JPH0920989A - Zinc electrolyzing method for controlling pb grade in electrolytic zing by using automatic pb analyzer - Google Patents

Abstract

PURPOSE: To efficiently and stably produce the electrolytic zinc low in Pb by continuously monitoring the Pb concn. in a zinc electrolyte to predict the Pb grade of an electrolytic zinc slab and controlling the amt. of an additive to be added and so on. CONSTITUTION: An anode 2 consisting of lead electrode and a cathode 3 are dipped in a zinc electrolyte, power is supplied from an SCR 5 to bring about electrolysis, and an electrolytic zinc slab is deposited on the cathode 3. In this zinc electrolyzing method, the overflowing waste electrolyte is introduced into a circulating tank 6, a frsh electrolyte is replenished to make up for the deficiency, the mixture is transferred to a mixing tank 4 through a circulating pump 7, a lead absorptive additive such as strontium carbonate is added, and the admixture is returned to an electrolytic cell. In that case, the waste electrolyte is sampled in a lead analyzer 8, the Pb in the electrolyte is measured at least every 120min, and the amt. of additive to be added is controlled. A stripping voltammetry analyzer is used as the lead analyzer 8, and the Pb is preferably measured at 43-43 deg.C. An ultrapure zinc contg. <=10ppm Pb is obtained in this way.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to hydrometallurgical zinc smelting, and more particularly to a method for smelting high-purity electrolytic zinc for economically electrolytically extracting high-purity electrolytic zinc having low lead grade.

[0002]

2. Description of the Related Art FIG. 2 shows a system diagram of an electrolysis process in wet zinc smelting. The anode (anode) 2 and the cathode (cathode) 3 immersed in the electrolytic solution in the electrolytic cell 1 are connected to the positive and negative electrodes of the SCR (rectifier), respectively, to supply electric power. The electrolytic solution (electrolytic drainage solution) overflowing from the electrolytic cell 1 is collected in the circulation tank 6, and the electrolytic solution having the zinc concentration increased by adding and mixing the electrolytic stock solution is mixed by the circulation pump 7 to add the additive. It is returned to the electrolytic cell 1 via the cell 4. The anode (anode) 2 is generally made of sulfuric acid-insoluble lead or lead-silver (1 to 3% Ag-containing alloy), and although this is a very small amount during electrolysis, lead ions or It migrates as lead oxide fine powder, and a part of this is deposited or adhered on the cathode (cathode) 3 and mixed into the deposited zinc. Since it is impossible to separate lead from zinc in the casting process where molten zinc is melted and cast into electric zinc, a method has been developed to remove lead that has migrated into the electrolytic solution by adsorbing it to an additive. , Is generally done. That is, FIG.
In the mixing tank 4 described above, a small amount of strontium carbonate or barium carbonate is added to the electrolytic solution to adsorb and remove lead ions and lead oxide fine powder in the electrolytic solution, thereby preventing the zinc from depositing on the cathode plate. . Precipitated zinc is electrodeposited for several hours to several tens of hours for post-analysis, so whether the additive amount of the additive was appropriate during the course of electrolysis, and to control the lead content to a predetermined value, for example, additive amount It is inevitable to judge from the analysis result of the deposited zinc to verify how effective the action is to increase or decrease the temperature, change the control temperature of the electrolytic solution, detect and cope with abnormal occurrence in the process, Since it is often a time lag and proper measures cannot be taken, it is unavoidable that additives are added in a fairly excessive amount in consideration of safety.

The lead content of pure zinc is 30 ppm or less and JI
Although it is regulated by S, in recent years, the demands on the quality of customers have become strict, and the demand for 10ppm or less, which is said to be a low lead product, is increasing. Thus, it has become necessary to efficiently and stably produce low lead grade zinc.

[0004]

The object of the present invention is to study a rapid method for analyzing lead in an electrolytic solution in order to solve the above-mentioned problems, devise a method for incorporating it into an electrolysis process, and obtain a lead content. Is to develop a method for efficiently and stably producing the most pure zinc having a concentration of 10 ppm or less.

[0005]

In order to solve such a problem, the present inventors first observed the behavior of lead in the electrolyte that is constantly circulated, and examined the sampling location and sampling method. . As a result, by continuously monitoring the Pb concentration of the electrolytic solution, the Pb quality of the electrozinc slab is predicted, and based on this prediction, the additive amount of the additive is controlled to control the operating conditions of the process. It has been found that high-quality, low-cost electrolytic zinc can be stably produced by properly controlling the Pb concentration of the electrolytic solution. Here, “continuously monitoring” means that at least 12 electrolytes are constantly circulated.
Once every 0 minutes, preferably once every 60 minutes, it is taken from the electrolytic solution immediately after being discharged from the electrolytic cell, and this sample solution is analyzed within 10 minutes, preferably within 5 minutes, and the lead of the electrolytic solution is analyzed. A method of confirming the content. As a result, it is possible to take action measures such as adjusting the amount of additives required to maintain the lead content in the deposited zinc at a prescribed level, changing the electrolyte control temperature, and checking process abnormalities. The amount is 10ppm
The following pure zinc could be efficiently and stably produced.

An apparatus for measuring the lead content of an electrolytic solution does not require pretreatment of a sample, and can perform accurate measurement in a short time.
We have found that the stripping voltammetry device is most suitable because of its low cost and easy integration as an automatic control device.

As a method for controlling the lead content in the electrolytic solution, the strontium carbonate addition method is generally known.
It is well known from experience that the lead content in precipitated zinc is further reduced by increasing the addition amount.

The temperature of the electrolytic solution, the circulating fluid amount, the current density,
It is known that the suitability of the electrode arrangement also affects the lead content in the electrolytic solution, but according to the present invention, the inclusion of lead in the electrolytic solution is caused by a factor such that an abnormality occurs in the process. Even if the amount rises, it can be detected early so that it can be dealt with promptly.

The present inventors have found that the lead content of precipitated zinc is 10 pp.
In order to maintain the temperature at or below m, the lead content in the electrolyte should be less than 0.2 under the electrolytic conditions of the temperature of the electrolyte of 42 ° C., the circulation rate of 1 cycle / 30 minutes, and the current density of 400 A / m ² . It was confirmed that it is necessary to control to 12 ppm or less, preferably 0.10 ppm or less. However, the process to be measured cannot be accurately controlled unless the sample to be measured is taken from the drainage of the electrolytic cell before adding the additive. An empirical formula showing the relationship between the amount of strontium carbonate added and the lead concentration in the electrolyte was obtained based on the data obtained from various experiments and actual operations.

Lead concentration = A (strontium carbonate) + B where A and B are constants obtained from actual operation. The addition amount of strontium carbonate is calculated from this formula.

[0011]

The essence of the present invention is to quickly and accurately measure the lead content contained in the zinc electrolyte. For this purpose, it is necessary to use an analytical method that can automatically obtain a measured value in a short time without requiring pretreatment of the electrolytic solution sample. Microanalysis methods include colorimetric analysis, emission spectroscopic analysis, atomic absorption analysis, and ICP analysis, but none of them can directly use the zinc electrolyte solution as a sample, and in any analysis method, lead analysis accuracy is high. Badly adopted.

On the other hand, in the polarographic method and the stripping voltammetry method, the zinc electrolytic solution can be directly measured as a sample, and the analysis accuracy for lead is not so low. Polarographic analyzer P1100 was adopted. This analyzer can be applied to both polarographic method and stripping voltammetric method. The polarographic method here is a method of knowing the target ion concentration by measuring the current value at each potential while gradually decreasing the cathode potential (the current value at a specific potential is the number of ions deposited on the cathode at that time). The stripping voltammetry method keeps the cathode below the deposition potential of the target ions, performs preliminary electrolysis at a constant potential for a certain period of time, and after the preliminary electrolysis, gradually raises the cathode potential to each potential. Is a method of knowing the target ion concentration by measuring the current value at (the current value corresponds to the number of ions eluted from the cathode). For the purpose of the present invention, it was confirmed that the latter has a higher analysis accuracy. With this device, it is possible to perform analysis without pretreatment of the sample electrolyte, so a portion of the electrolyte is extracted from the electrolyte, put on the analyzer as is, and the switch is turned on to immediately calculate the lead concentration and display it on the CRT. To be done. in this case,
By taking the method of stripping voltammetry by keeping the temperature of the sample electrolyte solution for analysis at a constant value within the range of 41 to 43 ° C, it is possible to obtain lead analysis values of surprisingly stable and high precision rapidly. I found it. Therefore, by this method, the operator can confirm the CRT and substitute it into the above-mentioned empirical formula: A (strontium carbonate) + B to know the proper addition amount of strontium carbonate and precisely control it.

Thus, the operator can immediately adjust the input amount of strontium carbonate. Furthermore, by linking the CRT display and the additive injection device, complete automation becomes possible.
That is, the object of the present invention has been completely achieved.

Next, the present invention will be described in more detail by way of examples.

[0015]

【Example】

1. Measuring apparatus The analyzing apparatus used in the present invention is a polarographic analyzer P1100 manufactured by Yanaco Co., which has a Zn of 53 g / l,
Three levels of lead were added to a H ₂ SO ₄ 190 g / l solution to prepare a sample solution. These sample solutions were analyzed by the stripping voltammetry method using the above-mentioned analyzer to examine the analysis accuracy, and the result was ± 0.01 mg / l. The time required for measurement was 10 minutes or less.

2. Installation Position and Operation of Measuring Device FIG. 1 shows a position where the measuring device according to the present invention is installed in FIG. 2 showing a conventional zinc electrolysis process. In the figure, 8 is a lead analyzer,
9 is a CRT. A part of the electrolytic solution (electrolytic drainage solution) discharged from the electrolytic cell 1 is directly diluted in the measuring instrument without the need of diluting and charging the reagent. The analytical value is calculated as the concentration of lead (Pb) and displayed on the CRT 9. The operator confirms the CRT display, calculates the necessary amount of strontium carbonate by the above-mentioned empirical formula: lead concentration = A (strontium carbonate) + B, and puts it in the mixing tank 4 for adding the additive. Complete automation can be achieved by installing a charging device that combines CRT display and empirical formula.

3. Measurement results In order to investigate the effect of the present invention, the effect of the conventional zinc electrolysis operation process and the operation in which the apparatus and the work process according to the present invention are incorporated is circulated, the transition of the lead content in the zinc electrolytic solution and the product, the maximum The lead content in pure zinc and the input unit of strontium carbonate were compared.

(I) Operation according to the present invention (example of control) When the operation is performed based on the process according to the present invention, as shown in FIG.
As shown in, the Pb ²⁺ ion concentration in the electrolyte is 0.10 pp
It was confirmed to be controlled below m. FIG. 4 illustrates the transition of the lead content in the product zinc and the basic unit of the additive when the Pb content in the electrolytic solution is controlled. As a result of controlling the lead content in the electrolytic solution to 10 ppm or less as Pb ²⁺ , the lead content in the purest zinc in the product is 10 ppm or less, the variation in the additive usage amount is small, and 1 ton of deposited zinc is 1 It was 12 kg, which is a decrease from the past.

(Ii) Operation by Conventional Operation (Comparative Example) FIG. 5 shows the relationship between the lead content in the product zinc and the additive basic unit by the conventional operation. The lead content in the product zinc exceeds the upper limit of 10 ppm, and there are large variations. In addition, since the change in the basic unit of the additive is large and the variation is large, it can be seen that the adjustment of the additive has been delayed. Furthermore, the average additive amount of the additive is as high as 1.23 kg per ton of deposited zinc.

[0020]

According to the method of the present invention, at least one part of the electrolytic cell discharge liquid in the electrolysis step is used as an analytical sample.
Once every 20 minutes, preferably once every 60 minutes, lead analysis is carried out by a stripping voltammetry device as it is, in order to control the lead content in the precipitated zinc, adjustment of the additive addition amount, Since it became possible to immediately know the action effects such as temperature control, detection of abnormalities in the process, and quick response, the additive amount could be saved and the pure zinc with a lead content of 10 ppm or less would be efficient. It has become possible to produce well.

[Brief description of drawings]

FIG. 1 is a zinc electrolytic operation system diagram according to the present invention in which a lead analyzer is incorporated in a conventional zinc electrolytic operation process.

FIG. 2 is a conventional zinc electrolytic operation system diagram.

FIG. 3 is an example of a chart showing the transition of the lead content in the electrolytic solution during one day in the operation according to the present invention.

FIG. 4 is a control chart of the lead content of the product zinc and the strontium carbonate basic unit in the operation according to the present invention.

FIG. 5 is a control chart of lead content of product zinc and strontium carbonate basic unit in a conventional operation.

[Explanation of symbols]

 1 Electrolysis tank 2 Anode 3 Cathode 4 Mixing tank 5 SCR 6 Circulation tank 7 Circulation pump 8 Lead analyzer 9 CRT

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Taro Aichi 217-9 Shimokawabata, Koichi Iwajima, Akita City, Akita Prefecture Akita Smelting Co., Ltd.

Claims (4)

[Claims] 1. A Pb grade of an electric zinc slab is predicted by continuously monitoring a Pb concentration in an electrolytic solution,
A zinc electrolysis method characterized in that the Pb quality in electrozinc is controlled by performing a process operation including control of the additive amount based on this prediction. 2. The lead content of the precipitated zinc is controlled by measuring the lead content in the electrolytic solution at least once every 120 minutes as the continuous monitor and operating the electrolysis step. The zinc electrolysis method according to claim 1. 3. The electrolytic solution sample used for the measurement is taken from the electrolytic solution discharged from the electrolytic cell before adding the additive, and the lead content is measured by an analyzer to obtain an experimental formula prepared in advance. The zinc electrolysis method according to claim 2, wherein the additive addition amount is controlled by fitting, calculating the additive addition amount, and adding. 4. A stripping voltammetry analyzer is used as a device for measuring the lead content in an electrolytic solution,
The lead ion concentration of the electrolyte is measured while maintaining the temperature of the analytical sample of the electrolyte at 41 to 43 ° C.
The zinc electrolysis method described.