A method for preparing a solid chromium two-mineral clinker by using chromium-containing steel slag, a product and applications thereof

Abstract

The application provides a method for preparing solid-chromium two-mineral clinker by using chromium-containing steel slag, a product and application, the preparation method takes the chromium-containing steel slag as a main raw material, after being preprocessed by grinding, the chromium-containing steel slag is homogenized with calcareous raw material, siliceous raw material and aluminiferous and ferruginous raw material, and after being pressed, the mixture is calcined at 1200-1380 DEG C, and then is rapidly cooled to obtain the solid-chromium two-mineral clinker with beta-C2S and C4AF as main crystal phases. In the preparation method, the main crystal phases of the solid-chromium two-mineral clinker are limited to beta-C2S and C4AF, and the medium-temperature calcination process at 1200-1380 DEG C is matched, so that the chromium element can be stably sealed in the two mineral lattices, the dissolution of the chromium ions, especially the hexavalent chromium, is fundamentally inhibited, and the low-chromium dissolution characteristic of the clinker is realized.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to a method, product, and application of preparing solid chromium two-mineral clinker using chromium-containing steel slag. Background Technology

[0002] The steel metallurgical industry generates a large amount of steel slag solid waste during production, with slag from processes such as stainless steel smelting and special steel refining generally rich in chromium. The annual discharge of chromium-containing steel slag is enormous. Large-scale stockpiling not only occupies land resources, but chromium also exhibits multiple valence transformations. Hexavalent chromium, which is highly toxic, easily leaches out with rainwater and migrates to surrounding areas, causing heavy metal pollution of soil, groundwater, and surface water. Currently, the conventional resource utilization methods for chromium-containing steel slag mainly involve simple crushing and use as building aggregate, roadbed filler, or as a small amount of auxiliary cementitious material added to cement-based materials. These extensive utilization methods cannot achieve stable sequestration of chromium. Chromium remaining in the slag is easily leached out under complex environmental conditions such as alternating wet and dry conditions and acid / alkali corrosion, posing serious ecological and environmental risks and greatly limiting the large-scale resource utilization and application of chromium-containing steel slag.

[0003] To address the risk of chromium leaching, some existing research has attempted to use chromium-containing steel slag in cement clinker production, utilizing the lattice-sealing effect of clinker minerals to stabilize chromium and achieve harmless disposal of the chromium-containing steel slag. However, traditional silicate clinker systems, with tricalcium silicate as the main crystalline phase, require high firing temperatures and strong oxidizing atmospheres within the kiln. During firing, trivalent chromium in the steel slag is easily oxidized to highly toxic hexavalent chromium, and chromium ions are difficult to stably dissolve in the traditional clinker mineral lattice. Therefore, the risk of excessive chromium leaching remains during the later stages of clinker service. Furthermore, traditional clinker production processes have strict limitations on the doping ratio of chromium-containing steel slag, resulting in low overall utilization of the steel slag and hindering large-scale solid waste disposal. The resulting clinker also suffers from poor volume stability and difficulty in controlling heavy metal safety, making it difficult to meet national mandatory safety requirements for building materials.

[0004] Overall, existing technologies for the resource utilization of chromium-containing steel slag generally suffer from prominent shortcomings such as poor chromium element consolidation effect, high long-term leaching risk, low solid waste disposal ratio, and poor adaptability to production processes. The industry urgently needs to develop a clinker preparation technology that can consume large quantities of chromium-containing steel slag, has low chromium leaching, and stable finished product performance, so as to ultimately achieve the harmless, high-value resource utilization of chromium-containing steel slag. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method, product and application for preparing solid chromium two-mineral clinker using chromium-containing steel slag. This invention solves the technical problems of high chromium leaching risk, low solid waste utilization rate, unstable clinker performance and inability to be applied on a large scale in the resource utilization of chromium-containing steel slag, and realizes efficient and harmless disposal of chromium-containing steel slag and high-value building material utilization.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing chromium-fixed two-mineral clinker using chromium-containing steel slag, comprising the following steps: S10, chromium-containing steel slag is crushed and ground in sequence, and after screening, steel slag powder with a particle size ≤75μm is obtained; S20: Steel slag powder, calcareous raw materials, siliceous corrective raw materials and aluminum-iron corrective raw materials are thoroughly mixed evenly according to a preset ratio to obtain homogeneous raw meal. S30 involves pressing homogeneous raw materials into cakes, heating them to 1200–1380°C, and then subjecting them to heat preservation and calcination treatment to obtain high-temperature clinker. S40 involves rapidly cooling high-temperature clinker to obtain a chromium-fixing two-mineral clinker with β-C2S and C4AF as the main crystalline phases. The β-C2S content is 59–75 wt.%, the C4AF content is 20–40 wt.%, the impurity phase content is 1–5 wt.%, and the total content of β-C2S and C4AF is 95–99 wt.%.

[0007] Specifically, step S10 eliminates the problem of poor reactivity caused by the hardness difference of chromium-containing steel slag, ensuring that the subsequent calcination reaction proceeds synchronously and avoiding local under-burning and over-burning. Furthermore, the fine-particle steel slag powder significantly increases the contact area with other raw materials, lowers the solid-phase reaction energy barrier, and allows the chromium components present in the steel slag powder to more easily enter the target mineral lattice during calcination, improving the solid solution efficiency of chromium. Step S20 produces homogeneous raw material that can precisely balance the proportions of calcium, silicon, aluminum, and iron oxides, providing a suitable chemical environment for the formation of the two target minerals, β-C2S and C4AF, reducing harmful impurity phases such as free calcium oxide that affect stability. It also avoids the problem of uneven mineral composition and ineffective solid solution of chromium caused by chromium enrichment. Step S30, compaction, increases the density of the raw material and accelerates the solid-phase reaction. Mass transfer: The medium-temperature calcination regime of 1200–1380℃ is lower than the traditional silicate clinker calcination temperature, which can reduce calcination energy consumption and promote the directional formation of target minerals β-C2S and C4AF. This allows chromium ions to fully dissolve and enter the mineral lattice at high temperatures, reducing the residue of free chromium. The rapid cooling and shaping in step S40 can quickly cross the crystal transformation temperature range of β-C2S to γ-C2S, stabilize the high-temperature crystal form of β-C2S, and avoid clinker pulverization and reduced gelling properties caused by crystal volume expansion. On the other hand, rapid cooling can quickly freeze the chromium ions already dissolved in the crystal lattice, preventing chromium from migrating to the grain boundaries during slow cooling. This further improves the long-term stability of chromium solidification from the cooling end, ultimately yielding a solidified chromium two-mineral clinker with a total β-C2S and C4AF content of 95–99 wt.%.

[0008] In summary, by limiting the main crystalline phases of the two chromium-fixing mineral clinker to β-C2S and C4AF, and using a medium-temperature calcination process of 1200–1380℃, the present invention can stably fix chromium elements in the crystal lattice of the two minerals, fundamentally inhibiting the dissolution of chromium ions, especially hexavalent chromium, and achieving low chromium dissolution characteristics in the clinker.

[0009] Preferably, in step S10, the chromium-containing steel slag is one or more of converter steel slag, electric furnace steel slag, stainless steel slag, and refined steel slag.

[0010] Specifically, the aforementioned chromium-containing steel slag raw materials have strong adaptability and can be flexibly selected according to the waste production situation of steel plants, realizing the large-scale consumption of chromium-containing steel slag from different sources and greatly improving the universality of the process. Among them, the present invention prefers converter steel slag as production raw material, whose own calcium, silicon, aluminum and iron chemical composition is more compatible with the element requirements of the two target mineral clinker of the present invention, which can reduce the additional addition ratio of silicon and aluminum correction raw materials and reduce the batching cost.

[0011] Preferably, in step S20, based on the total dry weight of the homogeneous raw material, the content of chromium-containing steel slag is 13–44 wt.% (more preferably 10–40 wt.%), the content of calcareous raw materials is 40–66 wt.%, the content of silica-correcting raw materials is 1.7–20 wt.%, and the content of aluminum-iron-correcting raw materials is 1.5–14 wt.%; the sum of the mass percentages of each raw material is 100%.

[0012] Specifically, the lower limit of 13 wt.% chromium-containing steel slag ensures a significantly better solid waste utilization rate than traditional steel slag blending processes. The upper limit of 44 wt.% chromium-containing steel slag maximizes the utilization of steel slag while avoiding the total chromium input exceeding the solid solution capacity of β-C2S and C4AF crystal lattices, thus preventing the risk of leaching caused by increased free chromium. The lower limit of 40 wt.% calcium-based raw materials ensures the full development of the β-C2S main crystal phase, while the upper limit of 66 wt.% calcium-based raw materials avoids excessive calcium oxide generation, which could affect clinker stability, and also prevents the formation of large amounts of silicon under high calcium conditions. Tricalcium phosphate; a lower limit of 1.7 wt.% silica-correcting raw material ensures sufficient silica to react with calcium oxide to generate β-C2S, while an upper limit of 20 wt.% silica-correcting raw material avoids excessive silicon content from generating too much inert glass and crowding out the formation of C4AF, while also improving and reducing calcination energy consumption; a lower limit of 1.5 wt.% aluminum-iron correcting raw material ensures the stable formation of C4AF as the second main crystalline phase, relying on the stronger heavy metal solid solution ability of C4AF to synergistically seal chromium ions, while an upper limit of 14 wt.% aluminum-iron correcting raw material avoids excessive aluminum-iron components leading to abnormal clinker condensation.

[0013] Preferably, in step S20, the calcareous raw material is one or more of limestone, quicklime, hydrated lime, and calcium-containing steel slag; the siliceous correcting raw material is one or more of quartz sand, fly ash, and silica fume; and the aluminum-iron correcting raw material is one or more of bauxite, red mud, iron tailings, and aluminum-iron steel slag.

[0014] Specifically, the aforementioned raw materials are widely available and have low procurement costs. They can simultaneously dispose of bulk industrial solid waste from other industries while disposing of chromium-containing steel slag, further improving the comprehensive utilization rate of solid waste in the process and reducing the consumption of natural mineral resources. Among them, limestone, sandstone, and wet ash are preferred as raw material combinations. The three types of raw materials have stable and easily controllable compositions and low acquisition costs. Wet ash, as a stockpiled solid waste in the thermal power industry, can further realize cross-industry collaborative disposal of solid waste.

[0015] Preferably, in step S30, the calcination temperature is preferably 1250–1350°C; the calcination is carried out under a neutral atmosphere or a weakly reducing atmosphere, and the volume concentration of reducing gas in the weakly reducing atmosphere is not higher than 10%.

[0016] Specifically, the temperature range of 1250–1350℃ is highly matched with the optimal formation temperature of the two target minerals, β-C2S and C4AF. This avoids the problem of insufficient solid-phase reaction caused by excessively low temperature, and also prevents energy waste and high-temperature volatilization of chromium caused by excessively high temperature. This reduces the energy consumption of firing while ensuring the full formation of the target minerals. At the same time, it is clear that a neutral or weakly reducing atmosphere is used in the calcination and heat preservation section. This atmosphere can effectively inhibit the oxidation reaction of Cr(III) to highly toxic Cr(VI) at high temperature from the source, reduce the amount of hexavalent chromium generated from the source, reduce the risk of chromium leaching in the later stage, and avoid the problem of excessive generation of low-valent iron under a strong reducing atmosphere. This balances the effect of chromium pollution control and the physical cementitious properties of clinker.

[0017] More preferably, step S30 further includes: pressing the prepared homogeneous raw meal into Φ50mm raw meal cakes under a pressure of 60MPa, feeding them into a box-type high-temperature furnace and calcining them at 10℃ / min to 1320℃ and holding them at that temperature for 30min to obtain high-temperature clinker; during the calcination process, by adjusting the air intake, the box-type high-temperature furnace is kept in a weakly reducing atmosphere to regulate the clinker mineral formation system.

[0018] Preferably, in step S40, the rapid cooling process specifically involves cooling the high-temperature clinker to below 500°C at a cooling rate of not less than 20°C / min.

[0019] Specifically, the aforementioned rapid cooling process can, on the one hand, drive the high-temperature clinker to quickly cross the sensitive range of the β-C2S to γ-C2S crystal transformation, avoiding the volume expansion caused by the crystal transformation of dicalcium silicate during slow cooling, and stably retaining the cementing properties of the β-C2S main crystal phase; on the other hand, a sufficient cooling rate can quickly freeze chromium ions that have been chemically bonded and dissolved in the β-C2S and C4AF lattices at high temperatures, preventing the migration of chromium ions to the grain boundaries to generate highly toxic hexavalent chromium during slow cooling, and significantly improving the long-term stability of chromium sealing; after cooling to below 500℃, the mineral crystal transformation inside the high-temperature clinker basically stops, which can completely lock the β-C2S crystal form to prevent transformation, and also completely block the dissolution channel of chromium elements in the later stage of cooling, ultimately obtaining a solidified chromium two-mineral clinker with stable mineral composition and low risk of hexavalent chromium dissolution; at the same time, the cooling rate requirement of 20℃ / min can be easily achieved by the existing air cooling and grate cooling equipment of cement production lines, without the need for additional special rapid cooling devices, with strong process adaptability, low additional cost, and easy industrialization.

[0020] Preferably, the cooling method is natural cooling, air cooling, or forced air cooling.

[0021] Specifically, the above-mentioned cooling methods can quickly stabilize the β-C2S crystal form, avoid structural loosening and chromium precipitation caused by mineral phase transformation, and ensure the structural stability of clinker.

[0022] In a second aspect, the present invention also provides a chromium-fixing two-mineral clinker, which is prepared by any of the methods described above; based on the total mass of the chromium-fixing two-mineral clinker, the β-C2S content is 59-75 wt.%, the C4AF content is 20-40 wt.%, the impurity phase content is 1-5 wt.%, and the total content of β-C2S and C4AF is 95-99 wt.%.

[0023] Specifically, β-C2S, accounting for 59–75 wt.%, provides stable gelling activity for the two mineral clinker containing chromium; C4AF, accounting for 20–40 wt.%, can rely on its own high heavy metal solid solution capacity in its crystal structure to work with β-C2S to stably lock chromium in the crystal lattice through chemical bonding; the extremely low proportion of impurity phases not only avoids the volume stability problems caused by harmful phases such as free calcium oxide, but also reduces the free occurrence of chromium in impurity phases, thus ensuring the long-term solidification stability of chromium from the mineral structure level.

[0024] Thirdly, the present invention provides a cementitious material, which is prepared by grinding the above-mentioned chromium-fixing mineral clinker together with gypsum accounting for 4 to 7 wt.% of the total mass; wherein the water-soluble hexavalent chromium content of the cementitious material, as measured according to the method of GB31893-2015 national standard, is not higher than 10 mg / kg.

[0025] Specifically, the cementitious material provided by the present invention is prepared by co-grinding the aforementioned two mineral clinker for fixing chromium with 4-7 wt.% gypsum. The process is simple and the cost is low. The water-soluble hexavalent chromium of the product meets the safety limit of GB31893-2015 national standard, the cementitious performance meets the standard, and it can dispose of a large proportion of chromium-containing steel slag without the risk of chromium leaching.

[0026] Fourthly, the present invention also provides an application of chromium-fixing two-mineral clinker or cementing material in the preparation of cement, mortar, and concrete.

[0027] Specifically, the aforementioned chromium-fixing mineral clinker and cementitious materials can be directly used in the preparation of cement, mortar, and concrete without modifying existing building material production and construction processes. The mechanical properties of the prepared building materials meet the standards, and the leaching of hexavalent chromium meets the national mandatory safety standards. This not only realizes the large-scale high-value disposal of chromium-containing steel slag, but also avoids the chromium pollution risk of traditional chromium-containing steel slag building materials from the source. It is suitable for various engineering construction scenarios and has both environmental benefits and economic advantages.

[0028] Compared with the prior art, the present invention has the following beneficial effects: (1) Efficiently realize the harmless and resource-based treatment of chromium-containing steel slag: This invention breaks through the bottleneck of traditional steel slag utilization technology. By constructing a C2S-C4AF dual mineral clinker system, chromium is stably sealed in the dense mineral lattice. Combined with a neutral / weak reducing calcination atmosphere, trivalent chromium is inhibited from being oxidized to hexavalent chromium. The content of water-soluble hexavalent chromium in the clinker is ≤10mg / kg, which solves the problem of chromium leaching pollution during the utilization of chromium-containing steel slag. Solid waste disposal is safe and environmentally friendly.

[0029] (2) High utilization rate of solid waste and good economic benefits: This invention can achieve a high proportion of chromium-containing steel slag doping of 13-44 wt.%, and can consume large quantities of metallurgical solid waste. At the same time, it can also utilize various industrial solid wastes such as fly ash, red mud, and iron tailings. The raw material cost is low, and the synergistic resource utilization of multiple solid wastes can be realized, resulting in significant industrial economic benefits.

[0030] (3) Simple process and strong adaptability: The firing temperature of this invention is 1200~1380℃, which is much lower than the traditional silicate cement clinker firing temperature of 1450℃. The energy consumption is greatly reduced, the production process is simple, no complicated modification equipment is required, and it can be directly modified to produce existing cement and clinker production lines. The difficulty of industrialization is low. Attached Figure Description

[0031] Figure 1 This is a flowchart of a method for preparing solid chromium two-mineral clinker using chromium-containing steel slag, as provided in Example 1. Detailed Implementation

[0032] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] To address the shortcomings of existing technologies, this invention aims to provide a method, product, and application for preparing chromium-fixed two-mineral clinker from chromium-containing steel slag. This addresses the problems of poor chromium encapsulation stability, easy leaching of hexavalent chromium causing environmental pollution, and the difficulty in simultaneously ensuring the performance and safety of the prepared building materials during the resource utilization process of chromium-containing steel slag. This invention constructs a two-mineral clinker system with β-C2S and C4AF lattices as the main crystalline phases, combined with a process of calcination in a weak reducing atmosphere and rapid cooling to stabilize the crystal form. This process stably encapsulates chromium within the mineral lattice, inhibiting the formation and leaching of hexavalent chromium at its source, and enabling the large-scale utilization of chromium-containing steel slag. The final chromium-fixed two-mineral clinker and cementitious materials meet performance standards, exhibit high environmental safety, are compatible with existing cement production processes, and can achieve the harmless, high-value, and large-scale utilization of chromium-containing steel slag.

[0034] The technical solution of the present invention will now be further described with reference to specific embodiments.

[0035] Unless otherwise specified, all raw materials and reagents used in the embodiments of this invention are commercially available conventional industrial raw materials; all grinding, calcining, and cooling equipment used are conventional industrial equipment in the cement production field; performance testing, unless otherwise specified, adopts standard methods in the field: the mineral composition of clinker is quantitatively determined by X-ray diffraction combined with Rietveld full-spectrum fitting method, and the water-soluble hexavalent chromium content in the cementitious material aqueous solution is tested according to GB31893-2015 "Limits and Determination Methods for Water-Soluble Chromium (VI) in Cement". The converter steel slag, limestone, sandstone, and wet ash used in the embodiments of this invention are all obtained from domestic steel and building materials production enterprises. The main chemical components of the raw materials on a dry basis are shown in Table 1.

[0036] Table 1. Main chemical composition (wt.%) of raw materials for each embodiment and comparative example Example 1: Please see Figure 1 This embodiment 1 provides a method for preparing solid chromium two-mineral clinker using chromium-containing steel slag, and the specific operation is as follows: (1) Raw material pretreatment: stainless steel refining slag is selected as raw material, crushed by jaw crusher, ground by ball mill and passed through 200 mesh square hole screen (screen residue particle size ≤75μm) to obtain homogenized steel slag powder; (2) Raw meal preparation: Weigh 13wt.% steel slag powder, 66wt.% limestone, 20wt.% sandstone and 1.5wt.% wet ash according to the total dry basis raw meal mass, put them in a mixer and mix for 30 minutes until uniform to obtain homogeneous raw meal; (3) Calcination: The homogeneous raw material is pressed into a 5mm thick cake and placed in a high-temperature box furnace. The temperature is raised to 1350℃ at a rate of 10℃ / min. The carbon monoxide volume concentration in the furnace is controlled at 6% in the highest temperature section (weak reducing atmosphere, reducing gas concentration ≤10%). The calcination is completed after holding the temperature for 30min to obtain high-temperature clinker. (4) Cooling: After calcination, the clinker is taken out immediately and forced to cool to below 500°C using a high-pressure blower at a cooling rate of 50°C / min. Then, it is cooled to room temperature to obtain chromium-fixing mineral clinker.

[0037] According to the test results, the chromium-fixing two-mineral clinker prepared in Example 1 contained: β-C2S content of 78 wt.%, C4AF content of 19 wt.%, impurity phase content of 3 wt.%, and total content of the two main crystalline phases of 97 wt.%.

[0038] The cementitious material was prepared by grinding the solidified chromium two-mineral clinker prepared in Example 1 with 4 wt.% natural dihydrate gypsum. The water-soluble hexavalent chromium content was found to be 8.2 mg / kg, which meets the safety requirements of GB31893-2015 national standard for low-chromium building materials ≤10 mg / kg.

[0039] Example 2: This embodiment 2 provides a method for preparing chromium-fixed two-mineral clinker using chromium-containing steel slag, the specific operation of which is as follows: (1) Raw material pretreatment: Select chromium-containing steel slag from converter, crush and grind it, and then pass it through a 200-mesh square hole sieve (the particle size of the sieve residue is ≤75μm) for later use to obtain homogenized steel slag powder; (2) Raw meal preparation: Weigh 23wt.% steel slag powder, 58wt.% quicklime, 14wt.% sandstone and 5wt.% wet ash according to the total dry basis raw meal mass, and mix them evenly to obtain homogeneous raw meal; (3) Calcination: The raw material is pressed into a 5mm thick cake, heated to 1335℃, and air is introduced into the highest temperature section to maintain a neutral atmosphere in the furnace. The cake is kept at the temperature for 25 minutes to obtain high-temperature clinker. (4) Cooling: Forced air cooling at a cooling rate of 50℃ / min to below 500℃, then taken out and placed in a room temperature environment to cool naturally to room temperature, to obtain chromium-fixed mineral clinker.

[0040] According to the test results, the chromium-fixing two-mineral clinker prepared in Example 2 has the following contents: β-C2S content is 71 wt.%, C4AF content is 28 wt.%, impurity phase content is 1 wt.%, and the total content of the two main crystalline phases is 99 wt.%.

[0041] The cementitious material was prepared by grinding the solidified chromium two-mineral clinker prepared in Example 2 with 5 wt.% gypsum dihydrate. The water-soluble hexavalent chromium content was found to be 6.1 mg / kg, which meets the safety requirements of GB31893-2015 national standard for low-chromium building materials ≤10 mg / kg.

[0042] Example 3: This embodiment 3 provides a method for preparing chromium-fixed two-mineral clinker using chromium-containing steel slag, the specific operation of which is as follows: (1) Raw material pretreatment: Select chromium-containing steel slag from converter, crush and grind it, and then pass it through a 200-mesh square hole sieve (the particle size of the sieve residue is ≤75μm) for later use to obtain homogenized steel slag powder; (2) Raw meal preparation: Weigh 33wt.% steel slag powder, 49wt.% limestone, 8wt.% sandstone and 10wt.% wet ash according to the total dry basis raw meal mass, mix and grind to obtain homogeneous raw meal; (3) Calcination: The raw material is pressed into a 5mm thick cake, heated to 1285℃, and the carbon monoxide volume concentration in the furnace is controlled at 6% (weak reducing atmosphere) in the highest temperature section. The high temperature is maintained for 30 minutes to obtain high temperature clinker. (4) Cooling: Cool to below 500°C at a cooling rate of 50°C / min, and then remove and cool to room temperature to obtain solid chromium mineral clinker.

[0043] According to the test results, the chromium-fixing two-mineral clinker prepared in Example 3 contained: β-C2S content of 58 wt.%, C4AF content of 37 wt.%, impurity phase content of 5 wt.%, and total content of the two main crystalline phases of 95 wt.%.

[0044] The cementitious material was prepared by grinding the solidified chromium two-mineral clinker prepared in Example 3 with 6 wt.% gypsum dihydrate. The water-soluble hexavalent chromium content was found to be 5.5 mg / kg, which meets the safety requirements of GB31893-2015 national standard for low-chromium building materials ≤10 mg / kg.

[0045] Example 4: This embodiment 4 provides a method for preparing chromium-fixed two-mineral clinker using chromium-containing steel slag, the specific operation of which is as follows: (1) Raw material pretreatment: The chromium-containing steel slag from the converter is crushed, ground and then passed through a 200-mesh square hole sieve (the particle size of the sieve residue is ≤75μm) to obtain steel slag powder; (2) Raw meal preparation: Weigh 44wt.% steel slag powder, 40wt.% limestone, 1.7wt.% sandstone and 14wt.% wet ash according to the total dry basis raw meal mass, and mix them to obtain homogeneous raw meal; (3) Calcination: The raw material is pressed into a 5mm thick cake, heated to 1250℃, and the carbon monoxide volume concentration in the furnace is controlled at 6% (weak reducing atmosphere) in the highest temperature section. The high temperature is maintained for 30 minutes to obtain high temperature clinker. (4) Cooling: Cool to below 500°C at a cooling rate of 50°C / min, and then remove and cool to room temperature to obtain solid chromium mineral clinker.

[0046] According to the test results, the chromium-fixing two-mineral clinker prepared in Example 4 contained: β-C2S content of 49 wt.%, C4AF content of 48 wt.%, impurity phase content of 3 wt.%, and total content of the two main crystalline phases of 97 wt.%.

[0047] The cementitious material was prepared by grinding the solidified chromium two-mineral clinker prepared in Example 4 with 7wt.% gypsum dihydrate. The water-soluble hexavalent chromium content was found to be 4.5 mg / kg, which meets the safety requirements of GB31893-2015 national standard for low-chromium building materials ≤10 mg / kg.

[0048] Comparative Example 1 (Traditional Silicate Clinker Comparison Process): Comparative Example 1 uses a traditional silicate cement clinker process to prepare steel slag clinker. It uses 15 wt.% of the same chromium-containing steel slag as in Example 1 as raw material, combined with conventional calcareous and siliceous raw materials. The clinker is calcined at 1450℃ in an oxidizing atmosphere and then air-cooled. Testing revealed that the clinker minerals are mainly tricalcium silicate, and the water-soluble hexavalent chromium content is 18.5 mg / kg. The chromium leaching amount is severely excessive and cannot meet the standards for use in building materials.

[0049] Results and Analysis: Please refer to Table 2, which shows the chromium ion leaching concentrations of Examples 1-4 and Comparative Example 1:

[0050] As can be seen from Table 2, the hexavalent chromium leaching concentration of the chromium-containing cementitious materials prepared in Examples 1 to 4 all meet the national standard GB31893-2015, indicating that the method for preparing chromium-fixing two-mineral clinker using chromium-containing steel slag provided by the present invention can effectively fix chromium.

[0051] By comparing Examples 1-4 with Comparative Example 1, it can be seen that the present invention can significantly reduce the leaching of hexavalent chromium from chromium-containing clinker by limiting the dual-mineral clinker system, low-temperature calcination, neutral / weak reducing atmosphere and rapid cooling process, thereby achieving the harmless and high-value utilization of chromium-containing steel slag.

[0052] It should be noted that all the above embodiments belong to the same inventive concept, and the descriptions of each embodiment have different focuses. Where the description in a particular embodiment is not detailed, please refer to the description in other embodiments.

[0053] The above embodiments merely illustrate implementation methods of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing solid chromium dimineral clinker using chromium-containing steel slag, characterized in that, Includes the following steps: S10, chromium-containing steel slag is crushed and ground in sequence, and after screening, steel slag powder with a particle size ≤75μm is obtained; S20, the steel slag powder, calcareous raw material, siliceous corrective raw material and aluminum-iron corrective raw material are thoroughly mixed evenly according to a preset ratio to obtain homogeneous raw material; S30, after pressing the homogeneous raw material into a cake, the temperature is raised to 1200-1380℃ and then subjected to heat preservation calcination treatment to obtain high-temperature clinker; S40, the high-temperature clinker is rapidly cooled to obtain a chromium-fixing two-mineral clinker with β-C2S and C4AF as the main crystalline phases; wherein, based on the total mass of the chromium-fixing two-mineral clinker, the β-C2S content is 59-75 wt.%, the C4AF content is 20-40 wt.%, the impurity phase content is 1-5 wt.%, and the total content of β-C2S and C4AF is 95-99 wt.%.

2. The method for preparing solid chromium two-mineral clinker using chromium-containing steel slag according to claim 1, characterized in that, In step S10, the chromium-containing steel slag is one or more of the following: converter steel slag, electric furnace steel slag, stainless steel slag, and refined steel slag.

3. The method for preparing solid chromium two-mineral clinker using chromium-containing steel slag according to claim 2, characterized in that, In step S20, based on the total dry weight of the homogeneous raw material, the content of the chromium-containing steel slag is 13-44 wt.%, the content of the calcareous raw material is 40-66 wt.%, the content of the silica-correcting raw material is 1.7-20 wt.%, and the content of the aluminum-iron-correcting raw material is 1.5-14 wt.%; the sum of the mass percentages of each raw material is 100%.

4. The method for preparing solid chromium two-mineral clinker using chromium-containing steel slag according to claim 1, characterized in that, In step S20, the calcareous raw material is one or more of limestone, quicklime, hydrated lime, and calcium-containing steel slag; the siliceous correcting raw material is one or more of quartz sand, fly ash, and silica fume; and the aluminum-iron correcting raw material is one or more of bauxite, red mud, iron tailings, and aluminum-iron steel slag.

5. The method for preparing solid chromium dimineral clinker using chromium-containing steel slag according to claim 1, characterized in that, In step S30, the heat preservation calcination treatment is carried out in a neutral atmosphere or a weakly reducing atmosphere, wherein the volume concentration of reducing gas in the weakly reducing atmosphere is not higher than 10%.

6. The method for preparing solid chromium two-mineral clinker using chromium-containing steel slag according to claim 1, characterized in that, In step S40, the rapid cooling process specifically involves cooling the high-temperature clinker to below 500°C at a cooling rate of not less than 20°C / min.

7. The method for preparing solid chromium two-mineral clinker using chromium-containing steel slag according to claim 6, characterized in that, The rapid cooling process uses either natural cooling or air cooling.

8. A chromium-fixing two-mineral clinker, characterized in that, The product is prepared by the method according to any one of claims 1 to 7; based on the total mass of the two chromium-fixing mineral clinker, the β-C2S content is 59-75 wt.%, the C4AF content is 20-40 wt.%, the impurity phase content is 1-5 wt.%, and the total content of β-C2S and C4AF is 95-99 wt.%.

9. A cementitious material, characterized in that, It is prepared by grinding the chromium-fixing two-mineral clinker as described in claim 8 with gypsum accounting for 4 to 7 wt.% of the total mass; wherein the water-soluble hexavalent chromium content of the cementitious material, as measured according to the method of GB31893-2015 national standard, is not higher than 10 mg / kg.

10. The application of a chromium-fixing two-mineral clinker as described in claim 9 or a cementitious material as described in claim 7 in the preparation of cement, mortar, and concrete.

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