the zinc chloride combines with 6. The process of claim 2 in which the amine extracsodium
in the. zinc carbonate precipitate to form so- 45 tion agent is used at a basic pH.,' , ' , . ' ,
dium chloride which goes to electrolysis where tbe 7. The process of claim 2 ,inwhich theferric chloride
chlorine given off atthe anode is used in the wet or dry leaching step is conducted so that suj:>statltially aU of
chlorination of the metals in the starting material. the. iron in the leach solution is in the ferrous state, .
The ferrous. chloride after the extraction' step, con- 8. The process of claim 1 in which the alkali' met~
taining most of the iron which was in the ore and the 50 chloride from the zinc .carbot1ate precipitation step is
ferric chloride leaching agent, is sent to the iron chlori- electrolyzed in the, electrolytic cell. toJor:m chlOrine
nation and hydrolysis step for conversion to ferric and alkali metal hydroxide. ' . '
chloride for re-use in the ferric chloride leach. The iron 9. The process of claim 8 in which the alkali metal
used for cementation is removed by hydrolysis. The hydroxide is converted to alkali metal carbonate for the
result is that very little of the iron in the original ferric 55 zinc carbonate precipitation step.
chloride leaching agent and the starting material is lost 10. The process of claim 1 in which the zinc containfrom
the system. ing material is a complex zinc sulfide ore.
Use of sodium chloride as a stripping agent is a dis- 11. The process of claim 10 in which the ore contains
tinctive advantage as the cell can be used to continu- sulfides of lead and silver.
ously reduce its chlorine content so that it does not 60 12. The process of claim 1 in which the stripping and
become overloaded with chlorine in the stripping cir- electrolysis is conducted with alkali metal chloride
cuit. Production of sodium chloride in the zinc carbon- solution having a molality of about 1-2.
ate precipitation step provides a brine electrolyte for 13. The process of claim 1 in which the ferrous chlorthe
electrolytic cell. Some of the zinc product can be ide from which zinc chloride is extracted is converted
reused in the zinc dust purification step and some of the 65 to ferric chloride for leaching by chlorine from the
carbon dioxide formed in the zinc calcination step can electrolytic cell.
be used in the carbonation of sodium hydroxide to 14. The process of claim 1 in which lead is recovered
sodium carbonate. from the crystallized lead chloride by fused bath elec3,973,949
7
trolysis and the chlorine given off at the anode reused
to convert ferrous chloride to ferric chloride for leaching.
15. The process of claim 1 in which the alkali metal
compounds are sodium compounds.
16. The process of claim 1 in which the concentration
of the ferrous ion for chlorination leaching is at
least about I mole per liter to maintain solubility of
lead chloride.
17. A process for recovering metal values from zinc
containing material including lead, copper, silver, iron
and trace metals comprising the following steps:
a. converting the metals in the material to chlorides
including ferric chloride by wet chlorination with
ferric chloride leaching or dry chlorination with
chlorine gas to form a leach solution of metal chlorides,
b. removing lead chlorine from the leach solution by
crystallization and recovering lead from the recovered
lead chloride,
c. removing copper, silver and trace metals from the
leach solution by cementation,
d. reducing the ferric iron in the leach solution substantially
all to ferrous iron,
e. separating zinc chloride and ferrous chloride in the
metal depleted leach solution by contacting the
leach solution with an extraction agent selective for
zinc chloride selected from the group consisting of
lower alkylphosphates and tertiary amines,
f. stripping zinc chloride from the extraction agent
with alkali metal chloride solution,
g. precipitating zinc from the stripping solution with
alkali metal carbonate to fonn alkali metal chloride
and zinc carbonate from which latter zinc is recovered,
h. sending the' alkallmetal chloride from the zinc
precipitation step to an electrolytic cell,
i. electrolyzing part of the alkali metal chloride in the
electrolytic cell to form chlorine at the anode and
alkali metal hydroxide,
j. carbonating the alkali hydroxide from step (i) to
fonn' alkali metal carbonate which is sent to the
zinc carbonation step, and
k. returning the remainder of the alkali metal chloride
to stripping step (f) after it has been depleted in
the cell of chlorine ions picked up in the stripping.
18. The process of claim 17 in which ferrous chloride
from step (e) is oxidized to ferric chloride for leaching
in step (a).
19. The process of claim 18in which the oxidation is
performedwiih chlorinegas from the electrolysis.
8
20. The process of claim 17 in which the alkali metal
compounds are sodium compounds.
21. The process ofclaim 17 in which metallic iron is
used in steps (c) and (d) to cement out lead, silver, and
5 other trace metals and to reduce ferric iron in the leach
solution to ferrous iron:
22. The process of claim 17 in which the extraction
agent ilian amine and loading is performed ata basic
pH.
10 23. The process of claim 17 in which the stripping of
step (f) and the electrolysis (i) are performed with
sodium chloride having a molality of about 1-'2 moles
per liter.
\"5 24. The process of claim 17 in 'which lead is recovered
from lead chloride by fused bath electrolysis and
the chlorine formed is' used to oxidize ferrous chloride
to ferric chloride forleaching step (a).
25. The process of claim 17 in which the zinc con20
taining material is a complex zinc s~lfide ore.
26. In the process for treatment of materials contain~
ing zinc and other metals including lead, copper, silver;
iron and trace metals, the process including conversion
of the metals to chlorides including ferik 'chloride
25 either by wet chlorination with femc chloride leaChing
or dry chlorinationtofom.:\aleach solution followed by
recovery oflead from the leach sohition by crystallizing
the lead as lead chloride, removal ofcopper; silver, a.nd
trace metals from the leach solution, reducing substan-
30 tially all of the ferric chloride in the leach solution'to
ferrous chloride, ultimately'precipitatirtgZinc from the
leach solution as zinc carbonate with alkali metal carbonate
and electrolyzing alkali, metal 'chloride fonned
by the precipitation of-zinc carbonate with alkali metal
35 carbonate to produce chlorine gas~hichis returned to
leaching and alkali metal hydroxide which is converted
to a.lkali metal carbonate and 'the lattercy'ded to the
zinc carbonate, precipitation step". the improvement
whieh comprises: recovering zinc' chloride from the
40 lead~ copper, silver "and' trace metal 'depIeted'Ieach
solution prior to zinccarbbnate' precipitation with'ari
extraction agent selective for zinc chloride dissolved in
an immiscible organic solvent, and stripping the zinc
chloride from the extraction with an alkali metal chlor-
45 ide stripping solutionfrom the electrolytic cell through
which the alkali metal chloride solution from the zinc
carbonate precipitation step is passed for remova.l from
it of excess chlorine ion picked up in the stripping.
27. The process of claim 26 in which the alkali metal
50 compounds are sodium compounds.
* * * '* *
55
60
65