U.S. patent application number 12/311044 was filed with the patent office on 2009-12-31 for method and an electrolysis cell for production of a metal from a molten chloride.
Invention is credited to Christian Rosenkilde.
Application Number | 20090321273 12/311044 |
Document ID | / |
Family ID | 39200734 |
Filed Date | 2009-12-31 |
United States Patent
Application |
20090321273 |
Kind Code |
A1 |
Rosenkilde; Christian |
December 31, 2009 |
Method and an electrolysis cell for production of a metal from a
molten chloride
Abstract
The present method relates to a method and a cell for
electrolytic production of zinc from a salt melt comprising zinc
chloride. The cell has at least one electrolysis chamber (2)
containing an electrolyte and at least one adjacent chamber (1)
separated from said electrolysis chamber by means of at least one
partition wall (7, 8). The atmosphere(s) in the electrolysis
chamber(s) is separated from the atmosphere(s) in the adjacent
chamber(s) by the at least one partition wall. The electrolyte is
directed to flow between the electrolysis chamber(s) and the
adjacent chamber(s) through at least one opening in or at the
partition wall(s) below the level of the electrolyte level. The
Zinc metal produced is collected in the bottom of the cell. The
electrolyte flow can be controlled in a substantial laminar
manner.
Inventors: |
Rosenkilde; Christian;
(Porsgrunn, NO) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
1030 15th Street, N.W.,, Suite 400 East
Washington
DC
20005-1503
US
|
Family ID: |
39200734 |
Appl. No.: |
12/311044 |
Filed: |
September 17, 2007 |
PCT Filed: |
September 17, 2007 |
PCT NO: |
PCT/NO2007/000327 |
371 Date: |
May 21, 2009 |
Current U.S.
Class: |
205/369 ;
204/243.1; 204/247.4 |
Current CPC
Class: |
C25C 3/34 20130101; C25C
7/005 20130101 |
Class at
Publication: |
205/369 ;
204/243.1; 204/247.4 |
International
Class: |
C25C 3/34 20060101
C25C003/34; C25C 3/08 20060101 C25C003/08; C25C 7/00 20060101
C25C007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 22, 2006 |
NO |
20064308 |
Claims
1-9. (canceled)
10. A method for electrolytic production of zinc from a salt melt
comprising zinc chloride by the use of an electrolysis cell having
at least one electrolysis chamber (2) containing an electrolyte and
at least one adjacent chamber (1) separated from said electrolysis
chamber by means of at least one partition wall (7, 8), wherein the
atmosphere(s) in the electrolysis chamber(s) is separated from the
atmosphere(s) in the adjacent chamber(s) by the at least one
partition wall, and where the electrolyte is directed to flow
between the electrolysis chamber(s) and the adjacent chamber(s)
through at least one opening in or at the partition wall(s) below
the level of the electrolyte level, and where zinc produced is
collected in the bottom of the cell.
11. A method according to claim 10, wherein the liquid zinc
produced is pumped out of the cell.
12. A method according to claim 10, wherein solid or liquid
ZnCl.sub.2 is fed in a continuous or semi-continuous manner.
13. An electrolysis cell for electrolytic production of zinc from a
salt melt comprising zinc chloride, the cell having at least one
electrolysis chamber (2) with electrodes and further containing an
electrolyte, the cell further comprises at least one adjacent
chamber (1) separated from said electrolysis chamber by means of at
least one partition wall (7, 8), wherein at least one partition
wall is arranged to separate the atmosphere(s) in the electrolysis
chamber(s) from the atmosphere(s) in the adjacent chamber(s), and
where at least one opening in or at the partition wall is arranged
below the level of the electrolyte to allow the electrolyte to flow
between the electrolysis chamber(s) and the adjacent chamber(s) and
where the bottom of the cell is adapted to collect the zinc
produced.
14. An electrolysis cell according to claim 13, wherein the cell
comprises two or more monopolar electrodes.
15. An electrolysis cell according to claim 13, wherein the cell
comprises two monopolar electrodes and one or more bipolar
electrodes.
16. An electrolysis cell according to claim 14, wherein the
monopolar electrodes are cooled by a cooling medium such as
water.
17. An electrolysis cell according to claim 13, wherein the cell
comprises electrode(s) based upon a graphitic material.
18. An electrolysis cell according to claim 13, wherein the
material in the cell's lining is containing more than 95%
SiO.sub.2
19. A method according to claim 11, wherein solid or liquid
ZnCl.sub.2 is fed in a continuous or semi-continuous manner.
20. An electrolysis cell according to claim 15, wherein the
monopolar electrodes are cooled by a cooling medium such as water.
Description
[0001] The present invention relates to a method for production of
liquid zinc and gaseous chlorine from a molten chloride electrolyte
containing zinc chloride and an electrolysis cell for performing
the method.
[0002] Several patents and other literature related to the
electrolytic production of zinc from zinc chloride exist. These
patents and reports essentially describe electrolytic cells with a
single compartment containing all the electrodes. The present
invention, on the other hand, describes an electrolytic cell with
at least two compartments, of which at least one compartment
contains the electrodes (electrode chamber) and at least one
compartment lies next to the electrode chamber. The chambers are
separated by a partition wall that allows for flow of electrolyte
between the compartments. The electrodes are vertical, horizontal
or tilted with some angle.
[0003] Bureau of Mines reports 8133 and 8524 (US Dep. of the
Interior) both describe electrowinning of zinc from ZnCl.sub.2
fused salt cells. Report 8133 presents results from electrolysis
using two monopolar electrodes, while report 8524 relates to
electrolysis in both monopolar and bipolar cells. The electrodes in
all cells are horizontal or slightly tilted from the horisontal
position.
[0004] WO 2004/074552 A1 describes production of zinc and chlorine
from molten ZnCl.sub.2 in bipolar electrolysis cells with tilted
electrodes.
[0005] Further cell designs are known from electrolytic production
of magnesium, and are used for both multi-monopolar (U.S. Pat. No.
4,308,116) and multi-bipolar electrodes (GB 8800674). However,
magnesium metal is lighter than the electrolyte and floats on top
of it while zinc is heavier than the electrolyte and will collect
on the bottom of the cell. The design of a cell with two or more
compartments for electrolytic production of zinc will therefore
differ considerably from an electrolytic cell for magnesium
production.
[0006] EP 1364077 B1 describes an electrolytic cell for production
of aluminium and oxygen from a molten fluoride/oxide electrolyte
comprising non-consumable anodes. The described cell has separate
compartments, one compartment for the electrodes, and one gas
separation chamber. The purpose of the gas separation chamber is to
ensure efficient removal of oxygen from the electrolyte. The
produced aluminium sinks to the bottom of the cell where it enters
a third metal collection compartment to protect it from the oxygen
dissolved in the electrolyte.
[0007] In accordance with the present invention as defined in the
accompanying claims, there is now presented a novel method and
electrolysis cell for production of Zinc that will ensure proper
flow conditions in the electrolyte.
[0008] Due to the design of the cell and the corresponding method
for operating same, the upward flow of the chlorine bubbles
produced on the anode (3) creates a drag on the electrolyte which
leads to an upward flow between the anodes and the cathodes. In a
single compartment cell, this flow can lead to volumes with
particularly turbulent electrolyte flow (upper part of the cell)
and volumes with almost zero flow velocities (below the
electrodes). Both situations are undesirable. High turbulence can
lead to increased cell wear and recombination between chlorine and
zinc, while low velocities can cause collection of sludge. In the
following, the present invention shall be described by examples and
figures where:
[0009] FIG. 1 shows the principal components of a cell with two
compartments according to the present invention, shown in a cross
sectional end view,
[0010] FIG. 2 shows the principal components of the cell shown in
FIG. 1, shown in a cross sectional top view,
[0011] FIG. 3 shows the principal components of the cell shown in
FIG. 1, shown in a cross sectional side view.
[0012] With reference to FIG. 1 there is in a cross sectional view
shown an electrolysis cell with an electrolysis chamber 2 and one
adjacent chamber 1. FIG. 2 shows a top view of the same cell in the
level of the cathodes with the same numerical references. It should
be understood that several configurations of chambers are possible.
One may for example have two separated electrolysis chambers
sharing a central common adjacent chamber. In the Figures,
reference numerals 3 and 4 are the anode and cathode, respectively.
In the embodiment shown, the anode 3 is inserted through the top,
while the cathode 4 is inserted from the side. It should be
understood that the opposite configuration is equally possible, as
are configurations with only top inserted electrodes, only
side-inserted electrodes, or configurations with bottom-inserted
electrodes. For bottom or side inserted electrodes, proper cooling
of the electrode head is important to avoid electrolyte leakage
from the cell. Bipolar electrode configurations are also possible.
In that case, only the end cathode(s) and anode(s) need to be
inserted into the cell. The bipolar electrodes will be completely
immersed into the electrolyte. Bipolar electrodes also allow for
inclination of the electrodes. Inclination to nearly horizontal
electrode configuration is possible. On inclined electrodes,
chlorine is produced on the electrode surface facing downwards, and
Zn on the surface facing upwards.
[0013] Further with reference to FIG. 1, reference numeral 5 is
indicating the Zn pool. As Zn is produced, it will collect on the
bottom of the cell, and regular metal tapping is required. At the
upper part of the cell, there is arranged a chlorine outlet 6.
Metal can be removed through opening 9 and ZnCl.sub.2 addition can
be performed through one opening 10. Depending on the height
between the cell bottom and the cell lid, the metal can be sucked
off or pumped out of the cell. Due to the density of Zn, suction is
only efficient for heights below approx. 1.5 m. At larger heights,
pumping is required. Addition of ZnCl.sub.2 is preferably made into
the electrolysis chamber since ZnCl.sub.2 usually has a higher
density than the electrolyte. The mixing in of ZnCl.sub.2 is more
effective in the electrolysis chamber than in the adjacent chamber
since convection is stronger in the electrolysis chamber.
ZnCl.sub.2 addition in to the adjacent chamber is, however, also
possible. ZnCl.sub.2 can be fed as either a liquid or a solid.
Reference numerals 7 and 8 are indicating the partition walls (in
cross sectional view) separating the electrolysis chamber from the
adjacent chamber.
[0014] FIG. 3 shows a side view section through the partition wall
with the same numerical references as FIGS. 1 and 2. By sufficient
immersion of partition wall 8, separation of the atmospheres in the
two chambers is achieved. The electrolysis chamber then contains
mainly chlorine, while the adjacent chamber contains mainly air or
a suitable inert gas. Partition wall 7 will assist the generation
of a circular electrolyte flow indicated by the arrows in FIG. 1.
The velocity of the electrolyte can be controlled by adjustment of
the gap between wall 7 and 8, and/or the gap between wall 7 and the
bottom of the cell. With reference to FIG. 3, reference numerals 11
and 12 indicate support pillars for the upper and lower partition
walls.
[0015] The purpose of a cell design with two or more compartments
for the production of zinc is to set up a controllable flow of the
electrolyte in the cell. The upward flow of the chlorine bubbles
produced on the anode (3) creates a drag on the electrolyte, which
leads to an upward flow between the anodes and the cathodes. In a
cell with two or more compartments, the upward flow of electrolyte
can be directed from the electrode compartment 2 to the adjacent
compartment(s) 1, and from the adjacent compartment(s) the
electrolyte will flow back into the electrode compartment below the
electrodes, thereby creating a circular flow. The downward flow in
the adjacent chamber is preferably slower than the upward flow in
the electrode chamber, which can be achieved by a large flow
cross-section in the adjacent chambers.
[0016] This circular flow has several advantages: The electrolyte
flow can be of a rather substantial laminar nature; the flow
through the adjacent chamber(s) allows for efficient separation of
small chlorine bubbles and electrolyte; small metal droplets that
settle slowly will settle in the adjacent chamber(s) rather than
recombine with chlorine in the turbulent flow above the electrodes;
the residence time of low-density solid oxide particles in the
electrolyte will increase, thereby reducing sludge formation by
allowing for more efficient chlorination
(M.sub.xO+Cl.sub.2.dbd.MCl.sub.2+O.sub.2). Chambers separate from
the electrode chamber also have the advantage that metal removal
and chlorine extraction can be separated. Otherwise special means
to avoid Cl.sub.2 leakage from the cell during metal removal must
be implemented.
[0017] In the cell, several materials choices can be made. The
anode is preferably a carbon material. Graphite is preferred due to
its relatively low electrical resistance. The cathode can also be a
carbon material, but electronically conductive ceramics such as
TiB.sub.2, can also be used. Inert or near inert metals such as Mo,
W and Nb can be applied. The advantage of conductive ceramics and
metals over carbon is that carbon does not wet liquid Zn, and
therefore the Zn is produced as very fine droplets. Larger Zn
droplets are advantageous from both a current efficiency and metal
collection point of view.
[0018] The cell itself can be made from a steel shell lined with
suitable brickwork, e.g. alumina based, silica based, carbon
materials, silicon nitride based, silicon carbide based, aluminium
nitride based, or combinations of these.
[0019] The electrolyte must contain ZnCl.sub.2. The ZnCl.sub.2
should preferably be free from moisture, oxides and hydroxides, but
some contaminations can be accepted. In addition, it is preferable
to use one or more other chlorides to increase electrical
conductivity, reduce the viscosity, hygroscopicity, and the vapour
pressure of ZnCl.sub.2. Typical chlorides to add are LiCl, NaCl and
KCl, but also alkali earth chlorides and other alkali chlorides can
be used. The ZnCl.sub.2 concentration can range from a few weight
percent up to 80 w %. The temperature of the electrolysis can range
from the melting point of Zn (420.degree. C.) and upwards.
* * * * *