CA1174200A - Method and apparatus for controlling the quality of zinc sulfate electrolyte - Google Patents
Method and apparatus for controlling the quality of zinc sulfate electrolyteInfo
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- CA1174200A CA1174200A CA000332698A CA332698A CA1174200A CA 1174200 A CA1174200 A CA 1174200A CA 000332698 A CA000332698 A CA 000332698A CA 332698 A CA332698 A CA 332698A CA 1174200 A CA1174200 A CA 1174200A
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
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- G01N27/4161—Systems measuring the voltage and using a constant current supply, e.g. chronopotentiometry
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Abstract
ABSTRACT OF THE DISCLOSURE
A method and apparatus for controlling a process for the recovery of zinc from zinc sulfate electrolyte containing concentrations of impurities and addition agents. The method and apparatus include a test circuit comprising a test cell, a sample of electrolyte, a moving cathode, an anode and a reference electrode immersed in said sample, a constant current source and measuring means electrically connected to the electrodes. A controlled low current is applied to the electrodes in the test cell to measure the activation overpotential between the cathode and the reference electrode. The activation overpotential is measured at the point of inchoate deposition of zinc and is related to the concentration of impurities and addition agents in the sample.
The processes for the purification of zinc sulfate electrolyte and the recovery of zinc from zinc sulfate electrolyte are subsequently adjusted in relation to the measured value of the activation overpotential to obtain optimum zinc recovery.
A method and apparatus for controlling a process for the recovery of zinc from zinc sulfate electrolyte containing concentrations of impurities and addition agents. The method and apparatus include a test circuit comprising a test cell, a sample of electrolyte, a moving cathode, an anode and a reference electrode immersed in said sample, a constant current source and measuring means electrically connected to the electrodes. A controlled low current is applied to the electrodes in the test cell to measure the activation overpotential between the cathode and the reference electrode. The activation overpotential is measured at the point of inchoate deposition of zinc and is related to the concentration of impurities and addition agents in the sample.
The processes for the purification of zinc sulfate electrolyte and the recovery of zinc from zinc sulfate electrolyte are subsequently adjusted in relation to the measured value of the activation overpotential to obtain optimum zinc recovery.
Description
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This invention Telates to a method and apparatus for con-tinuously monitoring the quality of zinc sulfate electrolyte and, more particularly, to a method for measuring the activation overpotential of zinc deposition onto aluminum and controlling the electrolyte purifi-cation and electrowinning processes in response to deviations of recorded values of the overpotential from the desired values and an apparatus to carry out the method.
In the process for electrowinning zinc from zinc sulfate solutions, impurities such as antimony~ germanium, copper, nickel, cobalt, iron, cadmium and lead, when present above certain critical concentrations, cause re-solution of deposited zinc and a corresponding decrease in the current efficiency of the zinc deposition. To reduce the concentration of impurities in electrolyte to the desired low levels, thereby to reduce these effects to a minimum, a complex purification procedure, which generally includes an iron oxide precipitation and a zinc dust treatment, is employed prior to electrolysis. In addition to ~he purification, polarizing additives such as glue are added to the electrolyte to reduce the effects of the remaining impurities, as well as to provide smooth and level deposits, and, to some extent, to control acid mist evolution.
The procedures presently used for determining the purity of electrolyte are based on chemical analyses and determination of current efficiencies as a measure of impurity content, while those for the additions of polarizing additives such as animal glue and the like are based on maintaining a constant concentration of additive in the electrolyte despite variations in the concentration of impurities.
l~ese procedures result in variations in the quality of the deposited , ~il1 742~
zinc and the current efficiency of the electrowinning process.
The prior art contains a number of references related to methods for determining the effects of impurities, glue and other addition a~ents on electrodeposition processes for metals and for determining the purity of zinc sulfate solutions.
According to United States Patent 3,925,168, L.P. Costas, December 9, 1975, there is disclosed a method and apparatus for determining the content of colloidal material, glue or active roughening agent in a copper plating bath by determining the overpotential-current density relationships of solutions having varying known reagent content and comparing the results with that of a solution with a known plating behaviour and roughening agent content. According ~o Canadian Patent 988,879, C.J. Krauss et al, May 11, 1976, there is disclosed a method for determining and controlling the cathode polarization voltage in relation to current d~nsity of a lead refinery electrolyte, wherein the slope of the polarization vol~age-current density curve is a measure of the amount of addition agents and wherein the effectiveness of addition agents is changed when the cathode polarization voltage attains values outside the predetermined range of values.
A number of studies are reported in the published literature which relate to similar methods. C.L. Mantell et al (Trans. Met.
Soc. of AIME, 236, 718-725, May 1966) determined the feasibility of current-potential curves as an analytical tool for monitoring manganese electrowinning solutions for metallic impurities. Polarization curves related to hydrogen evolution were shown ~o be sensitive to metallic impurities which affect the cathode surface thereby altering the hydrogen overvoltage. H.S. Jennings et al ~Metallurgical Transactions, ~, 921-926, April 1973) describe a method for measuring cathodic polarization ~L~74~
curves of copper sulate solutions containing varying amounts of addition agents by varying an applied voltage and recording the relationship between voltage and current density. 0. Vennesland et al CActa Chem.
Scand., 27, 3, 846-850, 1973) studied the effects of antimony, cobalt, and beta-naphthol concentrations in zinc sulfate electrolyte on the '' current-poten~ial curve ~y changing the ca~hode potential at a programmed rate, recording the curves and comparing the curves with a standard.
T.N. Anderson et al ~Metallurgical Transactions B, 7B, 333-338, September 1976~ discuss a method for measuring the concentration of glue in copper refinery electrolyte by determining polarization scan curves, which upon comparison provide a measure of glue concentration. According to United States Patent 4,146,437 issued March 27, 1979, T.J. O'Keefe there is disclosed the use of cyclic voltammetry for the evaluation of zinc sulfate electrolytes. Cyclic voltammograms, which include the cathodic deposition as well as the anodic dissolution portions of *he current-potential relationships, and polarization curves, are recorded as a means for approximating the quantities of impurities and addition agents in zinc sulfate electrolytes.
This first group of references discloses methods wherein metal is deposited on an electrode and wherein current, or current density-potential, curves represent cathode polarization potentials in relation to varying currents and/or current densities.
T.R. Ingraham et al (Can. Met. Quarterly, 11, 2, ~51-454, 1972) describe a meter for measuring the quality of zinc electrolytes for measuring the amount of cathodic hydrogen released during electrodeposition of zinc and indicating current ef~iciency by comparing the weight of deposited zinc with both the amount of zinc to be expected and the rate of hydrogen evolution. In United States Patent 4,013,~12, Satoshi Mukae, 1~174~0(~
March 22, 1977, there is disclosed a method for judging purity of purified zinc sulfate solution by subjecting a sample of solution to electrolysis, combusting generated gases and measuring the internal pressure in the combustion chamber which is an indirect measure of current efficiency. M. Maja et al (J. Electrochem. Soc., 118, 9, 1538-1540, 1971) and P. Benvenuti et al (La Metallurgia Italiana, 60, 5, 417-423, 1968) describe methods for detection of impurities and measuring the purity of zinc sulfate solutions by depositing zinc and then dissolving deposited zinc electrolytically and relat-ing calculated current efficiency to impurity content.
This second group of references relates to methods andapparatus for determining electrolyte purity wherein electrolysis of solutions is used to determine current efficiency which is subseq-uently related to electrolyte purity.
In my co-pending Canadian Patent Application 306,805 which was filed on July 5, 1978, there is disclosed a method for controlling a process for the recovery of zinc from a zinc sulfate electrowinning solution which comprises decreasing a potential, which is applied between electrodes in a test cell containing a sample of solution, at a constant rate at substantially zero cur-rent, measuring the decreasing potential, terminating the decreasing of the potential at a value corresponding to the point at which zinc starts to deposit, determining the activation overpotential, relating the activation overpotential to the concentration of impurities and adjusting the process to obtain optimum recovery of zinc.
*
Issued as Canadian Patent 1,111,125 ~ .t?
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Although the method according to my co-pending application overcomes the necessity for electrolyzing solution to determine current ef~iciencies or for measuring polarization potentials in relation -4a-~,. ..
~, 1~74~6~0 to varying c~rrents or current densities, several disadvantages still exist. The method is not continuous and it is necessary to determine the value of the activation overpotential for each sa~ple by decreasing the applied potential each time until the value is reached at which zinc starts to deposit and the current density increases from its substantially zero value for a fu~ther small decrease in potential.
I have now found that it is unnecessary to decrease the applied potential in order to determine the value of the activation overpotential.
Thus, I have found that the activation overpotential can be measured as a function of time at a controlle~, low current, and that the purification and electrowdnning processes can be controlled by correcting the amounts of reagents in response to deviations of recorded values of the over-potential from desired values in order to return to the desired optimum values.
The method and apparatus of the invention apply to zinc sulfate solutions which are obtained in processes for the treatment of zinc containing materials such as ores, concentrates, etc. Treatment includes thermal treatments and hydro-metallurgical treatments such as roasting, leaching, in situ leaching, bacterial leaching and pressure leaching. Such solutions, which are referred to in this application as zinc sulfate electrolyte, may be acidic or neutral solutions.
When zinc sulfate electrolyte is subjected to a co~trolled low ourrent applied to electrodes placed in a test cell containing electrolyte and the current has a value which is sufficient to cause inchoate deposition of zinc on an aluminum cathode, the value of the résulting potential represents the activation overpotential for zinc deposition onto aluminum. ~hen the cathode is a moving cathode, values of the activation overpotential can be measured and recorded and the purification process of zinc sul-fate electrolyte and the electrowinning process of zinc from zinc sulfate electrolyte can be controlled in response to the measured and recorded values of the activation overpotential. Inchoate deposicion is defined, for the purpose of this invention, as the deposition of zinc which has just begun and is limited to partial covering of the moving cathode surface by zinc. The measured values of the activation over-potential can be used as a direct measure of the impurity concentration, i.e. the effectiveness of the purification process, and of the polarizing additive concentration relative to the impurity concentration in the electrolyte in the process for the recovery of zinc which includes the purification process and the electrowinning process. In response to measured values of the activation over-potential, the purification process can be adjusted, or the concentration of polarizing additive in the electrolyte can be adjusted relative to the impurity concentration and/or the impurity concentration can be adjusted, so that optimum current efficiency and level zinc deposits are obtained in the electrowinning process.
Accordingly, there is provided a method for controlling a process for the recovery of zinc from zinc sulphate electrolyte containing concentrations of impurities, said method comprising the steps of establishing a test circuit comprising a test cell, a sample of electrolyte, a moving cathode, made of an electrically conductive material other than zinc, which moving cathode has an area exposed to said electrolyte, an anode and a reference electrode, said electrodes being immersed in said sample, a constant current supply and measuring means electrically connected to said electrodes; applying a low current to the electrodes in said test cell, said current being sufficient to cause inchoate deposition of zinc on said cathode; measuring the activation overpotential at the point of inchoate deposition; relating said activation over-potential to the cencentration of impurities o in said sample; and adjusting the concentration of impurities in the electrolyte of the process for the recovery of zinc to obtain optimum recovery of zinc, wherein inchoate deposition is defined as the deposition of zinc which has just begun and is limited to a partial covering of the moving cathode surface by zinc.
In another embodiment, the method for controlling a process for the electrowinning of zinc from zinc sulfate electrolyte containing concentra-tions of impurities and at least one polarizing additive, said method comprising the steps of establishing an electrolytic test circuit comprising a test cell, a sample of electrolyte, a moving cathode, made of an electrically conductive material other than zinc, which moving cathode has an area exposed to said electrolyte, an anode and a reference electrode, said electrodes being immersed in said sample, a constant current supply and measuring means electric-ally connected to said electrodes; applying a low current to the electrodes in said te~t cell, said current being sufficient to cause inchoate deposition of zinc on said cathode; measuring the activation overpotential at the point of inchoate deposition; relating the measured activation overpotential to the concentration ratio between impurities and polarizing additive in said sample;
and adjusting the concentration ratio in the process electrolyte to obtain optimum current efficiency and level zinc deposits in the electrowinning process, wherein inchoate deposition is defined as the deposition of zinc which has just begun and is limited to a partial covering of the moving cathode surface by deposited zinc.
The invention will now be described in detail. The apparatus used in the method for measuring the activation overpotential of zinc consists of a test circuit which comprises a test cell, a sample of zinc sulfate electrolyLe, a moving cathode; an anode, a reference electrode, means to supply a constant current and means for measuriny the activation overpotential. The test cell is a small container of circular, square or rectangular cross-section made of a suitable material, which is preferably resistant to acid zinc sulfate electrolyte and large enough to hold a suitable sample of electrolyte. Means are provided in the cell to make it possible to continuously add electrolyte to, and to discharge electrolyte from, the test cell. The three electrodes are immersed in the electrolyte sample and are removably positioned in the cell at constant distances from each other.
-7a-d 1~4~:~0 The moving cathode is preferably made of aluminum or an alum mum alloy and has a constant area of its surface in contact with electrolyte in the cell. If desired, a moving cathode of other suitable materials such as titanium may ke used.
I have determined that a surface area in contact with electrolyte in the range of about 0.1 to 1 cm gives excellent results, me moving cathode is preferably made of aluminum or aluminum alloy wire or strip which is contained in and moves through a cathode holder. The holder envelopes the moving cathode except for the constant surface area which is in contact with electrolyte. Means are provided to move the moving cathode intermittently or continuously through the cathode holder and, consequently in contact with electrolyte. Preferably, these means include provisions to move the cathode continuously at a constant rate. The use of a moving cathode made of aluminum wire or strip has a number of advantages, No special preparation of the alum mum surface is necessary, aluminum or aluminum alloy wire or strip is readily available at low cost and test results are re-producible. The moving cathode does not have to be replaced and thus allows intermittent or continuous operation. I have found that m~st oommercially available aluminum and aluminum alloys in the form of wire and strip are suitable, as long as they have sufficiently smooth and clean surfaces and have electrochemical characteristics that produce reproducible test results.
me anode is made of a suitable material such as, for example, platinum or lead-silver alloy. I have found that anodes made of lead-silver alloy containing 0.75% silver are satisfactory. me reference electrode can be any one of a number of suitable reference electrodes such as, for example, a standard calomel electrode (SOE).
The three electrodes are electrically connected to a source 1174;2(~) of constant current and to measuring means for the activation overpotential.
The source of constant current is connected to the anode and the moving cathode. The measuring means for the activation overpotential measures the overpotential on the moving cathode relative to the reference electrode. The measured activation overpotential may, for example, be recorded on a meter or other suitable read-out instrument, or alternatively, may be recorded in the form of a line or trace as a function of time.
The electrodes are removably positioned in the cell in fixed relation to each other. I have found that good results are obtained when the surface area of the moving cathode that is in contact with electrolyte is kept at a fixed distance of about 4 cm from the surface of the anode and when the reference electrode is positioned between the cathode and the anode in such a way that the tip of the reference electrode is rigidly located at a distance of about 1 cm from but not covering the surface area of the moving cathode in contact with electrolyte.
Suitable means may be provided to maintain the electrolyte in the call at a suitable constant temperature. Such means may comprise controlled heating/cooling means for electrolyte prior to electrolyte entering the cell or a controlled heating/cooling coil placed in the test cell, or a constant temperature bath or the like.
In the method of the inven~ion, a sample of zinc sulfate electrolyte, which may be neutral or acidic and which may contain addition agents, and which may be obtained from either the purification process or the zinc electrowinning process, is added to the test cell.
To ensure reproducible results, the sample is kept in motion such as by agitation or circulation. Preferably, the sample is kept in motion by continuously passing a small flow of electrolyte through the test cel~. According to this preferred embodiment, a sample of ~t7~o electrolyte is continuously withdralnn from the purification or electrowinning process, passed through the test cell and subsequently returned to the respective process. Electrolyte added to the cell may be adjusted to a certain zinc or zinc and acid content in order to reduce to a minimum any variation in the test method that may be caused by variations in zinc or zinc and acid concentrations in the electrolyte. Adjustment of zinc concentration to, for example, 150 g/L zinc, or of zinc and acid concentrations to, for example 55 g/L zinc and 150 g/L sulfuric acid is satisfac~ory. However, concentrations in the range of 1 to 250 g/L zinc and 0 to 250 g/L sulfuric acid are equally satisfactory.
When using a continuous sample flow, excess electTolyte is discharged from the cell, for example5 by means of an overflow.
The moving cathode is advanced through the cathode holder intermittently or continuously at a rate sufficient to allow inchoate deposition of zinc. Preferably, the moving cathode is advanced continuously at a constant rate. The rate is dependent on the ratio between cathode length and cathode surface area, the value of the current density for inchoate deposition, the surface area of the cathode exposed to electrolyte, the fraction of exposed cathode area covered with deposited zinc and the weight of deposited zinc. The rate is also somewhat dependent on the degree of motion of elect~olyte in the cell. Thus, the rate at which the cathode is moved through the cathode holder and, consequently, through the electrolyte, may vary in a range of values. At rates lower than the minimum rate, the measured overpotential will be that of zinc onto zinc and will not b~ the activation overpotential of zinc onto aluminum. ~t Tates several orders of magnitude high~r than the minimum rate, such as fo~ example, one thousand times higher, the amount of zinc deposited may be insufficient to obtain reliable ~L~742(~0 and reproducible values for the activation overpotential. Preferably, the rate at which the cathsde is moved is about ten to five hundred times the minimum rate. The m mimum rate may be calculated by using the following formula:
~in _ _ , cm/h wherein:
a represents the cathode length to surface area ratios, cm/cm2;
b represents current density, A/cm2;
c represents cathode exposed area, cm2;
d represents the electrochemical equivalent for zinc deposition, g/Ah;
x represents fraction of cathode covered with zinc;
y represents the weight of deposited zinc per unit of cathode surfa oe area, g/cm .
When moving the cathode intermittently, the average rate of movement should be at least equal to the minimum rate for continuous movement, while the periods of time when the cathode is stationary should not exceed the period of time that will cause more than inchoate deposition.
A 1GW current is applied to the anode and the moving cathode to cause inchoate deposition of zinc onto the cathode. Preferably, the low current is controlled at a constant value. m e current should be limited to low values, which only cause inchoate deposition. This is necessary to avoid the deposition of zinc onto previously deposited zinc whereby values of the overpotential are obtained of zinc deposition onto zinc rather than values of the desired activation overpotential of zinc deposition onto aluminum. Thus, the deposition of too much ,~
i~7~Z(?O
æinc should be avoided. Preferably, not more than about 10 to 30% of the cathode surface in contact With electrolyte should b æame covered with deposited zinc at any time. Currents, expressed as current density, that cause inchoate deposition on the cathode moving at rates defined above should ~e at least 0.01 m~/cm . Current densities in respect of the moving cathode as hereafter discussed are to be taken as referring to the exposed area of the moving cathode. Below a value of the current, expressed as current density, of 0.01 m~/cm2, the current may be primarily associated with hydrogen deposition. For practical purposes, the current, expressed as current density, should be in the range of 0.01 to 4.0 mP/cm2. Values of the current higher than the equivalent current density of 4.0 m~/cm2 will require impractically high cathode movement rates. Preferably, current values, expressed as current density, are in the range of 0.1 to 0.4 m~/cm2.
For example, for inchoate zinc deposition at a current density of 0.4 m~/cm2 on a moving alumlnum cathcde, which has a ratio of length to surface area of 0.6 to 0.25, an exposed area of 0.25 cm2 of which 20% is c~vered with deposited zinc and on which 7 x 10 3g zinc/cm2 is deposited (determined fram scanning electron microscope examination of inchoate zinc deposits~, the minimum rate as calculated from the above formula is about 0.21 cmJh.
The temperature of the electrolyte being measured is usually maintained constant. Changes in temperature affect the measured activation overpotential, e.g., a decreasing temperature increases the measured over-potential. I'he cell and its c~ntents are adjusted to and maintained at a suitable, controlled, constant temperature, which may be between 0 and 100C, preferably ~etween 20 and 75C and, more preferably, in the range of 25 to 40 &. If desired, the constant ~74~
temperature may be approximately the same as the temperature of the electrolyte in the electrowinning process or purification process, whichever is applicable. If the temperature is not maintained constant, the value of the activation overpotential should be corrected for the temperature variations so that the results of the tests are comparable.
The activation overpotential is measured continuously or intermittently and is recorded at the point of inchoate deposition of zinc onto an aluminum cathode. For practical application of the method of this invention, the activation overpotential is expressed as the value of the measured overpotential at a current corresponding to a current density in the range of about 0.01 to 4.0 A/cm2, of exposed cathode area preferably in the range of about 0.1 to 0.4 m~/cm2. The activation overpotential is recorded on a suitable read-out instr~nent, or, alternatively, recorded as a function of time. The recorded values of the overpotential are maintained in a preferred range. This is accomplished by making adjustments to the purification and electrowinning processes when values of the overpotential deviate from the preferred range of values.
The activation overpotential has specific values dependent on the cc~position of the electrolyte~ As every electrolyte compo~ition can be purified to an optimum degree and as every electrolyte composition has an optimum range of polarizing additive contents relative to its impurity content, the activation overpotential will similarly have a range of values that is required to yield the desired optimum results.
Any one of a wide range of suitable polarizing additives may be used;
the most ccmmonly used polarizing additive is animal glue. I have determined that increasing concentrations of impurities such as antimDny, cobalt, nickel, germanium and copper cause a decrease in activation overpotential, while increasing polarizing additive concentrations ,, i~
~ 13 -~7~30 increase the overpotential.
If the value of the measured activation overpo~ential in the purification of electrolyte is too low, the impurity concentration is too high for optimum z;nc recovery in the electro~inning process. Thus, dependent on the composition o the electrolyte, the activation overpotential is an indicator of the effectiveness of the purification process and deviations from optimum operation can be corrected by adjusting the purification process in relation to values of the activation overpotential, whereby the impurity concentration is lowered. Correction of the zinc dust purification process, may be accomplished, for example, by adjusting the temperature of the purification process, adjusting the duration of the purification process, increasing the amount of zinc dust, or increasing the concentration of a zinc dust activator such as antimony, copper, or arsenic in ionic form. Alternatively, insuf~iciently purified electrolyte may be further purified in an additional purification step or by recirculation in the purification process.
If the value of the activation overpotential measured for the electrolyte in the electrowinning process is too low, the concentration of polarizing additive in the electrolyte is too low to adequately control cathodic zinc resolution caused by the impurities present, or the impurity concentration is too high relative to the cor.centration of polarizing additive. On the other hand, if the value is too high, the concentration of polarizing additive is too high relative to the impurity concentration, and a resultant loss in current efficiency and a rougher zinc deposit occur. Thus, depending on the composition of the electrolyte, the activation overpotential is an indicator of the efficiency of the electrowinning process and deviations from optimum operation can be corrected by changing the concentration of polarizing additive or the ~'7~QO
concentration of impuri~cies in the electrolyte as required in relation to values of the activation overpotential. Change in the concentration of polarizing additive may be accomplished in a suitable manner such as by increasing or decreasing the rate of addition of glue to the electroly~e. A decrease in the impurity concentration may be achieved by more effective purification of the electrolyte prior to the electrowinning process.
Similarly, in the case of the presence of an excess concentration of polarizing additive, corrective action may be taken by allowing the level of impurities in the electrolyte to rise in a controlled fashion. Preferably this is achieved by the controlled addition of antimony, which has the most economical effect in correcting the impurity to polarization additive concentration ratio, rather than by any change in the electrolyte purification procedure.
The method of the invention has a number of applications in the process for the recovery of zinc from zinc sulfa~e electrolyte~ '~hus, the method can be used before, during and after purification of zinc sulfate electrolyte and before, during and after the electrowinning of zinc from zinc sulfate electrolyte. For example, prior to the zinc dust purification process, the method can be used to determine the degree of iron oxide removal and the degree of removal by iron oxides of impurities such as arsenic, antimony and germanium from zinc sulfate solutions obtained in the leaching of ores, concentrates or calcines. During purification, the method can be used to determine the degree of purification obtained, for example, with zinc dust, in the various steps of the purification process. After purification, the effectiveness of the purification can be determined, as well as the possible need for adjustments to the purification process or to the subsequent electrowinning process. In the electrowinning process, the method can be advantageously used to determine the required amount of polarizing additive in relation to impurity concentration, the required 7~Z(~O
amount of impurities, such as, for example, antimony, in relation to concentration of polarizing additives, the need for adjustments to the electrolyte feed, or to electrolyte in process and the quality of return acid.
m e invention will now be descriked by means of the following non-limitative examples.
In the following examples, values of the activation overpotential were measured using a test cell having a sample volume of 500 ml. A
volume of electrolyte was passed through the cell. Immersed in the electrolyte in the cell were a moving cathode consisting of a 1.19 mm diameter wire of No. 4043 aluminum alloy ~length to surface area ratio
This invention Telates to a method and apparatus for con-tinuously monitoring the quality of zinc sulfate electrolyte and, more particularly, to a method for measuring the activation overpotential of zinc deposition onto aluminum and controlling the electrolyte purifi-cation and electrowinning processes in response to deviations of recorded values of the overpotential from the desired values and an apparatus to carry out the method.
In the process for electrowinning zinc from zinc sulfate solutions, impurities such as antimony~ germanium, copper, nickel, cobalt, iron, cadmium and lead, when present above certain critical concentrations, cause re-solution of deposited zinc and a corresponding decrease in the current efficiency of the zinc deposition. To reduce the concentration of impurities in electrolyte to the desired low levels, thereby to reduce these effects to a minimum, a complex purification procedure, which generally includes an iron oxide precipitation and a zinc dust treatment, is employed prior to electrolysis. In addition to ~he purification, polarizing additives such as glue are added to the electrolyte to reduce the effects of the remaining impurities, as well as to provide smooth and level deposits, and, to some extent, to control acid mist evolution.
The procedures presently used for determining the purity of electrolyte are based on chemical analyses and determination of current efficiencies as a measure of impurity content, while those for the additions of polarizing additives such as animal glue and the like are based on maintaining a constant concentration of additive in the electrolyte despite variations in the concentration of impurities.
l~ese procedures result in variations in the quality of the deposited , ~il1 742~
zinc and the current efficiency of the electrowinning process.
The prior art contains a number of references related to methods for determining the effects of impurities, glue and other addition a~ents on electrodeposition processes for metals and for determining the purity of zinc sulfate solutions.
According to United States Patent 3,925,168, L.P. Costas, December 9, 1975, there is disclosed a method and apparatus for determining the content of colloidal material, glue or active roughening agent in a copper plating bath by determining the overpotential-current density relationships of solutions having varying known reagent content and comparing the results with that of a solution with a known plating behaviour and roughening agent content. According ~o Canadian Patent 988,879, C.J. Krauss et al, May 11, 1976, there is disclosed a method for determining and controlling the cathode polarization voltage in relation to current d~nsity of a lead refinery electrolyte, wherein the slope of the polarization vol~age-current density curve is a measure of the amount of addition agents and wherein the effectiveness of addition agents is changed when the cathode polarization voltage attains values outside the predetermined range of values.
A number of studies are reported in the published literature which relate to similar methods. C.L. Mantell et al (Trans. Met.
Soc. of AIME, 236, 718-725, May 1966) determined the feasibility of current-potential curves as an analytical tool for monitoring manganese electrowinning solutions for metallic impurities. Polarization curves related to hydrogen evolution were shown ~o be sensitive to metallic impurities which affect the cathode surface thereby altering the hydrogen overvoltage. H.S. Jennings et al ~Metallurgical Transactions, ~, 921-926, April 1973) describe a method for measuring cathodic polarization ~L~74~
curves of copper sulate solutions containing varying amounts of addition agents by varying an applied voltage and recording the relationship between voltage and current density. 0. Vennesland et al CActa Chem.
Scand., 27, 3, 846-850, 1973) studied the effects of antimony, cobalt, and beta-naphthol concentrations in zinc sulfate electrolyte on the '' current-poten~ial curve ~y changing the ca~hode potential at a programmed rate, recording the curves and comparing the curves with a standard.
T.N. Anderson et al ~Metallurgical Transactions B, 7B, 333-338, September 1976~ discuss a method for measuring the concentration of glue in copper refinery electrolyte by determining polarization scan curves, which upon comparison provide a measure of glue concentration. According to United States Patent 4,146,437 issued March 27, 1979, T.J. O'Keefe there is disclosed the use of cyclic voltammetry for the evaluation of zinc sulfate electrolytes. Cyclic voltammograms, which include the cathodic deposition as well as the anodic dissolution portions of *he current-potential relationships, and polarization curves, are recorded as a means for approximating the quantities of impurities and addition agents in zinc sulfate electrolytes.
This first group of references discloses methods wherein metal is deposited on an electrode and wherein current, or current density-potential, curves represent cathode polarization potentials in relation to varying currents and/or current densities.
T.R. Ingraham et al (Can. Met. Quarterly, 11, 2, ~51-454, 1972) describe a meter for measuring the quality of zinc electrolytes for measuring the amount of cathodic hydrogen released during electrodeposition of zinc and indicating current ef~iciency by comparing the weight of deposited zinc with both the amount of zinc to be expected and the rate of hydrogen evolution. In United States Patent 4,013,~12, Satoshi Mukae, 1~174~0(~
March 22, 1977, there is disclosed a method for judging purity of purified zinc sulfate solution by subjecting a sample of solution to electrolysis, combusting generated gases and measuring the internal pressure in the combustion chamber which is an indirect measure of current efficiency. M. Maja et al (J. Electrochem. Soc., 118, 9, 1538-1540, 1971) and P. Benvenuti et al (La Metallurgia Italiana, 60, 5, 417-423, 1968) describe methods for detection of impurities and measuring the purity of zinc sulfate solutions by depositing zinc and then dissolving deposited zinc electrolytically and relat-ing calculated current efficiency to impurity content.
This second group of references relates to methods andapparatus for determining electrolyte purity wherein electrolysis of solutions is used to determine current efficiency which is subseq-uently related to electrolyte purity.
In my co-pending Canadian Patent Application 306,805 which was filed on July 5, 1978, there is disclosed a method for controlling a process for the recovery of zinc from a zinc sulfate electrowinning solution which comprises decreasing a potential, which is applied between electrodes in a test cell containing a sample of solution, at a constant rate at substantially zero cur-rent, measuring the decreasing potential, terminating the decreasing of the potential at a value corresponding to the point at which zinc starts to deposit, determining the activation overpotential, relating the activation overpotential to the concentration of impurities and adjusting the process to obtain optimum recovery of zinc.
*
Issued as Canadian Patent 1,111,125 ~ .t?
i~ 7~Z~
Although the method according to my co-pending application overcomes the necessity for electrolyzing solution to determine current ef~iciencies or for measuring polarization potentials in relation -4a-~,. ..
~, 1~74~6~0 to varying c~rrents or current densities, several disadvantages still exist. The method is not continuous and it is necessary to determine the value of the activation overpotential for each sa~ple by decreasing the applied potential each time until the value is reached at which zinc starts to deposit and the current density increases from its substantially zero value for a fu~ther small decrease in potential.
I have now found that it is unnecessary to decrease the applied potential in order to determine the value of the activation overpotential.
Thus, I have found that the activation overpotential can be measured as a function of time at a controlle~, low current, and that the purification and electrowdnning processes can be controlled by correcting the amounts of reagents in response to deviations of recorded values of the over-potential from desired values in order to return to the desired optimum values.
The method and apparatus of the invention apply to zinc sulfate solutions which are obtained in processes for the treatment of zinc containing materials such as ores, concentrates, etc. Treatment includes thermal treatments and hydro-metallurgical treatments such as roasting, leaching, in situ leaching, bacterial leaching and pressure leaching. Such solutions, which are referred to in this application as zinc sulfate electrolyte, may be acidic or neutral solutions.
When zinc sulfate electrolyte is subjected to a co~trolled low ourrent applied to electrodes placed in a test cell containing electrolyte and the current has a value which is sufficient to cause inchoate deposition of zinc on an aluminum cathode, the value of the résulting potential represents the activation overpotential for zinc deposition onto aluminum. ~hen the cathode is a moving cathode, values of the activation overpotential can be measured and recorded and the purification process of zinc sul-fate electrolyte and the electrowinning process of zinc from zinc sulfate electrolyte can be controlled in response to the measured and recorded values of the activation overpotential. Inchoate deposicion is defined, for the purpose of this invention, as the deposition of zinc which has just begun and is limited to partial covering of the moving cathode surface by zinc. The measured values of the activation over-potential can be used as a direct measure of the impurity concentration, i.e. the effectiveness of the purification process, and of the polarizing additive concentration relative to the impurity concentration in the electrolyte in the process for the recovery of zinc which includes the purification process and the electrowinning process. In response to measured values of the activation over-potential, the purification process can be adjusted, or the concentration of polarizing additive in the electrolyte can be adjusted relative to the impurity concentration and/or the impurity concentration can be adjusted, so that optimum current efficiency and level zinc deposits are obtained in the electrowinning process.
Accordingly, there is provided a method for controlling a process for the recovery of zinc from zinc sulphate electrolyte containing concentrations of impurities, said method comprising the steps of establishing a test circuit comprising a test cell, a sample of electrolyte, a moving cathode, made of an electrically conductive material other than zinc, which moving cathode has an area exposed to said electrolyte, an anode and a reference electrode, said electrodes being immersed in said sample, a constant current supply and measuring means electrically connected to said electrodes; applying a low current to the electrodes in said test cell, said current being sufficient to cause inchoate deposition of zinc on said cathode; measuring the activation overpotential at the point of inchoate deposition; relating said activation over-potential to the cencentration of impurities o in said sample; and adjusting the concentration of impurities in the electrolyte of the process for the recovery of zinc to obtain optimum recovery of zinc, wherein inchoate deposition is defined as the deposition of zinc which has just begun and is limited to a partial covering of the moving cathode surface by zinc.
In another embodiment, the method for controlling a process for the electrowinning of zinc from zinc sulfate electrolyte containing concentra-tions of impurities and at least one polarizing additive, said method comprising the steps of establishing an electrolytic test circuit comprising a test cell, a sample of electrolyte, a moving cathode, made of an electrically conductive material other than zinc, which moving cathode has an area exposed to said electrolyte, an anode and a reference electrode, said electrodes being immersed in said sample, a constant current supply and measuring means electric-ally connected to said electrodes; applying a low current to the electrodes in said te~t cell, said current being sufficient to cause inchoate deposition of zinc on said cathode; measuring the activation overpotential at the point of inchoate deposition; relating the measured activation overpotential to the concentration ratio between impurities and polarizing additive in said sample;
and adjusting the concentration ratio in the process electrolyte to obtain optimum current efficiency and level zinc deposits in the electrowinning process, wherein inchoate deposition is defined as the deposition of zinc which has just begun and is limited to a partial covering of the moving cathode surface by deposited zinc.
The invention will now be described in detail. The apparatus used in the method for measuring the activation overpotential of zinc consists of a test circuit which comprises a test cell, a sample of zinc sulfate electrolyLe, a moving cathode; an anode, a reference electrode, means to supply a constant current and means for measuriny the activation overpotential. The test cell is a small container of circular, square or rectangular cross-section made of a suitable material, which is preferably resistant to acid zinc sulfate electrolyte and large enough to hold a suitable sample of electrolyte. Means are provided in the cell to make it possible to continuously add electrolyte to, and to discharge electrolyte from, the test cell. The three electrodes are immersed in the electrolyte sample and are removably positioned in the cell at constant distances from each other.
-7a-d 1~4~:~0 The moving cathode is preferably made of aluminum or an alum mum alloy and has a constant area of its surface in contact with electrolyte in the cell. If desired, a moving cathode of other suitable materials such as titanium may ke used.
I have determined that a surface area in contact with electrolyte in the range of about 0.1 to 1 cm gives excellent results, me moving cathode is preferably made of aluminum or aluminum alloy wire or strip which is contained in and moves through a cathode holder. The holder envelopes the moving cathode except for the constant surface area which is in contact with electrolyte. Means are provided to move the moving cathode intermittently or continuously through the cathode holder and, consequently in contact with electrolyte. Preferably, these means include provisions to move the cathode continuously at a constant rate. The use of a moving cathode made of aluminum wire or strip has a number of advantages, No special preparation of the alum mum surface is necessary, aluminum or aluminum alloy wire or strip is readily available at low cost and test results are re-producible. The moving cathode does not have to be replaced and thus allows intermittent or continuous operation. I have found that m~st oommercially available aluminum and aluminum alloys in the form of wire and strip are suitable, as long as they have sufficiently smooth and clean surfaces and have electrochemical characteristics that produce reproducible test results.
me anode is made of a suitable material such as, for example, platinum or lead-silver alloy. I have found that anodes made of lead-silver alloy containing 0.75% silver are satisfactory. me reference electrode can be any one of a number of suitable reference electrodes such as, for example, a standard calomel electrode (SOE).
The three electrodes are electrically connected to a source 1174;2(~) of constant current and to measuring means for the activation overpotential.
The source of constant current is connected to the anode and the moving cathode. The measuring means for the activation overpotential measures the overpotential on the moving cathode relative to the reference electrode. The measured activation overpotential may, for example, be recorded on a meter or other suitable read-out instrument, or alternatively, may be recorded in the form of a line or trace as a function of time.
The electrodes are removably positioned in the cell in fixed relation to each other. I have found that good results are obtained when the surface area of the moving cathode that is in contact with electrolyte is kept at a fixed distance of about 4 cm from the surface of the anode and when the reference electrode is positioned between the cathode and the anode in such a way that the tip of the reference electrode is rigidly located at a distance of about 1 cm from but not covering the surface area of the moving cathode in contact with electrolyte.
Suitable means may be provided to maintain the electrolyte in the call at a suitable constant temperature. Such means may comprise controlled heating/cooling means for electrolyte prior to electrolyte entering the cell or a controlled heating/cooling coil placed in the test cell, or a constant temperature bath or the like.
In the method of the inven~ion, a sample of zinc sulfate electrolyte, which may be neutral or acidic and which may contain addition agents, and which may be obtained from either the purification process or the zinc electrowinning process, is added to the test cell.
To ensure reproducible results, the sample is kept in motion such as by agitation or circulation. Preferably, the sample is kept in motion by continuously passing a small flow of electrolyte through the test cel~. According to this preferred embodiment, a sample of ~t7~o electrolyte is continuously withdralnn from the purification or electrowinning process, passed through the test cell and subsequently returned to the respective process. Electrolyte added to the cell may be adjusted to a certain zinc or zinc and acid content in order to reduce to a minimum any variation in the test method that may be caused by variations in zinc or zinc and acid concentrations in the electrolyte. Adjustment of zinc concentration to, for example, 150 g/L zinc, or of zinc and acid concentrations to, for example 55 g/L zinc and 150 g/L sulfuric acid is satisfac~ory. However, concentrations in the range of 1 to 250 g/L zinc and 0 to 250 g/L sulfuric acid are equally satisfactory.
When using a continuous sample flow, excess electTolyte is discharged from the cell, for example5 by means of an overflow.
The moving cathode is advanced through the cathode holder intermittently or continuously at a rate sufficient to allow inchoate deposition of zinc. Preferably, the moving cathode is advanced continuously at a constant rate. The rate is dependent on the ratio between cathode length and cathode surface area, the value of the current density for inchoate deposition, the surface area of the cathode exposed to electrolyte, the fraction of exposed cathode area covered with deposited zinc and the weight of deposited zinc. The rate is also somewhat dependent on the degree of motion of elect~olyte in the cell. Thus, the rate at which the cathode is moved through the cathode holder and, consequently, through the electrolyte, may vary in a range of values. At rates lower than the minimum rate, the measured overpotential will be that of zinc onto zinc and will not b~ the activation overpotential of zinc onto aluminum. ~t Tates several orders of magnitude high~r than the minimum rate, such as fo~ example, one thousand times higher, the amount of zinc deposited may be insufficient to obtain reliable ~L~742(~0 and reproducible values for the activation overpotential. Preferably, the rate at which the cathsde is moved is about ten to five hundred times the minimum rate. The m mimum rate may be calculated by using the following formula:
~in _ _ , cm/h wherein:
a represents the cathode length to surface area ratios, cm/cm2;
b represents current density, A/cm2;
c represents cathode exposed area, cm2;
d represents the electrochemical equivalent for zinc deposition, g/Ah;
x represents fraction of cathode covered with zinc;
y represents the weight of deposited zinc per unit of cathode surfa oe area, g/cm .
When moving the cathode intermittently, the average rate of movement should be at least equal to the minimum rate for continuous movement, while the periods of time when the cathode is stationary should not exceed the period of time that will cause more than inchoate deposition.
A 1GW current is applied to the anode and the moving cathode to cause inchoate deposition of zinc onto the cathode. Preferably, the low current is controlled at a constant value. m e current should be limited to low values, which only cause inchoate deposition. This is necessary to avoid the deposition of zinc onto previously deposited zinc whereby values of the overpotential are obtained of zinc deposition onto zinc rather than values of the desired activation overpotential of zinc deposition onto aluminum. Thus, the deposition of too much ,~
i~7~Z(?O
æinc should be avoided. Preferably, not more than about 10 to 30% of the cathode surface in contact With electrolyte should b æame covered with deposited zinc at any time. Currents, expressed as current density, that cause inchoate deposition on the cathode moving at rates defined above should ~e at least 0.01 m~/cm . Current densities in respect of the moving cathode as hereafter discussed are to be taken as referring to the exposed area of the moving cathode. Below a value of the current, expressed as current density, of 0.01 m~/cm2, the current may be primarily associated with hydrogen deposition. For practical purposes, the current, expressed as current density, should be in the range of 0.01 to 4.0 mP/cm2. Values of the current higher than the equivalent current density of 4.0 m~/cm2 will require impractically high cathode movement rates. Preferably, current values, expressed as current density, are in the range of 0.1 to 0.4 m~/cm2.
For example, for inchoate zinc deposition at a current density of 0.4 m~/cm2 on a moving alumlnum cathcde, which has a ratio of length to surface area of 0.6 to 0.25, an exposed area of 0.25 cm2 of which 20% is c~vered with deposited zinc and on which 7 x 10 3g zinc/cm2 is deposited (determined fram scanning electron microscope examination of inchoate zinc deposits~, the minimum rate as calculated from the above formula is about 0.21 cmJh.
The temperature of the electrolyte being measured is usually maintained constant. Changes in temperature affect the measured activation overpotential, e.g., a decreasing temperature increases the measured over-potential. I'he cell and its c~ntents are adjusted to and maintained at a suitable, controlled, constant temperature, which may be between 0 and 100C, preferably ~etween 20 and 75C and, more preferably, in the range of 25 to 40 &. If desired, the constant ~74~
temperature may be approximately the same as the temperature of the electrolyte in the electrowinning process or purification process, whichever is applicable. If the temperature is not maintained constant, the value of the activation overpotential should be corrected for the temperature variations so that the results of the tests are comparable.
The activation overpotential is measured continuously or intermittently and is recorded at the point of inchoate deposition of zinc onto an aluminum cathode. For practical application of the method of this invention, the activation overpotential is expressed as the value of the measured overpotential at a current corresponding to a current density in the range of about 0.01 to 4.0 A/cm2, of exposed cathode area preferably in the range of about 0.1 to 0.4 m~/cm2. The activation overpotential is recorded on a suitable read-out instr~nent, or, alternatively, recorded as a function of time. The recorded values of the overpotential are maintained in a preferred range. This is accomplished by making adjustments to the purification and electrowinning processes when values of the overpotential deviate from the preferred range of values.
The activation overpotential has specific values dependent on the cc~position of the electrolyte~ As every electrolyte compo~ition can be purified to an optimum degree and as every electrolyte composition has an optimum range of polarizing additive contents relative to its impurity content, the activation overpotential will similarly have a range of values that is required to yield the desired optimum results.
Any one of a wide range of suitable polarizing additives may be used;
the most ccmmonly used polarizing additive is animal glue. I have determined that increasing concentrations of impurities such as antimDny, cobalt, nickel, germanium and copper cause a decrease in activation overpotential, while increasing polarizing additive concentrations ,, i~
~ 13 -~7~30 increase the overpotential.
If the value of the measured activation overpo~ential in the purification of electrolyte is too low, the impurity concentration is too high for optimum z;nc recovery in the electro~inning process. Thus, dependent on the composition o the electrolyte, the activation overpotential is an indicator of the effectiveness of the purification process and deviations from optimum operation can be corrected by adjusting the purification process in relation to values of the activation overpotential, whereby the impurity concentration is lowered. Correction of the zinc dust purification process, may be accomplished, for example, by adjusting the temperature of the purification process, adjusting the duration of the purification process, increasing the amount of zinc dust, or increasing the concentration of a zinc dust activator such as antimony, copper, or arsenic in ionic form. Alternatively, insuf~iciently purified electrolyte may be further purified in an additional purification step or by recirculation in the purification process.
If the value of the activation overpotential measured for the electrolyte in the electrowinning process is too low, the concentration of polarizing additive in the electrolyte is too low to adequately control cathodic zinc resolution caused by the impurities present, or the impurity concentration is too high relative to the cor.centration of polarizing additive. On the other hand, if the value is too high, the concentration of polarizing additive is too high relative to the impurity concentration, and a resultant loss in current efficiency and a rougher zinc deposit occur. Thus, depending on the composition of the electrolyte, the activation overpotential is an indicator of the efficiency of the electrowinning process and deviations from optimum operation can be corrected by changing the concentration of polarizing additive or the ~'7~QO
concentration of impuri~cies in the electrolyte as required in relation to values of the activation overpotential. Change in the concentration of polarizing additive may be accomplished in a suitable manner such as by increasing or decreasing the rate of addition of glue to the electroly~e. A decrease in the impurity concentration may be achieved by more effective purification of the electrolyte prior to the electrowinning process.
Similarly, in the case of the presence of an excess concentration of polarizing additive, corrective action may be taken by allowing the level of impurities in the electrolyte to rise in a controlled fashion. Preferably this is achieved by the controlled addition of antimony, which has the most economical effect in correcting the impurity to polarization additive concentration ratio, rather than by any change in the electrolyte purification procedure.
The method of the invention has a number of applications in the process for the recovery of zinc from zinc sulfa~e electrolyte~ '~hus, the method can be used before, during and after purification of zinc sulfate electrolyte and before, during and after the electrowinning of zinc from zinc sulfate electrolyte. For example, prior to the zinc dust purification process, the method can be used to determine the degree of iron oxide removal and the degree of removal by iron oxides of impurities such as arsenic, antimony and germanium from zinc sulfate solutions obtained in the leaching of ores, concentrates or calcines. During purification, the method can be used to determine the degree of purification obtained, for example, with zinc dust, in the various steps of the purification process. After purification, the effectiveness of the purification can be determined, as well as the possible need for adjustments to the purification process or to the subsequent electrowinning process. In the electrowinning process, the method can be advantageously used to determine the required amount of polarizing additive in relation to impurity concentration, the required 7~Z(~O
amount of impurities, such as, for example, antimony, in relation to concentration of polarizing additives, the need for adjustments to the electrolyte feed, or to electrolyte in process and the quality of return acid.
m e invention will now be descriked by means of the following non-limitative examples.
In the following examples, values of the activation overpotential were measured using a test cell having a sample volume of 500 ml. A
volume of electrolyte was passed through the cell. Immersed in the electrolyte in the cell were a moving cathode consisting of a 1.19 mm diameter wire of No. 4043 aluminum alloy ~length to surface area ratio
2.51 cm/cm2) contained in and advanced through a st~tionary cathode holder fixedly positioned in the cell allowing 0.25 cm2 of the cathode to be exposed to electrolyte, a lead -0.75~ silver anode and a SCE*
positioned ketween cathode and anode. m e surface of the exposed area of the moving cathode was 4 cm away from the surface of the anode and the tip of the S OE was 1 cm away from the cathode such that the tip was not in direct line between the anode and the exposed area of the cathode.
The temperature of the electrolyte flowing through the test cell was controlled at the desired valueO The anode and the maving cathode were connected to a source of constant current and the S OE and the cathode were connected ~o the measuring means for the activation overpotential using a voltmeter with digital read-out and a x-y recorder. A constant current was applied to cause inchoate deposition of zinc on the m~ving cathode and values of the activation overpotential were measured and recorded. m e minimum rate of movement of the cathode through the electrolyte was calculated to ke 1.1 cm/h for a current corresponding to a current density of 1 m~/cm2 and the fraction of the exposed cathode surface area covered with zinc being 0.1.
Example I
This example illustrates the effects of variations in the values of the applied current expressed as current density, the cathode wire speed~ the temperature of the electrolyte and the flowrate of the electrolyte. A quantity of plant electrolyte was analyzed and adjusted to 55 g/L Zn and 150 g/L H2SO4. The adjusted electrolyte also contained 0.01 mg/L Sb, 0.03 mg/L Cu, 0.1 mg/L Co, 0.1 mg/L Ni, 0.005 mg/L Ge, 0.5 mg/L Cd, 30 mg/L Cl and 2 mg/L F. Adjus*ed electrolyte io was continuously passed through the test cell and the activation overpo~ential measured and recorded as described. The results are tabulated in Table I.
TABLE I
Currentmoving cathode temperature flow rate activation densi~y speed of electro of electrooverpotential mA/cm cm/hr lyte Clyte mL/min. mV
0.1 60 30 668 10 1.0 60 30 668 75 1.0 180 30 668 82 1.0 300 30 668 90 1.0 60 21 668 83 1.0 60 35 668 55 1.0 60 60 668 20 1.0 60 30 100 70 0.4 60 30 668 35 2.0 60 30 668 75 4.0 60 30 668 115 The results clearly indicate the efect of variables in the 2~(~
method and the need for using standardized conditions for practical application.
Example 2 This example illustrates the effects of varying amounts of antimony, germanium, cobalt and glue added to adjusted electrolyte with the composi~ion as in Example 1. The activation overpotential was measured using a current corresponding to a current density of 1.0 mA/cm2, a cathode speed of 160 cm/hr, an electrolyte temperature of 35C, and an electrolyte flow rate of 660 mL/min. Values of the measured activation overpotential were recorded on an x-y recorder.
The results are tabulated in Table II. In the Table, the values of the overpotential represent the average recorded value.
TABLE II
Additions, in mg/L. Activation overpotential Glue Sb Ge Co m/V
0 0.02 0 0 58 10 0.02 ~ 0 89 20 0.02 0 0 106 30 0.02 0 0 109 0 0.04 0 0 53 10 0.04 0 0 90 30 0.04 0 0 96 5 0.06 0 0 76 0 0.08 0 0 50 ~con't) 1~7~L2(~
TABLE II ~con't) Additions, in mg/L. Activation overpotential Glue Sb Ge Co m/~
0.08 0 0 78 0.08 0 0 83 0 0 0.04 0 70 0 o o~ o 116 0 0.04 0 2.0 55 0.04 0 2.0 lO~
The results indicate that increasing concentrations of glue increase the activation overpotential and that increasing concentrations of impurities decrease the activation overpotential of zinc.
Example 3 This example illustrates that increasing concentrations of glue are required to give good current efficiency when increasing impurity concentrations are present in electrolyte and that optimum ranges for glue concentrations in relation to impurity concentrations exist to give highest current efficiencies. Samples of adjusted plant electralyte as used in Example 2, to which varying amounts of glue and antimony and/or cobalt were added as potassium antimony tartrate and cobalt sulfate, respectively, were subjected to electrolysis in a cell at a current density of 400 A/m2 at 35C for 24 hours. The current efficiencies for the zinc deposition were determined by determing the ratio of the weight of the deposited zinc to the calculated weight based on the total amount of current passed through the cell for the deposition of zinc. The results are given in Table III.
z~o TABLE III
g ue added in mg/L 0 10 15 20 25 30 40 45 50 Sb added Co added current efficiencies in %
in mg/L in mg/L _ _ _ _ _ _ _ _ _ 0.01 0 88 92 91 90 89 88 87 87 85 0.03 0 7~ 90 92 93 92 91 89 88 87 0.05 0 56 ~6 90 92 93 93 92 91 88 0.07 0 43 72 81 85 89 92 93 92 89 0.01 0.05 89 92 92 91 90 89 88 87 85 0.01 2 88 92 92 92 9~ 91 91 90 89 0.01 5 65 87 92 92 92 92 92 92 91 0.01 5* - 43 74 82 82 81 79 77 75 0.03 0.05 80 90 92 93 93 91 90 ~8 86 0.03 1 40 74 85 92 9~ 93 92 91 89 0.03 5 - 58 74 87 92 94 94 93 90 0.03 5* - - - 40 72 82 83 83 78 *48 hour deposit It is evident from the tabulated results that for each antimony concentration, a corresponding narrow range of glue concentrations was required to give the highest possible current efficiencies. Current efficiencies decreased for both deficient and excessive glue concentrations.
Thus, a range of op~imum glue concentrations exis~s for each antimony concentration. Similarly, when antimony and cobalt are present, glue additions are required to counteract the harmful effects of these impuTities and optimum glue concentrations exist for each antimony and cobalt concentration. The optimum glue concentrations were the same for 48 hours as for 24 hours deposits, but ~he current efficiencies had decreased.
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~xample 4 Values for the activation overpotential for glue and impurities concentrations obtained in tests as illustrated in Examples 1 and 2 and Tables I and II were combined with ranges of maximum current efficiencies for combinations of concentrations of glue and impurities obtained in t~sts as illustrated in Example 3 and Table III. Thus, the following ranges of values for optimum current efficiency were obtained in relation to ratios between glue and impurities as indicated by the values of the activation overpotential. The ranges are tabulated in Table IV.
TABLE IV
activati~n overpotential range of current efficiency in %
in mV
83~89 It can be seen from the tabulated figures that the highes~
ranges of current efficiencies are obtained when the activation over-potential is maintained in the range of 90 to 115 mV, measured at 35C.
~ 79~Z~O
Example 5 This example illustrates that the activation overpotential measurements can be used to determine whether the correct glue concentration is present in the electrolyte relative to the impurity concentration and what changes are required in glue concentration to optimize the zinc electrowinnin~ process. Using the same electrolyte as used in previous examples, tests as described in Example 2 were repeated, current efficiencies were determined as in Example 3 and the results combined as illustrated in Example 4. Using the results of the tests according to this example, the required change in glue concentration in mg/L
was determined at measured values for the activation overpotential to obtain the optimum value for the current efficiency in the electrolytic process. Data presented in Table V show the program to control the electrowinning process for zinc by making specified changes in glue concentration in zinc electrolyte.
TABLE V
measured activation overpotential required change in glue concen-in mV at 35C tration in mg/L for optimum current efficiency increase by 9 increase by 7 increase by 5 increase by 3 increase by 1 100 no change 105 no change 110 decrease by 1 115 decrease by 3 120 decrease by 5 125 decrease by 7 130 decrease by 9 Example 6 This example illustrates that antimony can be used in relation to measured values of the activation overpotential to control the zinc electrowinning process at optimum current efficiency.
In a series of electrowinning cells using an acidic zinc sulfate electrolyte, having the adjusted composition as given in Example 1, both glue and antimony are added. Glue is added to the electrolyte at a constant rate of 20 mg/L, while antimony is normally added at a rate of 0.04 mg/L.
Using the electrolyte and the above mentioned additions of glue and antimony, activation overpotentials and current efficiencies were determined as in Example 5. Optimum values ~or current efficiencies were attained with activation overpotentials of 100 to 105 mV. '13sing the results of these determinations, the required changes in antimony concentrations in the electrolyte in mg/L were determined at measured values for the activation overpotential to obtain the optimum value for the curr0nt efficiency in the electrolytic process. The control program is given in Table VI.
TABLE VI
__ measured activation required change in antimony overpotential in mV concentration in mg/L for optimum current efficiency decrease by 0.03 decrease by 0.02 decrease by 0.01 100 no change 105 no change 110 increase by ~.01 115 increase by 0.02 120 increase by 0.03 ,, ~'79~Z~O
Example 7 This example illus~rates that the removal of impurities from neutral zinc electrolyte by cementation with atomized zinc can be monitored by activation overpotential measurements. Impure plant electrolyte was subjected to purification with varying amounts of atomized zinc added to the electrolyte containing previously added antimony as antimony potassium tartrate in varying amounts. Cementation was carried out at 50C with agitation and using a retention time of one hour. A flow of purified electrolyte was filtered and cooled to 35C. The flow was then passed through the test cell for measurement of the activation overpotential. The purified electrolyte was analyzed to determine impurity concentrations. The results are tabulated in Table VII.
TABLE VII
Sb added atomized activation impurities in purified electrolyte in mg/L zinc overpotential in mg/L
added in in mV Cd Cu Co Ni Sb g/ L - -_ 0.75 0 34 200 3.5 1.6 1.8 0.75 0,75 0.5 48 21 4.1 0.3 0.9 0.09 0.751.0 64 1~ 3.4 0.3 0.5 0.05 0.751.5 74 3.9 1.3 0.2 0.6 0.04 0.75 2.0 76 1.9 1.0 0.2 0.4 0.03 0.75 2.5 88 0.4 0.8 0.3 0~3 0.03 0.75 3.0 94 0.3 0.6 0.2 0.2 0.02 0.25 2.0 70 2.2 0.5 0.2 ~0.1 0.07 0.50 2.0 74 2.2 0.6 0.1 0.1 0.03 l.00 2.0 85 0.6 0.6 0.1 ~0.1 0.02 --.
~74~
Example 8 This example illustrates how the activation overpotential measurements such as those given in Example 7 can ke used to determine what corrections must be made to the process for controlling variables such as zinc dust and antimony additions to optimize the zinc dust purification of electrolyte. Data presented in Table VIII shDw the program to control the zinc dust purification process by making specified changes in zinc dust or antimony salt additions to the zinc electrolyte during purification if the measured activation overpotential indicates purification has not proceeded to completion.
TABLE VIII
measured activation required additions overpotential in m~ of for neutral electrolyte zinc dust (g/L) Sb (mg/L) 0.3 0.1 0.6 0.2 1.2 0.4 1.5 0.5 1.8 0.5 ~0 2.1 0.5 ~,
positioned ketween cathode and anode. m e surface of the exposed area of the moving cathode was 4 cm away from the surface of the anode and the tip of the S OE was 1 cm away from the cathode such that the tip was not in direct line between the anode and the exposed area of the cathode.
The temperature of the electrolyte flowing through the test cell was controlled at the desired valueO The anode and the maving cathode were connected to a source of constant current and the S OE and the cathode were connected ~o the measuring means for the activation overpotential using a voltmeter with digital read-out and a x-y recorder. A constant current was applied to cause inchoate deposition of zinc on the m~ving cathode and values of the activation overpotential were measured and recorded. m e minimum rate of movement of the cathode through the electrolyte was calculated to ke 1.1 cm/h for a current corresponding to a current density of 1 m~/cm2 and the fraction of the exposed cathode surface area covered with zinc being 0.1.
Example I
This example illustrates the effects of variations in the values of the applied current expressed as current density, the cathode wire speed~ the temperature of the electrolyte and the flowrate of the electrolyte. A quantity of plant electrolyte was analyzed and adjusted to 55 g/L Zn and 150 g/L H2SO4. The adjusted electrolyte also contained 0.01 mg/L Sb, 0.03 mg/L Cu, 0.1 mg/L Co, 0.1 mg/L Ni, 0.005 mg/L Ge, 0.5 mg/L Cd, 30 mg/L Cl and 2 mg/L F. Adjus*ed electrolyte io was continuously passed through the test cell and the activation overpo~ential measured and recorded as described. The results are tabulated in Table I.
TABLE I
Currentmoving cathode temperature flow rate activation densi~y speed of electro of electrooverpotential mA/cm cm/hr lyte Clyte mL/min. mV
0.1 60 30 668 10 1.0 60 30 668 75 1.0 180 30 668 82 1.0 300 30 668 90 1.0 60 21 668 83 1.0 60 35 668 55 1.0 60 60 668 20 1.0 60 30 100 70 0.4 60 30 668 35 2.0 60 30 668 75 4.0 60 30 668 115 The results clearly indicate the efect of variables in the 2~(~
method and the need for using standardized conditions for practical application.
Example 2 This example illustrates the effects of varying amounts of antimony, germanium, cobalt and glue added to adjusted electrolyte with the composi~ion as in Example 1. The activation overpotential was measured using a current corresponding to a current density of 1.0 mA/cm2, a cathode speed of 160 cm/hr, an electrolyte temperature of 35C, and an electrolyte flow rate of 660 mL/min. Values of the measured activation overpotential were recorded on an x-y recorder.
The results are tabulated in Table II. In the Table, the values of the overpotential represent the average recorded value.
TABLE II
Additions, in mg/L. Activation overpotential Glue Sb Ge Co m/V
0 0.02 0 0 58 10 0.02 ~ 0 89 20 0.02 0 0 106 30 0.02 0 0 109 0 0.04 0 0 53 10 0.04 0 0 90 30 0.04 0 0 96 5 0.06 0 0 76 0 0.08 0 0 50 ~con't) 1~7~L2(~
TABLE II ~con't) Additions, in mg/L. Activation overpotential Glue Sb Ge Co m/~
0.08 0 0 78 0.08 0 0 83 0 0 0.04 0 70 0 o o~ o 116 0 0.04 0 2.0 55 0.04 0 2.0 lO~
The results indicate that increasing concentrations of glue increase the activation overpotential and that increasing concentrations of impurities decrease the activation overpotential of zinc.
Example 3 This example illustrates that increasing concentrations of glue are required to give good current efficiency when increasing impurity concentrations are present in electrolyte and that optimum ranges for glue concentrations in relation to impurity concentrations exist to give highest current efficiencies. Samples of adjusted plant electralyte as used in Example 2, to which varying amounts of glue and antimony and/or cobalt were added as potassium antimony tartrate and cobalt sulfate, respectively, were subjected to electrolysis in a cell at a current density of 400 A/m2 at 35C for 24 hours. The current efficiencies for the zinc deposition were determined by determing the ratio of the weight of the deposited zinc to the calculated weight based on the total amount of current passed through the cell for the deposition of zinc. The results are given in Table III.
z~o TABLE III
g ue added in mg/L 0 10 15 20 25 30 40 45 50 Sb added Co added current efficiencies in %
in mg/L in mg/L _ _ _ _ _ _ _ _ _ 0.01 0 88 92 91 90 89 88 87 87 85 0.03 0 7~ 90 92 93 92 91 89 88 87 0.05 0 56 ~6 90 92 93 93 92 91 88 0.07 0 43 72 81 85 89 92 93 92 89 0.01 0.05 89 92 92 91 90 89 88 87 85 0.01 2 88 92 92 92 9~ 91 91 90 89 0.01 5 65 87 92 92 92 92 92 92 91 0.01 5* - 43 74 82 82 81 79 77 75 0.03 0.05 80 90 92 93 93 91 90 ~8 86 0.03 1 40 74 85 92 9~ 93 92 91 89 0.03 5 - 58 74 87 92 94 94 93 90 0.03 5* - - - 40 72 82 83 83 78 *48 hour deposit It is evident from the tabulated results that for each antimony concentration, a corresponding narrow range of glue concentrations was required to give the highest possible current efficiencies. Current efficiencies decreased for both deficient and excessive glue concentrations.
Thus, a range of op~imum glue concentrations exis~s for each antimony concentration. Similarly, when antimony and cobalt are present, glue additions are required to counteract the harmful effects of these impuTities and optimum glue concentrations exist for each antimony and cobalt concentration. The optimum glue concentrations were the same for 48 hours as for 24 hours deposits, but ~he current efficiencies had decreased.
~4Z~
~xample 4 Values for the activation overpotential for glue and impurities concentrations obtained in tests as illustrated in Examples 1 and 2 and Tables I and II were combined with ranges of maximum current efficiencies for combinations of concentrations of glue and impurities obtained in t~sts as illustrated in Example 3 and Table III. Thus, the following ranges of values for optimum current efficiency were obtained in relation to ratios between glue and impurities as indicated by the values of the activation overpotential. The ranges are tabulated in Table IV.
TABLE IV
activati~n overpotential range of current efficiency in %
in mV
83~89 It can be seen from the tabulated figures that the highes~
ranges of current efficiencies are obtained when the activation over-potential is maintained in the range of 90 to 115 mV, measured at 35C.
~ 79~Z~O
Example 5 This example illustrates that the activation overpotential measurements can be used to determine whether the correct glue concentration is present in the electrolyte relative to the impurity concentration and what changes are required in glue concentration to optimize the zinc electrowinnin~ process. Using the same electrolyte as used in previous examples, tests as described in Example 2 were repeated, current efficiencies were determined as in Example 3 and the results combined as illustrated in Example 4. Using the results of the tests according to this example, the required change in glue concentration in mg/L
was determined at measured values for the activation overpotential to obtain the optimum value for the current efficiency in the electrolytic process. Data presented in Table V show the program to control the electrowinning process for zinc by making specified changes in glue concentration in zinc electrolyte.
TABLE V
measured activation overpotential required change in glue concen-in mV at 35C tration in mg/L for optimum current efficiency increase by 9 increase by 7 increase by 5 increase by 3 increase by 1 100 no change 105 no change 110 decrease by 1 115 decrease by 3 120 decrease by 5 125 decrease by 7 130 decrease by 9 Example 6 This example illustrates that antimony can be used in relation to measured values of the activation overpotential to control the zinc electrowinning process at optimum current efficiency.
In a series of electrowinning cells using an acidic zinc sulfate electrolyte, having the adjusted composition as given in Example 1, both glue and antimony are added. Glue is added to the electrolyte at a constant rate of 20 mg/L, while antimony is normally added at a rate of 0.04 mg/L.
Using the electrolyte and the above mentioned additions of glue and antimony, activation overpotentials and current efficiencies were determined as in Example 5. Optimum values ~or current efficiencies were attained with activation overpotentials of 100 to 105 mV. '13sing the results of these determinations, the required changes in antimony concentrations in the electrolyte in mg/L were determined at measured values for the activation overpotential to obtain the optimum value for the curr0nt efficiency in the electrolytic process. The control program is given in Table VI.
TABLE VI
__ measured activation required change in antimony overpotential in mV concentration in mg/L for optimum current efficiency decrease by 0.03 decrease by 0.02 decrease by 0.01 100 no change 105 no change 110 increase by ~.01 115 increase by 0.02 120 increase by 0.03 ,, ~'79~Z~O
Example 7 This example illus~rates that the removal of impurities from neutral zinc electrolyte by cementation with atomized zinc can be monitored by activation overpotential measurements. Impure plant electrolyte was subjected to purification with varying amounts of atomized zinc added to the electrolyte containing previously added antimony as antimony potassium tartrate in varying amounts. Cementation was carried out at 50C with agitation and using a retention time of one hour. A flow of purified electrolyte was filtered and cooled to 35C. The flow was then passed through the test cell for measurement of the activation overpotential. The purified electrolyte was analyzed to determine impurity concentrations. The results are tabulated in Table VII.
TABLE VII
Sb added atomized activation impurities in purified electrolyte in mg/L zinc overpotential in mg/L
added in in mV Cd Cu Co Ni Sb g/ L - -_ 0.75 0 34 200 3.5 1.6 1.8 0.75 0,75 0.5 48 21 4.1 0.3 0.9 0.09 0.751.0 64 1~ 3.4 0.3 0.5 0.05 0.751.5 74 3.9 1.3 0.2 0.6 0.04 0.75 2.0 76 1.9 1.0 0.2 0.4 0.03 0.75 2.5 88 0.4 0.8 0.3 0~3 0.03 0.75 3.0 94 0.3 0.6 0.2 0.2 0.02 0.25 2.0 70 2.2 0.5 0.2 ~0.1 0.07 0.50 2.0 74 2.2 0.6 0.1 0.1 0.03 l.00 2.0 85 0.6 0.6 0.1 ~0.1 0.02 --.
~74~
Example 8 This example illustrates how the activation overpotential measurements such as those given in Example 7 can ke used to determine what corrections must be made to the process for controlling variables such as zinc dust and antimony additions to optimize the zinc dust purification of electrolyte. Data presented in Table VIII shDw the program to control the zinc dust purification process by making specified changes in zinc dust or antimony salt additions to the zinc electrolyte during purification if the measured activation overpotential indicates purification has not proceeded to completion.
TABLE VIII
measured activation required additions overpotential in m~ of for neutral electrolyte zinc dust (g/L) Sb (mg/L) 0.3 0.1 0.6 0.2 1.2 0.4 1.5 0.5 1.8 0.5 ~0 2.1 0.5 ~,
Claims (32)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for controlling a process for the recovery of zinc from a zinc sulfate electrolyte containing concentrations of impurities, said method comprising the steps of establishing a test circuit comprising a test cell, a sample of electrolyte, a moving cathode, made of an electrically conductive material other than zinc, which moving cathode has an area exposed to said electrolyte, an anode and a reference electrode, said electrodes being immersed in said sample, a constant current supply and measuring means electrically connected to said electrodes; applying a low current to the electrodes in said test cell, said current being sufficient to cause inchoate deposition of zinc on said cathode; measuring the activation overpotential at the point of inchoate deposition, relating the measured activation overpotential to the concentration of impurities in said sample; and adjusting the concentration of impurities in the electrolyte of the process for the recovery of zinc to obtain optimum recovery of zinc, wherein inchoate deposition is defined as the deposition of zinc which has just begun and is limited to a partial covering of the moving cathode surface by zinc.
2. A method for controlling a process for the electrowinning of zinc from zinc sulfate electrolyte containing concentrations of impurities and at least one polarizing additive, said method comprising the steps of establishing an electrolytic test circuit comprising a test cell, a sample of electrolyte, a moving cathode, made of an electrically conductive material other than zinc, which moving cathode has an area exposed to said electrolyte, an anode and a reference electrode, said electrodes being immersed in said sample, a constant current supply and measuring means electrically connected to said electrodes; applying a low current to the electrodes in said test cell, said current being sufficient to cause inchoate deposition of zinc on said cathode; measuring the activation overpotential at the point of inchoate deposition; relating the measured activation overpotential to the concentration ratio between impurities and polarizing additive in said sample; and adjusting the concentration ratio in the process electrolyte to obtain optimum current efficiency and level zinc deposits in the electro-winning process, wherein inchoate deposition is defined as the deposition of zinc which has just begun and is limited to a partial covering of the moving cathode surface by deposited zinc.
3. A method as defined in claim 1 or 2, wherein the value of said current corresponds to a value of corresponding current density in the range of 0.01 to 4.0 mA/cm2, based on the exposed area of the moving cathode.
4. A method as defined in claim 1 or 2, wherein-the value of said current corresponds to a value of corresponding current density in the range of 0.1 to 0.4 mA/cm2, based on the exposed area of the moving cathode.
5. A method as defined in claim 1 or 2, wherein said low current has a constant value.
6. A method as defined in claim 1 or 2, wherein the activation overpotential is measured continuously.
7. A method as defined in claim 1 or 2, wherein the activa-tion overpotential is measured intermittently.
8. A method as defined in claim 1 or 2, wherein said sample of electrolyte is kept in motion.
9. A method as defined in claim 1 or 2, wherein said sample of electrolyte is kept in motion by continuously passing a flow of electrolyte through said test cell.
10. A method as defined in claim 1 or 2, wherein the value of said current causing inchoate deposition of zinc is sufficient to cause not more than 10 to 30% of the surface area of the cathode which is exposed to electrolyte to become covered with deposited zinc.
11. A method as defined in claim 1 or 2, wherein the moving cathode is advanced at a substantially constant rate.
12. A method as defined in claim 1 or 2, wherein the moving cathode is continuously advanced.
13. A method as defined in claims 1 or 2, wherein the moving cathode is advanced in intermittent fashion.
14. A method as defined in claim 1 or 2 wherein the moving cathode is advanced through the sample of electrolyte at a substantially constant rate, said substantially constant rate being at least equal to a minimum rate defined by the following formula:
wherein:
a represents the cathode length to surface area ratios, cm/cm2;
b represents current density, A/cm2;
c represents cathode exposed area, cm2;
d represents the electrochemical equivalent for zinc deposition, g/Ah;
x represents fraction of cathode covered with zinc;
y represents the weight of deposited zinc per unit of cathode surface area, g/cm2.
wherein:
a represents the cathode length to surface area ratios, cm/cm2;
b represents current density, A/cm2;
c represents cathode exposed area, cm2;
d represents the electrochemical equivalent for zinc deposition, g/Ah;
x represents fraction of cathode covered with zinc;
y represents the weight of deposited zinc per unit of cathode surface area, g/cm2.
15. A method as defined in claim 1 or 2, wherein the moving cathode is advanced through the sample of electrolyte at a substantially constant rate, said rate being in the range of 10 to 500 times the minimum rate, said minimum rate being defined by the following formula:
, wherein:
a represents the cathode length to surface area ratios, cm/cm2;
b represents current density, A/cm2;
c represents cathode exposed area, cm2;
d represents the electrochemical equivalent for zinc deposition, g/Ah;
x represents fraction of cathode covered with zinc;
y represents the weight of deposited zinc per unit of cathode surface area, g/cm2.
, wherein:
a represents the cathode length to surface area ratios, cm/cm2;
b represents current density, A/cm2;
c represents cathode exposed area, cm2;
d represents the electrochemical equivalent for zinc deposition, g/Ah;
x represents fraction of cathode covered with zinc;
y represents the weight of deposited zinc per unit of cathode surface area, g/cm2.
16. A method as defined in claim 1 or 2, wherein the electrolyte in the test cell is kept at a substantially constant temperature and wherein the constant temperature selected is between 20°C and 75°C.
17. A method as defined in claim l or 2, wherein the electrolyte in the test cell is kept at a substantially constant temperature, and wherein the constant temperature selected is between 25° and 40°C.
18. A method as defined in claim 1 or 2, wherein the moving cathode in the test cell is a wire made of a material chosen from aluminum and aluminum alloys.
19. A method as defined in claim 1 or 2, wherein the moving cathode in the test cell is a strip made of a material chosen from aluminum and aluminum alloys.
20. A method as defined in claim 1 or 2, wherein the electrodes are positioned in the cell in fixed relation to one another.
21. A method as defined in claim 1 or 2, wherein the measuring of the activation overpotential is effected by recording values of said activation overpotential as a function of time.
22. A method as defined in claim 2, wherein the adjusting of the concentration ratio comprises adjusting the concentration of said at least one polarizing additive relative to the impurity concentration.
23. A method as defined in claim 2, wherein the adjusting of the concentration ratio comprises adjusting the impurity concentration.
24. A method as defined in claim 2, wherein the polarizing additive is animal glue.
25. A method as defined in claim 2, wherein the impurities include antimony; and wherein the adjusting of the concentration ratio comprises adjusting the impurity concentration by adjusting the concentration of antimony.
26. A method as defined in claim 2, wherein the polarizing additive is animal glue, and in which the adjusting of the concentration ratio comprises adjusting the concentration of the glue relative to the impurity concentration.
27. A method as defined in claim 2, wherein the polarizing additive is animal glue; wherein the concentration ratio is adjusted by adjusting the concentration of glue to a value at which the activation overpotential measured at a temperature of between 25°C and 40°C is in the range of 70 to 150 millivolts; and wherein the activation overpotential is measured at a value of a low constant current which value corresponds to a value of corresponding current density in the range of 0.01 to 4.0 mA/cm2,based on the exposed area of the moving cathode.
28. A method as defined in claim 27, wherein the value of the low constant current correspond to a value of corresponding current density in the range of 0.1 to 0.4 mA/cm2, based on the exposed area of the moving cathode.
29. A method as defined in claim 27 or 28, wherein the concentration of glue is increased when the value of the measured activation overpotential decreases below about 70 mV and wherein the concentration of glue is descreased when the value of the measured activation overpotential increases above about 150 mV, whereby the value of the measured activation overpotential returns to within the range of 70 to 150 mV.
30. A method as defined in claim 2, wherein the polarizing additive is animal glue; wherein the impurities include antimony; wherein the concentration ratio is adjusted by adjusting the concentration of antimony to a value at which the activation overpotential measured at a temperature in the range of 25 to 40°C is in the range of 70 to 150 mV; and wherein the activation overpotential is measured at a value of a low constant current which corresponds to a value of corresponding current density in the range of 0.01 to 4.0 mA/cm2, based on the exposed area of the moving cathode.
31. A method as defined in claim 30, wherein the value of the low constant current corresponds to a value of corresponding current density in the range of 0.1 to 0.4 mA/cm2, based on the exposed area of the moving cathode.
32. A method defined in claim 30 or 31, wherein the concentration of antimony is increased when the value of the measured activation overpotential increases above about 150 mV and wherein the concentration of antimony is decreased when the value of the measured activation overpotential decreases below about 70 mV, whereby the value of the measured activation overpotential returns to within the range of 70 to 150 mV.
Priority Applications (15)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000332698A CA1174200A (en) | 1979-07-27 | 1979-07-27 | Method and apparatus for controlling the quality of zinc sulfate electrolyte |
| FR8016211A FR2462491A1 (en) | 1979-07-27 | 1980-07-23 | METHOD FOR ADJUSTING THE ELECTROLYTIC DEPOSITION OF A METAL IN THE PRESENCE OF IMPURITIES |
| DE19803027955 DE3027955A1 (en) | 1979-07-27 | 1980-07-23 | METHOD AND DEVICE FOR MONITORING A METHOD FOR ELECTROLYTICALLY DEPOSITING A METAL |
| SE8005337A SE451604B (en) | 1979-07-27 | 1980-07-23 | WAY TO CONTROL A GALVANIC COLLECTION OF A METAL |
| GB8024437A GB2057139B (en) | 1979-07-27 | 1980-07-25 | Method for determining electrolyte quality in electrodeposition |
| NO802251A NO158883C (en) | 1979-07-27 | 1980-07-25 | PROCEDURE FOR REGULATING A PROCESS FOR ELECTROLYTIC DISPOSAL OF A METAL. |
| JP10140880A JPS5655587A (en) | 1979-07-27 | 1980-07-25 | Control of metal electrodeposition method |
| BE0/201534A BE884484A (en) | 1979-07-27 | 1980-07-25 | IMPROVEMENTS IN METAL ELECTRODEPOSITION |
| ZA00804513A ZA804513B (en) | 1979-07-27 | 1980-07-25 | Method and apparatus for controlling the quality of electrolytes |
| AU60776/80A AU537936B2 (en) | 1979-07-27 | 1980-07-25 | Controlling electrodeposition processes |
| IT09502/80A IT1153840B (en) | 1979-07-27 | 1980-07-25 | METHOD AND APPARATUS FOR THE CONTROL OF A METAL ELECTRODEFOSITION PROCEDURE |
| FI802359A FI71027C (en) | 1979-07-27 | 1980-07-25 | FOERFARANDE FOER REGLERING AV EN ELEKTROLYTUTFAELLNINGSPROCESSFOER METALLER |
| NLAANVRAGE8004294,A NL189923C (en) | 1979-07-27 | 1980-07-25 | METHOD FOR CONTROLLING A PROCESS FOR THE ELECTROLYTIC PRECIPITATION OF METAL |
| IT1980A09502A IT8009502A1 (en) | 1979-07-27 | 1980-07-25 | METHOD AND APPARATUS FOR TESTING A PROCEDURE FOR THE ELECTRODEPOSITION OF METALS |
| ES80493738A ES493738A0 (en) | 1979-07-27 | 1980-07-26 | A METHOD FOR CONTROLLING A METAL ELECTROPOSITION PROCESS |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000332698A CA1174200A (en) | 1979-07-27 | 1979-07-27 | Method and apparatus for controlling the quality of zinc sulfate electrolyte |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1174200A true CA1174200A (en) | 1984-09-11 |
Family
ID=4114808
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000332698A Expired CA1174200A (en) | 1979-07-27 | 1979-07-27 | Method and apparatus for controlling the quality of zinc sulfate electrolyte |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS5655587A (en) |
| BE (1) | BE884484A (en) |
| CA (1) | CA1174200A (en) |
| IT (1) | IT8009502A1 (en) |
| ZA (1) | ZA804513B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA1179751A (en) * | 1982-01-07 | 1984-12-18 | Robert C. Kerby | Controlling metal electro-deposition using electrolyte containing, two polarizing agents |
| JPH07840B2 (en) * | 1985-11-25 | 1995-01-11 | 大和特殊株式会社 | Method for controlling electroplating additive and apparatus therefor |
-
1979
- 1979-07-27 CA CA000332698A patent/CA1174200A/en not_active Expired
-
1980
- 1980-07-25 IT IT1980A09502A patent/IT8009502A1/en unknown
- 1980-07-25 BE BE0/201534A patent/BE884484A/en not_active IP Right Cessation
- 1980-07-25 JP JP10140880A patent/JPS5655587A/en active Granted
- 1980-07-25 ZA ZA00804513A patent/ZA804513B/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| ZA804513B (en) | 1981-07-29 |
| JPS5655587A (en) | 1981-05-16 |
| IT8009502A1 (en) | 1982-01-25 |
| JPS6361392B2 (en) | 1988-11-29 |
| BE884484A (en) | 1980-11-17 |
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