WO2013011203A1

WO2013011203A1 - Internal box for an electrolytic manganese cell, provided with gas discharge openings, and associated cell and method

Info

Publication number: WO2013011203A1
Application number: PCT/FR2011/051699
Authority: WO
Inventors: Luc Albert; Benoît GIRARD
Original assignee: Eramet
Priority date: 2011-07-15
Filing date: 2011-07-15
Publication date: 2013-01-24
Also published as: ZA201400295B; UA110726C2; CN103857832A

Abstract

The invention relates to a box comprising a plurality of anode frames (66), a plurality of cathode frames (64) placed between the anode frames (66) and a plurality of diaphragms (68) disposed between each cathode frame (64) and each anode frame (66). Each cathode frame (64) delimits an inner cathode-receiving compartment (90) and at least one lateral supply opening (96) for supplying a feed solution containing manganese ions to the inner compartment (90). Each cathode frame (64) defines an upper lateral opening (98) for discharging cathode gases and said upper discharge opening (98) is disposed above the or each lateral supply opening (96) for the feed solution so that the discharge opening opens at least partially above the feed solution.

Description

Inner cell of manganese electrolysis cell provided with gas evacuation openings, cell and associated method

The present invention relates to an internal manganese electrolysis cell box, intended to be placed in a tank containing a feed solution, the box comprising:

a plurality of anode frames;

a plurality of cathode frames placed between the anode frames;

a plurality of diaphragms interposed between each cathode frame and each anode frame;

a clamping assembly capable of keeping the cathode frames, the anode frames and the diaphragms applied against each other,

each cathode frame defining an internal cathode receiving compartment, an upper cathode introduction opening in the inner compartment, and at least one lateral opening for supplying a feed solution containing manganese ions into the inner compartment .

Such a box is intended to be removably inserted into a cell of manganese electrolysis cell.

The book "Operation of Electrolytic Manganese Pilot Plant", Boulder City Nevada, USBM Bulletin 463, pages 64 and 65 describes, Figure 35, a box of the aforementioned type having a structure of "filter-press" type.

Such a box comprises an alternation of cathode frames and anode frames which are separated from each other by diaphragms. Longitudinal rods and end nuts hold the frames and the diaphragms applied against each other to ensure a good seal between the compartments delimited by each of the frames.

Lateral feed openings of a feed solution containing manganese ions are provided laterally in the cathode frameworks to allow feeding of each cathode compartment by the solution in the vessel.

Upper apertures opening upwardly are further provided in each cathode frame and in each anode frame to allow insertion of cathodes and anodes respectively.

Such a box has a compact and manageable structure. It does not, however, give complete satisfaction.

Indeed, the electrolysis reaction of manganese produces at the cathode a certain number of gases which must be evacuated. In particular, although the formation of metal manganese from the feed solution is predominant at the cathode, the reduction of hydronium ions (H +) present in the cathodic solution produces hydrogen, in competition with the deposited metal manganese on the cathodes.

In addition, in some cases, depending on the pH of the cathodic solution, the presence of ammonium ions (NH4 +) in the feed solution causes a parasitic release, more or less important, ammonia (NH3).

In the electrolysis cell described by the USBM, these cathode gases are evacuated directly through the upper insertion opening of the cathodes and are dispersed in the atmosphere of the electrolysis hall.

However, the current environmental, hygiene and safety constraints of industrial installations now require the control and limitation of potentially toxic or dangerous gas emissions.

An object of the invention is therefore to obtain an internal box of manganese electrolysis cell that meets the environmental and safety constraints, while remaining simple to handle and operate.

For this purpose, the subject of the invention is an internal box of the aforementioned type, characterized in that each cathode frame defines an upper lateral opening for discharging the cathode gases, the upper discharge opening being disposed above of the or each feed solution supply side opening to open at least partially above the feed solution and in that the upper gas discharge opening opens into the inner compartment and opens at the outside of the box.

The box according to the invention comprising one or more of the following characteristics, taken separately or in any technically possible combination:

- The upper gas discharge opening has a section greater than the section of the or each lateral electrolyte supply opening, preferably an oblong cross section, in particular elongated along a vertical axis.

each cathode frame delimits, above the upper gas discharge opening, a notch for receiving a blanking shutter from an electrolytic cell.

each cathode frame comprises two lateral uprights and an intermediate cross-member connecting the lateral uprights, the lateral uprights and the intermediate cross-member delimiting the internal cathode receiving compartment, each upper lateral opening of gas discharge being formed through a lateral upright; . each cathode frame delimits a lower cross-member connecting the two lateral uprights under the intermediate cross-member, the intermediate cross-member and the lower cross-member delimiting with the lateral uprights a lower anodic solution circulation window, the lower window being sealingly insulated from the compartment; internal.

each cathode frame comprises at least one transversely projecting lateral lug, the upper gas evacuation opening being formed through the lateral lug.

it comprises a cathode inserted in each cathode frame through the upper insertion opening, a sealing member sealing the upper cathode insertion opening in a sealed manner, when the cathode is received in the internal compartment of the cathode; cathode reception.

each anode frame has an interior anode receiving compartment delimited downwards by a bottom crossmember,

the anode frame having a plurality of disjointed support fingers projecting upwardly from the bottom crossmember, the diaphragms adjacent to the anode frame being laterally applied to the support fingers.

each diaphragm comprises a support frame carrying a grid, and a cloth applied to the grid, the support frame comprising an intermediate cross-member, the support fingers applying the intermediate cross-member of the cathode frame to the intermediate cross-member of the support frame; an adjacent anode frame.

The subject of the invention is also a cell for electrolysis of manganese, of the type comprising:

a tank delimiting an interior volume for receiving a feed solution, a box as defined above, arranged in the interior volume,

- A closure assembly, sealingly sealing the interior volume of the tank around the box above the upper gas evacuation openings;

The cell comprising at least one purge pipe discharged gases through each upper gas evacuation opening, to evacuate out of the tank.

The cell according to the invention may comprise one or more of the following characteristics, taken in isolation or in any technically possible combination.

the tank contains a feed solution in which the box is immersed, each lateral outlet of gas evacuation opening at least partially above the feed solution. the tank has a lateral wall extending facing each upper gas discharge opening, the box and the lateral wall delimiting an intermediate lateral space into which the upper gas discharge openings open, the assembly of shutter comprising at least one shutter closing up the intermediate space above each lateral gas evacuation opening.

- It has an end wall extending substantially transversely to the side wall, the end wall defining with the inner box an axial intermediate space, the closure assembly comprising an end cap closing the axial intermediate space upwards.

The subject of the invention is also a process for the electrolysis of manganese, of the type comprising:

- supply of a cell as defined above;

feeding the inner compartment of each cathode frame with a feed solution containing manganese ions;

- formation of metal manganese on each cathode received in each cathode frame;

- Generation of cathode gas, including ammonia and hydrogen, in the inner compartment of each cathode frame;

- evacuation of cathode gases through the upper gas evacuation openings outside the box,

collecting cathode gases produced by each cathode out of the box at the top of the intermediate space delimited between the tank, the box and the closure assembly;

- Evacuation of cathode gas collected in the top of the intermediate space through the purge pipe.

The invention will be better understood on reading the description which follows, given solely by way of example, and with reference to the appended drawings, in which:

- Figure 1 is a schematic side view of a first electrolytic cell of manganese according to the invention;

- Figure 2 is a partial perspective view from above of the cell of the

Figure 1 ;

- Figure 3 is a perspective view in partial section along a transverse plane III of Figure 2;

Figure 4 is an exploded perspective view of the inner box of the cell of Figure 1; Figure 5 is an exploded perspective view of a cathode frame of the box of Figure 4;

Figure 6 is an enlarged view of a marked detail VI in Figure 5;

Figure 7 is a view similar to Figure 5 of an anode frame;

Figure 8 is a view similar to Figure 5 of a diaphragm carrier;

- Figure 9 is a top view, taken in section along a horizontal plane, of the box of Figure 4, once assembled; and

- Figure 10 is a partial view taken along the arrow X of Figure 9.

Figures 1 to 10 illustrate a first electrolysis cell 10 according to the invention for performing an electrolysis of manganese metal or "EMM".

The metal manganese is advantageously formed on a plurality of cathodes by supplying an electric current, in contact with a feed solution containing Mn ²⁺ manganese ions, optionally in the presence of ammonium sulfate.

The metal manganese thus formed is deposited in solid form on each cathode.

The cell 10 is arranged in an installation comprising a plurality of cells 10 in series, for example a hundred cells 10.

As illustrated by FIG. 1, the electrolysis cell 10 comprises a tank 12 delimiting an interior volume 14 and an internal box 16 of the "filter-press" type disposed in the interior volume 14 of the tank 12.

According to the invention, the electrolysis cell 10 further comprises a closure assembly 18 of the interior volume for capturing and sealingly conveying the gases emitted at the cathode during the electrolysis.

It further comprises power supply means 19 which are partially visible in Figures 2 and 3, and a cooling heat exchanger 19A, partially visible in Figure 3.

With reference to FIGS. 1 to 3, the vessel 12 is of substantially parallelepipedal shape with a longitudinal axis A-A '. It comprises two transverse end walls 20A, 20B, interconnected by two longitudinal walls 22, only one of which is visible in FIGS. 1 and 2.

The tank 12 further comprises a bottom wall 24 which closes down the interior volume 14.

The transverse walls 20A, 20B advantageously have a height greater than that of the lateral walls 22. Thus, each transverse wall 20 delimits an upper strip 26 which protrudes above the side walls 22.

Each side wall 22 defines a flat upper edge 28 support. The edge 28 carries an upper support rod 30.

The rod 30 carries longitudinal electrical contacts 32A, 32B intended to connect the electrical supply means 19 respectively to the anodes and to the cathodes.

The tank 12 further comprises at least one feed supply line 34 in the interior volume 14, at least one anolyte solution discharge line 36 out of the inner box 16 and out of the tank 12 , and at least one pipe 38 for purging the gases produced at the cathodes, to evacuate them from the internal volume 14.

With reference to FIG. 1, the supply line 34 is connected to means

40, pumping or gravity feed supply solution in the tank 12. In this example, the supply line 34 through the transverse wall 20A at the strip 26.

In the example shown in Figure 2, the exhaust pipe 36 extends through the transverse wall 20A. It is connected upstream to the box 16 by a hose (not shown). It is connected downstream to means 42 for collecting and treating, arranged outside the tank 12.

With reference to FIG. 1, cathode gas purge lines 38 are connected to a facility 44 for collecting and treating these gases. This avoids disseminating the cathode gases in the atmosphere around the tank 12.

In this example, the purge lines 38 pass through the transverse wall 20A at the upper strip 26. They open through collection openings 46 which are situated above the upper edge 28 of the side walls 22, so as to remain free of liquid permanently, regardless of the level of cathodic solution contained in the interior volume 14.

In this example, the collecting openings 46 are disposed on either side of the transverse wall 20A, in the vicinity of the upper corners of this wall 20A, facing the lateral intermediate spaces 60 between the box 16 and the side walls 22 of tank.

The inner box 16 is disposed in the volume 14. It extends along an axis B-

B 'parallel or coincident with the axis AA' of the tank 12. It delimits in the interior volume 14 the lateral interspaces 60 visible in Figure 3, and axial interspaces 62 present between the end walls 20A, 20B and the box 16.

The intermediate spaces 60, 62 are intended to receive the feed solution. The intermediate spaces 60, 62 are covered by the closure assembly 18 for confining and evacuating the cathode gases, as will be seen below. The heat exchanger 19A is disposed in the intermediate spaces 60, 62.

The box 16 is removably placed in the interior volume 14 of the tank 12. It is thus movable and transportable, through the upper passage delimited between the walls 20A, 20B and 22, between a position extracted from the interior volume 14, and a position of implementation of the electrolysis process, placed against the bottom wall 24 in the interior volume 14. This makes it possible to easily extract the box 16 from the tank 12 in order to carry out maintenance operations and / or cleaning.

As mentioned above, the inner box 16 is of the "filter press" type. It thus has, with reference to FIG. 4, a plurality of cathode frames 64, a plurality of anode frames 66, and a plurality of diaphragm assemblies 68 disposed between each anode frame 66 and each cathode frame 64.

The box 16 also advantageously comprises two end frames 70A, 70B intended to transversely close the axial ends of the box 16, and a releasable clamping assembly 72 of the box 16.

The box 16 includes a cathode 74 received in each cathode frame 64 and an anode 76 received in each anode frame 66. The cathodes 74 and the anodes 76 are visible in FIG. 2.

As illustrated in FIG. 5, each cathode frame 64 has two lateral uprights 80A, 80B, an intermediate web 82, and a bottom rail 84 connecting the uprights 80A, 80B to each other.

The cathode frame 64 thus delimits an internal cathode receiving compartment 90 and a lower flow opening window 92 of an anolyte solution, sealingly sealed from the inner compartment 90.

The cathode frame 64 further delimits an upper opening 94 for introducing the cathode 74 into the internal compartment 90, transverse cathode solution feeding openings 96 into the internal compartment 90, and according to the invention, lateral openings. higher cathode gas evacuation 98 out of the box 16.

In this example, the height of the cathode frame 66 is substantially equal to the depth of the internal volume 14, taken between the upper edge 28 of the side wall 22 and the bottom wall 24.

The uprights 80A, 80B extend parallel to each other in a vertical direction. Each upright 80A, 80B has, at its upper end, a lateral lug 100 which protrudes transversely with respect to a longitudinal axis BB 'of the box 16, visible in FIG. 4. Each lug 100 delimits a transverse notch 101 for receiving a shutter from the shutter assembly 18. The notch 101 opens transversely facing the side wall 22, when the inner box 14 is disposed in the interior volume 14 of the tank 12. The notch 101 is located above the cathode gas discharge openings 98.

The lower cross member 84 horizontally connects the lower ends of the uprights 80A, 80B together. It delimits downward the anodic solution circulation window 92. In this example, the lower rail 84 is fixed on the uprights 80A, 80B. Triangular reinforcement spacers 102 are advantageously connected to the lower cross-member 84 and to the uprights 80A, 80B, at the inner corners delimited by the uprights 80A, 80B and the lower cross-member 84.

The intermediate cross member 82 is arranged parallel to the lower cross 84. It defines the window 92 upwards. It delimits downwards the internal compartment 90 for receiving cathode. It is reported between the amounts 80A, 80B.

Each upright 80A, 80B delimits, above the intermediate web 82 a vertical guide slot 104 opening laterally into the inner compartment 90 and opening upwards in the upper opening 94. The slots 104 are intended for guiding the cathode 74 when it is introduced into the inner compartment 90.

The inner compartment 90 is delimited downwards by the intermediate crossbeam

82, and laterally by the uprights 80A, 80B. It opens upwards through the opening opening 94.

In this example, each post 80A, 80B delimits a plurality of cathode solution feedthrough openings 96 into the inner compartment 90. Each opening 96 extends transversely across the post 80A, 80B. It opens out of the box 12 in the thickness of the upright 80A, 80B facing the intermediate space 60 between the box 16 and the side wall 22. It opens internally in the inner compartment 90.

In this example, each amount 80A, 80B comprises an opening 96 located in the vicinity of the intermediate cross member 82 and an opening 96 located in the vicinity of the ear 100.

In this example, the section of the openings 96 is smaller than the maximum thickness of the post 80A or 80B, taken along the axis B-B '. This section is advantageously circular. As illustrated in FIG. 6, each upright 80A, 80B delimits, in the lug 100, an upper gas evacuation lateral opening 98 located above each feed solution supply opening 96.

The upper opening 98 advantageously has a section greater than the maximum section of each feed opening 96 of feed solution.

The section of each upper opening 98 is advantageously oblong. Thus, the height of the upper opening 98 is greater than the maximum thickness of the frame 64, taken along the axis B-B '. The width of the upper opening 98 taken parallel to the axis B-B 'is less than the thickness of the frame 64.

In this example, the upper opening 98 has a constant section. It extends along a horizontal axis perpendicular to the axis B-B '. The upper opening 98 connects an upper region of the inner compartment 90 to the outside of the box 16. It is intended to be placed facing a side wall 22, while being at most partially immersed by the feed solution. present in the interior volume 14 between the tank 12 and the box 16.

In one example, the ratio of the minimum section of the gas evacuation side opening 98 to the maximum section of each solution supply opening 96 is greater than 1.

The presence of the upper openings 98 thus serves to purge the internal compartment 90 of the gases contained therein, even if this internal compartment 90 is partially immersed by the feed solution.

Given the section of each opening 98, the cathode gases are easily discharged outside the box 16, from each cathode frame 64. The evacuated gases do not pass through another cathode frame 64 or through another anode frame 66, but exit directly into the lateral intermediate space 60 into which the opening 98 opens. The cathode gases are thus collected between the tank 12 and the closure assembly 18, as can be seen in FIG. will see it below.

The solution supply openings 96 and the gas discharge openings 98 open exclusively into the internal compartment 90 and outside the inner box 16, without opening axially along the axis BB 'of the box 16. .

In particular, the openings 96, 98 do not open into the transverse faces of the cathode frames 64 and are not in communication with other gas evacuation openings provided in other cathode frames 64.

As illustrated by FIGS. 4 and 8, each diaphragm assembly 68 comprises a support frame 1 10 and a fabric 1 12 attached to the support frame 1 10. As illustrated by these figures, the support frame 1 10 comprises two lateral uprights 1 14A, 1 14B. The uprights 1 14A 1 14B are interconnected, from bottom to top, by a lower cross member 1 16, an intermediate cross member 1 18, and an upper cross member 120.

The support frame 1 10 further comprises a grid 122 for supporting the canvas

1 12.

The uprights 1 14A, 1 14B have a height substantially equal to the height of the uprights 80A, 80B of the cathode frame 64. The crosses of the support frame 1 10 are of slightly shorter length than the cross members 82, 84 of the cathode frame 64.

Each upright 1 14A, 1 14B has, in the vicinity of its upper end, a lateral lug 121 which protrudes transversely relative to a longitudinal axis BB 'of the box 16. Each lug 121 delimits a lateral notch 121A for receiving a shutter of the shutter assembly 18.

The lower cross member 1 16 is mounted between the uprights 1 14A, 1 14B and is advantageously reinforced by spacers 124.

It delimits downwards a bottom window 126 of anolyte solution passage intended to be placed opposite the bottom window 92 delimited in each cathode frame 64.

The intermediate cross member 1 18 defines upwardly the window 126. It is located substantially at the same height as the intermediate cross member 82 of each cathode frame 64. Thus, when the diaphragm 68 is applied against an adjacent cathode frame 64, the Lower sleepers 84, 1 16 are in contact with each other, and the intermediate cross members 82, 1 18 are also in contact with each other.

In this example, the grid 122 comprises a plurality of vertical rods 128 extending vertically between the intermediate cross member 1 18 and the upper cross member 120.

The rods 128 of the grid 122 delimit between them openings 129 of solution passage. The rods 128 of the grid 122 are flush with a first transverse face 130 of the support frame 1 10 intended to be placed facing an adjacent anode frame 66.

A seal 132 (FIG. 9) is carried by a second face 134 of the support frame 1 10 located facing and in contact with an adjacent cathode frame 64.

The seal 132 preferably extends at the periphery of the grid 122, along the uprights 1 14A, 1 14B and along the intermediate cross 1 18.

As illustrated by FIG. 4 and FIG. 9, the fabric 1 12 is attached to the first face 130 of the frame 1 10 along the uprights 1 14A, 1 14B, the cross member intermediate 1 18, and the upper cross 120. It is applied against the grid 122, and is preferably attached to the vertical rods 128.

The fabric 1 12 is advantageously fixed in several discrete points on the rods 128. In a variant, the fabric 1 12 is fixed over the entire length of each rod 128.

This attachment prevents the movement of the fabric January 12 to the anode frame. This prevents the narrowing of the evacuation space of the anode sludge by the fabric 1 12. In addition, this fixing of the fabric 1 12 prevents contact between the fabric 1 12 and the anode 76 which avoids the formation of hydronium ions directly into the inner compartment 90 which would be unfavorable to the current yield at the cathode.

The fabric 1 12 is permeable. It allows the passage of the catholyte solution present in the internal cathode receiving compartment 90 to an anode frame 66 through the passage openings 129 delimited by the rods 128.

The fabric 1 12 is for example made of a woven synthetic material, preferably a woven having mechanical and chemical strength properties compatible with its use in the electrolysis cell. The permeability of the web 1 12 is defined so as to establish a difference in height between the cathodic solution and the anodic solution. This difference in height, which varies according to the fouling of the fabric, generates a flow of solution from the cathode to the anode through the web 1 12. This flow of solution slows the retro-diffusion towards the cathode of the hydronium ions. produced at the anode and maintains the pH of the catholyte solution.

As illustrated in FIG. 7, each anode frame 66 has two parallel uprights 140A, 140B and a bottom bottom rail 142 connecting the lower ends of the uprights 140A, 140B. The bottom rail 142 defines with the amounts 140A, 140B, an interior compartment 144 of anode receiving.

According to the invention, each anode frame 66 further comprises a plurality of disjointed support pins 146 projecting upwardly from the bottom rail 142.

The posts 140A, 140B have a height substantially equal to that of the uprights 114 of the diaphragms 68 and that of the uprights 80A, 80B of the cathode frames 64.

Each amount 140A, 140B is intended to be applied to a respective amount

1 14A, 1 14B of an adjacent diaphragm 68.

The uprights 140A, 140B have, at their upper ends, side lugs 148 which protrude transversely to the axis B-B '. Each lateral ear 148 defines a transverse notch 150 for receiving a shutter of the shutter assembly 18. The bottom rail 142 is mounted between the two posts 140A, 140B. It has a width substantially equal to that of the bottom rail 84 of the cathode frames 64.

Advantageously, spacers 151 connect the uprights 140A, 140B with the bottom rail 142 at the lower right and left corners of the inner compartment 144.

According to the invention, each anode frame 66 comprises at least two bearing fingers 146, advantageously at least three disjointed fingers 146.

Each finger 146 extends vertically between a lower end 152 fixed to the lower cross member 142 and an upper free end 154 intended to protrude into the inner compartment 144.

The fingers 146 are located apart from each other and away from the spacers 151, when present. Thus, the intermediate space 156 located between two adjacent fingers 146, taken between the lower end 152 and the free end 154 is completely clear over the entire height and over the entire width of the frame 66.

Thus, the fingers 146 are connected to each other only by the lower cross 142, without being connected by other elements.

Each upper finger end 154 has a height greater than that of the respective windows 92, 126 of circulation, formed in the cathode frames 64 and in the frames 1 10 diaphragms.

Each finger 146 further has a thickness, taken along the axis B-B ', substantially equal to the thickness of the frame 66, and in particular to the thickness of the uprights 140A, 140B and the cross 142.

The fingers 146 have a vertical section which decreases upwards at their free ends 154. They have for example a rounded vertical section, taken in a plane perpendicular to the axis B-B '.

In this example, the fingers 146 extend vertically, parallel to the uprights 140A, 140B.

The width of each finger 146 is smaller than the width of the uprights, taken perpendicular to the axis B-B 'along a horizontal axis.

As illustrated in FIG. 9, and when the diaphragms 68 adjacent to the anode frame 66 are applied against the anode frame 66, on either side of the axis B-B ', the cross member bottom 142 of the anode frame 66 is applied against the lower cross members 116 of the adjacent support frames 110.

In addition, with reference to FIG. 9, the intermediate sleepers 1 18 of the frames

1 of the adjacent diaphragms 68 located on either side of the anode frame 66, maintains the webs 1 12 applied respectively to the two opposite transverse faces 156A, 156B of each finger 146, advantageously at an intermediate region 158 of the finger 146 situated in the vicinity of the free end 154 of the finger 146.

This support ensures precise positioning of the frames 1 10 of the diaphragms 68 when the box 16 is assembled. In addition, the vertical orientation of the grid 122 and the web 1 12 is ensured by the locking of the intermediate cross member 1 18 of each frame 1 10 of diaphragms between the fingers 146 of an adjacent cathode frame 66, and between the intermediate cross member 82 of the adjacent cathode frame 64.

In addition, the fingers 146 apply each intermediate cross member 1 18 of the support frame 1 10 against the intermediate cross member 82 of the adjacent cathode frame 64. This support ensures adequate sealing of the inner compartment 90 of the cathode frame 64, in particular by the sealing of the seal 132 between the crosspieces 82, 1 18.

Referring to Figure 4, the end frames 70A, 70B each have a solid shutter panel 170 to be placed facing the inner anode receiving compartments 144 of the adjacent anode frames 66. They each comprise a removable bottom panel 172 intended to be placed opposite the windows 92, 126 for circulating the anolyte solution. The removable panel 172 is retained by removable holding means 174, and can be passed in an open configuration to allow access to the respective windows 92, 126 and the bottom of the compartment 144.

For each box 16, one of the end frames 70A or 70B includes an anolyte solution outlet connector 176 for connection to the anolyte solution discharge line 36.

The clamping assembly 72 comprises a plurality of longitudinal rods 180 passing through the box 16, and tightening nuts 182 mounted on the rods 180.

The rods 180 are arranged in the vicinity of the lateral faces of the box 16. They extend parallel to the axis B-B '. They pass through the lateral uprights 80A, 80B of the cathode frames 64 and the lateral uprights 140A, 140B of the anode frames 66. The rods 180 are distributed over the height of each frame 64, 66.

In this example, the rods 180 are further disposed on either side of the lateral uprights 1 14A, 1 14B support frames 1 10 without crossing these uprights 1 14A, 1 14B.

Thus, in an inactive configuration of the clamp assembly 72, when the rods 180 are engaged through the cathode frames 64 and through the anode frames 66 and a clearance exists between the anode frames 66 and the cathode frames 64, each diaphragm 68 is removable with respect to the cathode frames 64 and the anode frames 66. This allows efficient and fast cleaning of the diaphragms 68, without having to disassemble the entire box 16.

When the box 16 is assembled, and the clamping assembly 72 is active, the rods 180 and the nuts 182 hold the cathode frames 64, the anode frames 66, and the diaphragms 68, applied against each other firmly and tightly.

Thus, as illustrated in FIG. 9, the box 16 then comprises a succession of unitary assemblies comprising a cathode frame 64, a diaphragm 68, an anode frame 66 and another diaphragm 68.

In this configuration, the uprights 80A, 80B, the intermediate cross member 82, and the lower cross member 84 of the cathode frame 64 are respectively applied to the uprights 1 14A, 1 14B, the intermediate cross member 1 18 and the lower cross member 1 16 of the frame 1 10 of the diaphragm 68, at the second face 134, with the interposition of the seal 132 to achieve a good seal.

The lateral uprights 1 14A, 1 14B, the lower cross member 1 16, and the intermediate cross member 1 18 of the frame 1 10 of the diaphragm 68 are applied respectively to the lateral uprights 140A, 140B, on the lower cross member 142 and on the fingers of FIG. support 146 of the anode frame 66, at the first face 130 of the diaphragm 68.

The fabric January 12 is interposed between the diaphragm frame 1 10 and the anode frame 66 and is held in a vertical position by both the fingers 146 and the gate 128 on which it can be advantageously attached.

This assembly is robust. It ensures a good seal between the internal anode receiving compartments 144 and the internal cathode receiving compartments 90 to ensure that the passage between these compartments is carried out exclusively through the web 1 12. It also ensures accurate positioning of the canvas 1 12, away from the anodes and cathodes.

This assembly can, however, be easily dismantled when it has to be cleaned, which reduces the time required for the production of the electrolysis cell 10 to be put back into production.

When the clamping assembly 72 is active, the windows 92, 126 are located opposite each other. They define in a lower part of the box 16, a continuous conduit 190 anolyte solution flow and anode sludge discharge.

The duct 190 communicates with the inner compartment 144 of each anode frame 66, while being sealingly insulated from each internal compartment 90 of cathode frame 64 and each diaphragm frame upper space 1 10, on the face 134.

The fingers 146 being disjoint, the intermediate passage 156 is completely cleared for the descent of the anode sludge towards the pipe 190 and for the circulation and the evacuation of anolyte and anode sludge through this conduit 190.

The cathodes 74 are formed by metal plates inserted in the inner compartments 90 of the cathode frames 64 through the upper openings 94. Each cathode 74 is provided, along its upper edge, with gripping hooks 160 visible in FIG. .

The anodes are inserted into the inner compartments 144 of the anode frames 66 through the upper openings 147. They are also provided with gripping hooks 162.

The hooks 160, 162 allow the cathodes 74 and the anodes 76 to be introduced and extracted into the box 16. The cathodes 74 and the anodes 76 are respectively connected to the power supply means via the paths 32B, 32A on which they rest respectively.

According to the invention, the closure assembly 18 closes the interior volume 14 upwardly opposite the intermediate spaces defined 60, 62 by the box 16.

The closure assembly 18 thus comprises lateral shutters 200 intended to close the lateral intermediate spaces 60 upwardly, an end cap 202 intended to close off each axial intermediate space 62 and a closure member 204 of each opening. upper 94 closing up the gap between each cathode 74 and the cathode frame 64

Each lateral shutter 200 is mounted between the side wall 22 and the frames 64, 66, 68. It is advantageously received in the notches 101, 121 A, 150 formed respectively in the frames 64, 1 10 and 66.

In particular, each shutter 200 is formed by a sealing plate. It is advantageously applied to a flange 202A integral with the upper strip 30 and received in the notches 101, 150.

The cover 202 advantageously extends opposite the upper strip 26.

As illustrated in Figure 2, the cover 202 is hollow. It has a base wall 205 advantageously in contact with a lateral edge 22 and each lateral shutter 200, a vertical peripheral wall 206 projecting from the base wall 204, and an upper wall 208 connecting the peripheral wall 206. at the upper edge of the band 26. Thus, the end cap 202 caps the axial intermediate space 62 and connects the lateral edges 22 to the strip 26 facing the gas collection openings 46.

The closure member 204 is formed by a seal disposed around each cathode 74 in its upper part to close up the internal compartment 90 at the insertion opening 94.

The closure member 204 is for example fixed on the periphery of the cathode 74. As a variant, it comprises two integral parts respectively of the anodes 76 adjacent to each cathode 74. Each part projects from the anode 76 towards the cathode 74 being applied to the cathode frame and to the cathode 74.

The hood 202 and the lateral shutters 200 thus define a collection path of the cathode gases comprising two axial channels 210 extending under the lateral shutters 200 facing each upper opening 98 and a common collection space 212 located under the hood. end 202 to open opposite openings 46.

The presence of the channels 210 and the common collection space 212 ensures efficient recovery of the cathode gases, regardless of the position of the cathode frame from which it is generated, with minimal pressure drop.

In particular, the risk of clogging cathode gas evacuation openings 98 is very limited, which ensures a safe conveyance of the cathode gas to the exhaust duct 38.

In addition, all the cathode gases are collected since the upper openings 94 are closed upwardly partly by the cathode 74 and partly by the closure member 204. This is the case, including when these cathode gases include ammonia or hydrogen. The security of the cell 10 is thus reinforced, which makes the cell 10 particularly suitable for a sensitive industrial environment.

In particular, the personnel present in the vicinity of the cell 10 is not subject to the emanations of cathode gas. In addition, the cell 10 collects the cathode gases for their treatment, without rejecting them in the atmosphere.

The operation of the electrolysis cell 10 according to the invention will now be described.

Initially, the inner box 16 is assembled. For this purpose, the cathode frames 64, the anode frames 66 are mounted on the longitudinal rods 180 of the clamping assembly. The diaphragms 68 are interposed between each anode frame 64 and each cathode frame 66. End frames 70A, 70B are then mounted at the ends of the box 16, and the nuts 182 are mounted on the rods 180 to tighten the assembly and form a structure of the "filter-press" type.

This being done, the inner box 16 is brought into the inner volume 14 of a tank 12. It is placed against the bottom wall 24 of the tank 12. The anolyte purge pipe 36 is connected to the end fitting 76 on the frame 70A, 70B.

The anodes 76 are inserted into the inner compartments 144. The cathodes 74 are inserted into the inner compartments 90.

The cathodes 74 and the anodes 76 are thus electrically connected respectively to the paths 32A, 32B.

Then, a feed solution containing manganese ions is pumped through the pumping means 40 to the inner volume 14 of the tank 12 through the supply line 34.

This feed solution has a mass concentration of manganese ion greater than 30 g / 1, and especially between 30 g / 1 and 40 g / 1. The feed solution comprises a mass concentration of ammonium sulphate of between 100 and 200 g / l, advantageously of the order of 125 g / l.

The pH of the feed solution is set to be close to 7, in particular between 6 and 7. The feed solution advantageously contains sulphite ions or selenium ions.

The feed solution partially fills the inner volume 14 of the tank 12. The level is adapted to totally drown the lateral inlet openings 96, without completely immersing the upper openings 98 of gas discharge.

The feed solution is fed into the inner compartments 90 to contact the cathode 74, through the side openings 96 in each cathode frame 64, and thereby form a cathodic solution.

A continuous supply electric current is supplied between the cathodes 74 and the anodes 76. The electrons supplied to the cathode 74 react with the manganese ions to form metal manganese on the cathode according to the reaction:

Mn ²⁺ + 2e ^" → Mn.

During this reaction, the electrons present at the cathode partially react with the hydronium ions present in the cathodic solution to form hydrogen.

In addition, in some cases, especially when the pH reaches too basic values, a small amount of ammonia is also formed at the cathode 74. The hydrogen formed at the cathode brews the cathodic solution in the internal compartment 90 allowing a good distribution of the solution around the cathode 74.

The gases formed, in particular hydrogen and ammonia, are then collected in the upper part of the inner compartment 90 and are confined in the compartment 90 by means of the closure members 204 interposed between the cathodes 74 and the frames of FIG. cathode 64 for closing the upper cathode introduction openings 94.

The gases formed are therefore evacuated exclusively through the upper gas evacuation openings 98 towards the outside of the inner box 16.

As discussed above, the presence of upper gas discharge openings 98 ensures effective evacuation of the cathode gases, regardless of the level of feed solution present in the interior compartment 90.

The gas evacuation is also very homogeneous and does not depend on the position of the cathode frame 64 in the box 16.

The evacuated gases are then collected in the axial channels 210 being confined between the surface of the feed solution and the lateral shutters 200.

The gases thus collected run along the box 16 outside thereof, in the axial channels 210 along the side walls 22 of the tank 12, to the transverse end walls 20A, 20B.

The gases are then collected in the common spaces 212 under the end covers 202 and are evacuated through the collection openings 46 and then through the purge lines 38.

The cathode gas thus collected can then be brought to the collection and treatment facility 44 for recycling or disposal in the atmosphere after treatment.

The toxic or dangerous gases that are likely to be generated by the electrolysis process are therefore perfectly confined by the closure assembly 18 of the cell 10 according to the invention.

This collection is carried out without disturbing the electrolysis process, in a simple and inexpensive way.

At the same time, part of the cathode solution present at the cathode 74 flows, under the effect of the hydrostatic pressure created by the difference in height between the catholyte and the anolyte, in the internal compartment 144 through the porous canvases 1 12 of the diaphragms 68, after having passed between the openings 129 delimited by the grid 122. The solution thus enters the inner anode frame compartments 144 and forms an anode solution.

In contact with the anode 76, the water present in the anodic solution reacts to form oxygen, hydronium ions, and electrons depending on the reaction.

3H20 - »½ 02 + 2 H30 + + 2 ^e

The pH of the solution present at the anode 76 is therefore much lower than that of the solution present at the cathode 74. However, the fabric 1 12 prevents the passage of hydronium ions from the interior compartment 144 receiving the anode 76 to the inner compartment 90 receiving the cathode 74. This maintains the pH of the solution present in the inner compartment 90 in the desired range to form metal manganese.

The anodic solution then descends between the support fingers 146, in the lower part of the internal volume 144, then is evacuated towards the ends of the box 16 through the conduit 190 defined by the windows 92, 126.

The tightness being perfectly achieved at the level of the box 16 by the "filter-press" structure, the anolyte solution is totally separated from the cathodic solution during its evacuation out of the box 16.

Then, the anode solution rises in the last anode frame 66 adjacent to each end frame 70A, 70B and is discharged through the end fitting 176, then through the conduit 36.

In the interior anode receiving compartments 144, the presence of manganese ions can lead to parasitic reactions with the water present in the solution to form manganese oxide, hydronium ions and electrons. In addition, gypsum formation can also occur in the anode compartment.

The solids thus formed constitute solid sludge which is evacuated downwards by their weight and partly stored in the compartment 190.

Given the effective maintenance of the webs 1 12 by the grid 122, the webs 1 12 have a flat surface that significantly limits the accumulation of solids, including anode mud on the webs 1 12. In addition, the fingers 146 being disjoint , they offer between them intermediate spaces 156 clear from top to bottom and over the entire thickness of the anode frame 66 for a very effective evacuation of the anode sludge to the exhaust pipes and storage 190 sludge.

The fouling of the anodes 76 and the fabrics 1 12 is delayed in the box 16 according to the invention. This contributes to increasing the productivity of the electrolysis process and to limiting the number of cleanings to be performed for each box 16. During the entire electrolysis process, water circulates continuously in the cooling exchangers 19A disposed between the tank 12 and the inner box 16.

When the fabrics January 12 are too dirty or the compartment 190 is filled with the anode sludge, the box 16 is raised out of the internal volume 14 of the tank 12. The clamping assembly 72 is then partially released to allow the extraction diaphragms 68 and their cleaning, without having to disassemble the entire box 16.

Similarly, when the exhaust ducts 190 are obstructed, they can be cleaned by a simple extraction of the box 16 from the tank 12, then by opening the movable shutter panels 172 located at the end frames 70A , 70B. The box 16 according to the invention therefore has a very advantageous design which limits the fouling by the anode sludge, and which allows a simple cleaning of the box 16, once the fouling become too important.

The metal manganese formed on the two electrodes is recovered by simply dismounting the cathodes 74 and by extracting the cathodes 74 through the upper openings 94.

Given the very precise control of the nature of the solutions present in contact with the cathode 74 and in contact with the anode 76, the efficiency of the electrolysis reaction of the manganese is maximized, and the presence of impurities in the manganese formed is very weak.

Claims

1. - Inner box (16) of manganese electrolysis cell, intended to be placed in a tank (12) containing a feed solution, the box (16) comprising:

a plurality of anode frames (66);

a plurality of cathode frames (64) placed between the anode frames (66);

a plurality of diaphragms (68) interposed between each cathode frame (64) and each anode frame (66);

a clamping assembly (72) capable of keeping the cathode frames (64), the anode frames (66) and the diaphragms (68) pressed against each other,

each cathode frame (64) defining an inner cathode receiving compartment (90), an upper cathode introducing opening (94) in the inner compartment (90), and at least one receiving side opening (96). a feed solution containing manganese ions in the inner compartment (90); characterized in that each cathode frame (64) defines an upper cathode gas discharge side opening (98), the upper discharge opening (98) being disposed above the or each lateral opening of the cathode gas outlet (98). supplying solution (96) to at least partially overflow the feed solution

and in that the upper gas discharge opening opens into the inner compartment (90) and opens out of the box (16).

2. - Box (16) according to claim 1, characterized in that the upper gas evacuation opening (98) has a section greater than the section of the or each lateral opening of electrolyte supply (96). ), advantageously a cross section of oblong shape, in particular elongated along a vertical axis.

3. - Box (16) according to claim 1 or 2, characterized in that each cathode frame (64) defines, above the upper gas discharge opening (98), a receiving notch of a blanking shutter of an electrolysis cell.

4. - Box (16) according to any one of the preceding claims, characterized in that each cathode frame (64) comprises two lateral uprights

(80A, 80B) and an intermediate cross member (82) connecting the lateral uprights (80A, 80B), the lateral uprights (80A, 80B) and the intermediate web (82) delimiting the internal cathode receiving compartment (90), each upper side opening (98) of gas discharge being formed through a lateral upright (80A, 80B).

5. Box (16) according to claim 4, characterized in that each cathode frame (64) defines a bottom rail (84) connecting the two lateral uprights (80A, 80B) under the intermediate cross member (82), the intermediate cross member (82) and the lower cross member (84) delimiting with the side posts (80A, 80B) a bottom window (92) of anodic solution circulation, the window lower portion (92) being sealingly insulated from the inner compartment (90).

6. Box (16) according to any one of the preceding claims, characterized in that each cathode frame (64) comprises at least one lateral lug (100) projecting transversely, the upper gas discharge opening ( 98) being formed through the lateral ear (100).

7. Box (16) according to any one of the preceding claims, characterized in that it comprises a cathode (74) inserted in each cathode frame (64) through the upper insertion opening (94), a sealing member (204) sealing the upper cathode insertion opening (94) in a sealed manner, when the cathode (74) is received in the cathode receiving inner compartment (90).

8. Box (16) according to any one of the preceding claims, characterized in that each anode frame (66) has an interior compartment (144) receiving anode delimited downwards by a bottom cross ( 142)

the anode frame (66) having a plurality of disjointed supporting fingers (146) projecting upwardly from the bottom rail (142), the diaphragms (68) adjacent to the anode frame (66) being applied laterally to the bearing fingers (146).

9. - Box (16) according to claim 8, characterized in that each diaphragm (68) comprises a support frame (1 10) carrying a grid (122), and a cloth (1 12) applied to the grid (122). ), the support frame (1 10) comprising an intermediate cross member (1 18), the bearing fingers (146) applying the intermediate cross member (82) of the cathode frame (64) to the intermediate cross member (1 18) of the support frame (1 10) of an adjacent anode frame (66).

10. Cell (10) for the electrolysis of manganese, of the type comprising:

a tank (12) delimiting an interior volume (14) for receiving a feed solution,

- A box (16) according to any one of the preceding claims, disposed in the interior volume (14),

- a closure assembly (18), sealingly sealing the interior volume (14) of the tank around the box (16) above the upper gas evacuation openings (98); the cell (10) having at least one conduit (36) for purging gases discharged through each upper gas evacuation opening (98) to evacuate them from the vessel (12).

1 1. -Cell (10) according to claim 10, characterized in that the tank (12) contains a feed solution in which the box (16) bathes, each lateral gas evacuation opening (98) opening at least partially to the above the feed solution.

12. - Cell (10) according to claim 10 or 1 1, characterized in that the tank comprises a side wall (22) extending opposite each upper gas discharge opening (98), the box (16). ) and the side wall (22) defining an intermediate lateral space (60) in which the upper gas discharge openings (98) open, the shutter assembly (18) comprising at least one shutter (200) closing towards the upper intermediate space (60) above each lateral gas discharge opening (98).

13.- Cell (10) according to claim 12, characterized in that it comprises an end wall (20A, 20B) extending substantially transversely to the side wall (22), the end wall ( 20A, 20B) delimiting with the inner box (16) an axial intermediate space (62), the closure assembly (18) having an end cap (202) closing the axial intermediate space (202) upwards .

14. A method of electrolysis of manganese, of the type comprising:

- providing a cell (10) according to any one of claims 10 to 13;

supplying the inner compartment (90) of each cathode frame (64) with a feed solution containing manganese ions;

- forming metal manganese on each cathode (74) received in each cathode frame (64);

- Generating cathode gas, especially ammonia and hydrogen, in the inner compartment (90) of each cathode frame (64);

- evacuation of the cathode gases through the upper gas evacuation openings (98) outside the box (16),

collection of the cathode gases produced by each cathode (74) out of the box

(16) in the top of the intermediate space (60) delimited between the tank (12), the box (16) and the closure assembly (18);

- Evacuation of the cathode gas collected in the top of the intermediate space (60) through the purge pipe (36).