METHOD FOR PRODUCING MAGNESIUM AND CHLORINE AND ELECTROLYTIC CELL FOR IMPLEMENTING SAME

Abstract

The invention relates to producing magnesium and chlorine from a solution of magnesium chloride-containing salts, using an electrolytic cell. A diaphragmless electrolytic cell includes: an electrolysis chamber with alternating anodes and cathodes; and a magnesium separation cell separated from the electrolysis chamber by a partition having upper V-shaped circulation channels and lower circulation channels. Electrolysis is carried out at 6-25 gas saturation of the electrolyte with chlorine bubbles in an interelectrode gap. The flow rate of the electrolyte in the upper circulation channels is 20-60. The ratio of current strength to electrolyte mass is 8-10. The ratio of the width of the electrolysis chamber to the width of the magnesium separation cell is 1.6-2.7. Additional channels are mounted in the partition, between the upper and lower circulation channels, said additional channels having a flow passage area of 0.016-0.048 of the area of the upper V-shaped channels.

Claims

1. A method for the production of magnesium and chlorine from a MgCl.sub.2-containing salt melt by using a diaphragm-less electrolytic cell, wherein the method comprises initiating a closed circulation of an electrolyte between an electrolysis chamber having alternating anodes and cathodes and a magnesium separation cell due to a gas saturation of the electrolyte with chlorine bubbles in an interelectrode gap, which is equal to 6÷25 and defined by: $\Pi =\frac{H_c.Math.d_c}{l_{a\nu erage}},$ where Π denotes the gas saturation of the electrolyte with the chlorine bubbles in the interelectrode gap; d.sub.c denotes a cathode current density, A/cm.sup.2; H.sub.c denotes a cathode height, cm. wherein a current strength (kA) and an electrolyte mass are set in the electrolytic cell in such a quantitative expression that a ratio of the current strength (kA) to the electrolyte mass (t) is 8÷10, and an electrolyte flow from the electrolysis chamber enters a collection cell in two ways: through upper circulation channels and additional channels arranged between the upper circulation channels and lower circulation channels, wherein an electrolyte flow rate in the upper V-shaped circulation channels is selected from the condition: $\frac{S_{\mathrm{upper}\mathrm{channels}}}{S_{\mathrm{additional}\mathrm{channels}}}=20÷60,$ where S.sub.upper channels denotes a total area of the upper circulation channels; S.sub.additional channels denotes a total area of the additional channels.

2. A diaphragm-less electrolytic cell for performing the method according to claim 1, wherein the electrolytic cell comprises an electrolysis chamber having alternating anodes and cathodes, a magnesium separation cell separated from the electrolysis chamber by a partition with upper V-shaped and lower circulation channels, wherein a ratio of widths of the electrolysis chamber and the magnesium separation cell is 1.6÷2.7, additional channels are mounted in the partition between the upper V-shaped and lower channels, the additional channels have a flow passage area equal to 0.016÷0.048 of an area of the upper V-shaped channels, and the additional channels in the partition are made of a fusion cast crystalline mica material, namely fluorophlogopite.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 shows a general view of a diaphragm-less electrolytic cell,

[0019] FIG. 2 shows a section taken along line A-A, and

[0020] FIG. 3 shows a section taken along line B-B.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0021] A diaphragm-less electrolytic cell comprises: a steel housing 1 lined internally with a refractory material 2; an electrolysis chamber 3 having alternating anodes 4 and cathodes 5, interelectrode gaps 6 and a shelter 7 from above; a magnesium separation cell 8; a partition 9 separating the electrolysis chamber 3 from the magnesium separation cell 8 and having upper V-shaped circulation channels 10, additional channels 11 lined with fluorophlogopite 12 and lower channels 13.

[0022] The electrolytic cell operates as follows:

[0023] After a melt is poured into the electrolytic cell, direct current is fed to the electrodes. At an electrolyte temperature of 655° C.-670° C., chlorine is released at the anodes (4), and magnesium is released at the cathodes (5). Due to the high gas saturation of an electrolyte with chlorine bubbles in the interelectrode gap (6), there are upward flows of the electrolyte together with magnesium and chlorine which is collected above the electrolyte in the electrolysis chamber (3) and then removed to a main chlorine pipeline. In the upper part of the interelectrode gap 6, most of the electrolyte together with magnesium enters the magnesium separation cell (8) through the upper V-shaped circulation channels (10). Another part of the electrolyte also enters the magnesium separation cell through the additional channels. Magnesium accumulates on the surface of the electrolyte in the separation cell (8) and is periodically selected by a vacuum ladle. The magnesium-free electrolyte in the cell (8) is directed downward, and the electrolyte flows then enter the interelectrode gaps (6) through the lower channels 13.

[0024] The ratio of widths of the electrolysis chamber and the magnesium separation cell is 1.6÷2.7. With this ratio, favorable conditions for magnesium settlement in the separation cell are provided.

[0025] The additional channels are mounted in the partition between the upper V-shaped and lower channels, and have a flow passage area of 0.016÷0.048 of the area of the upper V-shaped channels. This allows reducing the flow rate of the electrolyte and magnesium in the upper V-shaped channels, improving the conditions for magnesium settlement in the magnesium collection, reducing the removal of chlorine bubbles with the electrolyte flows from the electrolysis chamber to the collection cell, and, therefore, reducing the loss of chlorine with the plumbing gases and avoiding the contact between the cathodes and the partition.

[0026] The additional channels in the partition are made of a fusion cast crystalline mica material, namely fluorophlogopite, which allows increasing the resistance of the refractory separating partition and increasing the service life of the electrolytic cell.

TABLE-US-00001 TABLE Operating factors of the electrolytic cell For the electrolytic For the electrolytic cell according to cell disclosed in Factors the invention KZ 16980 Specific energy consumption 12960 13430 Service life of electrolytic cell, 48 40 months Current output of magnesium, % 85 82 Productivity gain, % 3.6 0 Loss of chlorine with plumbing 40 70 gases, kg/tMg

[0027] The method for the production of magnesium and chlorine from a MgCl.sub.2-containing salt melt is performed as follows:

[0028] A melt comprising magnesium, sodium and potassium chlorides is poured into the electrolytic cell lined with a refractory material, and direct current is fed to the electrodes. By changing the current strength (kA) and the electrolyte mass (t) in the electrolytic cell, the ratio of the current strength to the electrolyte mass is set equal to 8÷10. At an electrolyte temperature of 655° C.-670° C., chlorine is released at the anodes, and magnesium is released at the cathodes. Due to the high gas saturation of the electrolyte with chlorine bubbles, there are upward flows of the electrolyte together with magnesium and chlorine in the interelectrode gap. Chlorine is collected over the electrolyte in the electrolysis chamber, from where it is removed into the main chlorine pipeline. Most of the electrolyte, together with magnesium in the upper part above the cathodes, is directed through the upper V-shaped circulation channels in the separating partition into the magnesium separation cell. Another part of the electrolyte is directed from the electrolysis chamber to the separation cell through the additional channels arranged in the separating partition between the upper and lower circulation channels. Due to the fact that the electrolyte flow from the electrolysis chamber into the collection cell is bifurcated into two flows, the electrolyte flow rate in the upper circulation channels decreases and is determined by the ratio S.sub.upper channels:S.sub.lower channels equal to 20-60. Magnesium accumulates on the surface of the electrolyte in the magnesium separation cell and is periodically selected by the vacuum ladle. The magnesium-free electrolyte in the collection cell is directed downward and then directed through the lower channels of the separating partition to the interelectrode gaps of the electrolysis chamber.

[0029] The maximum current output is obtained at an electrolyte flow rate in the upper channels determined by the ratio S.sub.upper channels:S.sub.additional channels=20-60.

[0030] The current strength on the electrolytic cell is set based on conditions for maintaining heat balance and observing the ratio of the current strength to the electrolyte mass which is equal to 8-10, and the electrolyte mass is regulated by changing the electrolyte level in the electrolytic cell.

[0031] The electrolyte flow rate in the upper V-shaped circulation channels is selected based on the following condition:

[00006]$\frac{S_{\mathrm{upper}\mathrm{channels}}}{S_{\mathrm{additional}\mathrm{channels}}}=20÷60,$

where S.sub.upper channels is the total area of the upper circulation channels;
S.sub.additional channels is the total area of the additional channels,
and this selection is caused by the fact that when the ratio is less than 20, the conditions for magnesium removal from the electrolysis chamber to the separation cell are worsened, thereby decreasing the current output by 1-2%; and when the ratio is more than 60, the conditions for magnesium settlement in the separation cell are worsened, and small magnesium beads having a diameter of less than 1.0 mm are carried by downward electrolyte flows back into the electrolysis chamber, thereby decreasing the current output by 1-2%.

[0032] The selection of the ratio of the current strength (kA) to the electrolyte mass (t), i.e. 8-10, is due to the fact that when the ratio of the current strength to the electrolyte mass is more than 10, the thermal inertia of the electrolyte in the electrolytic cell decreases sharply, and the electrolyte temperature rises rapidly with the slightest decrease in the current output, thereby decreasing the current output; and when the ratio is less than 8, specific heat loss per square meter for the bottom area of the electrolytic cell increases, thereby increasing the specific energy consumption of the electrolytic cell. The electrolyte mass is maintained by changing the electrolyte level in the electrolytic cell.

TABLE-US-00002 TABLE 1 Dependence of the current output of magnesium on the ratio of the current strength (kA) to the electrolyte mass (t) Ratio of current output (kA) Current output of to electrolyte mass (t): magnesium, % 6 ÷ 8 83  8 ÷ 10 85 10 ÷ 12 83

TABLE-US-00003 TABLE 2 Dependence of the current output of magnesium on the electrolyte flow rate Electrolyte flow rate in upper V-shaped circulation channels, which is expressed as the following ratio of the total area of the upper Current output of circulation channels to the total area of magnesium according additional channels to the invention, % 10-20 84.0 20-60 85.0 60-70 83.5

TABLE-US-00004 TABLE 3 Comparative factors of the method according to the invention and the method disclosed in KZ 16980 For the method For the method according to disclosed in Factors the invention KZ 16980 Current strength, kA 225.0 220.0 Ratio of current strength to 8-10 10-12 electrolyte mass, kA/t Electrolyte flow rate in upper 20 ÷ 60 S.sub.additional channels = 0 circulation channels is governed by the ratio: [00007]$\frac{S_{\mathrm{upper}\mathrm{channels}}}{S_{\mathrm{additional}\mathrm{channels}}}$ Specific energy consumption, 12960 13430 kWh/tMg Service life of electrolytic cell, 48 40 months Current output of magnesium, 85 82 % Productivity, kgMg/day 2084 1966 Loss of chlorine with plumbing 40 70 gases, kg/tMg

[0033] By using the method according to the invention, there is a decrease in the specific energy consumption due to an increase in the current output and a decrease in the loss of chlorine with the plumbing gases.

[0034] The electrolytic cell according to the invention has an extended service life and provides a decrease in the loss of chlorine with the plumbing gases.

[0035] An economic result is as follows: a reduction in the specific energy consumption by 470 kWh/tones of magnesium (tMg), an increase in the current output of magnesium due to the improvement of magnesium removal from the electrolysis chamber into the collection cell and the improvement of the conditions for magnesium separation in the collection cell, an increase in the electrolytic cell productivity by 6.0%, a decrease in the loss of chlorine with the plumbing gases by 30 kg/tMg, and an increase in the service life of the electrolytic cell by 8 months.