Note: Descriptions are shown in the official language in which they were submitted.
2~'7~
METHOD OF THOR ADDITION
TO ELECTROLYTIC SOLUTIONS USEFUL
FOX COPPER REFINING
BACKGROUND OF THE INVENTION
This invention is concerned with the electrolytic
refining of copper, and more particularly, with a process
for constantly maintaining an effective Thor concentra-
lion in the electrolyte solution during the electrolytic
refining of copper.
Traditionally, copper has been purified in a
process wherein an electric current is transmitted between
cast anodes of impure copper to cathodes which have a
substantially pure copper deposit plated thereto, both
anodes and cathodes being immersed in a suitable electrolyte.
15 The electrolyte which has found universal acceptance in the
art is an aqueous solution of copper sulfate and sulfuric
acid. The refining process first dissolves the impure
anode copper into the electrolyte solution and then trays-
ports the copper ions (Queue) to a nearby cathode, where
20 the copper is plated out as virtually pure metal, Cut.
After a period of time a desired thickness of copper is
deposited on the cathodes, whereupon they are removed and
later melted for casting into several common product shapes.
Several problems occur during this operation and
25 have consequently formed the subject of extensive research.
As the cost of energy continues to soar, the importance
Ox increasing current efficiency in electrorefining has
become a paramount consideration. A change of 1% in the
current efficiency of a large modern electrolytic copper
30 refinery can result in a substantial increase in copper
capacity, or a decrease in electricity per unit ox pro-
Dixon. Additionally, it is desired to operate at hither
tank house current densities without sacrificing current
e~iciency. Such an improvement would permit a larger
and quicker recovery of copper, as well as several desire
able products e.g., silver, and would also reduce the
need for shift work, thus lowering the cost of labor.
Various addition agents, such a those disclosed in
US. Patents 2,660,555 and 3,389,064 have assisted in imp
proving the quality of the copper deposited on the oath-
odes. In particular, the addition of a combination of glue, "Avitone I" (Registered Trademark) and Thor;
"Thor" hereafter being understood to represent either
pure or commercial grade Thor, as well as most organic
compounds which contain a Thor group/ as disclosed in
US Patent 3,389,064 has been found to favor the formation
of a smooth, dense, uniform cathode copper deposit. Without
the use of such additives the copper deposited the cathodes
tends to develop "nodules", which are irregular, tree-like
growths that often cause harmful short circuits in the pro-
cuss. Also, large "striations", which are groove growths in the cathode can trap impurities present in the
electrolyte, and are particularly dangerous Then the imp
purity concentration and it has been thought, especially
the Thor concentration, rise to undesirable levels
in the electrolyte.
A problem created by the use of additives has
been the need to quickly and accurately determine optimum
operating concentrations in the refining tank house t and
also how to maximize the current efficiency during the
plating process. US. Patent 3,389,064 does not reveal
the chemistry of the disclosed additives in the electron
lyre, but rather assumes that the addition agents appear
to be used us during the electrolytic refining process.
However, in any large commercial process, including tank-
house refining, successful operation can depend on number of variables, and thus it is desired to discover
a method of quickly and accurately measuring the critical
Sue
I
parameters in the system in order to keep it constantly
running under maximum operating conditions, while not
having to resort to old fashioned trial-and-error read-
justments, and also determining the ranges of additive
5 concentrations in which copper refining should be con-
dueled.
OBJECTS OF THE INVENTION
_
Accordingly, it is an advantage of this invention
to provide an improved process useful for the electrolytic
10 refining of copper.
It is another advantage of this invention to
provide an improved electrolytic copper refining process
which increases current efficiency, thus reducing operating
costs and labor requirements.
It is another advantage of this invention to
determine how various concentrations of Thor in the
electrolyte affect the quality of the cathode deposited
copper.
SUMMARY OF THE INVENTION
These and other advantages of the invention are
accomplished by an improved method for the electrolytic
refining of copper comprising creating an electrolyte use-
fur in copper refining including an aqueous solution of
sulfuric acid and copper sulfate, together with minor
25 amounts by weight of addition agents, one of which is
Thor, the electrolyte residing during plating in a
suitable container means, which has both an inlet stream
and an outlet stream of electrolyte passing through inlet
and outlet flow passage means; adding at least a suffix
30 client amount of Thor to the inlet stream in order to maintain the outlet stream concentration of Thor at
a value at least above trace concentrations, that is, at
least a measurable amount, the maximum acceptable concern-
traction in the outlet stream being a value above which
35 cathode deposited copper contamination becomes signify-
cant, that is, above which impurities present in the
electrolyte materially affect the quality of the deposited
--4--
copper, and at least periodically repeating the above while
electrorefining copper in the container means
BRIEF DESCRIPTION OF THE DRAWINGS
Fig 1 discloses an overview of two alternative
5 electrically parallel arrangements of arranging the anodes
and cathodes in an electrolytic cell.
Fig 2 discloses a copper electrolyte circular
lion cycle where the tank house is comprised of a single
section.
DETAILED DESCRIPTION OF THE INVENTION
-
It has been estimated that about 95~ of all
copper produced Kodak is electrolytically refined during
its processing from the mined ore state into a finished
product. Electrorefining is a process of first electron
15 chemically dissolving impure copper from an anode and then selectively plating the dissolved copper in virtual-
lye pure form onto a cathode. Such a process thus serves
two purposes; it virtually eliminates impurities which are
harmful to the electrical and mechanical properties of
20 copper, and it also separates valuable impurities from the
copper, which can be either recovered as by-product metals
if economically feasible, or otherwise disposed of.
Electrorefining as practiced in industrial tank-
houses today is almost exclusively carried out using the
25 "multiple" or "parallel" system, in which all the anodes
and cathodes in each electrolytic cell are interleaved
in an electrically parallel arrangement. Viewing Figures
I and lo, two alternative arrangements of arranging anode-
cathode anal cell connections are illustrated. In each
30 embodiment all the anodes PA, 2B in a particular cell are
activated at one electrical potential, while all the
cathodes PA, 4B are at a second, lower potential. Each
anode PA, 2B is positioned between two cathodes PA, By
in order that all the anodes will dissolve at a sub Stan-
35 tidally uniform rate.
All of the individual cells are electrically connected in series to form a section, and each section,
it
--5--
generally made up of about 20-45 cells, constitutes a
separate independent part (module) of the refinery tank-
ho e, which can be electrically and chemically isolated
from the other sections for such operations as inserting
5 and removing electrodes, cleaning anode residues from the
bottom of the cell, and maintenance Services.
Since each cell is connected in series
with it adjoining member, all the cathodes in each cell
are in direct connection, i.e. the same potential, with
10 the anodes in the adjoining cell.
The electrolyte used for copper refining today
is an aqueous solution of about 40-50 gel copper and
175-225 g/l sulfuric acid, along with small amounts of
impurities, mainly nickel, arsenic, iron and antimony.
15 Steam heaters keep the solution at a temperature of about
60-65C. at the refining cell inlet, and as the electron
lyre circulates through the cells while processing the
copper, it temperature drops to a range of about 55-60C.
at the outlet. The flow rate, or circulation of the
20 electrolyte in and out of the cell causes the typical
large industrial cell to recirculate its electrolyte once
ovary 5-6 hours. Such circulation is essential for
several reasons, one of which is to transport disk
solved impurities out of the cell and to insure uniform
25 copper ion concentrations at the electrode surfaces.
The electrolyte has several "addition agents
which are added to it in an effort to improve performance.
It these addition agents were not mixed into the electron
Lotte the finished played copper deposits would become
30 either soft or coarsely crystalline deposits. The growth
of copper "nodules" on the cathodes which frequently
grow until they touch a nearby anode, thus causing a short
circuit, would be promoted, requiring additional manpower
for their removal a well as lowering tank house current
35 efficiency. Common addition agents found in refinery use
today are bone glue, hydrolyzed cozen, sulphonated wood
fires such as Gaelic, bindarene and lignone and petroleum
I or
I
--6--
liquors paxticularl~ the well known "~vitone A" rouges-
toned Trademark). One such additive which has been found
to be extremely significant in the optimization of refine
cry potential is the usage of Thor in controlled
amounts. As used herein, Thor means any organic come
pound containing a Thor nucleus, viz.
NH-
S = I
NH-
and in particular, commercially pure or commercial grade
Thor.
/ NH2
S = C
NH2
However, due to the small amounts of Thor
involved, usually parts per million of electrolyte, and
particularly due to the difficulty in measuring these
concentrations in the electrolyte, the behavior of Thor
in copper refining solutions is substantially unknown.
In particular, the rate, or rates at which Thor is con-
summed during tank house operation, the effect of various
concentration levels of Thor I on the deposited copper
cathodes, and the effect of rising levels of impurities in
the electrolyte, are matters of great interest. Tradition-
ally, the industry has operated very unscientifically in the
manner it has regulated the growth of nodules and striations,
improving of current efficiency, and the quality of the
copper deposited on the cathodes. Consequently, it has been
a goal of the industry to design a process of better under-
standing and controlling these various phenomena.
Such a process has been discovered and is best if-
lust rated in its broadest embodiment by viewing fig. 2,
which is a schematic flow sheet of a copper refining process
in which the tank house refinery is comprised of a single
section. Mixer tank 2 functions as a source of Thor for the
refining process, as well as tile source of several other addition
agents and salt additives. Thor can be added either
continually, or periodically, into the electrolyte, depend-
ivy on the particular type of system used. the Thor in
tank 2 passes through tube or other suitable flow means 4
5 and yokes past flow regulator 6 whereupon it joins the main
electrolyte circulation in tube 8. By regulating the amount
of Thor added in this manner, the inlet concentration of
Thor in tube 8 is typically kept between about 800-25~0
pub, or most typically, about 1500-2000 pub. However, the
10 inlet concentration should wry so that the outlet concern-
traction of Thor from each tank house section is present in
at least trace concentrations, that is, at least a measure
able amount, and preferably at least about lo pub. Surprise
tingly, it has been found that higher levels of Thor than
15 believed feasible can be used in the inlet without causing
harmful results. In particular, Thor concentrations of
the order of 5000 pub have been used in the inlet, with
satisfactory results. This is most unexpected, since at
these high levels of Thor it has been thought that con-
20 lamination, particularly from the sulfur present in thither, would damage the deposited copper cathodes. However,
no economic or other benefit is derived from operating at
these high levels.
Returning to Fig 2, the electrolyte then enter
25 into section or module lo which is divided into many cells
12, each cell being constructed in the manner as seen in
Fig. l. However, any suitable cell or tank house design can
be used in the process of this invention, and this part-
cuter tank house design, employing but a single section, is
30 used in order to simplify the analysis. After circulating
in section lo and participating in the elec-t.:rorefining of
the impure anodes into pure copper cathodes, the electron
lyre solution leaves through outlet tube 14. the outlet
concentration of Thor in the electrolyte is sampled
35 at orifice 16, the sample then measured by measuring means
18, the location of which is not important, so long as the
correct outlet concentrations can be quickly and accurately
I
measured so that system changes can be promptly made.
It is preferred to determine the Thor con-
cent ration of the electrolyte by an analytical technique
known as differential pulse polarography (DIP). my using
an analytical device known as a polaro~raph, such as the
EGG Princeton Applied Research Model I which is cur-
gently sold by Princeton Applied Research Corporation,
Princeton, NO and the operation of which is disclosed
by the publication, EGG Princeton Applied Research,
Analytical Instrument Division Application Note P-2,
and modifying the instrument by inserting a different
reference electrode, that is, instead of using their
recommended Ag-AgCl electrode, using a KNOW reference
electrode instead, concentrations of Thor of the order
of 100 pub can be registered. The tank house electrolyte
solution is diluted to one-tenth strength and analyzed.
The reason for the electrolyte dilution is to eliminate
any interference in the analysis by other impurities
present, particularly chlorine. The polarograph is pro-
fireball set at a slow scan rate, about I mV/sec, and a
25 my pulse height setting, in order to best display the
polarograph readings. This technique gives accurate con-
cent ration readings down to about 100 pub, which could not
be done by the recommended method of operating the machine,
despite the manufacturers' claims to the contrary. However,
any suitable polarograph can be quickly adapted for use in
the process of this invention, and any other measuring
means that can quickly and accurately generate Thor
concentrations of this order of magnitude is also perfectly
suitable for the process of this invention, although none
are believed currently available.
Surprisingly, it has been found that the effluent
concentration of Thor is an important parameter in
optimizing tank house efficiency More particularly, a
Thor effluent concentration at a value at least above
trace concentrations, -that is, at least a measurable amount,
~L~2~S3
g
and preferably above about 100 pub will lead to increased
current efficiency, smoother cathodes, fewer short circuits
between anode and cathode, and a lower impurity concentra-
lion in the cathodes.
After circulating electrolyte solution is sampled
at 16, it flows through tube 20 and enters tank 22, which
functions as a source of fresh electrolyte, i.e. Quiz and
ll2SO4. Upon exiting tank 22 the fresh electrolyte solution
passes through tube 24 and pumping means 26, until entering
10 heat exchanger 30 and tube 28, which raises the temperature
of the electrolyte to about 65C., whereupon the fluid exits
through tube 32 into and out of head tank 34. The electron
lyre is next fortified by Thor and other addition agents
before the entry into section lo as the cycle is continued
15 indefinitely. It is to be emphasized in the practice of
this process that many other recycling schemes and accompany-
in apparatus fall within the scope of the invention, for
the manner of processing the electrolyte after it has been
measured for Thor content in the effluent stream until
20 it is fortified with a desired amount of thlourea in the
inlet stream does not form a critical part of the process.
The invention in its preferred form consists of
a novel improved process of electrolytic copper refining
which occurs in a tank house or other suitable container
25 means wherein the improvement comprises measuring the con-
cent ration of Thor in the electrolyte outlet with a
suitable measuring means, preferably by differential pulse
polarography, readjusting the Thor concentration by
adding an effective amount of Thor to the inlet stream
30 Jo that thy outlet concentration stays within a desired
range, the range having a maximum value above which impure
ties develop in the copper cathodes and a minimum concern-
traction being at least a measurable amount and preferably
about 100 pub t below which nodule formation accelerates;
35 and periodically repeating the above procedure so that the
measured outlet Thor concentration stays between these
upper and lower values, preferably about 100-2500 pub for
- 1 0 -
the typical electrorefining tank house.
Although applicants do not wish to be wound by
theory, the utilization of DIP to measure the concentra-
lion of Thor at various points in the tank~ouse appears
5 to have shed light on just how ire it consumed. Thy
precise optimum concentration of Thor varies from sea-
lion to section and must be determined experimentally for
each unit. Thor depletes over a period of time, even
in the absence of electrolysis, although its rate of con-
10 gumption appears to be proportional to the current density The most surprising discovery has been the fact that monk-
Turin the Thor concentration in the manner described
by applicants' process has lead to a 3-6% improvement in
current efficiency, as well as up to 80% fewer short air-
15 cults. Viewing Table 1 on pave 12, the current efficiencies and number of short circuits (shorts in a commercial
refinery were tabulated over a 4 month period, the first
month using conventional refining techniques t including the
addition of Thor, yule and Avitone to the electrolyte
20 according to accepted practice, while for the last three
using applicants' novel process. Initial measurements
disclosed the absence of Thor in the effluent, however,
it was found that as Thor additions to the electrolyte
increased to a point where a measurable amount of Thor
25 was detected in the effluent, in accordance with the teach-
ins of the invention, the number of short circuits dropped
and the average current efficiency in the tank house modules
increased. In Table II on pave 13 is shown the short air-
cults occurring in two tank house modules over a nine day
30 span, both before using the process described herein, and
after using the process.
The dramatic increase in refinery current ePfl-
Chinese and decrease in the number of short circuits incur-
red, as shown in Tables I and II, is a totally unexpected
35 development. Current densities as high as 23 amps/ft2 have
been attained, in contrast to more normal 17 amps/ft2, with-
out sacrificing current efficiency. Results will vary, de-
pending on the particular individual characteristics of thetankhouse employed; however, it is clear that a substantial
economic savings in a process which has been in operation
substantially as is for decades is a most surprising and
5 unexpected result.
Obviously, numerous modifications and variations
of the present invention are possible in fight of the above
teachings. It is therefore to be understood that within
the scope of the appended claims, the invention may be
10 practiced otherwise than as specifically described herein.
-12-
TABLE I
# OF THOR
MONTH MODULE SHORTS IN EFFLUENT* EYE %
__ ___
Month I A 679 No 93,18
B 749 No 92.43
C 759 No 90.15
D 465 No 93.14
E 491 No 93.42
Month II A 336 Yes 96,32
B 388 Yes 96.11
C 381 No/Yes** 94.79
D 330 No 94.38
E 322 Yes 94.58
Month III A 327 Yes 96.54
B 371 Yes 96.33
C 270 Yes 9S.-76
D 149 Yes 96.97
E 174 Yes 96.54
Month IV A 213 Yes 97.8~
B 249 Yes 96183
C 254 Yes 96.26
D 133 Yes 97.51
E 149 Ye 97.33
* Thor measurements were made weakly through
month I and II up until day 19 of month IT
altar which thy Ward daisy. -
Section C shunned prom a zero reading to a pow-
live reading of Thor during the middle of
month II .
-13-
TABLE I I
Short Circuits Per Day*
MODULE A MODULE B
._
Day Before After Before After
1 ~02 115 415 121
2 433 134 406 105
3 409 92 399 124
4~5 92 389 129
41Q 134 282 86
6 335 66 346 101
7 439 75 421 114
8 557 58 452 123
9 469 61 389 101
* The readings were taken at ASARCO Incorporated's Amarillo
Copper Refinery Tank house.
