FI71027C - FOERFARANDE FOER REGLERING AV EN ELEKTROLYTUTFAELLNINGSPROCESSFOER METALLER - Google Patents

Description

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B ^ 11) UTLÄGGNINGSSKRIFT 7102 7 C (45) Patent y Jtty (51) Kv.lk. * / Lnt.Cl. 'G 05 D 21/00, C 25 D 21/12 FINLAND — FINLAND (21) Patent application Patentansöknlng 802359 (22) Application date Ansökningsdag 25-0 / .80 (23) Starting date - Giltighetsdag 25-07-80 (41) Has become public - Blivit offenclig 28.01 -8l

National Board of Patents and Registration KU .... ... ........... „.

1 (44) Date of publication and date of issue. 1 ο ηη Qf.

Patent and registration authorities V 'Ansökan utlagd och utl.skriften publicerad -u /.

(86) Kv. application Int. trap (32) (33) (31) Privilege requested - Begärd priority 27-07-79 »13-06.80 Canada (CA) 332698, 353993 26.12.79, 26.06.80 USA (US) 107180, 163282 (71) Cominco Ltd ., 200 Granville Street, Vancouver, British Columbia,

The present invention relates to a process for the control of a metal electrolytic process. The present invention relates to a process for the control of a metal electroplating process. to control the electroprecipitation process using an electrolyte containing impurity concentrations and / or at least one polarizing agent.

Methods for electroprecipitation of metals, such as electrolytic separation, electrolytic purification and electroplating, use electrolytes that contain impurities that, when present above certain critical concentrations, can electroprecipitate with the metal and contaminate or cause redissolution of the precipitate, resulting in a corresponding metal precipitation. . To reduce the concentration of impurities in the electrolyte, purification procedures can be used prior to electrolysis. In addition to purification, one or more polarizing additives may be added to the electrolyte to help provide smooth and even deposits as well as to reduce the effects of residual impurities.

2 71027 These polarizing additives work by changing the polarization. The polarization can be changed by increasing or decreasing the concentration of the polarizing agent. The polarization can also be changed by increasing or decreasing the concentration of the depolarizing agent. These substances, both polarizing and depolarizing, may be present in the electrolyte when it enters the cells from the treatment plant or may be substances such as animal glue that is added to the electrolyte to control the electroprecipitation process. Thus, it is to be clearly understood that the phrase "polarizing agents" includes both polarizing and depolarizing agents. It is also pertinent to note that the given substance does not work in the same way in different processes. Thus, a substance may act as a polarizing agent in another process, a depolarizing agent in another process involving a different metal; or it may be inactive in the third process. Nor is it unknown that impurities "catalyze" the effects of polarizing agents. Thus, it is well known that some experimental work may be required to determine which polarizing agents are suitable for a particular process.

The procedures currently used to determine the purity of an electrolyte are based on chemical analyzes and the determination of current efficiencies as a measure of impurity content, while the procedures used to add suitable polarizing agents are simply based on maintaining a constant concentration of substances in the electrolyte regardless of electrolyte quality. These procedures lead to variations in the quality of the deposited metal and the efficiency of the electroprecipitation process.

Numerous literature references can be found in the prior art regarding methods for determining the effects of impurities and additives for electroprecipitation processes for metals, and methods for determining the purity of electrolyte solutions.

U.S. Pat. No. 3,925,168 discloses a method and apparatus for determining the content of colloidal material, adhesive and / or active roughening material in a copper plating bath by determining the overvoltage current density ratios of solutions having a variable known reagent content and comparing the results to such a solution. and roughening content. Canadian Patent 988,879 discloses a method for determining and adjusting a cathode polarization voltage relative to a lead cleaning electrolyte current density, wherein the slope of the polarization voltage-current curve is a measure of

Numerous studies on similar methods are described in the published literature. C. L. Manteli et al. (Trans. Met. Soc. Of ΑΙΜΕ, 236, 718-725, May 1966) determine the applicability of current potential curves as an analytical tool in the monitoring of electrolytic recovery solutions of manganese for metallic impurities.

The polarization curves involved in the evolution of hydrogen were shown to be sensitive to metallic impurities that affect the cathode surface, thus altering the hydrogen overvoltage. H. S. Jennings et al., (Metallurgical Transactions £ 921-926, April 1973) describe a method for measuring cathodic polarization curves of copper sulfate solutions containing varying amounts of additives by varying the voltage used and recording the relationship between voltage and current density. O. Vennesland et al., (Acta Chem. Scand. 27, 3, 346-850, 1973) investigated the effects of antimony, cobalt, and meta-naphthol concentrations in a zinc sulfate electrolyte on a current-potential curve by changing the cathode potential at a programmed rate and plotting the curve . T. N. Anderson et al., (Metallurgical Transactions B, 7B, 333-338, September 1976) describe a method for measuring the concentration of an adhesive in a copper cleaning electrolyte by determining the polarization partition curves which, when compared, form a measure of the adhesive concentration. According to U.S. Patent 4,146,437, the use of cyclic gas coulometry to evaluate zinc and copper sulfate electrolytes is described. Cyclic gas flow curves containing cathodic precipitation as well as anodic dissolution portions of current-potential ratios, and polarization curves are plotted as a tool for estimating the amounts of impurities and additives in zinc sulfate electrolytes.

This first group of references describes methods in which metal is deposited on an electrode and current or current density potential curves represent cathode polarization potentials with varying currents and / or current densities.

T. R. Ingraham et al., (Can. Met. Quarterly, 11, 2, 451-454, 1972) describe a meter for measuring the quality of zinc electrolytes by measuring the amount of cathodic hydrogen released during electroprecipitation of zinc and for demonstrating current efficiency by comparing the weight of deposited zinc to both the expected amount of zinc and hydrogen evolution. U.S. Patent 4,013,412 discloses a method for evaluating the purification of a purified zinc sulfate solution by subjecting a sample of the solution to electrolysis, burning the resulting 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, 6_0, 5, 417-423, 1968) describe methods to detect impurities and to measure the purity of zinc sulphate solutions by precipitating zinc and then electrolytically dissolving the precipitated zinc and relating the calculated current efficiency to the impurity content.

This second set of literature references relates to methods and apparatus for determining the purity of an electrolyte, in which the electrolysis of solutions is used to determine the current efficiency, which is then related to the purity of the electrolyte.

A method is known for controlling a process for recovering zinc from an electrolytic recovery solution of zinc sulphate and reducing the potential applied between electrodes in a test cell containing a sample of solution at a constant rate of substantially zero current, measuring a descending potential of 5 71027, stopping zinc begins to precipitate, the activation overvoltage is determined, the activation overvoltage is proportional to the concentration of impurities, and the process is adjusted to achieve optimum zinc recovery.

Although this method avoids the need to electrolyze the solution to determine current efficiencies or to measure polarization potentials for varying currents and current densities, it still has several disadvantages, the method is not continuous and it is necessary to determine the value of begins to precipitate and the current density increases substantially from zero for a still small potential decrease.

It has been found that it is unnecessary to calculate the potential used to determine the value of the activation overvoltage. It has been found that the activation overvoltage can be measured as a function of time at a controlled, low current and that purification and electroprecipitation processes can be adjusted by correcting reagent amounts for deviations from the overvoltage measured values to desired values to restore desired optimum values.

The method and apparatus of the present invention are applicable to electroprecipitation processes of metals using electrolytes prepared for electroplating metals; used in processes for the electrolytic recovery of metals or used in processes for the electrolytic cleaning of metals. In many cases, electroprecipitation processes include a purification process. The method and apparatus of the invention can be used in electroprecipitation processes for metals such as zinc, copper, lead, iron, cobalt, nickel, manganese, chromium, tin, cadmium, bismuth, indium, silver, gold, rhodium and platinum.

When a solution or electrolyte containing a metal ion is subjected to a controlled low current applied to electrodes placed in a test cell containing the electrolyte and the current has a value sufficient to cause the initial deposition of metal on a suitable cathode made of another material than the metal to be deposited, the value of the resulting potential represents the activation overvoltage for the cathode suitable for metal deposition. When the cathode is a moving cathode, the activation overvoltage values can be measured and recorded, and the electroprecipitation process of the metal can be controlled according to the measured and recorded values of the activation overvoltage. Initial deposition is defined for purposes of this invention as the deposition of a metal that has just begun and is limited to the partial coverage of a moving cathode surface by a metal. The measured values of the activation overvoltage can be used as a direct measure of the impurity concentration (i.e., the efficiency of the cleaning process), the polarization agent concentration, and the polarization agent concentration in the electrolyte to the impurity concentration in the metal electroprecipitation process. According to the measured values of the activation overvoltage, several changes are possible, either alone or together; the cleaning process can be adjusted; the concentration of the polarizing agent in the electrolyte can be adjusted; or the concentration of the polarizing agent in the electrolyte can be adjusted in proportion to the impurity concentration; and the impurity concentration can be adjusted to provide optimum efficiency and uniform metal deposits in the electroprecipitation process.

According to the invention, there is provided a method for controlling an electroprecipitation process of a metal which does not have the disadvantages of known solutions, comprising the steps of forming an electrolytic test current circuit comprising a test cell, an electrolyte sample, a moving cathode having a surface exposed to said electrolyte, an anode and a reference electrode din, which electrodes are embedded in said sample, a constant current source and a measuring means electrically connected to said electrodes 2; applying a small current (0.01-4.0 mA / cm 2, preferably 0.01-0.4 mA / cm) to the electrodes in said test cell, which current is sufficient to cause the initial deposition of said metal on said cathode; measuring an activation overvoltage at the point of onset precipitation of said metal; comparing the measured activation overvoltage to the concentration of impurities or said at least one polarizing agent or to the concentration ratio of the impurities to said at least one polarizing agent in said sample; and adjusting the concentration of said impurities or said at least one polarizing agent or said concentration ratio in the electrolyte to provide optimum efficiency and uniform metal deposits in an electroprecipitation process, wherein the initial deposition is defined as metal deposition that has just begun Other preferred embodiments of the invention appear from the appended dependent claims.

The invention will now be described in detail. The apparatus used in the method for measuring metal activation overvoltage consists of a test flow circuit comprising a test cell, an electrolyte sample, a moving cathode, an anode, a reference electrode, for supplying a constant current to the device and for measuring the activation overvoltage of the device. The test cell is a small container with a circular, square or rectangular cross-section of 8 71027, made of a suitable material which preferably withstands corrosion caused by the electrolyte, and is large enough to contain a suitable electrolyte sample. If desired, the cell may be ventilated to remove evolved gas. The cell is equipped with a device that makes it possible to continuously add electrolyte to the test tube and discharge the electrolyte therefrom. All three electrodes are immersed in the electrolyte sample and placed in a cell to be removed at constant distances from each other.

The movable cathode is made of an electrically conductive material other than the metal to be deposited, which material is suitable for use in the electroprecipitation process of the metal to be deposited and which is compatible with the electrolyte used in the process. The material of the moving cathode can be made of the same material used for the cathodes in the electroprecipitation process, provided that the material is different from the metal to be deposited. For example, in the control of electroprecipitation processes using a sulfate-based electrolyte, such as processes for the precipitation of zinc, copper, manganese, nickel, cobalt, iron and cadmium, the mobile cathode is preferably made of aluminum or a suitable aluminum alloy. If desired, other suitable materials such as titanium, iron, steel, stainless steel, nickel, lead, copper, etc. can be used in the electroprecipitation process. A movable, flexible plastic electrode of a suitable electrically conductive material could also be used.

The moving cathode has a constant area from its surface in contact with the electrolyte in the cell. It has been determined that an area in contact with the cell electrolyte of about 0.1-1 cm 2 gives excellent results. The movable cathode is preferably a wire or strip contained in and passing through the cathode holder. The rack surrounds the movable cathode except for a constant surface area in contact with the electrolyte. A device is connected to the device for moving the movable cathode intermittently or continuously through the cathode holder and thus in contact with the electrolyte. Preferably, this means includes the ability to move the cathode continuously at a constant speed of 9,71027. The use of a movable cathode made of wire or strip has numerous advantages. No special preparation of the cathode surface is usually necessary, the wire or strip is easily available at low cost and the test results are reproducible. The mobile cathode does not need to be replaced and thus allows intermittent or continuous operation. Most commercially available suitable cathode materials in wire or strip form are useful if they have sufficiently smooth and clean surfaces, good corrosion resistance properties in the electrolyte, if they are flexible enough to move through the cathode support, and if they have electrochemical properties that give reproducible test results.

The anode is made of a suitable inert material that allows gas to evolve. For example, in a sulfate electrolyte, a suitable anode material may be a lead-silver alloy. It has been found that for sulphate electrolytes, anodes made of a lead-silver alloy containing 0.75% silver are satisfactory and that for chloride-containing electrodes other than platinum containing concentrated hydrochloric acid is satisfactory. Other inert materials suitable for the anode include carbon and graphite. The reference electrode may be any of a number of suitable reference electrodes, such as a standard calomel electrode (SCE).

All three electrodes are electrically connected to a constant current source and a measuring device for activating overvoltage. The constant current source is connected to the anode and the moving cathode. The measuring device for the activation overvoltage measures the overvoltage in the moving cathode relative to the reference electrode. The measured activation overvoltage may be recorded, for example, by a meter or other suitable reading instrument, or alternatively it may be recorded in the form of a line and a mark as a function of time. The electrodes are removably placed in the cell in a fixed position relative to each other. It has been found that good results are obtained when the area of the moving cathode in contact with the electrolyte is kept at a fixed distance of about 4 cm from the anode surface and when the reference electrode is placed between the cathode and the anode 71027 10 so that the tip of the reference electrode is fixed n. 1 cm from the moving cathode, but does not cover the area in contact with the electrolyte. If desired, a diaphragm or semipermeable membrane may be placed in a test cell between the anode and cathode to provide separate anode and cathode compartments; the reference electrode is then placed in the cathode compartment.

A suitable means may be connected to the apparatus for maintaining the electrolyte in the cell at a suitable constant temperature. Such a device may comprise a controlled heating / cooling device for the electrolyte before the electrolyte enters 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 invention, a sample of electrolyte, which may be basic, neutral or acidic and which may contain additives and which may be obtained from either the electrolyte purification process or the metal electroprecipitation process, is added to the test cell. To ensure reproducible results, the sample is kept in motion, for example by stirring or recycling. It is recommended to keep the sample in motion by continuously passing a small flow of electrolyte through the test cell. According to this preferred embodiment, the electrolyte sample is continuously removed from the purification or electroprecipitation process, passed through a test cell and then returned to the corresponding process. The electrolyte added to the cell can be adjusted to certain concentrations of the electrolyte components, such as the metal or acid content, to minimize any changes in the test method that may be caused by variations in the component concentrations in the electrolyte.

For example, in the electrolytic recovery of zinc, both zinc and acid concentrations can be adjusted. An adjustment of the zinc level to a concentration of 150 g / l could be used. Alternatively, the zinc concentration could be adjusted to 55 g / l and the acid concentration to 150 g / l. Concentrations between 1-250 g / l zinc and 0-250 g / l sulfuric acid have been found to be equally satisfactory for use in a test cell. When using a continuous sample flow, the excess electrolyte is discharged from the cell, for example by means of an overflow pipe.

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The moving cathode is passed through the cathode rack intermittently or continuously at a rate sufficient to allow the metal to begin to precipitate. Preferably, the moving cathode is continuously moved forward at a constant speed. The rate depends on the ratio between the cathode length and the cathode area, the value of the current density required for the initial deposition, the electrode area exposed to the electrolyte, the fraction of the exposed cathode surface covered by the precipitated metal and the weight of the precipitated metal. The speed also depends to some extent on the amount of electrolyte movement in the cell. Thus, the speed at which the cathode is moved through the cathode holder and, consequently, through the electrolyte may vary within a certain range of values. The overvoltage measured at speeds lower than the minimum speed is the metal overvoltage for this metal and not the metal activation voltage for the moving cathode. At speeds several orders of magnitude higher than the minimum speed, the amount of metal deposited may be insufficient to achieve reliable and reproducible values of activation overvoltage. Preferably, the speed at which the cathode is moved is 10-500 times the minimum speed. The minimum speed can be calculated using the following formula:. = äbcd · 'om / h mm xy where: a represents the ratio of cathode length to surface area, cm / cm 2 b represents current density, A / cm; 2 c represents the exposed area of the cathode, cm; d represents the electrochemical equivalent of the metal to be precipitated, g / Ah; x represents the metal-covered portion of the exposed cathode area; and y represents the weight of precipitated metal per unit area of the cathode, g / cm.

When moving the cathode intermittently, the average speed of movement should be at least equal to the minimum speed of continuous movement, while the periods when the cathode is stationary should not exceed the period causing more than the onset of precipitation.

12 71 027

A small current is applied to the anode and the moving cathode to cause the initial deposition of metal on the cathode. Preferably, this small current is set to a constant value. The current should be limited to low values that only cause initial precipitation. This is necessary to avoid metal precipitation on the previously precipitated metal, thus obtaining overvoltage values from the metal deposition on this metal and not the desired activation overvoltage values from the metal deposition on the moving cathode material. Therefore, precipitation of too much metal should be avoided. Preferably no more than approx.

10-30% of the cathode surface in contact with the electrolyte should be covered with the precipitated metal at any stage. The currents, expressed as the current density causing the initial deposition on the cathode moving at the speeds defined above, should be at least 0.01 mA / cm. With respect to the mobile cathode current densities described below, they are to be understood as referring to the exposed area of the mobile cathode. For currents below 0.01 mA / cm, expressed as current density, special measures may be required to achieve reliable measurements. For practical reasons, the current, expressed as 2 current densities, should be between 0.01 and 4.0 mA / cm.

Current values higher than the corresponding current density of 4.0 mA / cm2 require impractically high cathode travel rates.

Preferably, the current values, expressed as current density, are low

With 0.1-0.4 mA / cm. For example, for an incipient copper precipitation 2 for a moving aluminum cathode with a current density of 0.4 mA / cm and a surface area ratio of 2.4, the exposed area is 0.25 cm, of which 20% is covered by precipitated copper. 2 this 3a on which 7 x 10 g of copper / cm are precipitated, the minimum rate calculated from the above formula is about 0.20 cm / h. Using the same values for the parameters, the minimum speed for lead is about 0.65 cm / h, for zinc about 0.21 cm / h and for manganese about 0.17 cm / h.

The temperature of the electrolyte to be measured can be kept constant. Changes in temperature affect the measured activation voltage, eg a falling temperature raises the measured overvoltage. If desired, the cell and its contents are adjusted to a suitable, controlled constant temperature and maintained at a temperature which may be between 0 and 100 ° C, preferably between 20 and 75 ° C. If desired, the constant temperature may be approximately the same as the temperature of the electrolyte 71027 in the electroprecipitation process and / or the purification process, depending on the particular application. If the temperature is not kept constant, the value of the activation overvoltage must be corrected for temperature variations so that the test results are comparable.

The activation overvoltage is measured continuously or intermittently and is recorded on the moving cathode during the initial deposition of the metal. For the practice of the method of the present invention, the activation overvoltage is expressed as the value of the measured overvoltage at a current corresponding to a current density between about 0.01-4.0 mA / cm of cathode area, and preferably between about 0.1-0.4 mA / cm. The activation overvoltage is registered with a suitable reading instrument or alternatively is registered as a function of time. The registered overvoltage values are kept within the recommended range. This is accomplished by making adjustments to the cleaning and electroprecipitation processes when the overvoltage values deviate from the recommended range of values.

The activation overvoltage has values specific to each metal depending on the composition of the electrolyte. Since each electrolyte assembly can be purified to the optimum amount because it has the optimum range of polarization agent concentrations and the optimum range of polarization agent concentrations relative to its impurity concentration, the activation overvoltage also has a range of values required to achieve the desired optimum results. Any of a number of suitable polarizing agents known in the art can be used in the electroprecipitation processes of each metal.

One of the most commonly used polarizing agents is animal glue. It has been determined that increasing concentrations of impurities can cause a decrease in activation overvoltage, while increasing concentrations of polarizing agent increase overvoltage and increasing concentrations of depolarizing agent decrease overvoltage. If the value of the measured activation overvoltage in the electrolyte purification is too low, the impurity concentration is too high for optimal metal recovery in the electroprecipitation process. Thus, depending on the electrolyte configuration, the activation overvoltage is an indication of the efficiency of the purification process, and deviations from the optimum operation can be corrected by adjusting the 71027 14 purification process with respect to the activation overvoltage values, thereby decreasing the impurity concentration. Insufficiently purified electrolyte can be further purified in a further purification step or by recycling it in the purification process. For example, in zinc electrolytic recovery, repair of the zinc dust purification process can be accomplished by adjusting the purification process temperature, purification process duration, increasing the amount of zinc dust used, or increasing the amount of depolarizing agent such as antimony, copper, or arsenic present in the electrolyte.

If the value of the activation overvoltage measured for the electrolyte in the electroprecipitation process is too low, the concentration of polarizing agents in the electrolyte is insufficient to control the cathodic metal deposition in an appropriate manner, or the impurity concentration is too high relative to the polarizing agents. On the other hand, if the value is too high, the concentration of the polarizing agents is too high, resulting in a decrease in efficiency and a coarser metal precipitation. Thus, depending on the composition of the electrolyte, the activation overvoltage is an indication of the efficiency of the electroprecipitation process and deviations from optimal performance can be corrected by changing the concentration or nature of polarizing agents or changing the concentration ratio between polarizing agents and impurities in the electrolyte. The change in the concentration of the polarizing agents can be realized in a suitable manner, such as by increasing or decreasing the rate of addition of the polarizing agents to the electrolyte. Reduction of the concentration of impurities can be achieved by more efficient purification of the electrolyte before the electroprecipitation process. In the presence of an excessive concentration of polarizing agents, corrective action can also be taken by adding to the electrolyte a substance having opposite polarizing properties in a controlled manner to correct the ratio of impurities to polarizing agents. The addition of a depolarizing agent, if necessary, can be suitably made by a controlled addition of a metal salt which acts as a depolarizing agent, which addition results in a correction of the concentration ratio between the impurity and the polarizing agent. For example, in the electrolytic recovery of zinc, ionic antimony can be added as a depolarizing agent.

The method of the invention has numerous applications in processes for the electroprecipitation of metals. Thus, the method can be used before, during or after purification of the electrolyte and before, during or after electrodeposition of the metal from the electrolyte.

For example, in the purification of zinc sulfate electrolyte by electrolytic recovery of zinc, the method can be used to determine the degree of removal of iron oxide and to determine the degree of removal of impurities such as arsenic, antimony and germanium by means of iron oxides.

In the electroprecipitation process, the method can be advantageously used to determine the required amount of polarizing agents alone and in relation to the concentration of impurities, to determine the required amount of impurities relative to the concentration of polarizing agents, electrolyte supply or process electrolyte control and recycled electrolyte quality.

The invention will now be illustrated by the following non-limiting examples.

In the following examples, the activation overvoltage values were measured using a test cell with a sample volume of 500 ml. A certain volume of electrolyte was passed through the cell. A movable cathode consisting of a metal wire contained in a fixed cathode rack and passed through a fixed electrode was embedded in the electrolyte in the cell.

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into the cell so as to allow 0.25 cm 2 of the cathode to be exposed to the electrolyte, the anode and the SCE interposed between the cathode and the anode. The surface of the exposed area of the moving cathode was 4 cm from the surface of the anode and the tip of the SCE was 1 cm from the cathode so that the tip was not in a straight line between the anode and the exposed area of the cathode. The temperature of the electrolyte flowing through the test cell was adjusted to the desired value of 16,71027. The anode and mobile cathode were connected to a constant current source and the SCE and cathode were connected to an activation overvoltage measuring device using a voltmeter with a digital display and a plotter. The constant current was switched on to cause the initial deposition of metal on the moving cathode and the activation overvoltage values were measured and recorded. The metal-covered portion of the exposed cathode surface was 0.1.

Example 1 This example illustrates how activation overvoltage measurements can be used to control the electrical precipitation of copper. The activation overvoltage values were measured using a current corresponding to a current density of 1.0 mA / cm. The cathode was a 1.19 mm diameter aluminum alloy No. 1100 wire with a length to area ratio of 2.51 cm / cm. The minimum cathode flow rate through the electrolyte was calculated to be 1.09 cm / h. The cathode was moved through the cathode rack at a speed of 160 cm / h. The anode was a lead anode containing 0.75% silver. The electrolyte temperature was 50 ° C and the electrolyte flow rate was 660 ml / min. The values of the measured activation overvoltage were recorded on a recorder. The co-sulphate electrolyte contained 20 g / l copper and 150 g / l sulfuric acid as well as varying added amounts of glue, chloride and antimony.

2 The electroprecipitation process was performed at a current density of 400 A / m for 24 hours. After this 24 hour precipitation time, the precipitate was analyzed for its surface quality and formability. The formability was determined by the number of times the precipitate could be bent 180 ° before it showed cracking. The amounts of additives added to the electrolyte, the average of the recorded values of activation overvoltage for each electrolyte assembly, and the grades of electroprecipitated copper are given in Table 1.

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Table I

Test Added to electrolyte Activation-Formability Precipitate No. glues Cl Sb ions overvoltage 180 ° bending character _ mg / 1 Rog / 1 mg / 1_ mV number of strokes. _ 1 0 - 118 10 rough 2 2,5 - - 122 15 rough 3 5,0 - - 132 14 flat 4 7,5 - - 140 20 flat 5, 10 142 15 rough 6 20 - - 150 16 rough 7 0 1 - 129 29 rough 8 0 10 - 140 25 rough 9 0 30 - 145 10 rough 10 5 1 - 140 6 flat 11 7.5 1 - 143 7 rough 12 5 10 - 180 7 rough 13 5 30 - 182 10 rough 14 0 300 118 12 rough 15 2,5 - 300 125 7 flat 16 5 300 128 22 flat 17 10 - 300 153 18 rough 18 20 - 300 164 7 rough 19 0 10 300 140 25 rough 20 5 10 300 178 23 flat 21 30 10 300 203 LI rough 22 5 1 300 136 11 flat 23 5 30 300 181 13 flat 24 5 30 20 180 16 flat

The results of Experiments 1-6 show that the activation voltage values increase as the amount of adhesive in the electrolyte increases. To obtain a uniform precipitate, the activation overvoltage should be adjusted to between about 130-140 mV and the amount of adhesive in the electrolyte should be adjusted when the measured value of the activation overvoltage was outside this range.

The results of Experiments 7-13 show that the presence of chloride in the electrolyte results in coarse fines which, in addition to the presence of adhesive, also become less malleable.

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The results of Experiments 14-18 show that when the electrolyte contains antimony and increasing amounts of glue, the overvoltage values increase, but that the results of the precipitate formability test become irregular. To correct this irregular behavior, chloride must also be present. As can be seen from the results of Experiments 19-24, the presence of about 10 mg / L of chloride as well as 5 mg / L of adhesive gives smooth and malleable precipitates in the presence of antimony. In such a system, the activation overvoltage values are about 180 mV and the system can be adjusted to approximately this value by making sensible adjustments to the concentrations of either the adhesive or chloride, or both.

Example 2 This example illustrates how activation overvoltage measurements can be used to control the electroprecipitation of manganese. The activation overvoltage values were measured using a current corresponding to a current density of 1.0 mA / cm. The cathode was a 1.19 mm diameter aluminum alloy wire No. 1100 with a length to area ratio of 2.51 cm / cm 2. The minimum cathode velocity through the electrolyte was calculated to be 0.92 cm / h. The cathode was moved at a speed of 160 cm / h. The anode was a lead cyanide diode containing 0.75% silver. The electrolyte temperature was 50 ° C and the electrolyte flow rate was 660 ml / min. Measured activation overvoltage values were recorded on a recorder. The manganese sulfate electrolyte contained 45 g / L manganese sulfate, 135 g / L ammonium sulfate, and 0.1 g / L sulfur dioxide, as well as varying amounts of glue, copper, nickel, zinc, and antimony. The pH of the electrolyte was 7.0. Electrodeposition of manganese at a current density of 2,400 A / m requires the presence of 8-16 mg of adhesive / l of purified electrolyte to achieve optimum current efficiency and uniform fines. The values of the activation overvoltage for the electrolyte with certain additions are given in Table II.

Table II 71027 19

Additions to the electrolyte, mg / l Activation overvoltage glue Cu Ni Zn Sb _ mV_ 0 166 4 172 8 174 12 179 16 183 20 - - 190 24 196 0 5 - - 155 0 10 151 16 10 - - 151 0 - 1 168 0 - 2 166 16 2 - 183 16 10 2 - 158 0 0,5 - 168 0 - - 1 164 16--1-178 0 - - 1 166 0 - - - 10 160 0 --- 25 137 8 --- 25 139 20 - - 25 139 50 - 25 143 16 - - 1 1 172 16 - - 1 10 164

From the tabulated results, it can be seen that the adhesive acts as a polarizing agent, that copper, zinc and antimony act as depolarizing agents, and that the nickel is substantially inactive. Thus, increasing amounts of adhesive have the effect of increasing activation overvoltage values, whereas copper, zinc, and antimony have the opposite effect. The results also show that optimum adhesive levels of 8-16 mg / 171027 in purified electrolyte result in activation overvoltage values between 174-183 mV and that the amount of adhesive must be increased when depolarizing agents (impurities) are present in small concentrations to restore activation voltage values to the desired range 174-183. When impurity concentrations higher than a few mg / l are present, the method for electrolyte purification should be improved. In this connection, it also follows from the test results that the efficiency of the purification process can also advantageously be monitored by measuring the electrolyte activation surge.

Example 3 This example illustrates how activation overvoltage measurements can be used to control the electrical deposition of nickel. T'ktivoin overvoltage values were measured at 55 ° C using a current that

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corresponded to a current density of 1 mA / cm. The cathode was a 1.19 mm copper wire with a length to area ratio of 2.51 cm / cm 2. The minimum cathode flow rate through the electrolyte was calculated to be 0.98 cm / h. The cathode was moved through the cathode rack at a speed of 160 cm / h. The anode was a lead anode containing 0.75% silver.

The electrolyte temperature was 55 ° C and the electrolyte flow rate was 660 ml / min. The values of the measured activation overvoltage were recorded on a recorder. The electrolyte contained 50 g / l of nickel as nickel sulphate, 40 g / l of sulfuric acid, 90 g / l of sodium chloride and 16 g / l of boric acid and varying amounts of glue or lauryl sulphate. Sodium lauryl sulfate is an additive in the electrolytic recovery of nickel, which prevents pitting of doped nickel, and an adhesive is added in nickel electroplating as a leveling agent. The results are given in Table III.

Table III

Additions to electrolyte, mg / l

Sodium lauryl sulphate Adhesive Activation overvoltage, mV

0-70 5 - 50 20 - 44 - 0 70 - 5 84 50 93 21 71027

It can be seen from the results that sodium lauryl sulfate acts as a depolarizing agent and when present in increasing amounts it decreases the activation overvoltage values and that the adhesive acts as a polarizing agent and when present in increasing amounts it raises the activation overvoltage values. The values of the activation overvoltage can be kept at the desired values by adjusting the concentration of the additive which changes the polarization.

Example 4 This example illustrates how activation overvoltage measurements can be used to control the electrical precipitation of lead. The activation overvoltage values were measured using a current corresponding to a current density of 4.0 mA / cm. The cathode was a 1.19 mm diameter copper wire with a length to area ratio of 2.51 cm / cm. The minimum cathode flow rate through the electrolyte was calculated to be 13.8 cm / h. The cathode was moved through the cathode rack at a speed of 160 cm / h. The anode was a lead anode containing 0.75% silver.

The electrolyte temperature was 40 ° C and the electrolyte flow rate was 660 ml / min. The values of the measured activation overvoltage were recorded on a recorder. The lead fluorosilicate electrolyte contained 75 g / l lead as lead fluorosilicate, 90 g / l fluorosilicic acid, and varying amounts of ECA (Aloes extract), lignin sulfonate and sodium thiosulfate. Electrolysis was performed for 24 hours at a current density of 200 A / m 2 at 40 ° C using lead ingots to obtain a lead precipitate. The quality of the lead precipitate was determined.

Electrolyte additions, activation overvoltage, and the nature of the lead precipitate in each experiment are shown in Table IV.

2 2 710 9 7

Table IV <'Ό <L (

Addition to electrolyte____

Lignin sul- Sodium sul- Activation1j- Precipitation ECA phonate phate voltage nature

rag / 1 mg / 1 mg / 1_ mV

00 0 16 rough 04 0 3 5 rough 0.5 4 0 40 rough 1.0 4 0 43 rough 1'5 4 0 46 flat 2/0 4 0 62 flat 3.0 4 0 58 rough 3.0 4 50 18 rough

From the results in Table IV, it can be seen that both ECA and lignin sulfonate act as polarizing agents and sodium thiosulfate acts as a depolarizing agent. In the electroprecipitation of lead, the amount of lignin sulfonate is usually kept substantially constant, while the amount of ECA is adjusted to keep the activation overvoltage in the desired range of 45-55 mV to obtain a uniform and horizontal lead precipitate. When the desired activation overvoltage values are exceeded, sodium thiosulfate can be added to return the Akti lubrication overvoltage value to the desired range.

These examples relate to the electrolytic recovery of zinc. The moving cathode was a 1.19 mm diameter a luminescent alloy wire No. 4043 with a length to surface area ratio of 2.51 cm / cra. The anode was a lead-silver alloy containing 0.75% silver. The minimum cathodic motion was calculated to be 1.06 cm / h.

Example 5 This example illustrates the effects of changes in the current density of the applied current, the cathode wire speed, the electrolyte temperature and the electrolyte flow rate. The amount of electrolyte in the plant was analyzed and adjusted to 55 g / l Zn and 150 g / l H 2 SO 4. 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 Go, 8.5 mg / l Cd, 30 mg / l Cl and 2 mg / l F. The adjusted electrolyte was continuously passed through the cell and the activating overvoltage 23 71 027 was measured and recorded as described. The results are listed in Table IVA.

Table IVA

Test Current- Mobile ka- Electrolyte Electrolyte Activation No. Density Todin velocity, temperature flow rate overvoltage, _ mA / an2 cm / h_ ° C_ ml / inin_ mV_ 55 0.1 60 30 668 10 56 1.0 60 30 668 75 57 1.0 180 30 668 82 58 1.0 300 30 668 90 59 1.0 60 21 668 83 60 1.0 60 35 668 55 61 1.0 60 60 668 20 62 1.0 60 30 668 70 63 0 , 4 60 30 668 35 64 2.0 60 30 668 75 65 4.0 60 30 668 115

The results clearly show the effect of the method variables and the need to use standardized conditions for practical application.

Example 6 This example illustrates the effects obtained by varying the amounts of antimony, gemranium, cobalt and glue added to a controlled electrolyte having the composition shown in Example 5. The activation overvoltage was measured using a current corresponding to a current density of 1.0 mA / cm 2, a cathode speed of 160 cm / h, an electrolyte temperature of 35 ° C and an electrolyte flow rate of 660 ml / min. The values of the measured activation overvoltage were recorded on an x-y plotter. The results are listed in Table V. In the table, the overvoltage values represent the average recorded value.

71027 24

Table V

Test Additions, mg / 1_ Activation overvoltage No. Glue Sb Ge Co _ mV_ 66 0 0 0 0 80 67 10 0 0 0 98 68 20 0 0 0 110 69 30 0 0 0 120 70 0 0.02 0 0 58 71 10 0.02 0 0 89 72 20 0.02 0 0 106 73 30 0.02 0 0 109 74 0 0.04 0 0 53 75 10 0.04 0 0 90 76 30 0.04 0 0 96 77 5 0 06 0 0 76 78 0 0.08 0 0 50 79 10 0.08 0 0 78 80 30 0.08 0 0 83 81 0 0 0.04 0 70 82 30 0 0.04 0 116 83 0 0.04 0 2.0 55 84 30 0.04 0 2.0 105

The results show that increasing concentrations of adhesive increase the activation overvoltage of zinc and that increasing concentrations of impurities decrease its overvoltage.

Example 7 This example demonstrates that increasing concentrations of adhesive are required to obtain good current efficiency when increasing concentrations of impurities are present in the electrolyte and that there are optimal ranges for adhesive concentrations relative to the impurity concentrations that give the highest current efficiency. Samples of a controlled plant electrolyte such as that used in Example 6, to which varying amounts of glue and antimony and / or cobalt as potassium antimony tartrate and cobalt sulfate were added, were subjected to electrolysis at a current density of 400 A / m at 35 ° C for 24 hours. The current efficiencies for zinc precipitation were determined by determining the ratio of the weight of precipitated zinc to the calculated weight based on the total amount of current 71027 passed through the cell for zinc precipitation. The results are shown in Table VI.

Table VI

Test Glue added, mg / 1 0 10 15 20 25 30 40 45 50 No. Sb added Co added mg / 1 mg / 1 Current efficiency,% 85 0.01 0 88 92 91 90 89 88 87 87 85 86 0.03 0 79 90 92 93 92 91 89 88 87 87 0.05 0 56 86 90 92 93 93 92 91 88 88 0.07 0 43 72 81 85 89 92 93 92 89 89 0.01 0.05 89 92 92 91 90 89 88 87 85 90 0.01 2 88 92 92 92 92 91 91 90 89 91 0.01 5 65 87 92 92 92 92 92 92 91 92 0.01 5 * - 43 74 82 82 81 79 77 75 93 0 03 0.05 80 90 92 93 93 91 90 88 86 94 0.03 1 40 74 85 92 94 93 92 91 89 95 0.03 5 - 58 74 87 92 94 94 93 90 96 0.03 5 * 40 72 82 83 83 78 χ 48-hour precipitate

The tabulated results show that a corresponding narrow range of adhesive concentrations was required for each antimony concentration to give the highest possible current efficiencies. Current efficiencies decreased with both too low and too high adhesive concentrations. Thus, there are optimal concentrations for each antimony concentration. Just as antimony and cobalt are present, adhesive additions are required to counteract the detrimental effects of these contaminants and optimum adhesive concentrations exist for each antimony and cobalt content. The OP glue concentrations were the same for the 48-hour and 24-hour fines, but the current efficiencies had decreased.

Example 8

The activation overvoltage values obtained with the adhesive and impurity concentrations obtained in the experiments described in Examples 5 and 6 and Tables IV and V were combined with the maximum current efficiency ranges with the combinations of adhesive and impurity concentrations obtained in the experiments described in Example 7 and Table VI. Thus, the following ranges of values were obtained for the optimum current efficiency with respect to the ratios of adhesive to impurities indicated by the activation overvoltage values. The areas are listed in Table VII.

Table VII

Activation overvoltage Current efficiency range,% ____mV__ _ 75 75-83 80 79-86 85 83-89 90 86-91 95 88-93 100 90-94 105 90-94 110 89-93 115 87-92 120 86-89 125 83- 87

From the figures listed, it can be seen that the highest ranges of current efficiencies are obtained when the activation overvoltage is kept between 90 and 115 mV measured at 35 ° C.

Example 9 This invention illustrates that activation overvoltage measurements can be used to determine whether the electrolyte has the correct adhesive concentration relative to the impurity concentration and what changes are required to optimize the electrolytic recovery process of the adhesive zinc. Using the same electrolyte as used in the previous examples, the experiments described in Example 6 were repeated, the current efficiencies were determined as in Example 7, and the results were combined as described in Example 8. Using the results of the experiments of this example, the required change in adhesive concentration in mg / L of the activation overvoltage was determined from the measured values to obtain an optimum value for the current efficiency in the electrolysis process. The data presented in Table VIII represent a program for controlling the electrolytic recovery process of zinc by making defined changes to the adhesive content in the zinc electrolyte.

27 71027

Table VIII

Measured activation over- Voltage required for optimum current efficiency, mV at 35 ° C adhesive concentration change mg / l; silicon 75 increase 9: 11a 80 increase 7: 11a 85 increase by 5 90 increase 3: 11a 95 increase 1: 11a 100 no change 105 no changes 110 decrease by 1 115 decrease by 3 120 decrease by 5 125 decrease by 7 130 decrease by 9

Example 10 This example demonstrates that antimony can be used relative to measured activation overvoltage values to adjust the zinc electrolytic recovery process to an optimum current efficiency.

Both glue and antimony are added to a series of electrolytic recovery cells using an acidic zinc sulfate electrolyte having the controlled composition given in Example 5. The adhesive is added to the electrolyte in a constant amount of 20 mg / l, while antimony is normally added in an amount of 0.04 mg / l.

Using the electrolyte and the above-mentioned adhesive and antimony additions, activation overvoltages and current efficiencies were determined as in Example 9. Optimum values of current efficiencies were achieved at activation overvoltages of 100 and 105 mV. Using the results of these assays, the required changes in antimony concentrations in the electrolyte in mg / L were determined from the values measured for the activation overvoltage to obtain the optimum value for the current efficiency of the electrolysis process. The adjustment program is shown in Table IX.

28

Table IX 710 2 7

Measured activation- Overvoltage required for optimum current efficiency, mV_ change in antimony content mg / 1 85 decrease 0.03 90 decrease 0.02 95 decrease 0.01 100 no change 105 no change 110 increase 0.01 115 increase 0 , 02: 11a 120 increase 0.03: 11a

Example 11 This example shows that the removal of impurities from a neutral zinc electrolyte by settling with zinc dust can be monitored by activation overvoltage measurements. The impure plant electrolyte was purified with varying amounts of zinc dust, which was added to the electrolyte containing previously added antimony as antimony potassium tartrate in varying amounts. The settling was performed at 50 ° C with stirring and using a residence time of one hour. The purified electrolyte stream was filtered and cooled to 35 ° C. The flow was then passed through a test cell for measuring the activation overvoltage. The purified electrolyte was analyzed to determine impurity concentrations. The results are listed in Table X.

Table X

Added Sb, Added zinc- Activation- Purified electrolyte mg / 1 dust, g / 1 overvoltage, mv impurities, mg / 1_ _ _ _ Cd Cu Co Ni Sb 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 0.75 1.0 64 12 3.4 0.3 0.5 0.05 0.75 1.5 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 .07.50 2.0 74 2.2 0.6 0.1 0.1 0.03 1.00 2.0 85 0.6 0.6 0.1 0.1 0.02 71 027 29

Example 12 This example shows how activation overvoltage measurements such as those in Example 11 can be used to determine what process corrections need to be made to control the addition of variables such as zinc dust and antimony to optimize zinc dust purification of the electrolyte. The results shown in Table XI show a program for controlling the zinc dust purification process by making determined changes to the additions of zinc dust or antimony salt to the zinc electrolyte during purification if the measured activation overvoltage indicates that purification is not complete.

Table XI

Measured activation overvoltage Required increments_ in mV for neutral electro- Zinc dust Antimony for lithium_____g / 1_ mg / 1 80 0 0 75 0 0 70 0.3 0.1 65 0.6 0.2 60 0.9 0.3 55 55 1.2 0.4 50 1.5 0.5 45 1.8 0.5 40 2.1 0.5

Claims (7)

A method of controlling an electric precipitation process for metal using an electrolyte containing impurity levels and / or at least one substance which affects the polarization, characterized in that it comprises steps in which an electrolytic sample flow circuit is formed, which comprises a sample cell, an electrolyte sample, a movable cathode whose surface responds to said electrolyte, an anode and a comparison electrode, which electrodes are immersed in said sample, a constant current source, and a measuring instrument electrically connected to said electrode. 2 rudders; a layer of current (0.01-4.0 mA / cm, preferably 0.01-0.4 2 mA / cm) is run in the electrodes of said sample cell, which current is sufficient to induce the onset of said metal at said cathode; the activation overvoltage at the point of the initial precipitation of said metal is measured; the measured activation overvoltage is matched to the content of impurities or said eating tone to a substance acting on the polarization or to the relationship between the impurities and said eating at least one substance acting on the polarization in said sample; and the content of impurities or said at least one substance acting on the polarization or said content ratio is controlled in the electrolyte to provide an optimum utility ratio and even metal precipitation in the electrical precipitation process, where the initial precipitate is defined as precipitation of the metal, which is just as precipitation of the metal. limited to the extent that the surface of the movable cathode is partially covered with the precipitated metal. 2. A process according to claim 1, characterized in that the content of substances which act on the polarization is controlled either by increasing the amount of substance present or by adding another substance which has an effect on the polarization, which has opposite properties affecting the polarization in relation to that already present. the substance that has an effect on polarization. Process according to claim 1, characterized in that the ratio of the content is regulated by changing the content of impurities in the electrolyte.