JPS592756B2 - electrolytic cell - Google Patents

Description

[Detailed description of the invention] The present invention relates to a novel electrolytic cell.

More specifically, the electrolytic cell 3 can be used for electrolytic deposition of metals from dilute solutions when high deposition rates are required.
Regarding 0. Conventionally known electrolytic cells with plate or mesh electrodes (C, L, Ma
Electrochemical Technology (Electroch.
McGraw Bill Inc. 35 Rated (McGrawH)
Ill Inc., New York, 1960), when the concentration of the metal to be precipitated is less than 5 g/l, the gate L Fu is used for electrolysis of dilute solutions, and the space-time yield is so low that it cannot be used industrially. ) (hereinafter simply referred to as STY).

In that case, well-known porous electrodes or packed bed or fluidized bed electrodes can be used to obtain considerably high STY (
For example, D.N. BenniO
n), J. Newman;
Appl. ElectrOchem. , Volume 2 (197
2), 113 pages, A.K.P.C.
P. Chu), M. Fleischmann
chmann), G.J.Hi
lls): J. Appl. ElectrOchem. ,
Volume 4 (1974), p. 323, M. Fleischman, J.W.Ol.
dfield), L. Tennal
cOOn);J. Appl. ElectrOchem.
, Volume 1 (1971), p. 103, H.R. Backhurst, M.
Fleischmann, F.GOOdr.
i1Dge), R.I.Primley (R.E.P.
llmley); British Patent No. 1194181, F.J. Wilkinson
sOn), K. Haines; Tr.
ans. Inst. MiningMet. (Section C), Vol. 81 (1972), p. 157, D.S.
D.S. Flett; Chem. andI
nd. (1971), p. 300). Unless otherwise specified, these electrodes will be referred to as three-dimensional electrodes. For example, in an electrolytic tank commonly used for silver refining, 10 ppm of silver
When a solution containing is electrolyzed, the STY is 0.0017
f! /Eh, whereas if the same solution is electrolyzed in an electrolytic cell with a packed bed electrode, the STY is about 1.8 g/Eh. The dimension of the three-dimensional electrode parallel to the direction of current flow is limited by a length known as the effective bed depth.

This is because electrochemical changes only occur within this depth. Incidentally, the distance between the supply electrode and the partition given by the design is referred to as the geometric electrode bed depth (hereinafter abbreviated as the geometric bed depth) in the following description. Conventionally, the effective bed depth is generally only 1c! Since it was said to be on the order of the size of RL (M. Fleischmann, G.A. Double Oldfield; J. ElectrOa
nal. Chem. , Vol. 29 (1971), p. 211), the aforementioned limitations on the dimensions of three-dimensional electrodes were considered to be an important problem. All said known electrolytic cells with three-dimensional electrodes have a constant geometrical bed depth.

From the point of view of reducing costs, ie reducing the quantity of electrodes and membrane materials used, it is preferred that the three-dimensional electrode counter electrode area or septum area by the maximum possible volume. However, the volume of the three-dimensional electrode is limited by the fact that STY is reduced near the effective bed depth. An object of the present invention is to provide a new electrolytic cell whose STY is larger than that of a conventional electrolytic cell.

This object is achieved by what is stated in the claims. Next, the electrolytic cell of the present invention will be explained with reference to the attached drawings.

FIG. 1A is a graph showing the theoretical relationship between the electrode length 2 and the geometric bed depth h of the electrolytic cell of the present invention, and FIG. 1B is a graph showing the theoretical relationship between the electrode length 11 and the electrode width of the electrolytic cell of the present invention. Figure 2 is a schematic diagram of the electrolytic cell of the present invention, Figure 3 is a graph showing the theoretical relationship between
The figure is a longitudinal sectional view of the electrolytic cell of the present invention.

As illustrated by the drawings, the electrolyte enters the inlet chamber 7 through the inlet 1 .

The chamber is separated from the outflow chamber 12 by a partition wall 15. The electrolyte first flows into the inlet zone 8 through the mesh 13 . The zone serves to homogenize the flow rate and is filled with glass bulbs of diameter 111111t, for example. The electrolyte then flows into the electrode bed 2 through the separating mesh 14. The electrode bed comprises electrodes, for example 1.5 mm in diameter.
25H! 1 of graphite particles. Current is supplied to said electrode bed, which acts as a cathode, through a supply electrode 9, for example a graphite plate, which is mounted on the wall of the electrolytic cell. The electrolyte then passes through the upper restriction screen 10 and the overflow duct 3 to the anode chamber 16.
flows into. A partition or membrane unit 4, for example a cation exchange membrane, is arranged between the chamber 16 and the electrode bed 2. The unit contains an electrode bed and is reinforced with a frame 11. An anode 5, for example a graphite plate, is attached to the wall of the electrolytic cell. Gas generated in the anode space escapes through riser 17. The electrolyte then passes through the outlet chamber 12 and exits the electrolytic cell through the outlet 6. In the present invention, as a result of research and calculation regarding the effective bed depth, the effective bed depth is 10 (17
7! We found that it is possible to reach orders of magnitude of .

The optimum operating conditions for the electrode bed are also determined if the geometric bed depth along the length of the electrode (see Figure 2, which defines the bed dimensions) increases as the concentration in the electrolytic cell decreases. I found out that it can be achieved. The electrolytic cell of the present invention was completed based on reducing this principle to a practical configuration. Therefore, if the electrolytic cell of the present invention is used, the STY will be significantly higher than that of the known electrolytic cell having three-dimensional electrodes, and at the same time, the amount of raw materials used can be reduced. The geometry of the electrolytic cell of the invention is characterized in that the geometrical bed depth increases continuously along the length of the electrode from the inlet to the outlet.

Such electrode bed broadening can also be achieved by connecting electrolytic cells with increasing bed depths through which the electrolyte passes in turn. The width of the electrode may increase or decrease along its length, or it may be constant. Preferably, the width of the electrode is reduced to the extent that the flow area of the electrode remains constant or has the same value at the inlet and outlet. This allows the mass transfer coefficient to be substantially constant over the entire band of the electrode. Because the electrolytic cell of the invention has a spread electrode bed, it has the following advantages compared to known electrolytic cells with a constant geometric bed depth. (1) Even if the electrode bed is the same and the distance between the partition wall and the counter electrode is the same, the electrolytic cell of the present invention has a smaller volume of space for the counter electrode, so a higher STY can be obtained.

(2) The required bulkhead area for a given volume of electrode bed is considerably smaller in the electrolytic cell of the invention than in known electrolytic cells, so that the amount of raw material required is reduced.

(3) In the electrolytic cell of the present invention, the local current density decreases because the concentration decreases along the length of the electrode.

On the other hand, since the electrolytic sliding voltage is constant along the length of the electrode, the kinetic overvoltage increases and therefore the current efficiency is drastically reduced. Whereas in known electrolytic cells with a constant geometrical bed depth, the current density decreases proportionally to the factor f for decreasing concentration, in the electrolytic cell of the present invention, for the same decreasing concentration, the current density decreases simply by the factor f. decreases in proportion to This means that a considerably better current efficiency can be obtained in the electrolytic cell of the present invention. In the present invention, the anode and/or cathode may be three-dimensional electrodes with increasing geometric bed depth.

Also, in the case of two three-dimensional electrodes, it is only necessary that one of the electrodes has an electrode bed with increasing depth. The three-dimensional electrode may be composed of a known porous electrode or a particle-filled bed. Examples of electrode materials include metals, carbon, graphite, semiconductors, conductors, and nonconductors coated with semiconductors. The geometry of the particles is not critical. For example, spherical particles, granules, chips, etc. can be used. A septum or ion exchange membrane may be placed between the anode space and the cathode space to support the electrode bed. Examples of the electrolyte include inorganic and/or organic solutions of the metal to be electrolyzed. When the concentration of the reactants is in the range of , the conductivity of the electrolyte is
To obtain effective depths on the order of a few centimeters, typically 1 to 5 m.
s/(177!). The electrolytic cells of the present invention are operated in the anode and cathode spaces with homogeneous or dissimilar electrolytes, and the electrolytes may be used in a cocurrent or countercurrent configuration. The electrolytic system of the invention is particularly suitable for removing and/or recovering dissolved metals such as silver, copper, lead, mercury, gold, platinum, etc. from waste water or from ore waters with low metal content. It is used to precipitate .

After the treatment, the metal concentrated at the electrode is chemically or electrochemically dissolved in a known electrolyte to obtain a concentrated solution. If the metal to be deposited is also used as electrode material, the metal-enriched electrode material can be directly metallurgically further processed. Calculation of the concentration-dependent effective bed depth, whose depth is a function of the length of the electrode, represents the maximum bed depth, and within which electrochemical changes occur continuously, as well as in the direction of the length of the electrode. The concentration decrease along the line was calculated using the following differential equation.

By using well-known differential and iterative techniques, differential equations (1)-(5) can be solved numerically for each microkinetic equation, i(η,c), using a computer. Next, the present invention will be explained with reference to Examples.

EXAMPLE (EXAMPLE SHOWING CALCULATIONS) The complete equation below for calculating the dimensions of an electrolytic cell is a special case where separation of metals often occurs in diffusion-controlled first-order reactions in a packed bed cell with a constant flow area. We obtained the answers to differential equations (1) to (5) for the case.

The geometric bed depth of the electrolyzer should be dimensioned to provide full ultimate current density at all locations of the electrodes. 48b
1;'JI et al.
Wastewater containing 100 ppm of silver (X8 = 0.01
9S/Cfrl) is reduced to 1 ppm by electrolysis when fed at 502/h in a packed bed tank.

Other setting values were as follows.

A: 21.12Cf1/D d: 0.125CTrL p゜゜v: 0.56 u: 0.5CrrL/S k: 1.624・10-3cTn/s β: 0.60 η: 0.4 Formula (6 By using (8), in the case of the packed bed vessel shown schematically in FIG. 2, the dimensions of the electrode bed were obtained as follows.

Electrode length: 67.15 (1-J Mo V1 Geometric depth Electrode inlet position: 1.08cm Electrode outlet position: 10.80CTIL Electrode width Electrode inlet position: 25. 72cfn Location of the outlet of the electrode: 2.57C7rL Theoretical dependence of the geometrical bed depth h and the width b of the electrode on the length e of the electrode and the parameters H, b and ′
The relationship is shown in FIG. 1A and FIG. 1B.

If the distance between the ion exchange membrane and the anode is selected to be 1.789/Eh (
7) Has STY.

On the other hand, the same capacity and constant geometric depth is 1Cr1L
The STY of the electrolytic cell is only 1.39/Eh,
Approximately twice the amount of anode and membrane material is required compared to the electrolytic cell of this example. Also, the geometric floor depth is 1 CTIL.
In the case of an electrolytic cell in which the current density is constant, the local current density decreases to 1/100 between the current inlet and the current outlet, but in the electrolytic cell of this embodiment, the decrease is only 1/10.

For this reason, the calculations in this example involve and the electrolyzer of this example with increasing bed depth can provide significantly better current efficiency. Given a current yield of 60% in the electrolyzer of the invention, this figure is approximately 13% for an electrolyzer with a constant geometric depth.
decreases to . (Example illustrating construction) For the purpose of creating an experimental electrolytic cell, the theoretical profile shown in Figures 1A and 1B was modified by the use of a supply electrode with a curved surface as shown in Figure 3. did.

The electrolytic cells shown in Figures 2 and 3 are as described above (example showing calculations).
silver concentration from 100 ppm to 1 ppm as described in
can be reduced to.

To reduce in this way, the current efficiency must be reduced to 60 (!)
Assuming that, a current of 2.07A is required. 0.2 mol NaNO containing 100 ppm silver ions
3 solution (X5=0.019S/CTn)
The following experimental results were obtained in electrolysis supplied at 50'/h to the electrolytic cell of the present invention shown in Figure 3. Electrolytic cell current: 1.39 A Electrolytic cell voltage: 2.5 V Final concentration: 0.09 ppm Current efficiency: 0.85 These results are in close agreement with the work of an electrolytic cell designed for silver deposition. ing.

Furthermore, 0.15 mol Na containing 60 ppm of steel ions
The following experimental results were obtained in electrolysis using a 2sO4 solution (X820.021S/(7n) supplied at 25 e/h to the electrolytic cell of the present invention shown in FIGS. 2-3.

Electrolytic cell current: 1.97A Electrolytic cell voltage: 2.8V Final concentration: 0.005ppn1 Current efficiency: 0.64 Next, the known electrolytic cell in which the geometrical bed depth increases linearly and the present invention A comparison was made with an electrolytic cell.

Electrolytic cell A shown in the following table is formed in a straight line approximately approximating the theoretical profile of the geometric bed depth.
Cell B, on the other hand, has its theoretical profile accurately achieved by the use of a curved feed electrode as shown in FIG. For each electrolyzer A and B, add 50 copper ions
Dilute copper sulfate solution containing ppm (X8=0.0008S
/CTn) at a rate of 50'/h for electrolysis.

The test results are shown in the table below. Comparing these test results to the theoretical final concentration of 0.1 ppm shows that only electrolytic cells precisely designed in accordance with the present invention can achieve the theoretical concentration reduction.

[Brief explanation of the drawing]

Fig. 1A is a graph showing the theoretical relationship between the electrode length l and the geometric bed depth h of the electrolytic cell of the present invention, and Fig. 1B is a graph showing the theoretical relationship between the electrode length l and the electrode width of the electrolytic cell of the present invention. 1b, a schematic diagram of the electrolytic cell of the present invention in Figure 2, and Figure 3.
The figure is a longitudinal sectional view of the electrolytic cell of the present invention. Reference symbols in the drawings: 1: inlet, 2: electrode bed, 3: overflow duct, 4: unit, 5: anode, 6: outlet, 7: inlet chamber, 8: inlet zone, 9: supply electrode, 10: Upper restriction mesh, 11: Frame, 12: Outflow chamber, 13
: Mesh with seat, 14: Separation mesh, 15: Partition wall, 16
: anode chamber, 17: riser.

Claims (1)

[Scope of Claims] 1 Consisting of a supply electrode, partition wall or membrane forming one surface and a porous electrode or packed bed electrode confined between them, the porous electrode or packed bed electrode being a three-dimensional electrode, and Formulas: ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ A: Specific electrode area (cm^2/cm^3) c_o: Initial concentration (mol/cm^3) d_p: Particle diameter (cm) F: Faraday number (As /val) h(l): geometrical electrode bed depth at l (cm) k: mass transfer coefficient (cm/s) l: longitudinal coordinate of the electrode (cm) u: flow velocity (cm/s) v : Gap z: Number of charges in reaction (val/mol) β: Current efficiency η: Overvoltage of electrode bed (V) X_s: Electrolyte conductivity (S/cm) Electrolyte flow from the electrolyte inlet to satisfy It has a geometrical electrode bed depth that increases continuously towards the exit, where the distance between said face of the feed electrode and the septum or membrane at each point of the longitudinal coordinate l of the electrode is at said l It is characterized by being equal to the bed depth (h(l)). An electrolytic cell that deposits metals from highly dilute solutions by electrolysis. 2. The electrolytic cell according to claim 1, wherein the porous electrode or packed bed electrode is an anode and/or a cathode. 3. Electrolytic cell according to claim 1, characterized in that the width of the electrode remains constant, decreases or increases along the length of the electrode. 4. Claim characterized in that the width of the electrode decreases along the length of the electrode, and the flow area of the electrode remains constant or has the same value at the inlet and outlet. The electrolytic cell according to item 3.