Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
  • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
  • C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
  • C25C3/08—Cell construction, e.g. bottoms, walls, cathodes

Definitions

• the invention relates to a cathode for an electrolytic cell for the production of aluminum by fused-salt electrolysis.
• FIGS. 1 a to 1 c show a perspective view of an electrolytic cell.
• the reference numeral 1 denotes a cathode, which may be constructed, for example, from graphite, anthracite or a mixture thereof. Alternatively, graphitized coke-based cathodes can also be used.
• the cathode 1 is generally embedded in a skirt 2 of steel and / or refractory or the like. The cathode 1 can be constructed in one piece as well as from individual cathode blocks.
• a number of power supply bars 3 are introduced into the cathode 1, wherein only a single power supply bar 3 can be seen in the cross-sectional view of FIG. 1a.
• Fig. 1 c can be seen that each cathode block, for example, two power supply bars can be provided.
• the power supply bars serve to supply the cell with the electricity needed for the electrolysis process.
• Fig. 1c shows a detail Lierere arrangement of the anodes in an electrolytic cell.
• the aluminum oxide dissolved in cryolite is split into aluminum and oxygen ions, the aluminum ions moving to the molten aluminum - seen electrochemically the actual cathode - to pick up electrons there , Because of the higher density, aluminum 5 accumulates in the liquid phase below the molten mixture 6 of alumina and cryolite. The oxygen ions are reduced at the anode to oxygen, which reacts with the carbon of the anodes.
• the reference symbols 7 and 8 schematically indicate the negative or positive poles of a voltage source for the supply of the voltage required in the electrolysis process, the value of which is between, for example, approximately 3.5 and 5 V.
• the enclosure 2 and thus the entire electrolysis cell has an elongated shape, with numerous power supply bars 3 are guided vertically through the side walls of the enclosure 2.
• the longitudinal extent of currently deployed cells is between about 8 and 15 meters, while the width dimension is about 3 to 4 meters.
• a cathode, as shown here in FIG. 1 a, is disclosed, for example, in EP 1845174.
• a cathode for an electrolytic cell for recovering aluminum from its oxide in an electrolytic bath comprises: a) an upper part facing the electrolytic bath, and b) a lower part connected to terminals for the electrolysis bath
• the upper part and the lower part are detachably connected to each other at least in sections via an intermediate layer.
• the upper part represents a bottom pan, which is in use in direct contact with the electrolytic bath.
• cathode in the context of the present invention refers to the upper part in conjunction with the lower part.
• cathode is generally understood. It may, for example - but not exclusively - be a so-called cathode bottom, which is composed of a plurality of cathode blocks, so that the core aspects of the invention - namely the structure described above from an upper part in conjunction with a lower part - of this Cathode bottom can be realized as a whole.
• cathode is also intended to refer to the substructures forming such a cathode bottom in the sense of cathode blocks. All features which can contribute to the invention in conjunction with a “cathode” do so in the same way in conjunction with a “cathode block” without that this should be explicitly explained below.
• the upper part serves to accommodate in the process the liquid electrolyte as well as the final product, namely the molten aluminum.
• the upper region which may also be referred to as the "consumption fraction" of the cathode, should be as resistant as possible to wear, for example as a result of mechanical, thermal and / or chemical stress, with respect to its construction.
• the cost of the upper area material should be kept low.
• the lower part of the cathode is to be designed for optimum current supply and current distribution. Due to this division into two parts, as is the feature of the present invention, now the two parts (upper part and lower part) can be manufactured separately from each other and then joined together via the intermediate layer.
• each part can be optimized in terms of its function, without this affecting the function of the other part negative.
• the lower part of higher quality, expensive, but also less wear-resistant material can be formed, as it is the wear or wear Replacement of the upper part is not affected.
• the lower part can be protected by the intermediate layer from chemical influences from the electrolytic bath.
• the intermediate layer not only allows a first separate in an upper part and a lower part structure, but also helps that the advantage that the lower part is made of high quality material, not by penetrating to the lower part corrosive liquids or gases, such as z. B liquid aluminum or electrolyte components, is nullified.
• the intermediate layer which connects the upper part to the lower part, may for example be made of graphite foil, in particular a graphite foil.
• a graphite foil is particularly well suited to prevent penetration of liquid and / or gaseous bath constituents, such as liquid aluminum or electrolyte components, into the lower part or at least largely prevent it, wherein the actual function of the entire cathode is not significantly changed.
• the graphite foil as
• Interlayer has similar electrical properties as the components of the cathode, in particular as the lower part.
• Graphite foil which is produced by at least partial densification of expanded graphite, is particularly well suited to act as a separating layer against chemical influences from the electrolytic bath because of their anisotropy in the film surface and thus very low permeability perpendicular to the film.
• Graphite foil also has the effect of compensating for differences in the surface structure between the upper part and the lower part, as well as thermal expansion and contraction movements, in particular of the upper part.
• Graphite foil has low electrical contact resistance to other carbon materials and very good electrical conductivity. Although the electrical resistivity is normal to the graphite foil. Her is than in film surface, can be achieved due to the very small thickness of graphite foil, a very low absolute electrical resistance.
• the intermediate layer is preferably not provided according to the size of the cathode blocks, but advantageously covers a larger area than the respective lower part of the cathode blocks.
• the intermediate layer may advantageously have an area which corresponds to the size of the total cathode.
• the intermediate layer can be formed with a very small thickness.
• the layer may only be a single graphite foil.
• a suitable film thickness for example, the range between 1 mm and 5 mm has been found. This thickness is sufficient to perform the described functions and on the other hand thin enough that the properties of the film do not significantly affect the functionality of the entire cathode.
• the intermediate layer may be adjusted as desired or necessary with regard to its specific electrical conductivity and / or its electrical contact resistance.
• a coating of the intermediate layer can be provided, which reduces a contact resistance. It is also possible to specifically increase the specific electrical conductivity of the graphite foil in the thickness direction by known measures.
• a suitable current flow within the cathode is used according to the prior art to keep the loss of material on the cathode surface in the interior of the cathode basin as evenly as possible. Since an optimization of the current conduction in embodiments of the invention can be carried out specifically on the lower part, it is possible to adjust the upper part with regard to its design and thus its production in accordance with a to make it easy.
• the upper part may be integrally formed with a side wall of the electrolysis cell. This means that the bottom wall and side walls are molded in one piece. As a result, problems of sealing and jointing between the bottom wall and side walls are avoided.
• the resistance to mechanical or chemical wear in this part is not a criterion.
• this part is subject to little or even no maintenance susceptibility and does not need to be replaced at regular intervals, as is the case in the upper part. For this reason, higher quality materials can be used for the lower part.
• Such a material is, for example, highly conductive graphite, since a significant disadvantage of graphite, namely its low mechanical wear resistance, does not come into play for this application.
• the lower part can be produced according to a preferred embodiment, for example using needle coke as starting material.
• needle cokes are the highest quality petroleum coke and pitch coke, the name deriving from its needle-like structure. Needle coke is characterized, inter alia, by its lower coefficient of thermal expansion and its low electrical resistivity after graphitization, in the longitudinal direction of the needle-like structure. This is particularly advantageous in the lower part of the cathode, where the streams flow at high density.
• the alignment of the needle-shaped coke particles can be achieved in a vertical position.
• the reduction in electrical resistivity causes a lower voltage drop across the cathode and helps to achieve better energy efficiency in fused-salt electrolysis. Since the energy Costs make up a large part of the total cost of the process, which can bring significant savings.
• the upper part of the cathode can be made of any known materials suitable for use as a cathode.
• calcined anthracite, coke or graphite are to be mentioned as starting materials in this context.
• the starting material is ground and sorted by particle size.
• a defined mixture of the fractions of the grain is mixed with pitch and then formed from the upper part. Following this, one or more production steps take place at elevated temperature, based on the heat treatment temperature and
• the cathode may have a vertical power supply.
• This is to be understood as meaning a vertical introduction of current into the lower part of the cathode from below. This advantageously makes it possible to avoid an uneven current distribution in the cathode as in a conventional horizontal power supply.
• the lower part may be provided with vertical pins as power supply lines.
• These pins can be designed as threaded pins, wherein the lower part has threaded holes as connections for receiving the threaded pins.
• pins provided with an external thread can be screwed vertically or approximately perpendicularly into the lower part of the cathode.
• the current can be introduced approximately perpendicularly into the cathode.
• the power supply can be kept very homogeneous by the number and diameter of the pins of the geometry of the cathode is adjusted.
• the geometry of the pins may advantageously correspond to the geometry of threaded nipples for graphite electrodes for electrical steel production. In terms of Current distribution, mechanical strength and screwability, this geometry has proven to be particularly good.
• the relatively large cross-section of the pins causes a high electrical current flow, the length of a sufficiently large distance of the cathode and thus the electrolysis cell from the power supply bar, so that a strong cooling is possible.
• the pins are made of graphite.
• a high thermal stability of the pins and a low electrical resistance can be achieved, which leads to a reduction in the specific energy costs in carrying out the fused-salt electrolysis.
• the lower part of the cathode is in the form of a downwardly tapered trapezoidal body.
• the vertically or approximately perpendicularly introduced stream is homogeneously and evenly distributed in the upper part of the cathode.
• at least some of the cathode blocks of the cathode have such a downwardly tapered trapezoidal body, which advantageously extend parallel to each other.
• the trapezoidal bodies may extend, for example, in the longitudinal direction of the cathode or perpendicular thereto.
• FIG. 1 a schematically shows an electrolysis cell for the extraction of aluminum Prior art aluminum oxide minium in cross section
• Fig. 1b the electrolytic cell of Fig. 1 a in a longitudinal view of
• Fig. 1 c shows an electrolytic cell for the extraction of aluminum from alumina according to the prior art in a perspective view, partially sectioned;
• Fig. 2a is a perspective view of a cathode unit according to a
• Fig. 2b shows a representation of the cathode unit of Fig. 2a from a order
• an electrolysis cell with an embodiment of a cathode 1 according to the invention is shown from different perspectives.
• the illustrated cathode 1 is suitable for use in the recovery of aluminum from alumina according to the Hall-Heroult process.
• the electrolytic cell is provided here with two side walls 1 a1, which together with a bottom wall 1 a2 absorb the electrolytic bath.
• the side walls 1 a1 extend along the longitudinal side of the cathode 1.
• the side wall 1 a1 is composed of individual side wall blocks 1 a3.
• the bottom wall 1 a2 represents an upper or first part 1 a of the cathode 1.
• the cathode 1 is constructed in this embodiment of individual cathode blocks 1 1.
• a lower part 1 b of the cathode 1 comprises, in the exemplary embodiment shown. play a number of terminals 1 b1, which are formed in a lower portion of trapezoidal bodies 1 b2, which taper downwardly in a V-shape.
• the terminals 1 b1 can be designed, for example, in the form of internal threads (not visible in the figures) in order to receive in each case a pin 9 with a corresponding external thread for the power supply to the cathode 1.
• Several of the pins 9 are connected at their opposite sides of the terminals 1 b1 with power supply bars 3, which lead to bus bars 10 to connect the cathode 1 to the corresponding pole of a voltage source.
• the upper part 1 a and the lower part 1 b are connected via an intermediate layer 1 c with each other, which may be, for example, a graphite foil.
• an intermediate layer 1 c with each other, which may be, for example, a graphite foil.
• the graphite foil ensures that no liquid aluminum or electrolyte penetrates to the lower part and in this sense acts as a separating layer.
• the graphite foil has a very low absolute electrical resistance despite poorer specific electrical conductivity perpendicular to the film plane compared to the conductivity within the film plane because of its small thickness of for example a few millimeters and causes a very good electrical contact between the upper part and lower part, so that the Functionality of the cathode is not disturbed.
• the intermediate layer compensates an expansion of the two parts 1 a, 1 b, for example due to thermal fluctuations.
• the two parts may be made of different materials and have different properties with respect to thermal expansion and electrical resistance. So each part can be optimized especially with regard to its function.
• the upper part 1 a is to be designed so that it can withstand wear as well as possible, for example due to mechanical abrasion and uneven electrochemical decomposition.
• the lower part 1 b should be designed with a view to the most homogeneous possible flow and highest energy efficiency. For this he can be optimized with regard to the materials used, since the relatively quickly wearing upper part 1 a, which must be replaced more frequently, is made separately from the lower part 1 b. So it can also be expensive materials such as needle coke can be selected to optimize the long-lived lower part 1 b in terms of the desired homogeneous current distribution.
• the power supply bars 3 in particular copper and aluminum have proven in terms of their low electrical resistivities. Since the power supply bars are spaced from the cathode 1 by the pins 9, they are strongly cooled and therefore it is not necessary to form them from high temperature resistant steel. Due to the lower specific electrical resistance of the metals mentioned for the power supply bars 3 less energy is converted into waste heat and the energy efficiency in the fused-salt electrolysis can be significantly increased.
• the tapers 1 d shown the trapezoidal body act as an increase in distance between the upper part 1 a of the cathode 1 and the current-carrying power supply bar 3 and thus a cooling of the power supply bar 3 supportive.
• Electrolysis bath mixture (aluminum oxide, cryolite)

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• 2010
  • 2010-09-20 DE DE102010041081.0A patent/DE102010041081B4/de not_active Expired - Fee Related
• 2011
  • 2011-09-20 UA UAA201305117A patent/UA104827C2/ru unknown
  • 2011-09-20 RU RU2013118311/02A patent/RU2529432C1/ru not_active IP Right Cessation
  • 2011-09-20 WO PCT/EP2011/066322 patent/WO2012038427A1/de active Application Filing
  • 2011-09-20 JP JP2013529634A patent/JP2013537940A/ja not_active Ceased
  • 2011-09-20 EP EP11760760.6A patent/EP2619352A1/de not_active Withdrawn
  • 2011-09-20 CA CA2811361A patent/CA2811361A1/en not_active Abandoned
  • 2011-09-20 CN CN2011800452821A patent/CN103140610A/zh active Pending

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