KR870002075B1 - Zinc electrolysis method of saving energy - Google Patents

Abstract

In the invention, the cathodic solution of 1.5M H2SO4+0.8M Zinc in mixture and the anodic solution of H2SO4+H2SO3 gas+ a small amount of Iodine ion are partitioned by a diaphragm in between the solutions with employment of a graphite anode and an aluminum cathode. Applying the current of a density 50mA/cm2, electrolysis is carried out at about 2.0V to lower about 1.5V from that of the conventional method.

Description

Energy saving zinc electrolytic method

FIG. 1 (a) is a cross-sectional view of a negative electrode and a positive electrode having one diaphragm in the zinc electrolytic cell of the present invention.

(B) is a cross-sectional view of a negative electrode and a positive electrode having two diaphragms in the zinc electrolytic cell of the present invention.

2 is a zinc electrolytic process diagram of the present invention

The present invention relates to a zinc inhibition method that saves energy by adding a small amount of iodine ions, which act as a catalyst in the oxidation reaction of sulfurous acid and sulfur sulfide, to a zinc electrolytic extraction solution to perform electrolysis at a low voltage.

There are two types of known zinc manufacturing methods, dry method and wet method. The double wet method is an electrolytic extraction method of zinc sulfate bath and most countries including Korea have adopted this method. In the known zinc sulphate electrolysis (Batt-elle, ANL / OEPM-79-3, 94 (1979)), different electrochemical reactions occur at the anode and the cathode, respectively, and the electrode potentials at the equilibrium state are as follows.

Cathode: Zn ⁺² + 2e → Zn E ⁰ = -0.76V (1)

Anode: 2H ₂ O → O ₂ + 4H ⁺ + 4e E ⁰ = 1.23V (2)

Therefore, the electrolytic method in the equilibrium state is only 0.76V + 1.23V = 1.99V, but is actually being operated at 3.5V under current density of 50 mA / cm 2 due to oxygen overvoltage. The theoretical energy consumption is 1630Kwh / t at the electrolytic voltage of 1.99V, but at 2,870Kwh / t at the actual electrolytic voltage of 3.5V, including loss due to current efficiency, loss of switching AC to DC, rectifier and Adding losses due to lead resistance between the electrolyzers requires about 3,500 Kwh / t of energy for one ton of zinc. The electrolytic voltage is much higher than the theoretical value because the cathodic reaction overvoltage is negligible at 0.06V, whereas the cathodic reaction overvoltage is quite high at 0.84V. The biggest drawback of this known zinc electrolysis method is the enormous energy consumption in the anode reaction. The enormous amount of oxygen generated at the anode during electrolytic production is of no use, but rather a side effect of evaporating the solution and promoting corrosion of the electrode. Doing

Anodic overelectrolysis can be reduced by oxidizing sulfite gas, known as a non-polar medium. The oxidation and zinc electrolytic reactions of sulfite gas in acidic solutions are as follows (AJ Applebyand B. Pichon, J. Electroanal. Chem., 95, 59 (1979)).

_{Anode: SO 2 + 2H 2 O →} HSO 4 - + 3H + + 2e E 0 = 0.12V (3)

Cathode: Zn ⁺² + 2e → Zn E ⁰ = -0.76V (1)

Therefore, the zinc electrolytic voltage in the sulfurous acid gas solution is only 0.76V + 0.12V = 0.88V, which is about 1.1V lower than the electrolytic voltage in the zinc sulfate bath and no oxygen overvoltage occurs.

In the present invention, instead of simply oxidizing a sulfurous acid gas solution, a small amount of iodine ion (potassium iodine or iodine), which acts as a catalyst for the oxidation of sulfurous acid gas, is added to allow oxidation of sulfite gas at a more negative (-) potential. . That is, in the present invention, the solution of the positive electrode chamber is 1.5 M sulfuric acid + sulfite gas + iodine ion and cathode chamber solution is 1.5 M sulfuric acid + 0.8 M zinc electrolytic at a current density of 50 mA / cm 2 using a porous graphite anode and an aluminum cathode The electrolytic voltage was about 2.0V, and the voltage drop of about 1.5V was obtained compared to the field operating voltage of the known method.

When electrolysis was carried out without injecting the catalyst (I ⁻ ) into the positive electrode solution, the electrolytic voltage was about 2.5V, which resulted in a voltage drop of about 1.0V compared to the field operating voltage of the known method.

Therefore, the addition of a small amount of the catalyst was able to achieve a voltage drop of about 0.5V than simply using a sulfurous acid gas solution. This oxidation reaction of sulfurous acid gas in the catalyst solution is ruthless (-) from the potential of reaction (4), the three iodine ions produced by (5) (I ₃ ^-) and iodine (I ₂₎ a catalyst for the oxidation of sulfur dioxide gas (GSCalabrese and MS Wrighton, JACS, 103 (21), 6273 (1981)).

_{^{3I - → I 3 - + 2e}} E 0 = 0.536V (4)

_{^{2I - → I 2 + 2e E}} 0 = 0.621V (5)

_{SO 2 + 2H 2 O + I} 3 - → H 2 SO 4 + 2H + + 3I - (6)

_{SO 2 + 2H 2 O + I} 2 → H 2 SO 4 + 2H + + 2I - (7)

The concentration of iodine ion at the oxidation reaction of sulfurous acid gas was 0.001M, and as the concentration was increased, the catalytic effect, that is, the voltage strengthening effect, was increased. Almost the same as in M. In the anodic oxidation of this solution, the sulfuric acid concentration was 0.5 M or less, the conductivity of the solution was lowered, and the electrolytic voltage was increased. When the sulfuric acid concentration was 5 M or more, the SO ₂ solubility was decreased and the limit current density was lowered. . In addition, the sulfurous acid gas concentration showed a voltage drop effect when the concentration was above 0.1M, and the voltage drop effect increased as the concentration was increased, but the effect was almost the same as that at 2.0M. Electrolysis is generally carried out at room temperature. As the result of electrolysis by changing the electrolysis temperature, the voltage drop effect increases as the temperature increases, but the voltage drop effect is almost similar to that at 40 ° C. above 40 ° C.

Therefore, in the oxidation reaction of sulfite gas, suitable working conditions are iodine ion concentration of 0.001M-0.1M, sulfuric acid concentration of 0.5M-2.0M, sulfurous acid gas concentration of 0.1M-2.0M, and temperature of 20 ° C-40 ° C. Using inexpensive iodine with respect to the catalyst per unit weight of the iodide instead of potassium iodide are iodine and the oxidation of sulfur dioxide gas reduced to iodide ion SO _2, I ^- because it exists in a state the same hyogwaeul and using the potassium iodide Can be obtained and the catalyst cost can be reduced.

In the present invention, the electrolytic voltage is 2.0V and the energy consumption is 1,640 Kwh / t, and if the loss due to current efficiency, loss for converting AC into direct current, loss due to lead resistance between the rectifier and the electrolytic cell are added. It takes about 2.000 Kwh of energy to deliver 1 ton of zinc. This energy consumption is about 57% of the energy consumption in the known method, and it can save 1,500Kwh of energy in 1 ton zinc.

According to the present invention, sulfuric acid is produced by oxidation of sulfurous acid gas in the anode chamber to increase sulfuric acid concentration. The anode chamber solution is reacted with limestone or slaked lime to produce gypsum, which is then filtered to separate gypsum and iodine ion. The dissolved filtrate can be recovered and reused as an anode chamber solution, making not only gypsum, but also a continuous process without the consumption of iodine ions (M. Grayson and D. Eckroth, Kirk-Othmer encyclopedia of chemical). technology, 4,443 (1978).

H ₂ SO ₄ + CaCO ₃ or Ca (OH) ₂ → CaSO ₄ , 2H ₂ O (8)

In addition, since the sulfurous acid gas in the anode chamber solution reacts with hydrated lime to produce gypsum, sulfuric acid gas in the sulfuric acid produced is not a problem.

H₂O (9)SO ₂ + Ca (OH) ₂ → CaSO ₃ ,

H ₂ O (9)

H₂O+O₂+3H₂O→ 2CaSO₄, 2H₂O (10)2CaSO ₃ ,

H ₂ O + O ₂ + 3H ₂ O → 2CaSO ₄ , 2H ₂ O (10)

After the electrolysis was carried out by adding a small amount of iodine ion to the cathode chamber solution, observing the surface of the electrolytically deposited zinc, there were no pores appearing in the electrolytic zinc when no addition, and the current efficiency also increased more than no addition.

In the present invention, when the current density is increased to 100 mA / cm 2, which is twice the operating current density of the known method, the voltage is about 2.2 V. In the known zinc sulfate bath electrolytic process, when the operation current density is increased to 100 mA / cm 2, the voltage is 3.8. Not only does it rise significantly to V, but because of the high voltage, the Pb-Ag anode melts and Pb is electrodeposited on the cathode, which makes the product poor. In addition, since the anode potential becomes more positive (+), more MnO ₂ is electrodeposited on the anode, thereby lowering the electrical conductivity of the electrode and causing a voltage increase. On the contrary, in the present invention, since the anode overvoltage is small due to the increase of the current density and the anode potential is negative, the melting of the graphite anode and electrodeposition of MnO ₂ are not performed. As such, by doubling the operating current density by the method of the present invention, the productivity is doubled, which can reduce the equipment installation and other expenses in half when compared to the known electrolytic method.

As described above, the present invention not only significantly reduces the energy required for zinc electrolysis compared to the known electrolytic method, but also doubles the productivity by producing gypsum with sulfuric acid produced at the anode and doubling the operating current density. It has advantages.

Example 1

Anode chamber solution is 1.5M sulfuric acid + 1M sulfurous acid gas + 0.01M iodine ion, the cathode chamber solution is 1.5M sulfuric acid + 0.8M zinc at 25 ℃ fixed the distance between the porous graphite anode and aluminum cathode at 5cm, In the electrolytic cell of FIG. 1 (a), electrolysis was performed at a current density of 50 mA / cm 2 for 20 hours. At this time, the anode chamber solution and the cathode chamber solution were continuously circulated in order to prevent the concentration of sulfurous acid gas and zinc from being lowered, and the separator was a battery separator. The current effect of the deposited electrolytic zinc was 89%, and the electrolytic voltage at the time of electrolysis was 2.0V.

Example 2

Electrolysis was carried out using the electrolytic conditions and the electrolytic method of Example 1, with the anode chamber solution being 1.5 M sulfuric acid + 1 M sulfurous acid gas + 0.01 M iodine ion and the cathode chamber solution being 1.5 M sulfuric acid + 0.8 M zinc. The current efficiency of the deposited electrolytic zinc was 89%, and the electrolytic voltage was 1.9V during electrolysis.

Example 3

Electrolyte was carried out by the electrolytic conditions and the electrolytic method of Example 1, using the positive electrode chamber solution as 1.5 M sulfuric acid + 1 M sulfite gas + 0.01 M iodine ion and the negative electrode chamber solution as 1.5 M sulfuric acid + 0.08 M zinc + 0.01 M iodide. The current efficiency of the deposited electrolytic zinc was 91%, and when iodine ion was added to the cathode chamber solution, no holes appeared in the electrolytic zinc. At this time, the electrolytic voltage was 2.0V.

Example 4

Interpolar distance between porous graphite anode and aluminum cathode with 1.5M sulfuric acid + 1M sulfite gas + 0.01M iodine ion, cathode chamber solution 1.5M sulfuric acid + 0.8M zinc, intermediate chamber solution 5M sulfuric acid at 30 ℃ Was fixed at 6 cm and inhibited for 20 hours at a current density of 50 mA / cm 2 in the electrolytic cell of FIG.

At this time, the anode chamber solution and the cathode chamber solution were continuously circulated in order to prevent the concentration of sulfurous acid gas and zinc from being lowered, and the separator was a battery separator.

The current efficiency of the deposited electrolytic zinc was 90%, and the electrolytic voltage at the time of electrolysis was 2.1V.

Claims (3)

An energy-saving zinc electrolysis method in which sulfuric acid and a zinc solution are mixed to form a cathode chamber solution, and sulfuric acid gas and a small amount of iodine ion or iodine are added to sulfuric acid to form a cathode chamber solution to separate and electrolyze a good solution through a diaphragm. The method of claim 1, Method of making working conditions into iodine ion concentration 0.001M-0.1M, sulfuric acid concentration 0.5M-2.0M, sulfurous acid concentration 0.1M-2.0M, temperature 20-40 degreeC. The method of claim 1, A method of producing gypsum by reacting sulfuric acid produced in the anode chamber with limestone or slaked lime, and filtering and separating the iodine ion into the anode chamber solution.

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