EP4186963A1 - Storage-stable spent pot-lining material, method for its preparation and its use as fuel - Google Patents

Abstract

The present invention relates to cathodic breakout material containing cathode breakout, in particular from aluminum electrolytic cells, and at least one hydrophobic binder, wherein the hydrophobic binder is selected from wax, a waxy compound or mixtures thereof. A further object of the invention is a method for the production of a cathode scrap material, comprising the following steps: (a) providing cathode scrap, in particular aluminum electrolytic cells, (b) crushing the cathode scrap in at least one crushing device, (c) fractionating the cathode scrap by a Separating device, (d) mixing the cathode slag with at least one hydrophobic binder selected from wax, a waxy compound or mixtures thereof, in a mixing device, (e) portioning the mixture obtained in step (d), (f) removing the cathode slag material, wherein steps (b) to (d) are carried out under an inert gas atmosphere. The invention also relates to the use of the cathode spoilage material as a fuel, preferably in power stations and in the manufacture of mineral wool, cement and steel.

Description

The invention relates to a cathodic material, a process for its production and its use as a fuel, preferably in power stations and in the production of mineral wool, cement and steel.

Aluminum is usually produced by fused-salt electrolysis in aluminum electrolytic cells using the Hall-Heroult process. During the electrolysis of the molten mixture of alumina and cryolite, the aluminum formed is deposited on the cathode and, on the anode, oxygen reacts with the graphite of the anode to form carbon dioxide and carbon monoxide. Over time, the graphite anodes will wear out and need to be replaced.

The cathode lining, which also consists primarily of graphite, is inert to aluminum. However, sodium from the molten bath is absorbed by the cathode lining and forms intercalation compounds that change the wetting behavior of the cathode lining with respect to the electrolyte. The molten cryolite and alumina salts can then more easily penetrate through pores and cracks into the cathode lining and over time completely impregnate it, thereby degrading the electrolytic cell's productivity and energy consumption. Furthermore, the content of iron and silicon impurities in the aluminum is increased.

For this reason, the average service life of the cathode lining in industrial aluminum electrolytic cells is usually between 4 and 7 years. Actual lifetime can also be significantly shorter if premature cathode liner failure occurs, usually caused by cracks in the cathode liner.

To replace the cathode liner of the aluminum electrolytic cell, the cathode liner is broken open and removed mechanically, for example using jackhammers. The resulting cathode spall, also known as "spent pot lining (SPL)", is industrially divided into a "first cut" containing cathode lining material and a "second cut" containing a mixture of cathode lining material and refractory lining material , divided.

Depending on the further disposal of the cathode scrap, the first cut, which consists of the cathode lining graphite, is separated from the second cut, which is a mixture of the cathode lining graphite and the refractory lining. Typically, the cathodic breakout consists of about 55% of the first cut and 45% of the second cut.

The first cut cathode breakout is predominantly graphite with low volatiles and sulfur content. However, toxic compounds, such as cyanides, for example in the form of sodium cyanide, and fluoride compounds accumulate during aluminum electrolysis on or in the cathode lining. These toxic compounds have a high reactivity with water and/or air, in particular oxygen, which can lead to the development of heat, toxic gases and inflammation. Cathode flare is therefore classified as hazardous waste and dangerous goods in most countries, for example under the European Agreement concerning the International Carriage of Dangerous Goods by Road (ADR). In particular, cathodic flare is identified in the transport documents as UN3170 WASTE, ALUMINUM PRODUCTION BY-PRODUCTS, 4.3, III, (E) and is classified as a Dangerous Good of Class 4.3: "Substances which, in contact with water, emit flammable gases".

The reactivity with water and/or atmospheric oxygen limits the usability of the broken-out cathode or requires more complex storage conditions and disposal methods and increases the associated costs.

At present, the major part of the cathodic waste produced during aluminum production is dumped worldwide. On the one hand, landfills are carried out in countries with less strict regulations without any further treatment of the cathode eruption. In other countries, complex thermal or wet-chemical processing has been recognized as necessary before landfilling and is state of the art. At the same time, due to the high carbon content, cathode slag has a thermally interesting calorific value, so that the use of cathode skeleton as fuel is desirable as a possible disposal route.

However, the use of cathodic debris classified as dangerous goods as a fuel is limited by the complex transport, storage and processability. In addition, the usefulness of the cathode spall as a fuel, as well as its disposal costs, is highly dependent on the size of the cathodic spall fragments.

While larger fractions of the cathode slag can be sent to a recycler for use as fuel at comparatively low cost, it is difficult to find a use for smaller grit-like fractions and dusts of the cathode slag because of their large surface area, and associated higher reactivity, often cannot be used as fuel in the recycling plants. The higher reactivity of the smaller fractions of cathodic breakout make them more hazardous and thus more difficult to transport and handle. The disposal of these small fractions of the cathode eruption is correspondingly complicated and expensive.

The WO 2014/026138 A1 describes a cathodic eruption containing at least 65% by weight carbon content and its use as a fuel. The high carbon content is produced by using only the first cut of the cathode breakout and optionally adding thereto a carbon-enriching compound, the carbon-enriching compound being selected from compatible metallurgical residues such as by-products of graphite anode or graphite cathode production. Such by-products are WO 2014/026138 A1 unspecified, but could be, for example, dust, fragments or offcuts from production scrap. Although the carbon-enriched cathode slag generated in this way has a higher calorific value, it is still a hazardous material due to the cyanides and fluorides contained in the cathode sliver, which are highly reactive with water and/or atmospheric oxygen.

The WO 88/06572 A1 describes a process for the production of mineral wool in which, inter alia, briquettes consisting of a mixture of cathode spoil and bituminous coke and coke oven pitch are used as part of the fuel charge of the mineral wool cupola furnace. This is intended to reduce unwanted silicon deposits in the furnace that occur during the manufacture of the mineral wool. The briquette should preferably contain about 40% hard coal coke, 0.45% cathodic debris and 15% coke pitch. A disadvantage of these briquettes is that they contain only extremely small amounts of cathode debris and therefore only small portions of the cathode debris can be used as fuel and disposed of. Furthermore, the coke oven pitch used as a binder is technically difficult to handle due to its high stickiness, the processing window at high temperatures and the partly carcinogenic ingredients such as polycyclic aromatic hydrocarbons.

Against this background, the object of the invention was to provide a cathode breakout material, which allows for safe storage and safe transport of smaller-grain fractions and dusts of the Guaranteed cathode eruption and does not have the disadvantages mentioned in the prior art. Another object of the invention was to provide a simple method for producing such a cathode blast material.

This object is achieved by a cathodic material, containing cathodic material, in particular from aluminum electrolytic cells, and at least one hydrophobic binder, the hydrophobic binder being selected from wax, a waxy compound or mixtures thereof.

The subject matter of the invention is also a method for the production of a cathode spoilage material and the use of the cathode spoilage material according to the invention as a fuel.

Surprisingly, it was found that by adding a hydrophobic binder selected from wax, a waxy compound or mixtures thereof to the cathode blast, a cathode blast material is obtained which has no appreciable reactivity towards water and/or atmospheric oxygen, so that its storage and transport stability is ensured. The cathode eruption is rendered inert to such a complete extent by the addition of the hydrophobic binders provided according to the invention that it is no longer considered hazardous waste to be transported. In particular, the cathode breakout material according to the invention no longer develops any flammable gases when it comes into contact with water and therefore no longer has to be transported as dangerous goods of subclass 4.3 and provided with the appropriate transport documents. Thus, the cathode scrap material according to the invention can be stored and transported without difficulty, which makes its disposal as fuel, preferably in power plants and in the production of mineral wool, cement and steel, cheaper and therefore economically more attractive than landfilling. From an ecological point of view, using it as a fuel is preferable to dumping it in a heap.

A further advantage of the solution according to the invention is that the presence of the hydrophobic binder, selected from wax, a waxy compound or mixtures thereof, in the cathode excavation material according to the invention further increases the calorific value of the cathode excavation according to the added proportion of hydrophobic binder, so that calorific value fluctuations between different batches of cathodic eruption are of no consequence when used as fuel. Surprisingly, it was found that with the cathode waste material according to the invention it is possible to set the combustion behavior within a large degree of freedom and therefore to optimize it when used as fuel for the respective recycling process, so that it can be precisely adapted to the requirements of the corresponding further processing method.

An additional advantage of the invention is that the small, semolina-like fractions and dusts of the cathode eruption, which are highly reactive with water and/or atmospheric oxygen due to their high surface area, also agglomerate with the hydrophobic binder selected from wax, a waxy compound or mixtures thereof and become largely inert so that these components of the cathode eruption, which previously could only be disposed of in a complex and expensive manner due to their reactivity and size, can also be used inexpensively and safely as fuel. For example, the size of the cathode breakout that can be used for the production of mineral wool is usually limited to fractions larger than 50 mm in order to ensure a certain gas permeability of the furnace charge. With the method according to the invention, it is also possible to agglomerate the small fractions of less than 50 mm of the cathode debris using the hydrophobic binder, selected from wax, a waxy compound or mixtures thereof, to a cathode debris material adapted in size to the specifications of the respective further processing method.

Within the scope of the present invention, a distinction is made between cathodic debris and cathodic debris. Cathode debris within the meaning of the invention means that the cathode debris is present with the hydrophobic binder in agglomerated form. Agglomerated means that the individual particles of the cathode eruption are bound together to form larger assemblies by means of the hydrophobic binder.

The cathodic spatter material of the present invention includes cathodic spall, particularly from aluminum electrolytic cells.

In contrast to the cathode spoilage material, cathode spoilage is understood according to the invention as the raw material that is obtained during the mechanical breaking up and removal of the cathode lining, in particular the cathode lining of an aluminum electrolytic cell. Cathode eruption within the meaning of the invention is also referred to as spent pot lining (SPL). The cathode breakout is free of a hydrophobic binder.

In practice, a distinction is made between the first cut and the second cut of a cathode breakout of aluminum electrolytic cells. While the first cut consists only of the material of the cathode lining of the electrolytic cell and thus essentially of graphite, the second cut also contains parts of the refractory lining of the electrolytic cell.

The cathodic breakout in the cathodic breakout material of the present invention may consist of the first cut or the second cut or a mixture of the first and second cuts. It is thus possible to adjust the cathode material that has been broken out to the specifications of the respective further processing method. For example, when using cathodic breakout as fuel in the manufacture of cement, the first and second cuts are typically used, while in the manufacture of mineral wool only the first cut is typically used.

The first cut of the cathode breakout typically comprises 40 to 75 wt% carbon, 10 to 20 wt% fluoride, 8 to 17 wt% sodium, up to 10 wt% alumina, up to 5 wt% aluminum (metal), 0.01-0.5 wt% cyanide, up to 6 wt% silica, 1 to 6 wt% calcium oxide, 0.1 to 0.3 wt% sulfur, and up to to 300 ppm polycyclic aromatic hydrocarbons.

The second cut of the cathode breakout typically comprises 0 to 20 wt% carbon, 4 to 10 wt% fluoride, 6 to 14 wt% sodium, 10 to 50 wt% alumina, 10 to 50 wt% silicon dioxide, 1 to 8% by weight calcium and 0.1 to 0.3% by weight sulfur.

The composition of the first cut of the cathode breakout varies depending on the service life of the cathode lining before it breaks off. The composition of the second cut, consisting of the refractory lining and a small proportion of the cathode lining, is less dependent on the service life of the cathode lining. However, their composition can also vary due to different ratios of the proportions of refractory lining and cathode lining when the same is broken off.

A mixture of the first and second cuts of the cathode breakout typically comprises 25 to 35 wt% carbon, 12 to 18 wt% fluoride, 12 to 18 wt% sodium, 12 to 18 wt% aluminum, bis up to 0.28% by weight cyanide, up to 3.5% by weight silicon dioxide, up to 3.5% by weight calcium oxide, 0.1 to 0.3% by weight sulfur and up to 165 ppm polycyclic aromatics hydrocarbons.

Preferably, a mixture of the first and second cuts of the cathode breakout comprises 50 to 60% by weight of the first cut and 40 to 50% by weight of the second cut.

The cathode rupture contained in the invention cathodic material can in principle for agglomeration with a hydrophobic binder suitable shape and size. However, for the production of pellets, castings, briquettes or extrudates, it has proven to be advantageous in terms of process engineering if the cathode eruption is as homogeneous as possible in grain size. By using the most homogeneous possible particle sizes of the cathode debris, the pellets, castings, briquettes or extrudates produced with it are more stable and there can be a uniform quality in terms of properties, such as the calorific value, from one individual pellet, casting, briquette or extrudate to the next individual pellet, casting , briquette or extrudate can be ensured.

The cathode eruption therefore preferably has a grain size of less than 50 mm, in particular less than 30 mm, particularly preferably less than 0.2 mm. The cathode spall can be ground to the target fineness using a suitable grinder. The individual fines can be separated into suitable fractions by classification using a sieving process. Depending on the desired end product (pellet, casting, briquette or extrudate), different particle sizes can be advantageous. For example, grain sizes that are as small and homogeneous as possible are advantageous for the production of pellets and extrudates, while coarser grain sizes and less homogeneous grain size distributions can also be used for the production of castings and briquettes.

The cathodic breakout material of the present invention contains at least one hydrophobic binder selected from wax, a waxy compound, or mixtures thereof.

A hydrophobic binder within the meaning of the invention is understood as meaning a binder which is immiscible with water. While hydrophobic binders are almost insoluble in water, they are soluble in organic, non-polar media.

Substances or mixtures of substances which can be kneaded at 20° C., are solid to brittle-hard and have a coarse to fine-crystalline structure are usually referred to as waxes have, are translucent to opaque in color, but not transparent, and melt above 40°C without decomposition and are already fluid a little above the melting point or have a low viscosity, have a strongly temperature-dependent consistency and solubility and can be polished under slight pressure.

A waxy compound is understood to mean a compound that has physical behavior similar to that of a wax.

According to the invention, all natural, partially synthetic and synthetic waxes known to those skilled in the art can be used as hydrophobic binders.

Examples of natural waxes are wool wax, China wax, beeswax, preen gland fat, tallow, sugarcane wax, carnauba wax, candelilla wax, cork wax, guruma wax, ouicuri wax, cuba palm wax, espartowa wax, cotton wax, rice bran wax, flax wax, peat wax, rose wax, jasmine wax, peetha wax, myrtle wax , wax fig wax, petroleum wax, earth wax, stuff wax, vein wax, montan wax, petroleum wax and paraffin wax.

Examples of partially synthetic waxes are ester waxes of long-chain wax acids with monohydric fatty or wax alcohols, amides of fatty and wax acids, amide waxes based on fatty acids, such as distearylethylenediamide, ethylene disteamide, stearic acid amide, behenic acid amide, erucic acid amide, oleic acid amide, soy wax, castor wax, rapeseed wax, phthalamide waxes and acylated amides of fatty and wax acids.

Examples of synthetic waxes are hydrocarbon waxes, polyolefin waxes such as polyethylene wax, EVA wax and polypropylene wax, polyester wax and Fischer-Tropsch wax.

The wax is preferably selected from polyolefin waxes, in particular polyethylene waxes, or paraffin waxes.

The use of customary waxy compounds known to those skilled in the art is also fundamentally possible according to the invention.

Preferably, the waxy compound is selected from esters of glycerol with fatty acids, preferably linear carbon chains having 4 to 26, typically 12 to 22, carbon atoms, fatty acids, especially linear aliphatic monocarboxylic acids having 13 to 21 carbon atoms, and mixtures thereof, preferably stearin.

The use of at least one hydrophobic binder, selected from wax, a waxy compound or mixtures thereof, which has a dropping point according to DIN ISO 2176 between 35° C. and 75° C. has proven to be particularly practical.

Hydrophobic binders with a dropping point in this range strike a good balance between adequate strength at ambient temperature and the most energy efficient method of making the cathode breakout material. Due to the comparatively low dropping point, the amount of energy that has to be supplied to liquefy the hydrophobic binder during the production of the cathode breakout material is lower than for hydrophobic binders with a dropping point according to DIN ISO 2176 of over 75° C. and more.

The dropping point of the hydrophobic binder may advantageously be selected depending on the time of year and/or the climate zone in which the cathodic spoil is to be stored and transported to ensure that the hydrophobic binder is sufficiently solid at ambient temperature. A hydrophobic binder with a drop point according to DIN ISO 2176 in the range between 35°C and 45°C is sufficient in a colder season and/or moderate climate zone, while in the warmer season and/or subtropical and tropical climate zones a hydrophobic binder with one Dropping point according to DIN ISO 2176 in the range between 45°C and 75°C can be advantageous.

It is also particularly advantageous if the hydrophobic binder contains the smallest possible proportion of functional groups, preferably is free of functional groups. In the present case, functional groups are understood to mean chemical groups which differ from pure carbon-carbon or carbon-hydrogen single bonds. Such a hydrophobic binder brings about a further significantly reduced reactivity of the cathode breakout material according to the invention with water and/or atmospheric oxygen, so that its storage and transport stability is further improved. Furthermore, the higher proportion of carbon in the hydrophobic binder also increases the calorific value of the cathode debris when it is used as a fuel.

According to a particularly preferred embodiment of the invention, the cathode debris has a calorific value of between 10,500 and 31,000 kJ/kg, determined according to the RAL-GZ 724 method of the Federal Quality Association for Secondary Fuels. The addition of the hydrophobic binder significantly increases the calorific value of the cathode eruption, which is usually in the range from 7500 to at most 10000 kJ/kg.

The cathode spoilage material according to the invention can be adapted to the requirements of the respective further processing method. Depending on the further processing method, the cathode scrap material can advantageously be in the form of pellets, cocoons, castings, briquettes or extrudates.

According to a preferred embodiment of the invention, the cathode breakout material is in the form of pellets or extrudates and contains 75 to 90% by weight cathode breakout and 10 to 25% by weight hydrophobic binder based on the total weight of the cathode breakout material. Cathode spoilage in the form of pellets or extrudates that can be easily dosed is advantageous for using the cathode spoilage material as a fuel in combustions controlled by calorific value, for example in the production of cement in a rotary kiln or in the operation of a power plant. Here, the target temperature can be reliably predicted by charging with a homogeneous fuel with a known calorific value. The smaller the dosage form of the fuel, the more precisely the temperature that is reached can be regulated. Reaching a target temperature within certain limits can be important for maintaining the quality of the manufactured product.

According to an alternative preferred embodiment of the invention, the cathode spoil is in the form of briquettes and contains 60 to 80% by weight cathode spoil and 20 to 40% by weight hydrophobic binder based on the total weight of the cathode spoil.

Cathode spoilage material in the form of briquettes is advantageous for using the cathode spoilage material as a fuel in roughly calorific value-controlled combustion, for example in cupola furnaces used in the manufacture of mineral wool, and in batch furnaces, for example in electric arc furnaces used in steelmaking . With briquettes, the necessary gas permeability of the feed can be achieved more easily due to the coarser form of administration compared to pellets. At the same time, despite the coarser form of administration, the target temperature can be reliably set by charging with homogeneous fuel with a known calorific value.

According to a further alternative preferred embodiment of the invention, the cathode breakout material is in the form of castings and contains 30 to 80% by weight cathode breakout and 20 to 70% by weight hydrophobic binder, based on the total weight of the cathode breakout material. Cathode spoilage in the form of castings is advantageous for using the cathode spoilage as fuel in roughly calorific value-controlled combustions, for example in cupola furnaces used in the production of mineral wool and in batch furnaces, eg electric arc furnaces. As with the use of briquettes, the casting molds make it possible to introduce a large amount of fuel into the process in a gas-permeable manner and at the same time enable a reliable temperature setting due to the homogeneous fuel with a known calorific value.

1. (a) Bereitstellen von Kathodenausbruch, insbesondere von Aluminium-Elektrolysezellen,
2. (b) Zerkleinern des Kathodenausbruchs in mindestens einer Zerkleinerungsvorrichtung,
3. (c) Fraktionieren des Kathodenausbruchs durch eine Trennvorrichtung,
4. (d) Mischen des Kathodenausbruchs mit mindestens einem hydrophoben Bindemittel, ausgewählt aus Wachs, einer wachsartigen Verbindung oder Mischungen davon, in einer Mischvorrichtung,
5. (e) Portionieren der in Schritt (d) erhaltenen Mischung,
6. (f) Entnehmen des Kathodenausbruchsmaterials,

wobei die Schritte (b) bis (d) unter Inertgas-Atmosphäre durchgeführt werden.A further object of the invention is a method for the production of a cathode breakout material, comprising the following steps:

1. (a) providing cathode breakout, especially aluminum electrolytic cells,
2. (b) comminuting the cathode spall in at least one comminuting device,
3. (c) fractionating the cathodic breakout through a separator,
4. (d) mixing the cathode spall with at least one hydrophobic binder selected from wax, a waxy compound or mixtures thereof in a mixing device,
5. (e) portioning of the mixture obtained in step (d),
6. (f) removing the cathode spoil,

wherein steps (b) to (d) are carried out under an inert gas atmosphere.

The method according to the invention is characterized in that it ensures a simple, cost-effective and energy-efficient production of the cathode excavation material. In this case, what was said above in relation to the cathode spoilage material according to the invention in relation to individual technical features applies correspondingly to the corresponding technical features of the method according to the invention.

Step (a) of the method according to the invention provides for the provision of cathodic breakout, in particular aluminum electrolytic cells. The provision of the cathode breakout in step (a) can take place in any shape and size of the cathode breakout and is only limited by the technical possibilities of transporting the cathode breakout. Thus, according to the invention, both coarse pieces and plates of cathode debris more than 1 m in length and very fine dusts of cathode debris and mixtures with a wide variety of grain sizes and plate sizes, such as are usually obtained when a cathode lining is mechanically demolished, can be used in step (a).

In step (b) of the method, the broken cathode is comminuted in at least one comminution device. In principle, a comminution device known to those skilled in the art can be used as at least one comminution device. The at least one comminution device in step (b) is preferably a mill or a crusher. For example, ball mills, impact mills, hammer mills, vertical mills or shredders can be used here. The at least one comminution device causes a reduction in the plate and/or particle size of the cathodic breakout.

In step (c) of the method according to the invention, the cathode eruption is fractionated by a separating device. According to the invention, such separating devices can be used which ensure a homogeneous particle size of the cathode debris. Preferably, the separating device in step (c) is a screen. In principle, however, other separating devices are also conceivable with which a fine fraction of a specific grain size of the cathode sliver can be separated from the cathode sliver comminuted in step (b). The fractionation in step (c) can preferably take place at the same time as the comminution in step (b). However, it is also conceivable that the fractionation takes place only after the comminution in step (b).

The method according to the invention provides that in step d) the cathode debris is mixed with at least one hydrophobic binder selected from wax, a waxy compound or mixtures thereof in a mixing device. Such mixing devices are fundamentally familiar to a person skilled in the art. The at least one hydrophobic binder is preferably metered into the mixing device in step (d) in liquid form or liquefied by heating in the mixing device. The dosing in liquid form can be achieved, for example, by supplying the hydrophobic binder to the mixing device from a separate heated reservoir. However, it is also conceivable that the mixing device itself can be heated or that the wax is liquefied by the energy input of the mixing unit in the mixing device.

Steps (b) to (d) of the process according to the invention are carried out under an inert gas atmosphere. This is necessary because the cathode eruption, in particular the fine fractions thereof produced in step (b), are highly reactive with water and/or atmospheric oxygen, which, as already explained at the beginning, can lead to heat development, toxic gas development and ignition. Such a reaction must therefore be avoided at all costs from a safety perspective. For example, noble gases such as helium, neon, argon, krypton and xenon, as well as nitrogen, can be used as the inert gas. For economic reasons, the use of nitrogen is preferred according to the invention.

In step (e) of the process according to the invention, the mixture obtained in step (d) is portioned. The portioning in step (e) is preferably selected from casting, briquetting, extruding or pelletizing.

In addition, it is also conceivable to fill the mixture obtained in step (d) into previously provided solid cocoons of the hydrophobic binder. The advantage of this variant is that less homogeneous cathode eruptions can also be processed. So for this embodiment the fractionation in step (c) is not indispensable. The hydrophobic binder cocoon can be a geometric hollow shape, in particular a hollow sphere or a hollow cylinder, with a hollow sphere being preferred. The portioning in step (e) would take place for the hollow sphere-cocoon embodiment in such a way that the mixture obtained in step (d) is filled into a solid hollow hemisphere made of the hydrophobic binder and the other solid hollow hemisphere after heating and thus softening the surrounding The edge of the hollow hemisphere is then placed like a lid on the hollow hemisphere filled with the cathode rupture, so that the cathode rupture is completely enclosed by the solid cocoon of hydrophobic binder.

Depending on the type of portioning desired in step (e) of the process according to the invention, different proportions of cathode debris and binder are preferably mixed in step (d).

According to a preferred embodiment of the invention the portioning is pelletizing or extruding and in step (d) 75 to 90% by weight cathode slag and 10 to 25% by weight hydrophobic binder based on the total weight of the mixture of cathode slag and hydrophobic binder , mixed.

According to an alternative preferred embodiment of the invention, the portioning is briquetting and in step (d) 60 to 80% by weight of cathode slag and 20 to 40% by weight of hydrophobic binder, based on the total weight of the mixture of cathode slag and hydrophobic binder, mixed.

According to a further alternative preferred embodiment of the invention, the portioning is in-mold casting and in step (d) 30 to 80% by weight of cathode eruption and 20 to 70% by weight of hydrophobic binder, based on the Total weight of mixture of cathode spall and hydrophobic binder, mixed.

The method according to the invention provides that the cathode debris is removed in step (f). The cathode debris removed in step (f) is preferably present in the administration forms mentioned above.

Before removal in step (f), the broken-out cathode material can be treated with a separating agent in order to prevent the broken-out cathode material from sticking together during storage and transport. Powdered substances are conceivable as release agents. Exemplary release agents are calcium carbonate, talc or silicates.

The process according to the invention can be carried out semi-continuously or continuously.

Finally, the invention relates to the use of the cathode spoilage material according to the invention as a fuel, preferably in power stations and in the production of mineral wool, cement and steel.

Depending on the recycling process in which the cathode scrap material is ultimately used as fuel, the combustion behavior of the cathode scrap material must be adapted to the different requirements of the respective recycling process. This can be achieved with the cathodic material according to the invention by different adjustment of the proportions of cathodic material to hydrophobic binder, by selection of the hydrophobic binder and by different dosage forms such as granules, pellets, briquettes, cocoons, extrudates and casts.

With regard to the technical features of the cathode excavation material according to the invention and its design and production, what was said above in relation to the cathode material according to the invention and in relation to the method for its production applies accordingly to the use.

Fig. 1

Schematische Darstellung einer Ausführungsform des erfindungsgemäßen Verfahrens zur Herstellung von Kathodenausbruchsmaterial

The invention is described in more detail below using an exemplary embodiment with reference to the attached figure. The example is only intended to illustrate the invention and does not limit the scope of the invention.

1

Schematic representation of an embodiment of the method of the invention for the production of cathode spoil

In figure 1 1 is a schematic representation of an embodiment of the method of the present invention for producing cathode spoil. First, a nitrogen-inerted mill with the prepared cathode burst 2 with a particle size of less than 50 mm is charged via a vibrating hopper 3 . If fragments are too coarse or the range in size distribution is too large to be fed to a mill, a nitrogen-inerted crusher can also be installed upstream. The served cathode breakout 2 acts at the same time as a dust separator. Using a sieve 4 close to the ground, the final grain size with which the fine fraction of the cathode debris is discharged from the mill into the heated mixer 5 is determined. In the mixer 5, liquefied wax is added via a dosing unit 6 to a concentration of 20 to 40% by weight of wax based on the total weight of the cathode spoilage material. The wax was liquefied beforehand in a heated wax storage tank 7 . When the correct mixing ratio of wax and cathodic debris has been reached in the mixer 5, the mill 1, the crusher that may be connected upstream and the addition of wax via the dosing unit 6 are stopped. The direction of mixing rotation in the mixer 5 is changed and the cathode spoilage material/wax mixture is poured into slightly conical molds 8 . After cooling to room temperature the finished cathode spoilage material can be removed from the molds 8 and is therefore available as a casting.

EXAMPLES

1300 kg of broken cathode was delivered to a vertical mill. The cathode breakout was pre-sorted, free from impurities such as corundum or aluminum and contained no pieces larger than 5 cm.

The grinding process took place under a nitrogen atmosphere and was carried out with a target fineness of 10% > 90 µm. This means that after grinding was complete, 90% of the cathode breakout was smaller than 90 µm, the remaining 10% was between approx. 150 and 200 µm.

Pellet production - variant A - partial pelleting

1800g of the ground cathode slag was placed on a pelletizer plate preheated to 70°C. The addition of 10 to 15% by weight of wax gave pellets which had formed a solid, round shell on the outside but contained virtually dry ground material on the inside

Pellet production - variant B - full pelleting

In another example, 1800 g of the ground cathode slag was placed on a pan pelletizer preheated to 80°C and 17-21% by weight of wax was added. Pellets were obtained which contained a mixture of wax and ground material over the entire diameter. The angle of attack of the pelletizing disk during the production of the pellets was 30° to the perpendicular and the number of revolutions was 30 rpm.

The pelleting was carried out in a semi-continuous process, in that the ground cathode debris was tracked in such a way that the pellet removal (falling over the edge) turned out to be proportional to the mass. The preheated, liquid wax was dosed (or sprayed on) in the appropriate ratio. The angle of attack of the pelletizing disk during the production of the pellets was 30° to the perpendicular and the number of revolutions was 30 rpm.

Calorific value and calorific value analyzes according to RAL-GZ 724 were then carried out for both partial pelleting and full pelleting. The results are summarized in Table 1.

The "original substance" given in Table 1 means the pellets as they were removed from the pelletizing machine. "Dry matter" refers to the pellets that have been subjected to drying in accordance with DIN EN 14346 after removal from the pelletizing machine.

By varying the rotation speed from 20 to 40 rpm and the angle of attack from 15° to 30° to the perpendicular, pellets with different average diameters d=8 to 17 mm of the pellets can be obtained.

Production of castings

In another example, castings were made. For this purpose, a sieve fraction <3 mm was separated from the fine fraction of the cathode debris and used.

Approx. 3 kg of paraffin with a melting point between 70 and 80 °C were liquefied and heated to approx. 100 °C in a batch process. The kinematic viscosity at 100 °C is between 3 and 10 mm ² /sec.

With constant stirring, 10 kg of the sieve fraction <3 mm separated from the fine fraction of the cathode debris were slowly added in small portions. After everything had been stirred into a homogeneous mass, a casting weighing 8 kg was first cast. The mass remaining in the mixer was again added Add 3 kg of paraffin and, after melting, another 10 kg of fines of the sieve fraction <3 mm separated from the fines of the cathode breakout are added with stirring. The second casting was created from this. Other castings were similarly made by repeating the respective steps.

The castings of the sieve fraction < 3 mm separated from the fine fraction of the cathode debris dehomogenize somewhat during the solidification process. This leads to a higher concentration of wax near the surface of the casting.

It can be assumed that, with increasing fineness of the cathode breakout, less wax is required for stable shaping, regardless of the dosage form chosen. The addition of more wax than is necessary for physical stability is a good means of increasing the calorific value at will and adapting it to the requirement of subsequent use.

Claims (15)

Cathode spatter material containing cathode spatter, in particular from aluminum electrolytic cells, and at least one hydrophobic binder, characterized in that the hydrophobic binder is selected from wax, a waxy compound or mixtures thereof. Cathode breakout material according to claim 1, characterized in that it contains 30 to 90% by weight of cathode breakout and 10 to 70% by weight of hydrophobic binder based on the total weight of the cathode breakout material. Cathode debris according to Claim 1 or 2, characterized in that the cathode debris has a particle size of less than 50 mm. Cathode breakout material according to any one of the preceding claims, characterized in that the cathode breakout consists of the first cut or the second cut or a mixture of the first and second cuts. Cathode breakout material according to one of the preceding claims, characterized in that the hydrophobic binder has a dropping point according to DIN ISO 2176 between 35°C and 75°C. Cathode breakout material according to any one of the preceding claims, characterized in that the wax is selected from natural wax, semi-synthetic wax or synthetic wax and mixtures thereof, preferably from polyolefin waxes, in particular polyethylene waxes, or paraffin waxes. Cathode breakout material according to any one of the preceding claims, characterized in that the waxy compound is selected from esters of glycerol with fatty acids, preferably linear carbon chains having 4 to 26, typically 12 to 22 carbon atoms, fatty acids, in particular linear aliphatic monocarboxylic acids having 13 to 21 carbon atoms , and mixtures thereof, preferably the waxy compound is stearin. Cathode spoilage according to any one of the preceding claims, characterized in that the cathode spoilage material is in the form of pellets, cocoons, castings, briquettes or extrudates. Cathode spoilage material according to one of the preceding claims, characterized in that the cathode material has a calorific value of between 10,500 and 31,000 kJ/kg, determined according to the RAL-GZ 724 method of the Federal Quality Association for Secondary Fuels. A method of making a cathodic breakout material, comprising the steps of: (a) providing cathode breakout, especially aluminum electrolytic cells, (b) crushing the cathode spall in at least one crushing device, (c) fractionating the cathodic breakout through a separator, (d) mixing the cathode spall with at least one hydrophobic binder selected from wax, a waxy compound or mixtures thereof in a mixing device, (e) portioning of the mixture obtained in step (d), (f) removing the cathode spoil, wherein steps (b) to (d) are carried out under an inert gas atmosphere. 11. A method for producing a cathode waste material according to claim 10, characterized in that the at least one comminuting device in step (b) is a mill or a crusher. 12. A method for producing a cathodic waste material according to claim 10 or 11, characterized in that the separating device in step (c) is a screen. Method for producing a cathode blast material according to one of the preceding claims, characterized in that the at least one hydrophobic binder is dosed into the mixing device in step (d) in liquid form or is liquefied by heating in the mixing device. A method of making a cathodic spoil as claimed in any one of the preceding claims, characterized in that the portioning in step (e) is selected from pouring into shape, briquetting, extruding or pelletizing. Use of the broken-out cathode material according to any one of Claims 1 to 9 as fuel, preferably in power stations and in the manufacture of mineral wool, cement and steel.

Images