EP3551772B1 - Method for handling a slag tank and use of calcium particle slurry to line an inside wall of a slag tank - Google Patents

Description

The present invention relates to the field of handling slag tanks and ladles used in ferrous or non-ferrous metallurgy.

Typically, the pyro-metallurgical industry produces slag, also called slag (“slag”) which floats above the bath of molten metal due to its lower density than that of the molten metal.

Slag collection is carried out in different ways. A first technique lies in tilting the tank in which it floats above the bath of molten metal. Slag can also be collected by scraping or overflowing during tipping.

It is then recovered in tanks or slag ladles (in English “slag pot” or “slag laddle”), which are typically made of refractories, cast iron or steel (in English cast iron or steel).

In the ferrous metallurgical industry, a distinction is made between blast furnace slag and steelworks slag.

Blast furnace slag is a co-product resulting from the manufacture of cast iron in a blast furnace, where it corresponds to the sterile gangue of iron ore to which are added mineral additions and fuel ashes, in particular coke, coal and/or alternative fuels. It therefore separates from the liquid cast iron by difference in density.

The amount of slag produced corresponds directly to the richness of the iron ore used. For a blast furnace operating with iron-rich ores, a proportion of 180 to 350 kg of slag is generally reached for one tonne of cast iron produced.

Steelmaking slag comes from pyro-metallurgical tools, such as various refining tools like pig iron desulfurization tools, converters turning pig iron into steel (BOF- Basic Oxygen Furnace), electric furnaces (EAF-Electric Arc Furnace), stainless steel refining converters (AOD-Argon Oxygen Decarburization) and various secondary metallurgy grader tools. For one ton of steel produced, there are 50 to 150 kg of steel slag produced.

The function of steel mill slag is to collect impurities and unwanted chemical elements. The latter are in the vast majority of cases in the form of oxides. They are generally generated during the use of the pyro-metallurgical tool concerned.

For this, it is essential to manage its composition, so as to make it reactive. A high lime content will, for example, make the slag capable of capturing phosphorus oxides in the converter, which makes its use as a fertilizer possible. In ladle metallurgy, a high lime content makes the slag basic, which is favorable to the capture of alumina inclusions. However, this slag must also spare the refractory bricks.

The present invention relates more particularly to the field of handling slag tanks and ladles but also crucibles and shells, made of steel or cast iron, used in metal preparation workshops in ferrous or non-ferrous metallurgy.

More particularly, the slag concerned in the context of the present invention is slag from steelmaking or non-ferrous metallurgy.

In the context of the present invention, we will simply call “slag tanks” the tanks, ladles, crucibles, shells and the like made of steel or cast iron intended to collect slag from the steelworks or the metallurgical industry.

In the metallurgical industry, the handling of slag tanks is often entrusted to subcontractors, the slag tanks forming part of the boilermaking often belonging to the metallurgical industry.

Among other things during the conveying of the slag vats, for safety reasons, the slag vats should be kept above 150°C in order to avoid any accumulation of water. Indeed, this would generate explosions during the pouring of the slag itself at a temperature of more than 1200°C. It is therefore common practice to heat slag tanks prior to commissioning.

During normal use of slag tanks, their temperature remains stable and most often above 250°C thanks to the accumulation and retention of heat from the slag. The difference in coefficient of expansion between the slag and the cast iron or the steel constituting the tank should in fact cause separations when the temperature of the tank fluctuates. However, during use in regime, the latter does not fluctuate enough to cause separations. Therefore, the formation of "wolf" or "mâchefer" (in English "skull" or in German "bär" or in Dutch "beer") is favored. The present invention aims, among other things, to remedy this lack.

Of course, the formation of "wolf" or "clinker" is inherent in the process and occurs in all cases. However, it can occur to a greater or lesser extent depending on whether the handling process is optimal or not.

The formation of “wolf” or “clinker” also depends on the steelmaking tool that generated the slag. Some being by physical and chemical nature more prone than others to the formation of wolves.

In addition, when the cleaning of the slag tanks is long and it is necessary to "unloop" (mechanically remove the layer of clinker or the wolf which adheres to the walls of the slag tank), the slag tanks cool significantly following the exposure to climatic conditions and to the duration of the “deloupage” process (“deskulling” in English or “ontbering” in Dutch). They must then be reheated later. However, this reheating represents significant calorific energy that is too expensive to return to the optimum temperature ranges around 250°C. Also, generally, after cleaning, the tanks are reheated to around 150°C for the safety reasons mentioned above.

Nowadays, a mineral layer can be deposited on the inside wall of slag tanks. This solution mainly affects the formation of intermediate slag phases. For example, this layer deposited mineral may involve the formation of an intermediate slag phase by means of an endothermic reaction which provides a cooling effect, or on the contrary, the formation of an intermediate phase with a higher melting point, or even play on other effects related to a phase transformation, such as playing on the dilation or on the shrinkage.

These techniques mentioned above mainly use refractory suspensions or mineral suspensions of lime and slag in a mixture. However, these suspensions include mixed compounds whose composition has an impact on the composition of the slag, the chemical properties of which are thus modified, such as for example the basicity (determined by the ratio of the quantity of basic elements to the quantity of acid elements in the solid fraction), basicity which is modified by adapting the basicity of the suspension according to the basicity of the slag poured into the tank or slag ladle.

Although these technical solutions involving suspensions are currently considered to work well, they are also strongly dependent on the chemical composition and the homogeneity of the slag which is poured into the slag tanks or ladles. Consequently, as the composition of slags is frankly not always homogeneous, as its overall composition can also vary from one tool to another or even vary over time for the same tool, the composition of these suspensions must also be adapted. , which makes the process particularly complex and very manual. This is for example described in the document US 5437890 .

The document US5437890 discloses a pretreatment of the walls of slag tanks made of refractory materials with an essentially mineral mixture comprising lime, slag fines and water in order to prevent the adhesion of the slag to the refractory walls, which destroy the walls of the tank.

In the past, sometimes lime slurries were used in this type of application. The workshops of the metallurgical industry then roughly produced a suspension of lime, which had many drawbacks such as low efficiency, a significant thickness of coating on the walls, the presence of residual water in the tank or in the slag ladle, which represents a danger , very dirty and complex applications, very manual and finally, these solutions were very expensive compared to the poor results obtained in terms of simplification of handling.

The documents JP2015094020 , JPH085260 and the document JPS63295458 refer, for example, to treatment with lime suspensions.

For example, the document JP2015094020 discloses a treatment of the inner surface of the slag tanks by spraying a lime suspension to be used in the hot slag recycling process during the realization of the desulfurization treatment. The lime slurry spray nozzle is connected to a lime slurry tank, wherein the lime slurry has a lime concentration of 13.5 to 15% by weight based on the total lime slurry weight. Excess lime slurry and wash water both sprayed on the inner surface of the slag vats returns to the lime slurry tank.

The document JPS63295458 also discloses that slaked lime is fed to the wall of the slag vats to facilitate the draining of slag from the vat when the slag is cooled and solidified. However, this document does not disclose any characteristic of the lime, nor how, nor even at what content it is applied to the inner wall of the slag tanks. Moreover, it does not describe anything regarding the removal of slag by pouring. On the contrary, according to this document, the solidification of the slag is expected in order to be able to remove it from the tank or the slag ladle.

As can be seen, the existing techniques use either mineral suspensions whose composition is complex and requires formulation stages that can be adapted to the composition of the slags, or very coarse mineral suspensions, uncontrolled and ultimately little effective. There therefore remains a need to provide handling of the slag tanks or ladles that is optimized, simple to implement and efficient.

The object of the invention is to overcome the drawbacks of the state of the art by providing a process providing optimized pre-treatment of steel or cast iron slag tanks and ladles in order to facilitate handling thereof on pyro steelmaking sites. -metallurgical between the slag collection point at the iron and steel or pyro-metallurgical tool and the dumping of the slag into a deposit site, typically a landfill site.

To solve this problem, there is provided according to the invention a method for handling a slag tank or ladle comprising an inner wall and an outer wall, according to claim 1.

The method according to the present invention is characterized in that said slag tank or ladle is a steel or cast iron tank or ladle and in that said mineral suspension comprises calcium particles in suspension in an aqueous phase forming a milk of calcium particles , and additives, said calcium particles being chosen from the group consisting of slaked lime, decarbonated dolomite at least partially slaked, limestone and mixtures thereof and having a content of calcium particles of between 20 and 60% by weight relative to the weight of said milk of calcium particles, said mineral layer being a thin layer.

Within the meaning of the present invention, the term "commissioning" means the circulation of the slag tank or ladle for the role expected of a slag tank or ladle, namely the collection of dairy.

As can be seen, the method according to the present invention focuses on steel or cast iron tanks.

Indeed, in the context of the present invention, the choice concerning ladles or slag tanks made of steel or cast iron (and not of refractory), makes it possible to make the most of the difference in coefficient of expansion between the materials. metallic type forming the slag tanks or ladles and the oxides forming the slag.

When milk of calcium particles chosen exclusively from the restricted group consisting of slaked lime, at least partially slaked decarbonated dolomite, limestone and mixtures thereof has a content of calcium particles of between 20 and 60% by weight, relative to the total weight of the milk of calcium particles is lined on the inside wall of the slag tanks or pockets, a fine and homogeneous mineral layer is produced and it has been surprisingly noticed that the slag poured into it does not adhere or very little at the time of dumping in landfill. The layer thus formed acts as a mold release agent forming a layer that significantly reduces the formation of clinker by significantly reducing the adhesion between the slag tank or ladle and the slag that is poured into it.

The specific concentration of between 20 and 60% of calcium particles in the milk of calcium particles allows, when milk of calcium particles is sprayed, that the water contained in the suspension evaporates almost instantaneously on contact with the hot wall and that a layer of calcium particles is applied and thus forms a thin and homogeneous layer, which does not affect the concentration of calcium particles in the slag, but also avoids bringing residual water into the slag, which is dangerous for handling the tank or slag ladle.

Indeed, when the milk of calcium particles is sprayed, the temperature of the tank or the bag is higher than 100°C, which leads to the evaporation of the water contained in the milk of calcium particles and thus leaves a thin and homogeneous layer of calcium particles.

Within the meaning of the present invention, the terms "tank or slag ladle lined with a mineral layer on one surface" means that approximately 70%, for example more than 80%, in particular more than 85%, or even more 90% of the surface is lined with a fine mineral layer.

Calcium oxide, CaO, is often called "quicklime", while calcium hydroxide, Ca(OH) ₂ , is called "hydrated lime" or "slaked lime", the two compounds sometimes being informally called "lime". In other words, lime is an industrial product based on calcium oxide or hydroxide respectively.

“Quicklime” means a solid mineral material whose chemical composition is mainly calcium oxide, CaO. Quicklime is generally obtained by calcining limestone (mainly composed of CaCO ₃ ).

Quicklime can also contain impurities such as magnesium oxide, MgO, sulfur oxide, SO ₃ , silica, SiO ₂ , or even alumina, Al ₂ O ₃ , .. ., the sum of which is at a rate of a few% by weight. Impurities are expressed here in their oxide form, but of course they can appear in different phases. Quicklime generally also contains a few % by weight of residual limestone, called unfired residues.

Suitable quicklime according to the present invention may comprise MgO, expressed as MgO, in an amount ranging from 0.5 to 10% by weight, preferably less than or equal to 5% by weight, more preferably less than or equal to 3% by weight, most preferably less than or equal to 1% by weight relative to the total weight of the quicklime.

Typically, to form slaked lime, quicklime is used in the presence of water. Calcium oxide in quicklime reacts rapidly with water to form calcium dihydroxide Ca(OH) ₂ , in the form of slaked lime or hydrated lime, in a reaction called the hydration or slaking reaction which is very exothermic. In the following, calcium dihydroxide will be referred to simply as calcium hydroxide.

Hydrated lime can therefore contain the same impurities as those of the quicklime from which it is produced.

The slaked lime can also comprise Mg(OH) ₂ in an amount ranging from 0.5 to 10% by weight, preferably less than or equal to 5% by weight, more preferably less than or equal to 3% by weight. weight, most preferably less than or equal to 1% by weight relative to the total weight of the slaked lime.

The slaked lime may also include calcium oxide, which may not have been fully hydrated during the slaking step, or calcium carbonate CaCO ₃ . The calcium carbonate can come from the initial limestone (incuit) from which the said slaked lime is obtained (via calcium oxide), or come from a partial carbonation reaction of the slaked lime by contact with a atmosphere containing CO ₂ .

The amount of calcium oxide in the slaked lime according to the present invention is generally less than or equal to 3% by weight, preferably less than or equal to 2% by weight and more preferably less than or equal to 1% by weight with respect to the total weight of slaked lime.

The amount of CO ₂ in the slaked lime (mainly in the form of CaCO ₃ ) according to the present invention is less than or equal to 5% by weight, preferably less than or equal to 3% by weight, plus preferably less than or equal to 2% by weight, relative to the total weight of the slaked lime according to the present invention.

Within the meaning of the present invention, the term “milk of lime” is understood to mean a suspension of solid particles of slaked lime in an aqueous phase at a concentration greater than or equal to 200 g/kg. The solid particles can obviously contain impurities, namely phases derived from SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ , MnO, P ₂ O ₅ and/or SO ₃ , globally representing a few tens of grams per kilogram. These solid particles may also contain calcium oxide which would not have been hydrated during extinction, just as they may contain calcium carbonate CaCO ₃ and/or magnesium carbonate MgCO ₃ , optionally combined in the form of dolomite.

By analogy, within the meaning of the present invention, the term “milk of calcium particles” means a suspension of solid calcium particles in an aqueous phase at a concentration greater than or equal to 200 g/kg.

Dolomite includes both calcium carbonate and magnesium carbonate in varying proportions as well as various impurities. The cooking of the dolomite causes the release of CO ₂ (decarbonation) and a lively dolomitic product is obtained, namely composed mainly of CaO and MgO, although carbonates, especially CaCO ₃ , can remain in more or less significant quantity. . During quenching to produce an at least partially hydrated decarbonated dolomite, water is added to hydrate the live part of the decarbonated dolomite. The avidity of CaO for water being much higher than that of MgO for water, it is often necessary to hydrate under pressure, for example in an autoclave, resulting in a product that is at least partially hydrated. It is indeed common for a part of the MgO to remain in the form of MgO. The Ca/Mg proportions between the oxide, carbonate and hydrate part are highly variable in decarbonated dolomite that is at least partially hydrated.

The term “limestone” is understood to mean, within the meaning of the present invention, a natural mineral material derived from limestone ore or, when the properties must be controlled, derived from the carbonation of quicklime. Limestone responds to the general formula CaCO ₃ and can obviously contain impurities.

In a particular embodiment according to the present invention, the milk of calcium particles is a milk of lime and said calcium particles are particles of slaked lime.

When the slag is poured into the slag tank or ladle, it is possible that the slaked lime particles of the mineral layer are transformed in situ, entirely or partially into quicklime. However, in one case as in the other, the mold release effect of the mineral layer allows the slag to be discharged, carrying the mineral layer with it and thus leaving the tank or slag pocket perfectly clean for the following operations.

More particularly, when the slag is poured out, the slaked lime is transformed anyway into quicklime because of the temperature of the slag which is higher than 1200°C. This transformation releases water vapor which detaches the spilled slag from the many attachment points formed between the slag and the inner wall of the tank or slag ladle. This significantly reduces the total surface area of slag adhering to the mineral layer formed of lime particles.

Even if the coating is applied and the slag tank or ladle is stored for an indefinite period of time, the mineral layer comprising calcium hydrate carbonates and thus transforms into a layer of calcium carbonate. When the slag is poured onto the calcium carbonate, given the temperature of the slag above 1200°C, the calcium carbonate decarbonates and forms quicklime by releasing CO ₂ and no longer water vapor ( although the two phenomena can occur simultaneously).

Consequently, the handling of slag tanks or ladles is simplified because it is no longer necessary to carry out mechanical lifting of clinker formed, nor to bring the tank or ladle to a sufficient temperature for its commissioning. Once the slag has been deposited in landfill, it is only necessary to spray lime milk again.

The thinness of the layer as well as its homogeneity, being a consequence of the concentration and the size of the particles of slaked lime in the milk of lime, is obviously of considerable importance to achieve the elimination of the mineral layer with the slag during disposal in landfill, but also simultaneously to achieve the "stripping effect" effect.

Said calcium particles in the milk of calcium particles of said mineral suspension have an average particle size d ₅₀ of between 1.5 μm and 10 μm.

Advantageously, said calcium particles in the milk of calcium particles of said mineral suspension have an average particle size d ₅₀ less than or equal to 8 μm, in particular less than or equal to 6 μm, more particularly less than or equal to 5 μm, particularly less than 4 μm.

Advantageously, said calcium particles in the milk of calcium particles of said mineral suspension have an average particle size d ₅₀ greater than or equal to 2 μm, in particular greater than or equal to 2.5 μm.

The notation d _X represents a diameter, expressed in µm, compared to which X % of the particles or grains measured are smaller.

The finer the particles, the better the reaction of releasing water vapor or CO ₂ takes place, which allows the separation of the slag as indicated above.

The reactivity of milks of lime is characterized within the meaning of the present invention according to European standard EN12485 (2010), § 6.11 “Determination of solubility index by conductivity”. This method is itself derived from the work of van Eekeren et al. disclosed in the document " 'Improved milk-of-lime for softening of drinking water', MWM van Eekeren, JAM van Paassen, CWAM Merks, KIWA NV Research and Consultancy, Nieuwegein, September 1993 "produced and distributed by KIWA, Royal Netherlands Institute for Water Analysis (KIWA NV Research and Consultancy, Groningenhaven 7, PO Box 1072, 3430BB Nieuwegein).

The reactivity of a milk of lime is therefore evaluated by the evolution over time of the measurement of the conductivity of a solution prepared by diluting a small quantity of milk of lime in a large volume of demineralised water. In particular, the points corresponding to a conductivity of x% are identified for x% = 63%, 80%, 90% and 95% of the maximum conductivity at the end point (see EN12485(2010) §6.11.6.2). The corresponding dissolution time , t(x%) in s, is then obtained from the graph conductivity vs. time (see Figure 2 of EN12485(2010)).

It is known that the dissolution rate of lime particles in demineralized water is faster (t(x%) smaller) when the particle size is smaller. In other words, the reactivity of milk of lime is generally higher when its constituent particles are smaller.

In a preferred mode of the process according to the present invention, when said mineral suspension contains or is a milk of lime, the latter has a reactivity expressed in the form of a dissolution time t (90%) greater than 0.1 s in particular greater than 0.2 s and less than 10 s, in particular less than 5 s.

When the milk of lime has such a reactivity, the particles of slaked lime have a sufficiently fine particle size to also contribute to the formation of a fine mineral layer, in particular homogeneous, contributing to the simplification of the demoulding of the slag.

Advantageously, said milk of calcium particles has a stability characterized by the bottle test as described in the document WO 2001/096240 .

Said additives of said mineral suspension are chosen from the group consisting of carbohydrates as well as dispersants and plasticizing additives, such as polycarbonates or polyacrylates, or polyphosphonates, in particular DTPMP.

Advantageously, said dispersing or thinning additives of said mineral suspension are present at a mass content of between 0.2 and 5% relative to the weight of said mineral suspension. Preferably, the content of the aforementioned additives is less than or equal to 3%, in particular less than or equal to 2%, more particularly less than or equal to 1.5% relative to the weight of the said mineral suspension. Preferably, the content of the aforementioned additives is greater than or equal to 0.5%, relative to the weight of the said mineral suspension.

In the case of the presence of a carbohydrate, for example at a content of between 0.2 and 3%, preferably between 0.4 and 2%, more preferably between 0.5 and 1.5%, even more advantageously between 0.5% and 1% by weight relative to the total weight of said mineral suspension, the mineral suspension is coated on the inner wall of the slag tanks or ladles.

It is understood that several aforementioned additives may be present in said mineral suspension, in particular one or more carbohydrates with one or more dispersing or thinning agents.

As mentioned above, when the mineral suspension is sprayed, the water contained in the suspension evaporates almost instantaneously on contact with the hot wall. If the mineral suspension contains a carbohydrate, the evaporation of the water contained in the mineral suspension causes a rapid increase in the concentration of carbohydrate until it forms a weak glue favoring the adhesion of the calcium particles to the walls. of the slag tank, also due to the temperature of the slag tank or ladle, which is above 100°C.

When the slag is poured into the tank or slag ladle, on leaving the furnace, the temperature of the slag produces a reaction of calcination of the carbohydrate, possibly simultaneously with the dehydration of the calcium hydroxide when the calcium particles are particles of slaked lime or decarbonated dolomite at least partially hydrated, which facilitates the demolding of the slag, these phenomena occurring from 500°C.

Indeed, the fine mineral layer formed by spraying allows, when the slag is poured into the tank or slag ladle, to produce a shear plane behind the mineral layer (at the interface between the inner wall of the tank or slag ladle and the mineral layer). The shear plane can be produced a priori because the presence of the carbohydrate acts as a weak glue, compared to the potential adhesion of the slag to the inner wall of the slag vessel or ladle.

Then, the mineral layer "stuck" on the inner wall of the slag tank or ladle is composed of fine mineral particles. The temperature of the tank or slag ladle, just before the pouring of the slag, typically has a temperature of 100° C. to 350° C., the temperature at which the mineral particles are stable. The mineral layer can therefore be applied to the slag tank or ladle well before it is used. The slag tanks or ladles thus coated can even be stored

The dispersants or the thinning agents, for example at a content between 0 and 5%, preferably between 0.05 and 3%, more particularly between 0.1 and 2%, can be, for example, polymer or mineral additives such as, for example, anionic polymers or acidic polymers, boric acid and water-soluble salts of boric acid, such as alkali metal borates, aluminum borates, C ₂ -C ₁₀ carboxylic acids , for example containing at least 2 acid groups and the salts thereof, such as for example alkali metal salts or ammonium salts; hydroxides, carbonates, sulphates, nitrates, phosphates, of alkali metals or of ammonium.

The term "anionic polymer" used in the context of the present invention describes all polymers containing acid groups, in free, neutralized or partially neutralized form.

• homopolymères préparés en utilisant un monomère acide tel que l'acide acrylique, l'acide méthacrylique, l'acide maléique, l'anhydride maléique, l'acide fumarique, l'acide itaconique, l'anhydride itaconique, l'acide aconitique, l'acide crotonique, l'acode isocrotonique, l'acide mésaconique, l'acide acétique vinylique, l'acide hydroxyacrylique, l'acide undécylénique, l'acide sulphonique allylique, l'acide sulphonique vinylique, l'acide phosphonique allylique, l'acide phosphonique vinylique, l'acide 2-acrylamido-2-methyl propane sulphonique ou l'acide 2-acrylamidoglycolique.
• copolymères préparés en utilisant au moins un monomère du groupe mentionné ci-dessus et éventuellement un ou plusieurs monomère non acide comme par exemple l'acrylamide, les esters d'acide acrylique, l'acroléine, les esters d'acide méthacrylique, les esters d'acide maléique, les esters d'acide itaconique, les esters d'acide fumarique, l'acétate de vinyle, l'acrylonitrile, le styrène, l'alpha-méthyl styrène, la N-vinyle pyrrolidone, l'acrylate de 2-hydroxyéthyle, le méthacrylate de 2-hydroxyéthyle, l'acrylamide diméthylique, le N-(hydroxyméthyl)acrylamide ou le formamide vinylique.

Examples of such anionic polymers, which are suitable in the context of the present invention, can be chosen from the commercially available anionic dispersants used for the production of mineral suspensions such as:

• homopolymers prepared using an acid monomer such as acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, itaconic anhydride, aconitic acid, l crotonic acid, isocrotonic acode, mesaconic acid, vinyl acetic acid, hydroxyacrylic acid, undecylenic acid, allylic sulphonic acid, vinyl sulphonic acid, allylic phosphonic acid, vinyl phosphonic acid, 2-acrylamido-2-methyl propane sulphonic acid or 2-acrylamidoglycolic acid.
• copolymers prepared using at least one monomer from the group mentioned above and optionally one or more non-acidic monomers such as for example acrylamide, esters of acrylic acid, acrolein, esters of methacrylic acid, esters of maleic acid, itaconic acid esters, fumaric acid esters, vinyl acetate, acrylonitrile, styrene, alpha-methyl styrene, N-vinyl pyrrolidone, 2-acrylate hydroxyethyl, 2-hydroxyethyl methacrylate, dimethyl acrylamide, N-(hydroxymethyl)acrylamide or vinyl formamide.

These polymers can be in the form of free acid, alkali metal salts, partially or entirely, of mixed salts, soluble in water. The preferred anionic polymers are formed from acrylic acid with one or other of the monomers chosen from acrylamide, dimethylacrylamide, methacrylic acid, maleic acid or AMPS (2-acrylamido-2-acid). sulfonic methylpropane) in a preferred composition of 100:0 to 50:50 (by weight) and completely neutralized in the form of a sodium salt.

In a particular embodiment of the present invention, said dispersant or plasticizing agent is a phosphonate or a phosphonic acid chosen from organophosphonic acids, nitrogenous or not, or their salts, more particularly from the group consisting of aminoalkylene polyphosphonic acids, where the alkylene radical contains from 1 to 20 carbon atoms, hydroxyalkylidene polyphosphonic acids, where the alkylidene radical contains from 2 to 50 carbon atoms, phosphono- alkanepolycarboxylics, where the alkane group contains from 3 to 12 carbon atoms and where the molar ratio of the alkylphosphonic acid radical to the carboxylic acid radical is in the range from 1:2 to 1:4, their derivatives, such as their salts, and their mixtures.

In another particular embodiment of the invention, said phosphonate or phosphonic acid comprises, in acid form, from 2 to 8, preferably from 2 to 6 “phosphonic acid” characteristic groups.

More particularly, said phosphonate or phosphonic acid is chosen from the group consisting of aminotris(methylenephosphonic) acid (ATMP), 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), ethylenediamine tetrakis( methylenephosphonic acid) (EDTMP), hexamethylenediamine tetrakis(methylenephosphonic) acid (HDTMP), diethylenetriamine pentakis(methylenephosphonic) acid (DTPMP), (2-hydroxy)ethylamino-N,N-bis(methylenephosphonic ) (HEMPA), 2-phosphono-1,2,4-butanetricarboxylic acid (PBTC), 6-amino-1-hydroxyhexylene-N,N-diphosphonic acid (neridronic acid), N,N'-bis(3-aminopropyl)ethylenediamine hexakis(methylenephosphonic), bis(hexamethylenetriamine)pentakis(methylenephosphonic acid), aminotris(methylenephosphonic) acid oxide, their derivatives such as their salts and their mixtures

In a particular embodiment of the present invention, said carbohydrate is chosen from the group consisting of disaccharides, such as sucrose or sucrose, sorbitol, monosaccharides, oligosaccharides, xylose, glucose, galactose, fructose, mannose, lactose, maltose, glucuronic acid, gluconic acid, erythritol, xylitol, lactitol, maltitol, dextrins, cyclodextrins, inulin, glucitol, uronic acid, rhamnose, arabinose, erythrose, threose, ribose, allose, trehalose, galacturonic acid, and mixtures thereof.

In a particularly preferred embodiment of the method according to the present invention, said carbohydrate is chosen from the group consisting of disaccharides, such as sucrose or sucrose, sorbitol and mixtures thereof.

Besides the aspect of the reduced cost of these carbohydrates, combined with their perfect compatibility with milk of lime, these carbohydrates are known to reduce the viscosity of milk of lime and keep it low over time, thus facilitating the storage conditions of the milk of lime.

In one embodiment of the method according to the present invention, said milk of calcium particles has a viscosity of between 0.1 Pa.s and 2 Pa.s, ie between 100 cps and 2000 cps. Advantageously, the viscosity is greater than 0.15 Pa.s and less than 1 Pa.s, preferably less than 0.6 Pa.s, more preferably less than 0.5 Pa.s, even more preferably less than 0 .3 Pa.s.

The viscosity of a milk of lime is a determining property with regard to the implementation and handling (pumping, transport by pipe, etc.) of the suspension. To this end, experience has established that the dynamic viscosity of the suspension must be less than 2 Pa.s ( US 5616283 ) and that it is desirable not to exceed a dynamic viscosity of 1.5 Pa.s ( WO 2007110401 ).

The viscosity in the context of the present invention is measured by means of a Brookfield viscometer (rheometer) of the DV-III type at 100 rotations/min (rpm) using a No. 3 LV needle.

In yet another variant of the present invention, said calcium particles of the milk of calcium particles have a particle size d ₉₇ of between 7 and 100 μm.

Advantageously, said calcium particles of the milk calcium particles have a particle size d ₉₇ greater than or equal to 10 μm and less than or equal to 20 μm, in particular less than or equal to 15 μm.

More particularly, in the method according to the present invention, said milk of calcium particles has a content of calcium particles greater than or equal to 25% by weight, preferably greater than or equal to 27% by weight, preferably greater than or equal to 30 % by weight, preferably greater than or equal to 35% by weight, relative to the total weight of the milk of calcium particles and a content of calcium particles less than or equal to 55% by weight, preferably less than or equal to 50% by weight, preferably less than or equal to 48% by weight, relative to the total weight of the milk of calcium particles.

In the method according to the present invention, said mineral layer, carpeted on the inner wall has a layer thickness of between 0.1 and 0.5 mm.

Other embodiments of the process according to the invention are indicated in the appended claims.

A subject of the invention is also a use of a milk of calcium particles according to claim 8.

Said milk mineral layer of calcium particles has a layer thickness between 0.1 and 0.5 mm.

According to a preferred use, the milk of calcium particles is a milk of lime and said calcium particles are particles of slaked lime.

Said calcium particles of said mineral suspension have an average particle size d ₅₀ of between 1.5 μm and 10 μm.

Advantageously, said calcium particles in the milk of calcium particles of said mineral suspension have an average particle size d ₅₀ less than or equal to 8 μm, in particular less than or equal to 6 μm, more particularly less than or equal to 5 μm, particularly less than 4 μm.

Advantageously, said calcium particles in the milk of calcium particles of said mineral suspension have an average particle size d ₅₀ greater than or equal to 2 μm, in particular greater than or equal to 2.5 μm.

Said additives of said mineral suspension are chosen from the group consisting of carbohydrates, dispersants, plasticizing additives, such as polycarbonates or polyacrylates, or polyphosphonates, in particular DTPMP.

According to a more preferential use of the present invention, said carbohydrate is chosen from the group consisting of disaccharides, such as sucrose or sucrose, sorbitol, monosaccharides, oligosaccharides, xylose, glucose, galactose, fructose, mannose, lactose, maltose, glucuronic acid, gluconic acid, erythritol, xylitol, lactitol, maltitol, dextrins, cyclodextrins, inulin, glucitol , uronic acid, rhamnose, arabinose, erythrose, threose, ribose, allose, trehalose, galacturonic acid, and mixtures thereof.

More particularly, said carbohydrate is chosen from the group consisting of disaccharides, such as sucrose or sucrose, sorbitol and mixtures thereof.

Preferably, according to the present invention, said milk of calcium particles has a viscosity of between 0.1 Pa.s and 2 Pa.s.

In a preferred use of the present invention, said calcium particles of the milk of calcium particles have a particle size d ₉₇ of between 7 and 100 μm.

Advantageously, according to the present invention, said milk of calcium particles has a content of calcium particles greater than or equal to 25% by weight, preferably greater than or equal to 27% by weight, preferably greater than or equal to 30% by weight, preferably greater than or equal to 35% by weight, relative to the total weight of the milk, of calcium particles and a content of calcium particles less than or equal to 55% by weight, preferably, less than or equal to 50% by weight, preferably less than or equal to 48% by weight, relative to the total weight of the milk, of calcium particles

Other forms of use according to the present invention are mentioned in the appended claims.

1. a) Utilisation dudit outil pyro-métallurgique,
2. b) Nettoyage dudit outil pyro-métallurgique,
3. c) Pulvérisation d'une suspension minérale sur ladite paroi intérieure et/ou sur ladite paroi extérieure dudit outil pyro-métallurgique, préalablement à au moins une étape d'utilisation dudit outil pyro-métallurgique, de manière à tapisser ladite paroi intérieure et/ou ladite paroi extérieure d'une couche minérale, et
4. d) mise en service dudit outil pyro-métallurgique dont ladite paroi intérieure et/ou sur ladite paroi extérieure est tapissée de ladite couche minérale en vue de son utilisation a).

In an unclaimed aspect, the present invention also relates to a method for handling pyro-metallurgical tools comprising an inner wall and an outer wall, said method comprising the steps of

1. a) Use of said pyro-metallurgical tool,
2. b) Cleaning of said pyro-metallurgical tool,
3. c) Spraying of a mineral suspension on said inner wall and/or on said outer wall of said pyro-metallurgical tool, prior to at least one step of using said pyro-metallurgical tool, so as to line said inner wall and/or said outer wall of a mineral layer, and
4. d) commissioning of said pyro-metallurgical tool of which said inner wall and/or on said outer wall is lined with said mineral layer with a view to its use a).

Said outer wall is sometimes also called boilerwork (“shell” in English or “pantser” in Dutch).

In the same unclaimed aspect, this method is characterized in that said pyro-metallurgical tool is a tool made of steel or cast iron and in that said mineral suspension comprises calcium particles in suspension in an aqueous phase forming a milk of calcium particles, and optionally additives, said calcium particles being chosen from the group consisting of slaked lime, at least partially slaked decarbonated dolomite, limestone and of their mixtures and having a content of calcium particles of between 20 and 60% by weight relative to the weight of said milk of calcium particles, said mineral layer being a thin layer.

As can be seen, the method according to the present invention focuses on steel or cast iron tanks.

Indeed, in the context of the present invention, the choice concerning ladles or slag tanks made of steel or cast iron (and not of refractory), makes it possible to make the most of the difference in coefficient of expansion between the materials. of metallic type forming the slag tanks or ladles and the slag oxides.

When milk of calcium particles chosen exclusively from the restricted group consisting of slaked lime, at least partially slaked decarbonated dolomite, limestone and mixtures thereof has a content of calcium particles of between 20 and 60% by weight, relative to the total weight of the milk of calcium particles is lined on the inner wall or the outer wall of the pyro-metallurgical tools, a fine and homogeneous mineral layer is formed, and it has been surprisingly noticed that the frequency of maintenance of these tools pyro-metallurgy was significantly reduced and easier.

In a particular embodiment of this unclaimed aspect, the milk of calcium particles is a milk of lime and said calcium particles are particles of slaked lime.

Advantageously, in this non-claimed aspect, said calcium particles in the milk of calcium particles of said mineral suspension have an average particle size d ₅₀ of between 1.5 μm and 10 μm.

Advantageously, in this unclaimed aspect, said calcium particles in the milk of calcium particles of said mineral suspension have a size mean of particles d ₅₀ less than or equal to 8 μm, in particular less than or equal to 6 μm, more particularly less than or equal to 5 μm, very particularly less than 4 μm.

Advantageously, in this aspect not claimed, said calcium particles in the milk of calcium particles of said mineral suspension have an average particle size d ₅₀ greater than or equal to 2 μm, in particular greater than or equal to 2.5 μm.

The notation d _X represents a diameter, expressed in µm, compared to which X % of the particles or grains measured are smaller.

The finer the particles, the better the water vapor or CO ₂ release reaction occurs which allows the slag to separate as indicated above.

The reactivity of milks of lime is characterized within the meaning of the present invention according to European standard EN12485 (2010), § 6.11 “Determination of solubility index by conductivity”. This method is itself derived from the work of van Eekeren et al. disclosed in the document " 'Improved milk-of-lime for softening of drinking water', MWM van Eekeren, JAM van Paassen, CWAM Merks, KIWA NV Research and Consultancy, Nieuwegein, September 1993 "produced and distributed by KIWA, Royal Netherlands Institute for Water Analysis (KIWA NV Research and Consultancy, Groningenhaven 7, PO Box 1072, 3430BB Nieuwegein).

The reactivity of a milk of lime is therefore evaluated by the evolution over time of the measurement of the conductivity of a solution prepared by diluting a small quantity of milk of lime in a large volume of demineralised water. In particular, the points corresponding to a conductivity of x% are identified for x% = 63%, 80%, 90% and 95% of the maximum conductivity at the end point (see EN12485(2010) §6.11.6.2). The corresponding dissolution time , t(x%) in s, is then obtained from the graph conductivity vs. time (see Figure 2 of EN12485(2010)).

It is known that the rate of dissolution of lime particles in demineralised water is faster (t(x%) smaller) when the size of the particles is smaller. In other words, the reactivity of milk of lime is generally higher when its constituent particles are smaller.

In a preferred mode of this aspect not claimed, when said mineral suspension contains or is a milk of lime, the latter has a reactivity expressed in the form of a dissolution time t (90%) greater than 0.1 s in in particular greater than 0.2 s and less than 10 s, in particular less than 5 s.

When the milk of lime has such a reactivity, the particles of slaked lime have a sufficiently fine particle size to also contribute to the formation of a fine mineral layer, in particular homogeneous, contributing to the simplification of the demoulding of the slag.

The stability of calcium particle milk or mineral suspension can be determined using the stability method called the bottle test as described in the document WO 2001/096240 .

Preferably, in this unclaimed aspect, said additives of said mineral suspension are chosen from the group consisting of carbohydrates as well as dispersants and plasticizing additives and their mixture, such as polycarbonates or polyacrylates, or polyphosphonates, in particular of the DTPMP.

The dispersants or thinners which can be used in the context of the present invention have been mentioned previously.

It is understood that several aforementioned additives may be present in said mineral suspension, in particular one or more carbohydrates with one or more dispersing or thinning agents.

In a particular embodiment of this unclaimed aspect, said carbohydrate is selected from the group consisting of disaccharides, such as sucrose or sucrose, sorbitol, monosaccharides, oligosaccharides, xylose, glucose, galactose , fructose, mannose, lactose, maltose, glucuronic acid, gluconic acid, erythritol, xylitol, lactitol, maltitol, dextrins, cyclodextrins, inulin, glucitol, uronic acid, rhamnose, arabinose, erythrose, threose, ribose, allose, trehalose, galacturonic acid, and mixtures thereof.

In a particularly preferred embodiment of this unclaimed aspect, said carbohydrate is selected from the group consisting of disaccharides, such as sucrose or sucrose, sorbitol and mixtures thereof.

Besides the aspect of the reduced cost of these carbohydrates, combined with their perfect compatibility with milk of lime, these carbohydrates are known to reduce the viscosity of milk of lime and keep it low over time, thus facilitating the storage conditions of the milk of lime.

In one embodiment of this unclaimed aspect, said milk of calcium particles has a viscosity of between 0.1 Pa.s and 2 Pa.s, ie between 100 cps and 2000 cps.

The viscosity of a milk of lime is a determining property with regard to the implementation and handling (pumping, transport by pipe, etc.) of the suspension. To this end, experience has established that the dynamic viscosity of the suspension must be less than 2 Pa.s ( US 5616283 ) and that it is desirable not to exceed a dynamic viscosity of 1.5 Pa.s ( WO 2007110401 ).

The viscosity in the context of the present invention is measured by means of a Brookfield viscometer (rheometer) of the DV-III type at 100 rotations/min (rpm) using a No. 3 LV needle.

In yet another variant of this unclaimed aspect, said calcium particles of the milk of calcium particles have a particle size d ₉₇ of between 7 and 100 μm.

More particularly, in the process according to this unclaimed aspect, said milk of calcium particles has a content of calcium particles greater than or equal to 25% by weight, preferably greater than or equal to 27% by weight, preferably greater than or equal to 30% by weight, of preferably greater than or equal to 35% by weight, relative to the total weight of the milk, of calcium particles and a content of calcium particles less than or equal to 55% by weight, preferably less than or equal to 50% by weight, preferably less or equal to 48% by weight, relative to the total weight of the milk of calcium particles.

Particularly advantageously, in this aspect not claimed, said mineral layer, carpeted on the inner wall has a layer thickness of between 0.1 and 5 mm, preferably between 0.15 and 3 mm, more preferably between 0 .2 and 2 mm, in particular between 0.5 and 1 mm.

In a second unclaimed aspect, the present invention finally relates to a use of a milk of calcium particles chosen from the restricted group consisting of slaked lime, at least partially slaked decarbonated dolomite, limestone and their mixtures for lining an inner wall and/or an outer wall with a mineral layer of a pyro-metallurgical tool made of steel or cast iron to reduce the frequency of handling of said pyro-metallurgical tool, in which said milk of calcium particles is sprayed and has a content of calcium particles of between 20 and 60% by weight, relative to the total weight of the milk of calcium particles.

Advantageously, in this second unclaimed aspect, the mineral layer of milk of lime has a layer thickness of between 0.1 and 5 mm, preferably between 0.15 and 3 mm, more preferably between 0.2 and 2 mm. , in particular between 0.5 and 1 mm.

According to a preferred use, in this second unclaimed aspect, the milk of calcium particles is a milk of lime and said calcium particles are particles of slaked lime.

More particularly, in this second unclaimed aspect, said calcium particles of said mineral suspension have an average particle size d ₅₀ of between 1.5 μm and 10 μm.

Advantageously, in this second aspect not claimed, said calcium particles in the milk of calcium particles of said mineral suspension have an average particle size d ₅₀ less than or equal to 8 μm, in particular less than or equal to 6 μm, more particularly less than or equal to 5 μm, very particularly less than 4 μm.

Advantageously, in this second aspect not claimed, said calcium particles in the milk of calcium particles of said mineral suspension have an average particle size d ₅₀ greater than or equal to 2 μm, in particular greater than or equal to 2.5 μm.

According to a preferred use of the present invention, in this second unclaimed aspect, said additives of said mineral suspension are chosen from the group consisting of carbohydrates as well as dispersants and plasticizing additives, such as polycarbonates or polyacrylates, or polyphosphonates, in particular DTPMP.

It is understood that several aforementioned additives may be present in said mineral suspension, in particular one or more carbohydrates with one or more dispersing or thinning agents.

According to a more preferential use in the context of this second unclaimed aspect, said carbohydrate is chosen from the group consisting of disaccharides, such as sucrose or sucrose, sorbitol, monosaccharides, oligosaccharides, xylose, glucose , galactose, fructose, mannose, lactose, maltose, glucuronic acid, gluconic acid, erythritol, xylitol, lactitol, maltitol, dextrins, cyclodextrins, inulin, glucitol, uronic acid, rhamnose, arabinose, erythrose, threose, ribose, allose, trehalose, galacturonic acid, and mixtures thereof.

More particularly, in this second unclaimed aspect, said carbohydrate is chosen from the group consisting of disaccharides, such as sucrose or sucrose, sorbitol and mixtures thereof.

Preferably, according to this second unclaimed aspect, said milk of calcium particles has a viscosity of between 0.1 Pa.s and 2 Pa.s.

In a preferential use in the context of this second aspect not claimed, said calcium particles of the milk of calcium particles have a particle size d ₉₇ of between 7 and 100 μm.

Advantageously, in the context of this second aspect not claimed, said milk of calcium particles has a content of calcium particles greater than or equal to 25% by weight, preferably greater than or equal to 27% by weight, preferably greater than or equal to 30% by weight, preferably greater than or equal to 35% by weight, relative to the total weight of the milk of calcium particles and a content of calcium particles less than or equal to 55% by weight, preferably less than or equal to 50% by weight, preferably less than or equal to 48% by weight, relative to the total weight of the milk, of calcium particles

It is understood that the present invention is in no way limited to the embodiments described above and that many modifications can be made thereto without departing from the scope of the appended claims.

Claims (13)

1. A method of handling a slag pot or ladle made of steel or cast iron comprising an inner wall and an outer wall, said method comprising the steps of

   a) collecting a slag from said slag pot or ladle of a pyrometallurgical tool,

   b) transporting said slag pot or ladle from said pyrometallurgical tool to a slag disposal site, typically to a landfill site,

   c) emptying said pot or ladle at said slag disposal site, typically at a landfill site, to remove the slag contained therein,

   d) spraying a mineral suspension onto said inner wall of said slag pot or ladle, prior to at least one step of said collection of said slag, so as to line said inner wall with a mineral layer, and

   e) operating said slag pot or ladle lined with said mineral layer for the collection of slag a),

   characterized in that said mineral suspension comprises calcic particles suspended in an aqueous phase forming a calcic particle milk, and additives selected from the group consisting of carbohydrates as well as dispersants and fluidizing additives, such as polycarbonates or polyacrylates or polyphosphonates, said calcic particles being selected from the group consisting of slaked lime, at least partially slaked decarbonated dolomite, limestone and mixtures thereof and having a calcic particles content of between 20 and 60% by weight based on the weight of said calcic particle milk, said calcic particles in the calcic particle milk of said mineral suspension having an average particle size d₅₀ of between 1.5 µm and 10 µm, and in that said mineral layer is a thin layer lined on the inner wall and having a layer thickness of between 0.1 and 0.5 mm.
2. The method according to claim 1, wherein said carbohydrate is selected from the group consisting of disaccharides, such as sucrose or saccharose, sorbitol, monosaccharides, oligosaccharides, xylose, glucose, galactose, fructose, mannose, lactose, maltose, glucuronic acid, gluconic acid, erythritol, xylitol, lactitol, maltitol, dextrins, cyclodextrins, inulin, glucitol, uronic acid, rhamnose, arabinose, erythrose, threose, ribose, allose, trehalose, galacturonic acid, and mixtures thereof.
3. The method according to claim 1 or 2, wherein said carbohydrate is selected from the group consisting of disaccharides, such as sucrose or saccharose, sorbitol, and mixtures thereof.
4. The method according to any one of the preceding claims, wherein said calcic particle milk has a viscosity of between 0.1 Pa.s and 2 Pa.s.
5. The method according to any one of the preceding claims, wherein said calcic particles of the calcic particle milk have a particle size d₉₇ between 7 and 100 µm.
6. The method according to any one of the preceding claims, wherein said calcic-particle milk is a milk of lime and said calcic particles are slaked lime particles, and wherein said milk of lime has a reactivity expressed as a dissolution time t(90%) of more than 0.1 s, in particular more than 0.2 s and less than 10 s, in particular less than 5 s.
7. The method according to any one of the preceding claims, wherein said calcic particle milk has a calcic particle content greater than or equal to 25% by weight, preferably greater than or equal to 27% by weight, preferably greater than or equal to 30% by weight, more preferably greater than or equal to 35% by weight, based on the total weight of the calcic particle milk and a calcic particle content of less than or equal to 55% by weight, preferably, less than or equal to 50% by weight, preferably less than or equal to 48% by weight, based on the total weight of the calcic particle milk .
8. Use of a calcic particle milk selected from the group consisting of the slaked lime, at least partially slaked decarbonated dolomite, limestone and mixtures thereof for lining an inner wall of a slag pot or ladle made of steel or cast iron with a mineral layer of calcic particles, wherein said calcic particle milk is sprayed and has a calcic particle content of between 20 and 60 % by weight, relative to the total weight of the calcic particle milk, said thin mineral layer of calcic particles having a layer thickness of between 0.1 and 0.5 mm, said calcic particles of said mineral suspension having an average particle size d₅₀ of between 1.5 µm and 10 µm, said suspension comprising additives selected from the group consisting of carbohydrates as well as dispersants and fluidizing additives, such as polycarbonates or polyacrylates or polyphosphonates.
9. Use of a calcic particle milk according to claim 8, wherein said carbohydrate is selected from the group consisting of disaccharides, such as sucrose or saccharose, sorbitol, monosaccharides, oligosaccharides, xylose, glucose, galactose, fructose, mannose, lactose, maltose, glucuronic acid, gluconic acid, erythritol, xylitol, lactitol, maltitol, dextrins, cyclodextrins, inulin, glucitol, uronic acid, rhamnose, arabinose, erythrose, threose, ribose, allose, trehalose, galacturonic acid and mixtures thereof.
10. Use of a calcic particle milk according to claim 8 or claim 9, wherein said carbohydrate is selected from the group consisting of disaccharides, such as sucrose or saccharose, sorbitol and mixtures thereof.
11. Use of a calcic particle milk according to any one of claims 8 to 10, wherein said calcic particle milk has a viscosity between 0.1 Pa.s and 2 Pa.s.
12. Use of a calcic particle milk according to any one of claims 8 to 11, wherein said calcic particles of the calcic particle milk have a particle size d₉₇ between 7 and 100 µm.
13. Use of a calcic particle milk according to any one of claims 8 to 12, wherein said calcic particle milk has a calcic particle content of greater than or equal to 25% by weight, preferably, greater than or equal to 27% by weight, more preferably greater than or equal to 30% by weight, preferably greater than or equal to 35% by weight, based on the total weight of the calcic particle milk , and a calcic particle content of less than or equal to 55% by weight, preferably less than or equal to 50% by weight, preferably less than or equal to 48% by weight, based on the total weight of the calcic particle milk .