Method for producing carbonate-bonded compressed products

Abstract

A method for producing a carbonate-bonded compressed product includes the steps of: preparing a particulate material containing a particulate carbonatable binder; compressing the particulate material to form a compressed body having pores containing porous water; and carbonating the compressed body to produce a carbonate containing calcium carbonate, thereby converting the compressed body into the carbonate-bonded compressed product. The carbonatable binder contains fluoride. To limit the leaching of fluoride from the carbon, a fluoride-adsorbing magnesium-containing solid compound containing surface hydroxyl groups bonded to magnesium atoms is provided in the compressed body. Prior to the carbonation step, at least one magnesium-containing additive is distributed throughout the particulate material. This additive has a magnesium content of at least 30% by weight MgO and contains a fluoride-adsorbing magnesium-containing solid compound, and / or generates this fluoride-adsorbing magnesium-containing solid compound in the particulate material by reaction in the porous water.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a carbonate-bound compressed product, comprising the steps of: preparing a particulate material containing a particulate carbonatable binder composed of particles having a sieve size of less than 500 μm; compressing the particulate material to form a compressed body having pores containing porous water; and carbonating the compressed body with a gas containing carbon dioxide for a predetermined period to produce a carbonate containing calcium carbonate, thereby converting the compressed body into the carbonate-bound compressed product. The particulate carbonatable binder contains calcium oxide and silicon dioxide, has a CaO / SiO2 ratio higher than 1.1 and a pH of at least 10.5 measured after 24 hours of contact according to DIN EN 12457-4:2003-01. Since the carbonatable binder also contains fluoride, i.e., fluoride ions, the carbonate-bound compressed product has a fluoride leaching value that can be measured according to DIN EN 12457-4:2003-01. [Background technology]

[0002] Various industrial manufacturing processes produce carbonatable materials as by-products. These by-products include, for example, fly ash, bottom ash (especially bottom ash from municipal waste incineration), and slag produced during phosphorus production, or slag produced during the production of iron or non-ferrous metals such as zinc, copper, lead, and iron or steel. Dust from steelmaking furnace air filters, for example, can also be carbonatable, especially if it contains calcium oxide and has a sufficiently high pH value. Some of these by-products can be used for different purposes. Blast furnace slag can be used, for example, in road construction and cement production. Some slags, such as general steelmaking slag with a high neutralization value (e.g., LD slag), can also be used, for example, as soil conditioners. However, other materials such as bottom ash and stainless steelmaking slag contain considerable amounts of heavy metals, which pose problems in terms of leaching behavior.

[0003] In order to limit the economic and environmental impacts of these household waste materials and industrial waste materials, attempts are increasingly being made to develop methods for treating these materials, i.e., methods for converting these waste materials into economically valuable materials. Many of these waste materials are alkaline and contain carbonatable phases such as calcium oxide and / or hydroxides. Other phases containing calcium silicate and calcium magnesium silicate, for example, may also be carbonatable. It is known that when the fine fraction of these carbonatable waste materials is used as a fine carbonatable binder, either alone or in combination with a coarser aggregate fraction, it is possible to obtain materials with good mechanical quality due to the carbonation of the fine binder fraction. Furthermore, carbonation can also help prevent the leaching of contaminants such as heavy metals that may be contained in these carbonatable binders.

[0004] One of the main groups of carbonatable materials is steelmaking slag. These slags include, for example, EAF slag, BOF (especially LD) slag, AOD slag, VOD slag, ladle slag and tundish slag. All of these slags usually contain fluorides. Fluorides can be added in the form of fluorite (CaF2) to the liquid slag present on top of the molten iron or steel in order to control the viscosity and melting point of the liquid slag. In particular, phosphorus slag produced in the process of yellow phosphorus production also has a high pH and fluoride content.

[0005] Stainless steel slag is a specific group of slags that contain not only fluorides but also relatively large amounts of heavy metals such as chromium and, often, nickel and molybdenum. As disclosed in Patent Documents 1, 2, and 3, the leaching problem of stainless steel slag can be solved by crushing the slag, removing the valuable stainless steel particles therefrom, and applying different fractions of the remaining crushed slag to limited uses, for example, as fine or coarse aggregate in concrete or asphalt. This method solves the leaching problem of fluorides as well as heavy metals. This method has been successfully used in practice to recycle the coarser fractions of stainless steel slag as aggregate for concrete or asphalt production.

[0006] A more problematic fraction of stainless steel slag is its fine powder, more specifically, the fine fraction of crushed steel slag with a particle size of less than 0.5 mm. This fine fraction has a significantly higher γ-C2S content than the coarser fraction. As a result, this fine fraction has high water absorption properties and is therefore unsuitable for use in concrete or asphalt applications. However, the fine fraction can be used as a carbonateable binder to produce carbonate binders for blocks, bricks, and even larger construction materials.

[0007] Patent Document 4 discloses a method in which a particulate carbonizable material, particularly fine powder of crushed stainless steel slag having a size of 0 mm to 0.5 mm, is used as a carbonizable binder for producing a high-quality carbonate-bonded compactor. In this known method, the particulate material is first compressed at a relatively high compression pressure of 5 MPa to 65 MPa, and the obtained compactor is subsequently carbonized under relatively high temperature and pressure. In this way, a carbonized compactor having high compressive strength can be produced. By controlling the porosity and intrinsic permeability of the compactor and carbonizing for several hours (more specifically, 18 hours under pressurization and heating), a compressive strength of 26 MPa to 66 MPa was obtained using fine stainless steel slag of 0 μm to 500 μm. Leaching of various heavy metals has been measured according to DIN EN 12457-4, but no mention is made of fluoride leaching.

[0008] Patent Document 5 discloses an alternative carbonization method capable of producing a high-strength carbonate-bonded compactor without the need to carbonize the compactor under high pressure and high temperature, that is, without the need to use a high-pressure carbonization chamber. In this known method, the compressed particulate carbonizable material is first carbonized at a low carbon dioxide partial pressure in a carbonization gas, and then the article is further carbonized at a high carbon dioxide partial pressure. Also, in this patent publication, no mention is made of fluoride leaching despite the fact that stainless steel slag was used as a binder and also as a coarser aggregate fraction.

[0009] Patent document 6 discloses a method for reducing fluoride leaching from steelmaking slag, particularly powdered steelmaking slag. To promote the elution of calcium ions from the slag surface, powdered steelmaking slag is mixed with a 5% to 20% ammonium chloride solution. The resulting mixture is placed in a reactor, and flue gas containing approximately 20% carbon dioxide is passed through the loose mass of powdered steelmaking slag for two hours. This uniformly carbonates the steelmaking slag particles, creating a calcium carbonate coating on the surface of the slag particles. This calcium carbonate coating has been found to reduce fluoride leaching from the slag particles.

[0010] A drawback of this method is that it is not suitable for reducing fluoride leaching from compressed carbonated steelmaking slag. When compressed steelmaking slag is carbonated, the steelmaking slag particles are not carbonated uniformly. In particular, if the porous water is rich in calcium ions due to the increased elution of calcium ions in the presence of ammonium chloride, most of the carbon dioxide gas has already reacted on the surface of the compressed material. The calcium ions consumed during the carbonation reaction are rapidly replenished by the diffusion of calcium ions from the center of the compressed material toward its surface. The calcium carbonate formed on the surface of the compressed material hinders the penetration of carbon dioxide into the compressed material and therefore hinders the carbonation of the central part of the compressed material.

[0011] Due to the non-uniform carbonation of steelmaking slag compresses, the method disclosed in Patent Document 6 is unsuitable for eliminating the fluoride leaching problem of such compresses. In the center of the compresse, the steelmaking slag particles are not sufficiently carbonated. On the surface, the steelmaking slag particles are carbonated over a much wider area. However, the inventors have found that when steelmaking slag compresses are strongly carbonated to obtain high compressive strength, the fluoride leaching value does not decrease, but rather substantially increases. The presence of ammonium chloride does not prevent this increased fluoride ion leaching because ammonium chloride does not immobilize fluoride ions. Ammonium chloride only increases the leaching of calcium ions in the pore water, thereby promoting the carbonation reaction.

[0012] Therefore, the inventors have found that when a fluoride-containing carbonatable binder is used in the production of carbonate-bound compresses, fluoride leaching due to the carbonation process is not reduced, but rather becomes even more problematic. In fact, the fluoride leaching values ​​of carbonate-bound compresses were found to be significantly higher than those of the particulate material before the carbonation process. Leaching limits are set by different governments for fluoride leaching and for various heavy metals. For example, in the Wallonia region of Belgium, an upper limit of 5.0 mg / L or 50 mg / kg of dry material is set for fluoride leaching (the liquid / solid ratio applied in the leaching test is 10 / 1). Fluoride leaching is measured according to the analytical method ISO10359-1(1992) DIN38405-19-88 in accordance with DIN 38414-S4(EN-12457-4). In the Wallonia region of Belgium, the upper limits for chromium (Cr(VI)) leaching are 0.1 mg / L (1.0 mg / kg dm), for molybdenum (Mo) leaching 0.15 mg / L (1.5 mg / kg dm), and for nickel (Ni) leaching 0.2 mg / L (2.0 mg / kg dm). All of these leaching values ​​must be measured according to the same EN-12457-4 standard, using the following analytical methods: for Cr(VI) ISO11083(1994) / calorimetric method, for Mo DIN3806-22(1988) ICP / AAS method, and for Ni ISO8288(19996) DIN38406-06-08-85 / DIN3806-22(1988). Regarding steelmaking slag, the upper limit for vanadium (V) leaching has not yet been established in many countries, but for example, it is 0.18 mg / L in Germany and 1.0 mg / kg dm (dry material) in the Netherlands. The inventors have found that when stainless steel manufacturing slag fine powder is used as a carbonatable binder, the upper limit of fluoride leaching, 50 mg / kg dm, is often exceeded after the carbonation process. This can possibly be explained as follows.

[0013] Fluorides in steelmaking slag are particularly present in the mineral phases of casspidin (Ca4Si2O7F2) and fluorite (CaF2). In the paper Non-Patent Literature 1 by Remus Ion Iacobescu et al. (2014), the mineral phase of the fine powder of AOD stainless steel converter slag used in the described experiment contained, for example, 21.2% by weight of casspidin and 0.3% by weight of fluorite.

[0014] CaF2(=[Ca 2+ ]·[F - ] 2 ) about K sp Value (solubility product): 3.9 10 -11 Based on this, a saturated aqueous solution of CaF2 contains approximately 8 mg / L (=0.68 mM) of fluoride (=F - ) will be contained. Therefore, such a CaF2 solution will exceed the fluoride leaching limit in the Walloon region. However, the pore water in steelmaking slag is a saturated solution of Ca(OH)2 and therefore contains a relatively large amount of calcium ions. K for Ca(OH)2 sp Value 5.02 × 10 -6 Based on this, porous water saturated with Ca(OH)2 and having a pH of 12.5 would have a calcium concentration of approximately 200 mg / L (= 5.0 mM). As a result of such a high calcium concentration in the porous water, the dissolution of CaF2 in the porous water is significantly suppressed to a value of less than 0.1 mM fluoride (= 1.9 mg F / L). This can also be seen in Figure 10 of the paper Non-Patent Literature 2 by Ryo Inoue et al. (2002).

[0015] Regarding the fluoride contained in caspidin, from Figure 14 of the same paper, it can be seen that when a dispersion of caspidin powder is shaken in water, caspidin releases fluoride, but at higher pH values, the release of fluoride significantly decreases. For example, at pH 12, only about 1 ppm to 2 ppm of F was released. Therefore, the leaching of fluoride from alkaline carbonizable materials such as ironmaking slag and steelmaking slag is extremely low as a result of the high pH of these materials and their high calcium content. When the pH of the pore water decreases, for example during the carbonation process, more fluoride may leach from caspidin.

[0016] However, the carbonation of the carbonizable binder not only decreases the pH of the particulate material but also, in particular, decreases the calcium concentration in the pore water. Based on the K 2+ value for CaCO3 (=[Ca 2- ·[CO3 sp ) of 3.3×10 -9 , a saturated calcium carbonate solution would actually contain only 2.3 mg / L (=0.057 mM) of calcium ions. At such a low calcium concentration in the pore water, a significant amount of CaF2 would dissolve, and based on the K sp value of CaF2, a fluoride concentration of about 16 mg / L (=0.8 mM) would result, which is significantly higher than the fluoride leaching limit of 5 mg / L. Suchandra Sar et al. (2020) also state in the paper of Non-Patent Document 3 that in order to efficiently remove fluoride from primary and secondary raw materials for zinc extraction, the CO3 2- concentration in the solution must be maintained sufficiently high to exceed the solubility product of CaCO3 before reaching the solubility product of CaF2. In this way, the available carbonate ions in the system limit the calcium ion concentration by the precipitation of CaCO3, which promotes the dissolution of CaF2.

Prior Art Documents

Patent Documents

[0017]

Patent Document 1

[0018] [Non-Patent Document 1] "Stabilization and Microstructural Modification of Stainless Steel Converter Slag by Addition of Aluminum Rich By-Product" [Non-Patent Document 2] "Fluorine-containing Mineral Phases in Ironmaking and Steelmaking Slags and Their Solubilities in Aqueous Solution" [Non-Patent Document 3] "Experimental Study on the Dissolution Behavior of Calcium Fluoride" [Overview of the project] [Problems that the invention aims to solve]

[0019] Therefore, a problem with conventional carbonation methods for producing carbonate-bound compresses with fluoride-containing carbonatable binders is that the carbonation process required to produce such carbonate-bound compresses, particularly those having a compressive strength of at least 10 MPa, significantly increases fluoride leaching, especially to an extent that may exceed existing fluoride leaching limits.

[0020] Another challenge with conventional carbonation methods is that if the carbonatable binder contains vanadium, the carbonation process also increases vanadium leaching. This effect on vanadium leaching is described in the paper "Changes in mineralogical and leaching properties of converter steel slag resulting from accelerated carbonation at low CO2 pressure" by Andre van Zomeren et al. (2011). [Means for solving the problem]

[0021] The primary objective of the present invention is to provide a novel method for producing carbonate-bound compresses with a fluoride-containing particulate carbonizable binder that enables limiting the fluoride leaching value of carbonoxides.

[0022] For this purpose, the method of the present invention is characterized in that, prior to the carbonation step, at least one magnesium-containing additive is distributed in the particulate material to provide a fluoride-adsorbing magnesium-containing solid compound containing surface hydroxyl groups bonded to magnesium atoms in the compressed body, wherein the additive has a magnesium content of at least 30% by weight MgO as expressed by dry weight as an oxide, and comprises the fluoride-adsorbing magnesium-containing solid compound, and / or generates the fluoride-adsorbing magnesium-containing solid compound in the particulate material by a reaction in the porous water.

[0023] According to the present invention, it has been found that fluoride ions adhere very strongly to the surface hydroxyl groups of a fluoride-adsorbing magnesium-containing solid compound. Fluoride ions can also be adsorbed onto the fluoride-adsorbing magnesium-containing solid compound by substitution of hydroxyl groups with fluoride. Therefore, the adsorption of fluoride onto the fluoride-adsorbing magnesium-containing solid compound can be chemical and / or physical. In this way, at least some of the fluoride ions released into the porous water from mineral phases such as fluorite and possibly cuspidine during the carbonation process can be bound by surface hydroxyl groups so that they are not released in the fluoride leaching test described in DIN EN 12457-4. The fluoride-adsorbing magnesium-containing solid compound may be added directly to the particulate material as a magnesium-containing additive, or a magnesium-containing additive that generates a fluoride-adsorbing magnesium-containing solid compound in the porous water may be used. The inventors have also found that carbonatable binders may have an extremely high fluoride content, and a very large amount of carbonate is produced during the carbonation process, but only a relatively small amount of magnesium-containing additive, especially an amount that does not interfere with the carbonation process, is required. This may be due to the fact that the carbonatable binder itself may generate other fluoride-bound phases during the carbonation process. The inventors have found, for example, that if the carbonatable binder contains periclase, periclase is not carbonated or is carbonated only in small amounts, but is hydrated during the carbonation process to produce brucite, which can immobilize fluoride, as described, for example, in the paper "Adsorption and co-precipitation behavior of fluoride onto Mg-bearing minerals in Si-Al-Mg mineral system at hyperalkaline conditions" by Liu Xiaoji et al. (2012). In addition to or instead of brucite, hydrated magnesium carbonate may be formed as a result of the carbonation process.Fluorides may also be bonded in these hydroxide-containing magnesium compounds by coprecipitation (by substitution of hydroxyl groups with fluorides), and / or particularly in magnesium carbonate / calcium carbonate (magnesian calcite) by coprecipitation in which carbonate groups may be substituted with fluorides.

[0024] In one embodiment of the method according to the present invention, the at least one magnesium-containing additive comprises magnesium-aluminum hydrotalcite, which in particular adsorbs at least a portion of the fluoride leached from the particulate carbonizable binder during the carbonation step.

[0025] Hydrotalcite is, for example, derived from the formula Mg6Al2CO3(OH) 16 It is a layered double-layer hydroxide containing 4H2O. The carbonate ions in hydrotalcite are loosely bonded between the layers and can be readily exchanged with other ions such as fluoride ions. CO3 2- The affinity of hydrotalcite for multivalent intercalation anions such as F - Although it has a higher affinity for monovalent anions than such, despite the fact that carbonates are formed in the porous water during the carbonation process, hydrotalcite is able to adsorb fluorides released from the carbonatable binder during the carbonation process and bind the fluorides sufficiently strongly, so that no fluorides leach out of the carbonate during leaching tests according to DIN EN 12457-4:2003-01.

[0026] In one embodiment of the method according to the present invention, or according to the embodiments described above, the at least one magnesium-containing additive comprises magnesia, droma, or magnesia-droma, preferably magnesia or magnesia-droma, having a magnesium content of at least 50% by weight of MgO, preferably at least 60% by weight of MgO.

[0027] Magnesia, droma, and magnesia-droma have limited solubility in water. They adsorb fluorides and can bind them sufficiently strongly that fluorides do not leach from the carbonite during leaching tests according to DIN EN 12457-4:2003-01. Magnesia, droma, and magnesia-droma can be hydrated in porous water to form Mg(OH)2 and / or hydrated magnesium carbonate, e.g., neskehonite (Mg5(HCO3)(OH)·2H2O) and hydromagnesite (Mg5(CO3)4(OH)2·4H2O). The inventors have found that even calcined magnesia (periclase) can be hydrated in porous water during the carbonation process. Therefore, since fluoride adsorption can be at least partially due to isomorphic substitution of hydroxyl groups by fluoride, fluoride strongly binds to at least partially hydrated magnesia, droma, or magnesia-droma.

[0028] In one embodiment of the method according to the present invention, or according to any one of the embodiments described above, the at least one magnesium-containing additive has a diameter of less than 15.0 μm, preferably less than 10.0 μm, and more preferably less than 5.0 μm. 50 It has a sieve size value.

[0029] If at least a portion of the magnesium-containing additive does not dissolve in the porous water, and the fluoride is chemically and / or physically adsorbed onto the surface of the magnesium-containing additive, or onto the surface of a fluoride-adsorbing compound produced by the magnesium-containing additive through reaction with the porous water, then reducing the particle size can increase the fluoride adsorption capacity. 50 The sieve size value may also increase its reactivity and / or the release of magnesium ions by this additive into the porous water.

[0030] In one embodiment of the method according to the present invention, or according to any one of the embodiments described above, the at least one magnesium-containing additive comprises magnesia, droma, or magnesia-droma, wherein the magnesia, droma, or magnesia-droma has a citric acid reactivity of less than 900 seconds, preferably less than 600 seconds, and more preferably less than 300 seconds. Preferably, the citric acid reactivity is greater than 60 seconds.

[0031] As a result of higher citrate reactivity, magnesia, droma, or magnesia-droma can be hydrated more easily and rapidly in porous water, and therefore provide more hydroxyl groups available for binding fluoride, particularly for exchange with fluoride. However, the inventors have found that citrate reactivity of less than 60 seconds is less effective. This may be because some further reaction of magnesia, droma, or magnesia-droma during the carbonation step generates carbonate groups that immobilize fluoride less weakly than surface hydroxyl groups, for example.

[0032] In another embodiment of the method according to the present invention, the at least one additive comprises magnesia, droma, or magnesia-droma, wherein the magnesia, droma, or magnesia-droma has a citric acid reactivity of more than 900 seconds, and the at least one magnesium-containing additive comprises used magnesia, droma, or magnesia-droma refractory material, in particular used refractory material recycled from ironmaking furnaces or steelmaking furnaces.

[0033] The inventors have found that used refractory magnesia, droma, or magnesia-droma can be used as magnesium-containing additives despite their low reactivity. Although these materials are refractory, the inventors have found that they can still be hydrated by reaction with porous water during the carbonation process and are therefore effective for fluoride adsorption. In particular, in this embodiment, the used refractory material has a surface area of ​​less than 15.0 μm, preferably less than 10.0 μm, more preferably less than 5.0 μm, to provide a larger surface area for hydration reactions and fluoride binding. 50 It has a sieve size value.

[0034] In one embodiment of the method according to the present invention, or according to any one of the embodiments described above, the at least one magnesium-containing additive comprises hydrated magnesia, hydrated droma, or hydrated magnesia-droma, and the at least one magnesium-containing additive preferably comprises hydrated magnesia (i.e., brucite).

[0035] The advantage of this embodiment is that, since magnesia, droma, or magnesia-droma is already hydrated, hydroxyl groups are readily available from the start of the carbonation process, and the fluoride released into the porous water as a result of the carbonation process can be immobilized.

[0036] In one embodiment of the method according to the present invention, or according to any one of the embodiments described above, the at least one magnesium-containing additive dissolves at least partially in the porous water to provide magnesium ions to the porous water, and at least a portion of the magnesium ions dissolved in the porous water precipitates by reaction with at least hydroxyl ions present in the porous water to produce, in particular brucite and / or hydrated magnesium carbonate, such as neskehonite and hydromagnesite, as the fluoride-adsorbing magnesium-containing solid compound. Fluoride ions can be physically adsorbed onto the hydroxyl groups of these magnesium compounds, or chemically adsorbed onto these compounds by substituting some of the hydroxyl groups. Preferably, the brucite and / or hydrated magnesium carbonate co-precipitates with at least a portion of the fluoride leaching from the particulate carbonacidable binder during the carbonation step. Preferably, during the carbonation step, the magnesium ions coprecipitate at least partially with the calcium ions and carbonate ions present in the porous water to form magnesian calcite, and during the carbonation step, the magnesian calcite coprecipitates with at least some of the fluoride leaching from the particulate carbonizable binder. In this specification, magnesian calcite is understood to include other forms of calcium magnesium carbonate, particularly magnesian aragonite, or combinations of magnesian aragonite and magnesian calcite.

[0037] The magnesium-containing additive may be water-soluble. In this specification, a water-soluble salt or additive means a salt or additive having a solubility of at least 10 g / 100 ml in water at 20°C, i.e., 100 ml of a saturated aqueous solution of the salt or additive at 20°C contains at least 10 g of the salt or additive. However, the magnesium-containing additive may have a lower solubility in water. However, in this embodiment, a portion of the magnesium-containing additive still dissolves in the porous water under general conditions, particularly during the carbonation process. Preferably, the citrate reactivity of the magnesium-containing additive is high enough to release more magnesium ions into the porous water, and the citrate reactivity is preferably less than 900 seconds, more preferably less than 600 seconds, and most preferably less than 300 seconds, as described above.

[0038] The solubility of magnesium hydroxide is strongly pH-dependent under alkaline conditions. For example, if the pH of pore water is approximately 12.5 and decreases to 10 during the carbonation process, the solubility of magnesium is 5.6 × 10⁻⁶. -6 The solubility product of Mg(OH)2 increases from mM to 0.56 mM (K sp 5.6 × 10 -12(Based on [the above]). At pH 9.5, the solubility of magnesium is approximately 5.6 mM or 134 mg / L. The pH may be further reduced during the carbonation process, allowing for a further increase in the magnesium concentration in the pore water. If a sufficiently large amount of magnesium is present in the pore water, magnesian calcite can be produced during the carbonation process instead of, or in addition to, calcite. A significant advantage of magnesian calcite is that fluoride can coprecipitate, and therefore immobilize, within the magnesian calcite. As can be seen from the paper "Coprecipitation of fluoride with calcium carbonate" by Kitano, Yasushi and Okumura, Minoru (1973), fluoride does not coprecipitate with pure calcite. However, in the presence of magnesium ions, fluoride coprecipitates with calcite to produce magnesian calcite. Calcite crystals in a solution containing magnesium ions tend to concentrate magnesium on their surface. Fluoride can readily associate with magnesium concentrated on the surface of calcite to form ion pairs, which explains why the amount of fluoride co-precipitated with calcite increases with increasing magnesium ion concentration in the solution. Alternatively, one can refer to the paper "Incorporation of fluoride ions into calcite - Effect of organic materials and magnesium ions in a parent solution" by Okumura et al. (1983). According to Figure 4 of this paper, 200 mg / L to 300 mg / L of magnesium in the parent solution may already have generated approximately 5 mol percent of magnesium carbonate in the magnesian calcite. Such high magnesium concentrations can be achieved in porous water at pH somewhat lower than 9.5, particularly at pH 9.0 to 9.5 or lower. Such pH values ​​can be easily obtained during the carbonation process.According to Figure 3 of this paper, 5 mole percent magnesium carbonate in magnesian calcite is already capable of immobilizing approximately 1000 ppm of fluoride in the magnesian calcite when the fluoride concentration in the solution is 1 ppm, and even more in the case of higher fluoride concentrations and / or higher magnesium content.

[0039] In one embodiment of the method according to the present invention, or according to any one of the embodiments described above, the gas used to carbonate the compressible body has a partial pressure of carbon dioxide of at least 0.10 bar, preferably at least 0.20 bar, more preferably at least 0.30 bar, and most preferably at least 0.40 bar, wherein the partial pressure of carbon dioxide in the gas is preferably lower than 5.0 bar, more preferably lower than 2.0 bar, and more preferably lower than 1.0 bar. In this specification, the unit bar refers to bara, which is absolute pressure.

[0040] Using CO2 partial pressures higher than these lower limits is advantageous in that it allows for lower pH in the porous water during the carbonation process. Compared to calcium hydroxide, magnesium hydroxide has a lower solubility product K sp Because of this, less magnesium dissolves in alkaline porous water. At lower pH values, more magnesium is present in the solution, so more calcium magnesium carbonate (especially magnesian calcite Ca) is dissolved. 1~0.85 Mg 0~0.15CO3 is generated. More fluoride can co-precipitate in magnesian calcite (i.e., more than in pure calcite), so more fluoride binds to these newly formed calcium magnesium carbonate phases, contributing to a reduction in fluoride leaching. Furthermore, the higher acidity of the porous water can contribute to the promotion of magnesium oxide hydration, and magnesium oxide may be contained in magnesium-containing additives such as magnesia, droma, and magnesia-droma, and / or in the carbonatable binder itself. In this regard, it has been found that the fine powders of ironmaking slag and steelmaking slag contain amounts of periclase (i.e., free lime or de-calcined magnesium oxide) that are hydrated during the carbonation process, despite their low reactivity. Small amounts of hydrated magnesium oxide can be carbonated as is to produce hydrated magnesium carbonate in particular, or co-carbonated with calcium hydroxide and small amounts of fluoride to produce magnesian calcite, but the majority of hydrated magnesium oxide is not carbonated and forms brucite, which is an effective adsorbent for fluoride. Additionally, phases such as Mg2Cl(OH)3·4H2O may form, which also immobilize the fluoride. Lower carbon dioxide partial pressures than the upper limit are advantageous in avoiding the need to use a high-pressure carbonation chamber. Furthermore, less magnesium oxide / magnesium hydroxide is carbonated, leaving more magnesium oxide / magnesium hydroxide to adsorb the fluoride.

[0041] In one embodiment of the method according to the present invention, or according to any one of the embodiments described above, the compressed body is carbonated until the carbonate-bonded compressed body has a pH lower than 11.0, preferably lower than 10.8, more preferably lower than 10.6, measured after 24 hours of contact according to DIN EN 12457-4:2003-01, wherein the pH of the carbonate-bonded compressed body is preferably higher than 9.0, more preferably higher than 9.5.

[0042] The decrease in pH after the carbonation process correlates with an increase in the degree of carbonation. As explained above, this may be advantageous in promoting the hydration of less reactive magnesium oxide, such as periclase, or calcined or de-calcined magnesia, droma, or magnesia-droma, e.g., recycled refractory magnesia, droma, or magnesia-droma materials, to produce brucite and / or hydrated magnesium carbonate, which can physically or chemically adsorb fluorides, particularly by coprecipitation. Furthermore, more magnesium may co-precipitate with calcium and fluorides to produce fluoride-containing magnesium calcium carbonate. However, since the pH remains sufficiently high after the carbonation process, less magnesium oxide / magnesium hydroxide is carbonated, leaving more magnesium oxide / magnesium hydroxide to adsorb fluorides.

[0043] In one embodiment of the method according to the present invention, or according to any one of the embodiments described above, the at least one magnesium-containing additive preferably comprises at least one water-soluble magnesium salt selected from the group consisting of magnesium chloride, magnesium nitrate, magnesium sulfate, and magnesium citrate, and more preferably selected from the group consisting of magnesium chloride, magnesium nitrate, and magnesium citrate, wherein the at least one additive preferably comprises magnesium chloride.

[0044] Water-soluble magnesium salts were found to be more effective in immobilizing fluoride in the pore water of the compressed material during the carbonation process. Due to the high pH value of the particulate material, some of the dissolved magnesium ions immediately precipitate in the form of magnesium hydroxide (brucite). Consequently, the pH of the particulate material decreases, releasing further hydroxides, which precipitate together with the dissolved magnesium ions in the form of magnesium hydroxide. Furthermore, even during the carbonation process itself, in the presence of a relatively large amount of magnesium ions introduced into the pore water by the water-soluble salts, further hydroxides may be released and precipitate as magnesium hydroxide and / or hydrated magnesium carbonate. As can be seen from Table 1 of the paper "Adsorption and co-precipitation behavior of fluoride onto Mg-bearing minerals in Si-Al-Mg mineral system at hyperalkaline conditions" by Liu Xiaoh et al. (2012), a certain amount of fluoride can be adsorbed onto the generated brucite, but when fluoride ions were co-precipitated with brucite, the removal of fluoride from the solution more than doubled. Fluoride ions can also be co-precipitated with hydrated magnesium carbonate. Another possible explanation for the enhanced immobilization of fluoride is that the precipitated magnesium hydroxide and / or precipitated hydrated magnesium carbonate may have a much higher specific surface area, particularly a larger BET specific surface area, than commercially available magnesium hydroxide powder, thus allowing a larger surface area to be used for fluoride adsorption. For example, one can refer to Chinese Patent Application Publication No. 107324753, in which Mg(OH)2 is produced by precipitation of MgCl2 solution with Ca(OH)2. In these examples, the precipitated Mg(OH)2 has a high BET specific surface area, i.e., 52 m², as measured by nitrogen absorption manometry. 2 / g~78m 2 It had a BET specific surface area of ​​ / g.

[0045] In one embodiment of the method according to the present invention, or according to any one of the embodiments described above, a predetermined amount of carbonate is generated during the carbonation step, and the at least one additive is distributed throughout the particulate material and expressed as an oxide, and an amount of magnesium of at least 2.0% by weight, preferably at least 3.0% by weight, more preferably at least 4.0% by weight of the predetermined amount of carbonate is added to the particulate material.

[0046] Even if the carbonatable binder contains phases such as periclase, these phases are not carbonated during the carbonation process, or are only carbonated to a limited extent. Therefore, if no magnesium-containing additive is added, only a limited amount of magnesian calcite will be produced. For example, see the paper "Accelerated mineral carbonation of stainless steel slags for CO2 storage and waste valorisation: effect of process parameters on geochemical properties" by Rafael M. Santos et al. (2013). According to Figure 5 of this paper, the AOD slag used in the described experiment had a pH of approximately 11.7 and contained a relatively large amount, i.e., 7%, of periclase. Approximately 10% of this was carbonated in the thin-film carbonation process, meaning that a total of approximately 0.7% of the MgO in the carbonatable stainless steel slag was carbonated by the thin-film carbonation process. CC stainless steel slag (continuous casting steel slag), which has a higher pH of approximately 12.3, contained even more periclase, namely 11%, but due to the high pH of the CC slag, the periclase was not carbonated at all. As shown in Figure 7, approximately 20% of the carbonate produced in AOD slag after 26 hours of carbonation was magnesian calcite.

[0047] In this embodiment of the method according to the present invention, the magnesium-containing additive is an amount of magnesium expressed as MgO, which is at least 2.0% by weight of the carbonate produced. In this way, more magnesian calcite is produced, or the produced magnesian calcite contains more MgO, and therefore more fluoride can be immobilized. Preferably, since the magnesian-containing additive is water-soluble, most of the magnesium contained in this additive can dissolve in the porous water and co-precipitate with the calcite to form magnesian calcite.

[0048] The magnesium-containing additive is preferably a salt that lowers the pH of the pore solution, thereby increasing the solubility of magnesium and allowing for the production of more magnesium calcite and / or magnesian calcite containing more magnesium, and therefore being more effective in immobilizing fluoride.

[0049] In one embodiment of the method according to the present invention, or according to any one of the embodiments described above, a certain amount of carbon dioxide is incorporated by the particulate carbonizable binder during the carbonation step to produce the carbonate, wherein the amount of carbon dioxide is at least 6% by dry weight of the particulate carbonizable binder, preferably at least 8% by dry weight.

[0050] The more carbon dioxide is incorporated, the more the carbonateable binder undergoes carbonation, resulting in a higher strength of the carbonate compound. Furthermore, in the case of less reactive magnesium-containing additives, more pronounced carbonation increases its hydration and thus enhances its fluoride adsorption capacity. Consequently, more brucite and hydrated magnesium carbonate can be produced, which are effective in immobilizing fluorides. Moreover, the more carbon dioxide is incorporated, the lower the pH of the carbonate compound, and the higher the solubility of magnesium in less alkaline porous water, allowing for the inclusion of more magnesian calcite.

[0051] In one embodiment of the method according to the present invention, or according to any one of the embodiments described above, the at least one magnesium-containing additive is distributed throughout the particulate material and adds to the particulate material an amount of magnesium of at least 0.50% by weight, preferably at least 0.75% by weight, and more preferably at least 1.00% by weight, which is represented as an oxide.

[0052] Such amounts of magnesium-containing additives were found to be effective in reducing the fluoride leaching value of carbonate compounds.

[0053] In one embodiment of the method according to the present invention, or according to any one of the embodiments described above, the carbonatable binder contains at least 4000 mg / kg, and more particularly at least 6000 mg / kg of fluoride. Preferably, the carbonatable binder contains less than 75000 mg / kg, more preferably less than 50000 mg / kg of fluoride (F - ) includes.

[0054] Such high fluoride content can result in extremely high fluoride leaching values ​​in the carbonite if the majority of the fluoride is not effectively immobilized within the carbonate compound.

[0055] In one embodiment of the method according to the present invention, or according to any one of the embodiments described above, when the carbonation step is started, the compressed body has a water content of 3.0% to 25% by weight, preferably 5.0% to 20% by weight.

[0056] Such a relatively low water content allows for effective carbonation of the carbonatable binder while ensuring that the pH of the carbonate compound does not drop excessively, especially not below 9.0, and even not below 9.5.

[0057] In one embodiment of the method according to the present invention, or according to any one of the embodiments described above, the particulate carbonatable binder comprises carbonatable slag from a metal manufacturing process, slag from phosphorus production, bottom ash and / or fly ash, wherein the particulate carbonatable binder preferably comprises steelmaking slag, particularly stainless steelmaking slag.

[0058] Since the viscosity and melting point of these slags are often reduced by the addition of fluorite, all carbonateable binder materials may contain leached fluorides. Carbonatable binder materials may also contain vanadium. The method according to the present invention has been found to reduce vanadium leaching as well.

[0059] In one embodiment of the method according to the present invention, or according to any one of the embodiments described above, the particulate carbonatable binder is at least partially crystalline and contains cuspidine and / or calcium fluoride.

[0060] The method according to the present invention is particularly suitable for solving the leaching problem that occurs when carbonating a carbonatable binder containing cuspidine and / or fluoride.

[0061] Other special features and advantages of the present invention will become apparent from the following more detailed descriptions of some specific embodiments. [Modes for carrying out the invention]

[0062] The present invention generally relates to a method for producing carbonate-bound compressions by compressing and carbonating a particulate material containing a particulate carbonizable binder.

[0063] The term "particulate material" refers to any material composed of loose particles. Since these particles can be of different sizes, the term "particulate material" encompasses not only coarse or fine particles, but also very fine particles, especially powders.

[0064] The particulate material may consist of one carbonatable particulate material, i.e., a carbonatable binder, or it may consist of a mixture of at least a carbonatable binder and at least one further particulate material, which may or may not be carbonatable. Non-carbonatable particulate materials include, for example, natural sand such as sea sand or river sand.

[0065] The particulate carbonatable binder consists of particles having a sieve size of less than 500 μm. The particulate carbonatable binder contains calcium oxide and silicon dioxide and has a CaO / SiO2 ratio (CaO wt% / SiO2 wt%) greater than 1.1 and a pH of at least 10.5, preferably at least 11.0, more preferably at least 11.5, or even more than 12.0, as measured after a 24-hour contact period according to DIN EN 12457-4:2003-01. Such carbonatable binders often contain fluoride. Since the method according to the present invention relates to the problem of reducing fluoride leaching from carbonate-bound compresses, such fluoride-containing binders are used in the method according to the present invention.

[0066] If the particulate material contains one or more further particulate materials, these materials may or may not be carbonatable, and may even be made of the same material as the carbonatable binder. In that case, the difference from the carbonatable binder is that the particles of these further particulate materials have a sieve size greater than 500 μm. Therefore, these particles can also be carbonated and may even release fluoride, but from the standpoint of their relatively small surface area, they have no or little effect as a binder.

[0067] The particle size distribution of the particulate material is preferably selected to achieve a higher packing density, or in other words, a lower total porosity, because this allows for higher compressive strength. The compressive strength of the compressed material before the carbonation process, i.e., the Green strength of the compressed material, and the compressive strength of the carbonated compressed material are determined according to the European standard EN 12390-3:2009.

[0068] The particulate carbonatable binder preferably contains by-products or waste. The particulate carbonatable binder may contain different crystalline and amorphous phases, preferably at least one alkaline earth metal silicate phase, particularly crystalline dicalcium silicate.

[0069] The particulate carbonatable binder preferably also contains free calcium oxide (free lime) and / or calcium hydroxide (portrundite), with the total amount of free calcium oxide and free calcium hydroxide preferably at least 1% by dry weight, more preferably at least 2% by dry weight. It may also contain free magnesium oxide and / or free magnesium hydroxide. These oxides and hydroxides may be amorphous and / or crystalline, in particular in the form of portrundite (Ca(OH)2), free lime (CaO), brucite (Mg(OH)2), and periclase (MgO). They may also exist amorphous or crystalline, containing various ratios of magnesium and calcium and oxygen. Initially, since they are often formed at high temperatures, newly formed carbonatable binders usually contain only oxides and no hydroxides, and hydroxides are formed during the aging (weathering) of the carbonatable material or during the carbonation process. Air also contains small amounts of carbon dioxide, so during the aging of carbonatable materials, some hydroxides may be further converted to carbonates (by spontaneous carbonation), which may still contain partially hydrated carbonates.

[0070] A wide variety of carbonatable materials are suitable for use as binders according to the method of the present invention. Preferred carbonatable materials include, for example, bottom ash, more specifically, bottom ash generated during the incineration of waste, particularly municipal waste (i.e., municipal waste incineration bottom ash). Fly ash, particularly non-coal fly ash, can also be carbonized, as can filter dust from steelmaking furnaces, particularly electric arc furnaces (EAF filter dust). However, the most preferred carbonatable materials are slag materials resulting from metal manufacturing processes (the production of iron, steel, and stainless steel, as well as non-ferrous metals such as copper and zinc) and the production of phosphorus. The carbonatable binder used is preferably a non-hydraulic or substantially non-hydraulic material. Since non-hydraulic materials cannot yield such a hardenable matrix through reaction with water (particularly by CSH formation), solids can still be produced by carbonation of this material.

[0071] The slag material is preferably steelmaking slag, more preferably stainless steelmaking slag. The steelmaking slag may be converter slag (e.g., LD slag, AOD slag, and VOD slag) or electric arc furnace slag (EAF slag). The steelmaking slag may also be ladle slag or tundish slag. General steelmaking slag does not contain heavy metals such as chromium and nickel, or contains only small amounts of them, and therefore does not exhibit the leaching problems that occur with stainless steelmaking slag. However, general steelmaking slag may contain relatively large amounts of vanadium. Stainless steelmaking slag generally contains more than 3000 mg / kg of chromium, usually more than 5000 mg / kg. Stainless steelmaking slag may also contain nickel, more specifically more than 300 mg / kg, especially more than 400 mg / kg, and often more than 500 mg / kg. By carbonating these carbonatable slags, the leaching of these heavy metals can be reduced or even prevented. However, it was found that vanadium leaching increased due to the carbonation process.

[0072] Steelmaking slag, especially stainless steelmaking slag, can usually be crushed to produce granular material from which the metal fraction can be recycled. The coarser fraction of crushed stainless steelmaking slag can be used as coarse or fine aggregate in asphalt concrete. However, the finer fraction, especially the 0 μm to 500 μm fraction, is not suitable for these applications as is due to its high water absorption properties. The finer fraction, i.e., the so-called fine powder, actually contains a larger amount of γ-dicalcium silicate (γ-C2S), which is produced when some of the β-dicalcium silicate (β-C2S) is further converted into γ-polymorphs during the solidification of liquid slag. Due to the resulting expansion, cracks are formed, and so-called falling slag with high water absorption properties is produced. In particular, this stainless steel slag material containing at least 3% by dry weight, more specifically at least 5% by dry weight, and even more specifically at least 7% by dry weight of γ-C2S, is preferably used as a carbonatable binder in the method of the present invention.

[0073] In the method of the present invention, a compressed body is first produced by compressing a particulate material. This can be done by placing the material in a mold and vibrating and / or compressing the material within it. In order to obtain a compressed body having a certain green strength, the particulate material contains water. Therefore, the compressed body has pores containing porous water. The presence of porous water is also essential for the following steps. After compressing the particulate material, the produced compressed body is carbonated with a gas containing carbon dioxide, thereby generating a carbonate containing calcium carbonate and converting the compressed body into a carbonate-bonded compressed body. When the carbonation step is started, the compressed body preferably has a water content of 3.0% to 25% by weight, more preferably 5.0% to 20% by weight.

[0074] The compressed material is preferably manufactured in a mold and, preferably, removed from the mold and placed in a carbonation chamber for carbonation. This chamber may be an autoclave to which relatively high gas pressure is applied. However, in the method according to the present invention, the carbonation step is preferably carried out at a lower gas pressure. The partial pressure of carbon dioxide in the carbonation gas is preferably lower than 5.0 bar, more preferably lower than 2.0 bar, and most preferably lower than 1.0 bar. The carbonation step can be carried out at atmospheric pressure in particular. Therefore, a less expensive artificial climate chamber can be used as the carbonation chamber. For effective carbonation, the partial pressure of carbon dioxide in the carbonation gas is preferably at least 0.10 bar, more preferably at least 0.20 bar, most preferably at least 0.30 bar, and even more preferably at least 0.40 bar.

[0075] The compressed material is carbonated for a period of preferably 16 to 32 hours, more preferably 18 to 28 hours, and most preferably 20 to 24 hours. In practice, a total carbonation time of up to 24 hours is preferred so that a new amount of compressed material can be carbonated each day.

[0076] The compressed material is preferably carbonated until the produced carbonate-bonded compressed product has a pH lower than 11.0, preferably lower than 10.8, and more preferably lower than 10.6, as measured after 24 hours of contact according to DIN EN 12457-4:2003-01. However, the pH of the carbonate-bonded compressed product is preferably higher than 9.0, and more preferably higher than 9.5.

[0077] During the carbonation process, a certain amount of carbon dioxide is incorporated by the particulate carbon-biacyl binder to produce carbonate. The carbonation process is preferably continued until the amount of carbon dioxide incorporated by the particulate carbon-biacyl binder reaches at least 6% by dry weight, preferably at least 8% by dry weight. This amount of carbon dioxide, i.e., the carbonate content expressed as carbon dioxide, can be easily determined by simultaneous thermal analysis (STA, DIN 51004, DIN 51006, and DIN 51007).

[0078] Carbonatable binders include fluoride F - In particular, at least 4000 mg / kg, or even more than 6000 mg / kg of fluoride (F - It contains (represented as ). The carbonatable binder is preferably at least partially crystalline and contains casspidin (Ca4Si2O7(F,OH)2) and / or calcium fluoride (CaF2).

[0079] The fine powder of stainless steel slag is the most problematic type of fine powder. These fine powders contain heavy metals such as chromium, vanadium, nickel, and molybdenum, as well as fluorides. Stainless steel slag fine powder formed from particles with a sieve size of less than 0.5 mm is very suitable for use as a carbonatable binder. For example, the coarser sand fraction of crushed stainless steel slag, having a particle size of 0.5 mm to 2.0 mm, can be used as fine aggregate in combination with a stainless steel slag binder to form particulate material. Therefore, further explanation of the present invention is given in relation to the use of this stainless steel slag binder, but other particulate carbonatable binders can also be used. In that case, the operating principle of the present invention is the same or at least similar.

[0080] Characteristics of air-cooled stainless steel slag fine powder Stainless steel slag was solidified by the method described in European Patent No. 3122909 to minimize the formation of fine particles. During the production of stainless steel slag aggregate from this solidified steel slag, the composition of newly produced fine particles with particle sizes of 0 mm to 0.5 mm was analyzed weekly for nine months. The volume percentage passing through different filters was determined by dry sieving. The fine particles were already hydrated and to some extent carbonated as a result of the manufacturing process before analysis. A wet process was used to remove fine particles and metal fractions from the crushed solidified steel slag, for example, by spraying water onto the solidified steel slag during the cooling process.

[0081] Fine powders are primarily used as binders in the production of carbonate-bound compressed materials such as blocks, bricks, and paving materials through accelerated carbonation processes. It is important to know how much carbon dioxide these fine powders can absorb. Therefore, the maximum carbonate content achievable in these fine powders was determined by carbonating a 10g sample each time using the following test method.

[0082] The steelmaking slag sample is dried at 110°C until there is no weight loss. Then, the sample is sieved through a 250 μm sieve. 10 g of the sample is placed in a cup without compression, 1.5 g of water is added, and it is mixed with the steelmaking slag. The cup is placed in an autoclave, flushed with 100% CO2 gas, and the pressure is increased to 0.5 barg (= 1.5 bara) with 100% CO2 gas. The autoclave is maintained at approximately 23°C for 24 hours. STA analysis is performed on the carbonated sample from 0°C to 1000°C. The weight loss from 550°C to 950°C is due to the release of carbon dioxide due to the decomposition of carbonates. Dividing this weight loss (due to the release of CO2 from the decomposition of carbonates) by the initial weight of the dried sample and multiplying by 100 gives the maximum carbonate content of the carbonated particulate steelmaking slag material, expressed as a dry weight percentage of carbon dioxide. This weight loss is converted to a weight percentage of CaO equivalent (by multiplying the weight loss by a coefficient of 56 / 44). The weight loss at 350°C to 550°C is also measured. This weight loss is considered to be the amount of water released by the decomposition of hydroxides and is converted to a weight percentage of CaO equivalent (by multiplying this weight loss by a coefficient of 56 / 18). Since brucite and hydrated magnesium carbonate also decompose at temperatures below 550°C, these are considered hydroxides rather than carbonates.

[0083] The average, minimum, and maximum values ​​of these measurements are shown in Table 1. Furthermore, the total amounts of periclase and brucite in the stainless steel slag fine powder before carbonation (both converted to CaO equivalents) are also shown in Table 1.

[0084] TIFF2026523139000001.tif40170

[0085] Table 2 shows the average amount of the major mineral phases in the steelmaking slag fine powder, expressed as weight percentage of the crystalline phase. The steelmaking slag fine powder contained approximately 25% amorphous phase and 75% crystalline phase.

[0086] TIFF2026523139000002.tif55170

[0087] The trace phase, separate from the other phases, contained brucite (0.19 wt%), dolomite (0.37 wt%), lime (0.08 wt%), and portlandite (0.51 wt%).

[0088] These data suggest that even with 100% carbon dioxide gas at a pressure of 1.5 bar, not all hydroxides are completely carbonated. The remaining hydroxides include magnesium hydroxide containing brucite, as well as partially hydrated magnesium carbonate such as neskehonite and hydromagnesite. These hydroxides and hydrated magnesium carbonates are at least partially generated during the carbonation process by the hydration and partial carbonation of periclase. Before the carbonation process, only a very small amount of brucite was generated. Since the amount of remaining hydroxides is greater than the amount of hydroxide that can be generated by the periclase and brucite present in the steelmaking slag powder before carbonation, it is thought that further magnesium hydroxides are generated by the carbonation of some of the marwinite, bridigite, and akermaite phases (see, for example, Figure 5 in Rafael M. Santos et al. 2013). Furthermore, partially carbonated magnesium hydroxides, i.e., hydrated magnesium carbonate such as neskehonite and hydromagnesite, are also generated during the carbonation process. These hydrated magnesium carbonates are not only dehydrated and oxidized at temperatures below 550°C (i.e., between 250°C and 350°C), but also decarboxylated at such lower temperatures. Therefore, their presence substantially contributes to the hydroxide content of the carbonated steelmaking slag determined by the above test method, particularly because the release of carbon dioxide due to decarboxylation causes a greater decrease in the mass of the test sample than the release of water due to dihydroxylation (since carbon dioxide has a larger molecular weight than water).

[0089] The chemical composition of stainless steel slag fine powder, expressed as an oxide, can vary to some extent. Typically, stainless steel slag fine powder contains approximately 40% to 60% CaO, 20% to 30% SiO2, approximately 9% to 10% MgO, and smaller amounts of Al2O3, Mn2O3, Cr2O3, Fe2O3, NiO, and Mo2O3. The basicity, i.e., the CaO / SiO2 weight ratio, is higher than 1.1, usually lower than 2.5, and particularly lower than 2.1.

[0090] Stainless steel slag fine powder also contains a certain amount of fluoride. Based on 14 total analyses of these fine powders over a 14-year period, the average fluoride content of the fine powder was 16,150 mg / kg, with a maximum of 25,400 mg / kg and a minimum of 4,220 mg / kg. During the same period, the fluoride leaching values ​​of non-carbonated stainless steel slag fine powder were also measured according to EN 12457-S4. The average fluoride leaching value of the fine powder was 3.33 mg / L (=33.3 mg / kg), with a maximum of 4.75 mg / L and a minimum of 2.29 mg / L.

[0091] According to the chemical formula of casspidin (Ca8(Si2O7)2F4), casspidin contains approximately 10.4% fluoride. If the average casspidin content of the crystalline phase is 8.46%, then stainless steel slag fine powder contains an average of approximately 6000 mg / kg of fluoride. - This will result in the fluoride being contained bound to casspidin. Therefore, the majority, i.e., an average of 10,000 mg / kg of fluoride, will be contained in other phases such as the fluorite phase (CaF2), which can release fluoride more readily than casspidin during the carbonation process.

[0092] As is clear from the above measurements, the stainless steel slag fine powder itself satisfies the fluoride leaching limit. However, the inventors here have found that when the fine powder is used as a carbonatable binder, fluoride leaching increases significantly.

[0093] Fluoride-adsorbing magnesium-containing solid compound According to the present invention, fluoride leaching from the carbonation binder is reduced by providing a fluoride-adsorbing magnesium-containing solid compound in the compressed material. This is done by distributing at least one magnesium-containing additive in the particulate material before the carbonation step. This additive has a magnesium content of at least 30% by dry weight of MgO. In this way, an effective amount of magnesium can be added to the particulate material without the need to add a large amount of magnesium-containing additive. The additive may be the fluoride-adsorbing magnesium-containing solid compound itself, or it may be a compound that generates the fluoride-adsorbing magnesium-containing solid compound in the porous water contained in the compressed material to be carbonated.

[0094] Carbonatable binders can already contain a magnesium-containing phase, which allows for the adsorption of fluorides either directly or after reaction in porous water. Marwinite, particularly bridigite, can release and produce, for example, Mg(OH)2 during the carbonation process, but because the MgO content of these mineral phases is far less than 30% by weight, only a small amount of brucite (Mg(OH)2) is formed, and furthermore, these mineral phases are not added to the particulate material as additives. Periclase can also be contained in carbonatable binders. As mentioned above, periclase has been found to hydrate and produce brucite during the carbonation process. However, periclase already present in the carbonatable binder as one of its contained mineral phases does not spread throughout the particulate material as a magnesium-containing additive. It is thought that a relatively large amount of brucite and other magnesium hydroxide-containing compounds such as hydrated magnesium or calcium magnesium carbonate can thus be generated in the particulate material, and therefore a relatively large portion of the fluorides released from the carbonatable binder during the carbonation process can be immobilized. However, the inventors found that this was insufficient to adequately limit fluoride leaching. They actually found that fluoride leaching increased significantly after the carbonation process in carbonatable binders, particularly stainless steel slag powder. For example, in the case of stainless steel slag powder, the fluoride leaching values ​​ranged from 3 mg / L to 4 mg / L, as measured according to DIN EN 12457-4:2003-01, to over 30 mg / L. This means that up to 300 mg / kg of fluoride can further leach from the carbonation binder, requiring that more of the fluoride contained in the carbonation binder be immobilized within it.

[0095] In a first embodiment of the method according to the present invention, this can be achieved by a magnesium-containing additive comprising magnesium-aluminum hydrotalcite. Hydrotalcite is a water-insoluble layered double hydroxide that exhibits various stoichiometrys resulting from differences in the arrangement of the layered structures, the order of the metal ions, and the arrangement of anions and water molecules in the interlayer gallery. Hydrotalcite consists of three layers: two positively charged outer layers and an inner intermediate layer containing water molecules and replaceable anions. Mineral hydrotalcite Mg6Al2(OH) 16 CO3·4H2O is the most well-known representative example of layered double hydroxides (LDHs) and is a preferred hydrotalcite used in the experiments described later. However, CO3 2- The group can be readily exchanged with other anions. The magnesium-aluminum hydrotalcite that can be used in the method according to the present invention has the general formula Mg 2+ 1-x Al 3+ x (OH2) x+ (A n- x / n (H2O) x- It has such that some divalent magnesium ions are isomorphically replaced by trivalent aluminum ions. The originally electrically neutral hydroxide layer acquires a positive charge as a result, which is an anion A present between the layers along with the molecules of crystal water. n- It is compensated for by the charge. The value of x is usually in the range of 0.20 to 0.33. Hydrotalcite's affinity for multivalent intercalation anions is higher than its affinity for monovalent anions, and its affinity for some ions is CO3 2- >SO4 2- >F - >HPO4 2- >Cl - >NO3 - It has been reported that the decrease is in the following order: CO3 2- Affinity for F -While a higher affinity for fluoride may be detrimental during carbonation, test results demonstrated that hydrotalcite can effectively capture the fluoride released during the carbonation of the carbonizable binder.

[0096] In a further embodiment of the method according to the present invention, the fluoride released during the carbonation step can be immobilized by at least one magnesium-containing additive comprising magnesia, droma, or magnesia-droma, having a magnesium content of at least 30% by weight, expressed as MgO. The additive preferably comprises magnesia or magnesia-droma having a magnesium content of at least 50% by weight, preferably at least 60% by weight, MgO, expressed as MgO.

[0097] Magnesia is a compound that contains MgO but not CaO. Droma is a compound that contains equimolar amounts of MgO and CaO, and its formula is Ca 0.5 Mg 0.5 It can be represented by O. Magnesia droma contains more moles of MgO than CaO, and the formula Ca 1-x Mg x It can be expressed as O(where x is greater than 0.5).

[0098] Magnesia, droma, or magnesia-droma additives are not water-soluble. In this specification, a water-soluble salt or additive means a salt or additive having a solubility of at least 10 g / 100 ml in water at 20°C; that is, 100 ml of a saturated aqueous solution of the salt or additive at 20°C contains at least 10 g of the salt or additive. Therefore, fluorides can adsorb to the surface of these magnesium oxides, but they adsorb much better when at least a portion of the oxide groups are hydrated with respect to surface hydroxyl groups. Since it has been found that periclase, i.e., dead-calcined magnesia, is hydrated during the carbonation process, it is likely that magnesia, droma, or magnesia-droma additives are also hydrated during the carbonation process, generating hydroxyl groups at least on their surfaces.

[0099] To enhance fluoride adsorption capacity, the magnesium-containing additive has a particle size of less than 15.0 μm, preferably less than 10.0 μm, and more preferably less than 5.0 μm. 50 It has a sieve size value. D 50 The sieve size value is the particle size at which the cumulative pass-through rate in volume is 50%. The particle size distribution can be tested using a sieve with a square opening, according to ASTM D6913 / D6913M-17. The volume percentage of particles can be calculated, in particular, by dividing the weight of the particles passing through the sieve by the average density of the material forming the particles. Alternatively, the particle size distribution can be determined by laser technology, for example, using a Horiba 250 analyzer with a material dispersed in isopropanol by sonication.

[0100] Even dead-burned magnesia is expected to be hydrated during the carbonation process, but magnesia, droma, or magnesia-droma preferably have a citrate reactivity of less than 900 seconds, preferably less than 600 seconds, and more preferably less than 300 seconds. In this way, magnesia, droma, or magnesia-droma can be hydrated under less severe carbonation conditions, and therefore, faster hydration allows for more rapid capture of released fluoride ions. However, magnesia, droma, or magnesia-droma may have lower citrate reactivity (more than 900 seconds), and may particularly contain spent magnesia, droma, or magnesia-droma refractory materials, especially spent refractory materials recycled from ironmaking furnaces or steelmaking furnaces. Even such extremely unreactive materials are expected to be at least partially hydrated during the carbonation process and are considered effective in immobilizing fluorides released during the carbonation process.

[0101] On the other hand, the magnesium-containing additive may already contain hydrated magnesia, hydrated droma, or hydrated magnesia-droma, in which case further hydration is not necessary.

[0102] The citric acid reactivity can be determined by the following test: Prepare a 0.40 N citric acid solution. Add a slurry of 2.0 g of powdered MgO to 100 ml of the 0.4 N citric acid solution and shake at 30°C using phenolphthalein as an indicator until the color changes from white to pink. Report the time required to completely neutralize the acid as the citric acid reactivity.

[0103] In a preferred embodiment, the magnesium-containing additive at least partially dissolves in the porous water contained in the compressed material, providing magnesium ions to the porous water, which may precipitate in the form of magnesium hydroxide. During the carbonation process, the dissolved magnesium ions may precipitate in the form of magnesium carbonate or hydrated magnesium carbonate, or they may at least partially co-precipitate with calcium ions and carbonate ions present in the porous water to form magnesian calcite. Hydroxides, hydrated carbonates, and magnesian calcite have been found to co-precipitate with fluorides leached from the particulate carbonacidable binder during the carbonation process.

[0104] To maximize this effect, the magnesium-containing additive preferably includes water-soluble magnesium salts such as magnesium chloride, magnesium nitrate, magnesium sulfate, and magnesium citrate. Preferably, a water-soluble magnesium salt other than magnesium sulfate is used as the additive because the addition of magnesium sulfate may produce calcium sulfate precipitate, which can interfere with the carbonation process. The additive most preferably contains magnesium chloride and optionally includes a certain amount of citrate-containing compound, preferably in combination with an alkali metal citrate salt such as sodium citrate. According to Figure 3 of the paper by Minoru Okumura et al. (1983), the presence of citrate ions in water actually significantly increases the amount of fluoride that can be immobilized in magnesian calcite.

[0105] When a water-soluble magnesium salt is brought into contact with porous water, which is highly alkaline as a result of the high pH of the carbonatable binder, some of the magnesium ions in the magnesium salt immediately precipitate in the form of magnesium hydroxide. This may be pure Mg(OH)2, or the magnesium hydroxide may be in the form of, for example, Mg2Cl(OH)3·4H2O. During the carbonation process, hydrated magnesium and / or calcium magnesium carbonate may be formed, but most of the water-soluble magnesium ions are incorporated into magnesian calcite.

[0106] Preferably, the magnesium-containing additive added to the particulate material, particularly the water-soluble magnesium salt, contains such an amount of magnesium, expressed as MgO, that this amount is at least 2.0% by weight, preferably at least 3.0% by weight, and more preferably at least 4.0% by weight, of the amount of carbonate produced during the carbonation process. The amount of carbonate is the actual amount of calcite or magnesian calcite. When these amounts of magnesium coprecipitate in magnesian calcite, it is effective in bringing the molar percentage MgCO3 in the magnesian calcite from at least about 5 mole percent to at least about 10 mole percent. According to the above properties of the stainless steel slag fine powder, the maximum amount of carbonate produced in these fine powders during the carbonation test corresponds to an average of 12.32% by weight of CaO equivalents, i.e., about 22% by weight of CaCO3 equivalents. Therefore, the above percentage is at least 0.44% by weight of MgO, preferably at least 0.66% by weight of MgO, and more preferably at least 0.88% by weight of MgO, of the amount of carbonatable binder.

[0107] If magnesian calcite contains 1000 mg / kg of fluoride, this corresponds to approximately 220 mg / kg of fluoride immobilized in the carbonation binder. However, since magnesian calcite can contain larger amounts of fluoride, such as 2000 mg / kg, approximately 440 mg / kg of fluoride can be immobilized in the carbonation binder. This amount of fluoride is comparable to the 300 mg / kg of fluoride found to leach out of the binder after carbonation. Furthermore, an additional amount of fluoride is immobilized by adhering to magnesium hydroxide and hydrated magnesium carbonate that precipitate when water-soluble magnesium salts come into contact with alkaline porous water and undergo carbonation.

[0108] Precipitated magnesium hydroxide and hydrated magnesium carbonate are effective in adsorbing large amounts of fluoride due to their high BET specific surface area. For example, brucite has a layered structure, while hydromagnecite has a lamellar structure, both of which have large BET specific surface areas. This BET specific surface area is determined by the BET method according to ISO 9277:2022(E). This is done by nitrogen absorption manometry after vacuum degassing at 190°C for at least 2 hours to remove all free moisture from the material.

[0109] Water-soluble salts can be distributed as dry particulate matter within particulate material. However, they can also be initially dissolved in water added to the particulate material to obtain the desired water content. Combinations of these two options are also possible. Furthermore, it is clear that the magnesium-containing additives described above can be used individually or in combination with each other.

[0110] Experimental test results Various experiments were conducted using fine stainless steel slag powder with particle sizes ranging from 0 mm to 0.5 mm, and in some experiments, further experiments were conducted using fine stainless steel slag sand fractions with particle sizes ranging from 0.5 mm to 2.0 mm. These two stainless steel slag fractions were obtained as follows.

[0111] Stainless steel slag material was crushed to a particle size of 0mm to 35mm and separated into a 10mm to 35mm fraction and a 0mm to 10mm fraction. The 0mm to 10mm fraction was separated into a 0mm to 2mm fraction and a 2mm to 10mm fraction. Steel particles were removed from the 0mm to 2mm fraction and the fraction was separated into a 0.5mm to 2mm fine sand fraction and a 0mm to 0.5mm fine powder fraction. These fine powders are carbonatable particulate materials used to produce carbonate-bound compressions. These articles can be produced entirely from these fine powders, but preferably other aggregate fractions such as natural sand or steel slag sand fractions are added. This steel slag sand fraction can also be carbonatable, but because its specific surface area is much smaller, it is far inferior to the fine powders, so carbonatable fine powders are required to obtain the required strength.

[0112] The compressive strength of carbonate-bonded compressible materials is determined according to the European standard EN 12390-3:2009. For articles manufactured according to the present invention, this compressive strength is preferably higher than 10 MPa, more preferably higher than 15 MPa, and most preferably higher than 20 MPa. The compressive strength that can be achieved is usually lower than 60 MPa. [Examples]

[0113] Examples 1 to 14 General Test Procedures Fine stainless steel slag powder F and fine stainless steel slag sand fraction S were dried at a temperature of 105°C under an inert N2 atmosphere. After drying, the fine powder was deagglomerated using a disc mill set to the minimum gap (0.1 mm).

[0114] Various mixtures were prepared, and all mixtures were moistened with 10% water at least two hours before compression. Compression was carried out in a 23 mm diameter cylinder with a compressive force of 15 MPa. The height of the cylinder was approximately 46 mm.

[0115] Carbonation was performed in a ventilated artificial climate chamber under the following conditions: 1 bar CO2 (total pressure 2 bar, 50% CO2), 40°C, 24 hours. Compressive strength was measured according to European standard EN 12390-3:2009. After the compressive strength test, the material was further reduced in size to less than 4 mm using a jaw crusher.

[0116] For materials with reduced size (less than 4 mm), a batch leaching test was performed in accordance with EN 12457-2, using fluoride conductivity measurement and / or analysis of fluoride in the eluent by liquid ion chromatography with UV detection. This test method differs from EN 12457-4:2003-01 only in that the material size was reduced to less than 4 mm instead of simply less than 10 mm.

[0117] Magnesium-containing additives Numerous different magnesium-containing additives were tested to investigate their effects in reducing fluoride leaching from carbonate-bound compressions manufactured according to the above procedure and containing 49 wt% stainless steel slag fine powder (0 mm to 0.5 mm), 49 wt% stainless steel slag sand fraction (0.5 mm to 2.0 mm), and 2 wts of magnesium-containing additives. These additives and their main properties are shown in Table 3.

[0118] TIFF2026523139000003.tif104170

[0119] Additives A1 to A5 are commercially available magnesium oxide. These additives are produced by calcining magnesium carbonate. When this phase decomposes, the release of CO2 gas initially forms a porous structure consisting of aggregates of many MgO microcrystals. These MgO crystals undergo sintering, increasing their average size and decreasing the internal porosity of the material. Therefore, the specific surface area and hydraulic reactivity of the resulting MgO strongly depend on the calcination conditions, namely the calcination temperature and residence time. MgO reacts with water and dilute acids, and its reactivity (reaction rate and degree of reactivity) largely depends on the physical properties and purity of the material. The reactivity of MgO increases by reducing its particle size, and therefore increasing its specific surface area. Both the surface area and particle size of MgO are controlled by the manufacturing conditions (type and purity of raw materials, calcination temperature, and residence time during calcination).

[0120] Generally, four types of MgO are produced: lightly calcined or caustically calcined MgO (calcined at 700°C to 1000°C), which has the highest reactivity and largest specific surface area; hard-calcined MgO (calcined at 1000°C to 1500°C), which has lower reactivity and specific surface area than lightly calcined MgO; de-calcined MgO or periclase (calcined at 1400°C to 2000°C), which has the lowest specific surface area and is almost unreactive; and molten MgO (calcined at 2800°C to 3000°C), which has the lowest reactivity. De-calcined MgO, formed above 1500°C, is used in refractories and is almost unreactive.

[0121] However, the inventors have found that even periclase present in stainless steel slag, which is burned out due to the high temperatures in the stainless steel slag furnace, can be hydrated when the fine powder of stainless steel slag is carbonated. Furthermore, refractory magnesia and droma, or magnesia droma, can be hydrated during the carbonation process if these refractory materials have sufficiently small particle sizes.

[0122] Additive A6 is MgO nanopowder. Based on the BET specific surface area, the average PSD is given by the equation: d BET =6 / (S BET ×ρ) (In the formula, d BET This is the average particle size, S BET (where is the BET surface and ρ is the theoretical density) was calculated using the formula.

[0123] A7 is commercially available Mg(OH)2, and A8 is formula Mg6Al2CO3(OH) 16 It is hydrotalcite containing 4H2O.

[0124] A9-A11 are spent EAF magnesia refractory materials, i.e., their finer fractions of 0mm-10mm, ground to different fineness levels. A12 is also spent EAF refractory materials, i.e., recycled larger EAF magnesia ore, ground to very fine particle sizes.

[0125] A13 and A14 are used AOD Droma refractory materials that have been crushed to different degrees.

[0126] Experimental results Various mixtures were prepared using stainless steel slag fine powder F, stainless steel slag sand fraction S, and various additives. As described in general procedures, carbonate-bound compressed bodies were prepared using the various mixtures, and their compressive strength and fluoride leaching were determined. The test results shown in Table 4 are the average values ​​of three measurements.

[0127] TIFF2026523139000004.tif109170

[0128] Before carbonation, the stainless steel slag fine powder F was optionally mixed with the stainless steel slag sand fraction S and had a pH of approximately 12.45. The solubility product of Ca(OH)2 was K. sp Based on this, it can be calculated that a saturated solution of Ca(OH)2 in water has a pH of approximately 12.33. Therefore, before carbonation, the pH of the mixture is thought to be mainly determined by portlandite, i.e., hydrated lime. After carbonation, the pH was approximately equal to 10.4. Solubility product of Mg(OH)2 K spBased on this, it can be calculated that a saturated solution of Mg(OH)2 in water has a pH of approximately 10.35. Therefore, after carbonation, the pH of the mixture is likely to be determined primarily by brucite, i.e., hydrated periclase. This calculation again indicates that during the carbonation process, periclase, or any other MgO, is hydrated, and at least a portion of the hydrated MgO remains in the carbon. This is advantageous because hydrated MgO has been found to adsorb fluorides more effectively than unhydrated MgO. This is still true even when the hydrated MgO is partially carbonated to produce hydrated magnesium carbonate. Furthermore, it has been found that a portion of the hydrated MgO can co-carbonate with CaO to produce magnesian calcite, and a relatively large amount of fluoride can co-precipitate.

[0129] The test results shown in Table 4 demonstrate that carbonated stainless steel slag fine powder releases significantly more fluoride than non-carbonated fine powder. The leaching value increased from 43 mg / kg (= 4.3 mg / L) to 370 mg / kg, indicating that fluoride exceeding 330 mg / kg needs to be further immobilized by the newly formed phase during the carbonation process.

[0130] Examples 1-6 demonstrate that MgO can immobilize fluoride. Additive A1, despite having the lowest specific surface area, showed the best results. This indicates that the reactivity of the additive is also important. Carbonation of the additive can increase its specific surface area. Furthermore, some of the Mg(OH)2 may dissolve and co-precipitate with the fluoride, both as brucite or hydrated magnesium carbonate and as magnesian calcite. Additive A6, i.e., MgO nanopowder, had a very high BET surface area, but was not the best MgO powder for reducing fluoride leaching. Moreover, MgO nanopowder is extremely expensive.

[0131] The Mg(OH)2 in Example 7 also appears to work well, especially considering the fact that more Mg(OH)2 should be added since it has a lower MgO content.

[0132] The hydrotalcite in Example 8 can also adsorb fluoride, but in order to reduce the fluoride leaching value to a sufficiently large extent, it is necessary to use a relatively large amount.

[0133] Furthermore, the refractory magnesia and doloma of Examples 9-14 appear to be effective despite the fact that the refractory magnesia and doloma are charred. In particular, doloma also appeared to be relatively effective, considering its low MgO content (a composition of 50 mol% CaO / 50 mol% MgO contains only about 41 wt% MgO). This may be due to the fact that doloma, and magnesia-doloma, also hydrate better and more rapidly than magnesia. This can be seen, for example, in the paper "Improving hydration resistance of magnesia-doloma refractories by iron oxide addition" by F. Kashaninia et al. (2011). According to this paper, since CaO hydrates much more easily than MgO, reducing the CaO content improved the hydration resistance of magnesia-doloma refractories.

[0134] The refractory magnesia of Examples 9-12 is less reactive than the commercially available MgO used in Examples 1-6. In the case of such less reactive magnesia, it is thought that finer grinding of the magnesia material can be obtained to obtain better fluoride adsorption properties. For example, as in Example 12, D 50 Even when the material was ground to a very fine size, extremely effective fluoride adsorption properties were obtained. While grinding the material to a finer size does not significantly increase the BET specific surface area, the inventors found that a larger surface area allows for the hydration of more MgO during the carbonation process, which significantly increases the BET specific surface area, especially when the material contains carbonatable CaO. For example, they found that a D of approximately 25 μm was obtained. 50When fine stainless steel slag powder with sieve size is carbonated, its BET specific surface area increases to, for example, approximately 2 m². 2 / g to 40m 2 We found that the BET specific surface area increases significantly to a level greater than / g.

[0135] Examples 15 to 33 General Test Procedures The general test procedure was the same as in Examples 1 to 14. The same stainless steel slag fine powder F and the same fine stainless steel slag sand fraction S were used. The compressed bodies produced had the same dimensions, but were produced at a slightly lower compression pressure of 10 MPa.

[0136] Carbonation was performed using the following three different methods. CM1: Atmospheric pressure, 50% CO2, 40℃, CM2: Atmospheric pressure, 50% CO2, 60°C, and CM3: Atmospheric pressure, 20% CO2, 60°C.

[0137] Magnesium-containing additives The following magnesium-containing additives were used.

[0138] TIFF2026523139000005.tif40170

[0139] Magnesia additive A15 is equivalent to additive A12 but has a slightly larger PSD. Droma additive A16 is equivalent to additive A13 but is ground to a smaller PSD.

[0140] Experimental results Various mixtures were prepared using stainless steel slag fine powder F, stainless steel slag sand fraction S, and various additives. As described in general procedures, carbonate-bound compressed bodies were prepared using various mixtures under various carbonation conditions, and their compressive strength and fluoride leaching were determined. The test results shown in Table 6 are the average values ​​of three measurements.

[0141] TIFF2026523139000006.tif220170

[0142] Compared to Comparative Example 4, the fluoride leaching in Comparative Example 5 is somewhat lower. This is because the carbonation conditions were not as severe. The fluoride leaching values ​​in Comparative Examples 6 and 7 are even lower because the degree of carbonation was somewhat lower.

[0143] Comparing Example 1 with Examples 15-21, it can be observed that increasing the amount of MgO additive can reduce fluoride leaching to a lower value, particularly below 5 mg / L (= 50 mg / kg). This is especially true when less stringent carbonation conditions are applied, as in Examples 17-18 and 20-21, resulting in less fluoride release. The compressive strength of the carbonite decreased to some extent, but remained sufficiently high. The decrease in compressive strength may be due to the fact that most of the MgO particles were only slightly hydrated and carbonated.

[0144] Comparing Example 12 with Examples 22-27, it can be observed that increasing the amount of finely ground spent magnesia refractory additive can reduce fluoride leaching to a lower value. However, stronger carbonation conditions appear to be required to reduce fluoride leaching to less than 5 mg / L. These stronger carbonation conditions may be necessary to enable the hydration of the decomposed magnesia. The compressive strength of the carbonite was also reduced to some extent.

[0145] Comparing Example 13 with Examples 28-33, it can be observed that the fluoride leaching value can be reduced by increasing the amount of finely ground spent droma refractory additive. Achieving a fluoride leaching value of less than 5 mg / L requires a relatively large amount of droma and relatively strong carbonation conditions. Clearly, the droma particles need to be carbonized to release the magnesium oxide contained therein. An advantage of using droma is that the compressive strength of the carbonite is not substantially adversely affected by the droma particles, which indicates that these particles, in particular the calcium oxide contained therein, contribute to the carbonation reaction.

[0146] In addition to leaching tests conducted according to EN 12457-2 for carbonites reduced in size to less than 4 mm, fluoride leaching values ​​for some carbonites were also tested according to DIN EN 12457-4:2003-01 using carbonites reduced in size to less than 10 mm. These test results were equivalent to those obtained according to EN 12457-2:2003-01.

[0147] Leachation results In addition to fluoride leaching, the leaching values ​​of other elements were also measured according to EN 12457-2, along with the analysis of all relevant parameters. The fluoride results for the three additives are shown in Table 6, and the leaching concentrations of all elements are shown in Table 7. For the following elements, all values ​​remained below the reporting limits: Cd (<1 μg / L); Co (<5 μg / L); Cu (<5 μg / L); Ni (<5 μg / L); As, Pb (<10 μg / L); Sb, Se, Sn (<20 μg / L); and Al (<25 μg / L). Therefore, these elements are not included in the table.

[0148] TIFF2026523139000007.tif129170

[0149] Under carbonation conditions CM1 and CM2, the addition of MgO additive A1 significantly suppressed chromium leaching. All three different additives also significantly reduced vanadium leaching.

[0150] Examples 34-43 General Test Procedures In comparison to the previously described examples, these examples used other new batches of stainless steel slag fine powder F and fine stainless steel slag sand fraction S taken from daily production. The fine powder F and sand fraction S were dried at a temperature of 110°C. After drying, the fine powder was sieved using a 500 μm sieve. In some examples, approximately 250 μm D 50 Natural sand NS with sieve size was added.

[0151] Various mixtures were prepared, and all mixtures were moistened with 10% water by dry weight at least two hours before compression. Compression was carried out in a cylindrical mold with a compressive force of 4 MPa. Approximately 800 g of the moist mixture was placed in the cylindrical mold. The compressed body was removed from the mold, and then the molded compressed body was carbonated. Two identical compressed bodies were prepared from each mixture, one for measuring compressive strength and the other for measuring fluoride leaching value according to DIN EN 12457-4:2003-01.

[0152] Carbonation was carried out in an artificial climate chamber maintained at atmospheric pressure, 40°C, 50% CO2, and 75%–80% relative humidity. Carbonation was performed for 24 or 48 hours.

[0153] Magnesium-containing additives The following magnesium-containing additives were used. MgO, and, MgCl2.

[0154] Magnesium chloride was dissolved in the water (MgCl2_D) used to prepare the mixture, and / or mixed into the mixture as a solid powder (MgCl2_S). 2% MgCl2 by dry weight could be dissolved in 10% water, which was used to prepare the mixture. Therefore, 20% by weight of MgCl2 was dissolved in the water.

[0155] Magnesium oxide was not water-soluble.

[0156] Experimental results Two different mixtures were prepared using stainless steel slag fine powder F, stainless steel slag sand fraction S, and natural sand NS. The first mixture M1 contained only stainless steel slag fine powder F. The second mixture M2 contained stainless steel slag fine powder F, stainless steel slag sand fraction S (0 mm to 0.5 mm), and natural sand NS in a ratio of 50 / 30 / 20. One or more of the additives were added to these mixtures. As described in the general procedure, carbonate-bound compressed bodies were prepared using the various mixtures, and fluoride leaching was determined. The test results shown in Table 8 are based on measurements of one carbonate compressed body each, which were much larger than those of the compressed bodies prepared in the previously described examples.

[0157] TIFF2026523139000008.tif137170

[0158] In the experiment using batch 2, more fluoride leached from the stainless steel slag fine powder. This may be due to the fluoride content of these fine powders.

[0159] Examples 34, 37, 39, and 42 demonstrate that the fluoride leaching values ​​of different mixtures M1 and M2 can be reduced to approximately 5 mg / L or less by dissolving only 2% by weight of MgCl2 (based on the dry weight of the mixture) in the water used to prepare the mixtures. These results are better than those obtained with the various MgO additives used in Examples 1-6.

[0160] The MgO additive may be hydrated in the pore water, particularly during the carbonation process, during which the pH of the pore water was found to decrease, for example, from a pH of approximately 12.5 to a pH of less than 8.2. The inventors actually prepared a cylindrical compressed body from mixture M1 and carbonized it at 40°C in 50% CO2 for 3 hours. Immediately after carbonation, the compressed body was cut into two test pieces, and the carbonation front was visualized with phenolphthalein. The center of the compressed body still had a pH of 8.2 to 12.5, but the outer edge had a pH of less than 8.2. At such low pH values, MgO was found to be hydrated even when de-carbonized. Therefore, MgO is an alkaline substance. MgO + H2O → Mg(OH)2. At lower pH values, especially below 10.33, the generated magnesium hydroxide can dissolve in the pore water, and therefore release hydroxyl ions into the pore water.

[0161] On the other hand, water-soluble magnesium salts such as MgCl2 have been found to be acidic substances, especially at pH values ​​higher than 10.33, which lowers the pH of pore water through the following precipitation reaction of magnesium hydroxide (and / or compounds such as Mg2Cl(OH)3·4H2O). MgCl2 + 2OH - →Mg(OH)2+2Cl - .

[0162] When magnesium chloride is added, a certain amount of hydroxide precipitates, causing the pH to drop to a value that depends on the amount of magnesium ions in the solution. This decrease in pH leads to the release of further CaO(Ca(OH)2) from the stainless steel slag fine powder.

[0163] The following tests were conducted by adding 2% and 5% MgCl2 to a mixture of M1 and M2, without a carbonation step.

[0164] 100g of the M1 or M2 mixture was added to 1L of water. 2g or 5g of MgCl2 was added, and the mixture was stirred for 2 hours or 24 hours, after which the pH of the liquid was measured.

[0165] TIFF2026523139000009.tif70170

[0166] It can be observed that the pH of water decreases when MgCl2 is added. The more MgCl2 added, the higher the magnesium concentration in the solution, and therefore the lower the pH (K of Mg(OH)2). sp Based on the values, this corresponds to a decrease in the amount of hydroxyl ions in the solution as the amount of magnesium increases.

[0167] MgCl2 can have two effects on fluoride immobilization. The addition of MgCl2 causes a rapid decrease in pH, leading to the release of fluoride and the formation of a Mg(OH)2 precipitate. This magnesium hydroxide has a high specific surface area. Furthermore, when fluoride co-precipitates with magnesium hydroxide, far more fluoride can be immobilized compared to a situation where the fluoride must be adsorbed onto the magnesium hydroxide added in solid powder form. This is evident, for example, from Examples 37 and 42, where 2% MgCl2 (=0.85% MgO equivalent) resulted in a greater reduction in fluoride leaching than 2% Mg(OH)2 (=1.23% MgO equivalent).

[0168] A second effect of using water-soluble MgCl2 is that, because the porous water has a higher magnesium concentration, more magnesian calcite can be formed, and because this has an even higher magnesium content, more fluoride can be immobilized by coprecipitation with the magnesian calcite. The inventors conducted several additional tests to demonstrate that the porous water still has a high magnesium concentration even at the end of the carbonation process. They actually measured the pH of stainless steel slag fine powder mixed with various amounts of magnesium chloride and carbonated in the same manner as in Examples 34-43, and also measured the magnesium and calcium leaching values ​​according to DIN EN 12457-4:2003-01.

[0169] TIFF2026523139000010.tif74170

[0170] The pH of carbonated stainless steel slag fine powder decreases when magnesium chloride is added to it. The pH of carbonated stainless steel slag fine powder without added magnesium chloride is approximately equivalent to the pH of a saturated Mg(OH)2 solution. Since the pH of carbonated stainless steel slag fine powder with added magnesium chloride is lower, the water must contain more dissolved magnesium. This is also evident from the magnesium leaching value from carbonated stainless steel slag fine powder. Therefore, throughout the entire carbonation process, magnesium ions are available in the solution, forming magnesian calcite that can effectively coprecipitate fluoride. The molar percentage of magnesium carbonate in this magnesian calcite is thought to be somewhat higher than 10%. According to Figure 3 in the paper by Minoru Okumura et al. (1983), such magnesian calcite is extremely effective in immobilizing fluoride.

[0171] As is evident from Examples 35 and 38, more fluoride can be immobilized by adding an additional amount of solid MgCl2 separately from the dissolved MgCl2. As more and more magnesium precipitates in the form of magnesium hydroxide and / or hydrated magnesium carbonate, more MgCl2 dissolves in the pore water. Therefore, during the carbonation reaction, a sufficiently high concentration of magnesium is always present in the pore water, producing magnesian calcite, magnesium hydroxide (brucite), and hydrated magnesium carbonate.

[0172] Example 40 demonstrates that even when only solid MgCl2 is added, most of the fluoride can be immobilized. It is possible to immobilize most of the fluoride by adding a relatively large amount of MgCl2. Considering Examples 41 and 43, using MgO in addition to MgCl2 appears to be less effective than using a larger amount of MgCl2. Therefore, water-soluble MgCl2 appears to be more effective than MgO.

Claims

1. A method for producing carbonate-bonded compressed products, comprising the following steps: A step of preparing a particulate material comprising a particulate carbonatable binder composed of particles having a sieve size of less than 500 μm, wherein the particulate carbonatable binder contains fluoride, calcium oxide, and silicon dioxide, and has a CaO / SiO ratio higher than 1.

1. ２ A step comprising: a ratio and a pH of at least 10.5, preferably at least 11.0, more preferably at least 11.5, measured after a 24-hour contact period according to DIN EN 12457-4:2003-01; A step of compressing the particulate material to form a compressed body having pores containing porous water, A step comprising carbonating the compressed body with a gas containing carbon dioxide for a predetermined period of time to produce a carbonate containing calcium carbonate, thereby converting the compressed body into the carbonate-bonded compressed product, wherein the carbonate-bonded compressed product has a fluoride leaching value measured according to DIN EN 12457-4:2003-01, Includes, Prior to the carbonation step, at least one magnesium-containing additive is distributed throughout the particulate material to provide a fluoride-adsorbing magnesium-containing solid compound containing surface hydroxyl groups bonded to magnesium atoms in the compressed body, wherein the additive has a magnesium content of at least 30% by weight MgO as expressed by dry weight as an oxide, and contains the fluoride-adsorbing magnesium-containing solid compound, and / or generates the fluoride-adsorbing magnesium-containing solid compound in the particulate material by reaction in the porous water. A method characterized by the following features.

2. The method according to claim 1, wherein the at least one magnesium-containing additive comprises magnesium-aluminum hydrotalcite.

3. The method according to claim 1 or 2, wherein the at least one magnesium-containing additive comprises magnesia, droma, or magnesia-droma having a magnesium content of at least 50% by weight of MgO, preferably at least 60% by weight of MgO, preferably magnesia or magnesia-droma.

4. The at least one magnesium-containing additive has a particle size of less than 15.0 μm, preferably less than 10.0 μm, and more preferably less than 5.0 μm. ５０ The method according to any one of claims 1 to 3, wherein the sieve size value is specified.

5. The method according to any one of claims 1 to 4, wherein the at least one magnesium-containing additive comprises magnesia, droma, or magnesia-droma, and the magnesia, droma, or magnesia-droma has a citric acid reactivity of less than 900 seconds, preferably less than 600 seconds, and more preferably less than 300 seconds.

6. The method according to any one of claims 1 to 5, wherein the at least one additive comprises magnesia, droma, or magnesia-droma, and the magnesia, droma, or magnesia-droma has a citric acid reactivity of more than 60 seconds.

7. The method according to any one of claims 1 to 6, wherein the at least one magnesium-containing additive comprises spent magnesia, droma, or magnesia-droma refractory material, particularly spent refractory material recycled from ironmaking furnaces or steelmaking furnaces.

8. The method according to any one of claims 1 to 7, wherein the at least one magnesium-containing additive comprises hydrated magnesia, hydrated droma, or hydrated magnesia-droma, and preferably the at least one magnesium-containing additive comprises hydrated magnesia.

9. The method according to any one of claims 1 to 8, wherein the at least one magnesium-containing additive dissolves at least partially in the porous water to provide magnesium ions to the porous water, and at least a portion of the magnesium ions dissolved in the porous water precipitates by reaction with at least hydroxyl ions present in the porous water to produce, in particular brucite and / or hydrated magnesium carbonate, such as neskehonite and hydromagnesite, as the fluoride-adsorbing magnesium-containing solid compound.

10. The method according to claim 9, wherein the brucite and / or the hydrated magnesium carbonate coprecipitates with at least a portion of the fluoride leached from the particulate carbonizable binder during the carbonation step.

11. The method according to claim 9 or 10, wherein during the carbonation step, the magnesium ions coprecipitate at least partially with calcium ions and carbonate ions present in the porous water to produce magnesian calcite, and during the carbonation step, the magnesian calcite coprecipitates with at least a portion of the fluoride leaching from the particulate carbonizable binder.

12. The method according to any one of claims 1 to 11, wherein the gas has a partial pressure of carbon dioxide of at least 0.10 bar, preferably at least 0.20 bar, more preferably at least 0.30 bar, and most preferably at least 0.40 bar, and the partial pressure of carbon dioxide in the gas is preferably lower than 5.0 bar, more preferably lower than 2.0 bar, and more preferably lower than 1.0 bar.

13. The method according to any one of claims 1 to 12, wherein the compressed body is carbonated until the carbonate-bonded compressed body has a pH lower than 11.0, preferably lower than 10.8, more preferably lower than 10.6, measured after a 24-hour contact period according to DIN EN 12457-4:2003-01, and the pH of the carbonate-bonded compressed body is preferably higher than 9.0, more preferably higher than 9.

5.

14. The method according to any one of claims 1 to 13, wherein the at least one magnesium-containing additive preferably comprises at least one water-soluble magnesium salt selected from the group consisting of magnesium chloride, magnesium nitrate, magnesium sulfate, and magnesium citrate, and more preferably from the group consisting of magnesium chloride, magnesium nitrate, and magnesium citrate, and the at least one additive preferably comprises magnesium chloride.

15. The method according to any one of claims 1 to 14, wherein during the carbonation step, a predetermined amount of carbonate is generated, and the at least one additive is distributed throughout the particulate material, and magnesium is added to the particulate material in an amount of at least 2.0% by weight, preferably at least 3.0% by weight, more preferably at least 4.0% by weight of the predetermined amount of carbonate, which is represented as an oxide.

16. The method according to any one of claims 1 to 15, wherein during the carbonation step, carbon dioxide is incorporated by the particulate carbonizable binder to produce the carbonate, and the amount of carbon dioxide incorporated by the particulate carbonizable binder is at least 6% by dry weight, preferably at least 8% by dry weight of the particulate carbonizable binder.

17. The method according to any one of claims 1 to 16, wherein the at least one additive is distributed throughout the particulate material and magnesium is added to the particulate material in an amount of at least 0.50% by weight, preferably at least 0.75% by weight, more preferably at least 1.00% by weight, which is represented as an oxide.

18. The method according to any one of claims 1 to 17, wherein the at least one magnesium-containing additive is distributed throughout the particulate material, and an amount of magnesium less than 10.0% by weight, preferably less than 8.0% by weight, more preferably less than 6.0% by weight, expressed as an oxide, is added to the particulate material.

19. The method according to any one of claims 1 to 18, wherein the carbonatable binder comprises at least 4,000 mg / kg, and in particular at least 6,000 mg / kg, of fluoride.

20. The method according to any one of claims 1 to 19, wherein when the carbonation step is started, the compressed body has a water content of 3.0% to 25% by weight, preferably 5.0% to 20% by weight.

21. The method according to any one of claims 1 to 20, wherein the particulate carbonatable binder comprises carbonatable slag from a metal manufacturing process, slag from phosphorus production, bottom ash and / or fly ash, and the particulate carbonatable binder preferably comprises steelmaking slag, particularly stainless steelmaking slag.

22. The method according to any one of claims 1 to 21, characterized in that the particulate carbonatable binder is at least partially crystalline and contains caspidin and / or calcium fluoride.

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