Method for improving stability of steel slag by inducing CO2 through microalgae culture

Abstract

The invention provides a method for improving stability of steel slag by inducing CO2 through microalgae culture, and relates to the technical field of steel slag reutilization. The method comprises the following specific steps: S1, crushing and screening steel slag to obtain steel slag particles; s2, adding concentrated salt wastewater into the steel slag particles, and stirring to obtain steel slag slurry; s3, placing the steel slag slurry in a microalgae culture device, introducing CO2 gas, stirring, carrying out induced carbonization reaction by using microorganisms, and carrying out solid-liquid separation to obtain calcium and magnesium removed steel slag precipitate and microalgae turbid liquid; s4, using the calcium and magnesium removed steel slag as machine-made sand; s5, using the microalgae turbid liquid for culturing shellfish and economic fish; and S6, filtering out residual shells eaten by the economic fishes through a filter screen, and using the shells as biological calcium magnesium carbonate. Through microalgae culture and carbonization reaction, the complex active free calcium and magnesium oxide conversion process is simplified by utilizing a biological process, so that the steel slag is suitable for concrete production. The stability of the steel slag and CO2 resource utilization are improved, and remarkable environmental and economic benefits are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of steel slag recycling, and particularly relates to a method for improving the soundness of steel slag by inducing CO2 through microalgae cultivation. Background Art

[0002] In the prior art, the soundness of steel slag generated by steel manufacturing (refer to the records in GB / T 32546 Technical Requirements for the Application of Steel Slag) is insufficient, and there is no ideal treatment solution to improve its soundness yet.

[0003] At present, the recycling of steel slag generated by steel manufacturing mainly involves grinding the magnetic separation tailings of steel slag obtained after magnetic separation and using it as a concrete admixture. However, the amount of steel slag used as an admixture does not exceed 10% of the total amount of concrete, and the utilization rate is extremely low; moreover, in recent years, the construction market has been saturated and the consumption of concrete has been limited, which restricts the large-scale application of the technology of doping steel slag in concrete.

[0004] In recent years, the production practice of using steel slag for mine filling has been successively carried out, but this utilization method is limited by underground mining mines and it is difficult to solve the problem of steel slag utilization from a global perspective.

[0005] Some steel slag recycling processes adopt a solution induction method, but high-cost organic solutions such as amino acids need to be used. Therefore, there is an urgent need to develop a universal resource utilization technology for steel slag.

[0006] For example, Chinese Patent CN116040973A discloses a preparation method of carbonization-modified steel slag with improved hydration activity, modified steel slag and an active admixture for cement-based binders, in which a large amount of high-cost amino acids are used for induction modification. The reaction process occurs between the active calcium oxide and magnesium oxide in the steel slag and CO2 gas, and deep carbonization of the steel slag cannot be achieved, and the utilization rate of the steel slag is low. The proportion of the modified steel slag in the binder is mostly 10%.

[0007] In order to better utilize steel slag, Chinese Patent CN219217860U discloses a steel slag sulfurization carbonization device. Although this device can adsorb carbon dioxide and sulfur dioxide simultaneously with steel slag as the raw material, deep carbonization of the steel slag still cannot be achieved, and the utilization rate of the steel slag is low; moreover, the purpose is to improve the mechanical strength of the recycled aggregate of the steel slag, and obviously the utilization rate of the steel slag is low.

[0008] Although Chinese Patent CN114538806A discloses a hydrated carbonized composite hardening binder based on steel slag and its preparation method, the utilization rate of the steel slag in the prepared hydrated carbonized composite hardening binder is about 42%. It is necessary to perform magnetic iron separation on the raw materials for preparation, and relatively expensive slaked lime is used. Obviously, the utilization rate of the steel slag is not very high, and the steel slag and the materials in its preparation process cannot be fully, reasonably and effectively utilized.

[0009] Chinese Patent CN115448628A discloses a carbonized porous steel slag aggregate and its preparation method, the components of which are 45 - 68% steel slag powder, 15 - 30% quick - hardening sulphoaluminate cement, 15 - 20% carbide slag and 2 - 5% paraffin powder. The preparation process requires heating, granulation and dewaxing, and the curing time is relatively long, so is the carbonization time. Moreover, the steel slag powder also needs to be specially treated. The way to increase the depth of carbonization treatment is by adding solid waste carbide slag and dewaxing, which increases the time and process steps of the technological process. Especially the secondary carbonization reaction proves this point. At the same time, it increases the production cost and the production efficiency is low.

[0010] Chinese Patent CN115340306A discloses a method for preparing carbonized steel slag by using high - gravity carbon dioxide capture. It is necessary to operate a high - cost high - gravity rotating packed bed for the carbonization process. However, the utilization rate of the prepared carbonized steel slag powder in cement products is at most only 30%, and the utilization method is not high. Moreover, the obtained solid carbonized steel slag needs to be dried and ground, which increases the production cost. The high - gravity field used further increases the cost and is not suitable for industrial production.

[0011] Chinese Patent CN113955999A discloses a retro - style brick based on steel slag carbonization and its preparation method, which uses steel slag in the preparation of retro - style bricks. However, according to calculations, the proportion of dry slag in the component raw materials is about 37 - 47%, and obviously the utilization rate is not high, and the technical effect of overall comprehensive utilization is not achieved. Moreover, the carbonization treatment needs to be combined with the hydration treatment of fly ash, the process time is lengthened, and the traditional carbonization pressure also needs to be considered, with great operation difficulty and low efficiency.

[0012] Due to the large number of mineral components and large composition fluctuations in steel slag, the disposal process of improving the soundness of steel slag is very complex. Steel slag has certain hydration and cementitious activity, and the consumption of concrete is huge. Adopting an economical and reasonable technology to improve the soundness of steel slag and applying it to concrete is one of the effective measures to improve the level of resource utilization of steel slag. Summary of the Invention

[0013] In view of the above problems in the prior art, the present invention simplifies the complex conversion process of active free calcium and magnesium oxides through microalgae cultivation and carbonization reaction, making the steel slag suitable for concrete production. It not only improves the soundness of steel slag but also realizes the resource utilization of CO2, with significant environmental and economic benefits.

[0014] The present invention provides a method for improving the soundness of steel slag by inducing CO2 through microalgae cultivation, and the specific steps are as follows:

[0015] S1. Steel slag crushing and screening: Crush and screen the steel slag to obtain steel slag particles.

[0016] S2. Preparation of steel slag slurry: Add concentrated salt wastewater to steel slag particles and stir to obtain steel slag slurry.

[0017] S3. Microalgae cultivation and carbonation reaction: Place the steel slag slurry in a microalgae cultivator, introduce CO2 gas and stir, and use microorganisms to induce a carbonation reaction. Then, perform solid-liquid separation to obtain de-calcium and magnesium steel slag precipitate and microalgae suspension.

[0018] S4. Utilization of de-calcium and magnesium steel slag: Use the de-calcium and magnesium steel slag as manufactured sand, and the de-calcium and magnesium steel slag meets the requirements of Class II sand or above in "Construction Sand" (GB / T 14684).

[0019] S5. Utilization of microalgae suspension: Use the microalgae suspension to cultivate shellfish and economic fish.

[0020] S6. Utilization of shells: Filter out the shells remaining after being eaten by economic fish through a filter screen and use them as biological calcium magnesium carbonate.

[0021] In the present invention, the steel slag is disposed of through a simple biological process, and the active free calcium and magnesium components therein are transferred to the aqueous phase and finally fixed in the shells (biological calcium magnesium carbonate), so that the direct carbonation of the steel slag with CO2 is transformed into indirect carbonation. Not only is the carbonation depth of the steel slag effectively enhanced, but also the soundness and activity of the steel slag are significantly enhanced, solving the technical problems of poor soundness of steel slag particles and the product not being directly used as manufactured sand.

[0022] Preferably, the steel slag in S1 is converter steel slag, and the particle size of the steel slag particles is 0.3 - 4.75 mm, preferably 0.5 - 2.5 mm. In the steel slag within the above particle size range, the migration efficiency of free active calcium and magnesium ions in the aqueous solution is appropriate, and this particle size meets the requirements of the manufactured sand particle size.

[0023] Preferably, the concentrated salt wastewater in S2 is the concentrated brine generated by membrane treatment in industrial sectors such as municipal, iron and steel, chemical, non-ferrous, and electric power industries, mainly composed of chlorides and sulfates of Na, Ca, and Mg, with a concentration of 3.5 - 9 g / L, preferably 4 - 6 g / L. Usually, the concentration of the concentrated salt wastewater discharged from the above industrial sectors is within the above range. The solid concentration in the steel slag slurry is 0.5 - 5 g / L, preferably 1 - 2.5 g / L.

[0024] Preferably, the algal species in S3 is selected according to the salt concentration and organic matter residue, and is selected from one or a combination of several of green algae, brown algae, red algae, dinoflagellates, diatoms, and cyanobacteria.

[0025] Preferably, after placing the steel slag slurry in the microalgae cultivator in S3, an excessive amount of CO2 gas is introduced into the microalgae cultivator, and the CO2 introduction amount is 2 - 35 L / min·m 2, the Reynolds number Re of the steel slag slurry in the reactor cross-section is 20 - 5500, and the microbial-induced carbonization reaction is carried out. After the biomass is increased to 1 - 10 g / L, solid-liquid separation is carried out. The biomass of the microalgae suspension is 0.5 - 35 g / L, preferably 10 - 35 g / L.

[0026] Preferably, in S5, the shellfish are selected from at least one of Ruditapes philippinarum, Perna viridis, Tegillarca granosa, Crassostrea gigas, Ostrea rivularis, Mactra veneriformis, Chlamys farreri, Ostrea edulis, Anadara granosa, Sinonovacula constricta, Corbicula fluminea, Anadara subcrenata, and Meretrix meretrix, etc. The economic fish are the edible fish and ornamental fish of the edible shellfish, and the edible fish are selected from at least one of Epinephelus spp., Oreochromis niloticus, and Paralichthys olivaceus.

[0027] Preferably, in S6, the filter screen aperture is 0.3 - 50 mm, preferably 0.3 - 4.75 mm.

[0028] The technical principle of the present invention is as follows:

[0029] The present invention provides a method for improving the soundness of steel slag by inducing CO2 through microalgae cultivation. The soundness of steel slag mainly depends on the content of active calcium and magnesium therein. After the steel slag enters the cultivation water body, the active calcium and magnesium are gradually dissolved in an ionic state. The solid concentration of the steel slag in the cultivation water body is relatively low, which will not affect the pH of the water body and the growth of microalgae and shellfish. The ionic calcium and magnesium ions can provide a calcium / magnesium source for the growth of microalgae, and these dissolved calcium and magnesium ions ultimately enter the shellfish through the food chain. The calcium and magnesium ions migrating through the food chain change the dissolution equilibrium of the steel slag in water. By cultivating microalgae and shellfish, the active calcium, magnesium, and phosphorus in the steel slag can be dissolved into the water phase. In addition, these dissolved calcium and magnesium also act as a medium to induce CO2 to enter the water phase as a carbon source. The water phase for microalgae cultivation is provided by concentrated salt wastewater, and the ammonia nitrogen and potassium and sodium therein can be used as the sources of nitrogen and inorganic salts required during the cultivation process.

[0030] Finally, the active calcium and magnesium in the steel slag are converted into calcium carbonate in the shell, becoming a biological calcium source. It is estimated that 30% - 65% of the active calcium oxide and magnesium in the steel slag particles are converted into biological calcium. The conversion process of the silicate minerals in the steel slag is similar to that of the active calcium and magnesium and is the main silicon source for microalgae and shellfish. However, the proportion of silicon migrating through the "microalgae - shellfish" food chain is extremely low, and more than 95% of the silicate minerals still remain in the steel slag particles. The ferrite minerals in the steel slag account for about 50% of the total mass of the steel slag, and these minerals remain stable during the above process and do not undergo conversion.

[0031] The present invention uses a microalgae - steel slag synergistic carbonization process to effectively sequester CO2 and solidify free calcium oxide in steel slag, improving its soundness; at the same time, it realizes the full - chain resource utilization of steel slag, concentrated salt wastewater, and CO2. By a simple biological process, the active calcium and magnesium in steel slag are removed and can be used as manufactured sand. Moreover, the by - product bio - calcium magnesium carbonate produced during the disposal process can be used as a sintering raw material for steel mills. Conventional processes select limestone as the calcium source, and the CO2 emissions account for about half of the smelting emissions. Using bio - calcium magnesium carbonate can significantly reduce the carbon footprint of steel products, and it has both environmental protection and economic value. The disposed steel slag can be used in products and projects such as cement concrete, non - fired bricks, and mine filling. It can solve the technical defects in the existing steel slag recycling technologies, such as high cost, low utilization rate, complex preparation process, large operation difficulty, long process, and low efficiency, enabling the full - component resource utilization of steel slag.

[0032] The above - mentioned technical solution has at least the following beneficial effects compared with the prior art:

[0033] (1) Use a simple biological process to improve the soundness of steel slag, and remove and utilize the active calcium and magnesium to overcome the technical obstacles to using it as concrete aggregate.

[0034] (2) A large amount of CO2 is used as the carbon source for microalgae growth during the disposal process, reducing the CO2 emissions of steel mills.

[0035] (3) The bio - calcium magnesium carbonate by - product during the steel slag disposal process can be used in steel production, further reducing the CO2 emissions during steel production. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0037] Figure 1 It is a process flow chart of a method for improving the soundness of steel slag by inducing CO2 through microalgae cultivation according to the present invention.

[0038] Figure 2 It is the transfer process of active calcium and magnesium in steel slag. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] To make the technical problems, technical solutions, and advantages to be solved by the present invention clearer, the following will be described in detail in combination with the drawings and specific embodiments.

[0040] The main chemical compositions of converter steel slag in the embodiment are shown in Table 1:

[0041] Table 1 Main Chemical Compositions of Converter Steel Slag (unit: wt.%)

[0042]

[0043] Example 1

[0044] A method for inducing CO2 to improve the stability of steel slag through microalgae cultivation. The steel slag is collected from a coastal steel plant in Shandong, and its composition is as shown in Sample 1 in Table 1 # in the said method for improving the stability of steel slag by microalgae cultivation combines the following steps: Figure 1 as follows:

[0045] S1. Crushing and screening of steel slag: The steel slag is crushed and screened to obtain steel slag particles with a particle size of 0.3 mm.

[0046] S2. Preparation of steel slag slurry: Concentrated saline wastewater with a concentration of 0.5 g / L is added to the steel slag particles, and stirred to obtain a steel slag slurry with a solid concentration of 0.5 g / L.

[0047] S3. Microalgae cultivation and carbonation reaction: The steel slag slurry is placed in a microalgae cultivator, and the algal species are green algae and brown algae. CO2 gas is introduced and stirred, the CO2 introduction amount is 2 L / min·m 2 , the induced carbonation time is 24 h, and the Reynolds number Re of the steel slag slurry in the reactor cross-section is 20. After solid-liquid separation, a microalgae suspension with a biomass of 0.5 g / L is obtained.

[0048] S4. Utilization of decalcified and demagnified steel slag: The decalcified and demagnified steel slag is used as manufactured sand.

[0049] S5. Utilization of microalgae suspension: The microalgae suspension is used for cultivating clams and groupers.

[0050] S6. Utilization of shells: The remaining shells are filtered out through a filter screen with a pore size of 0.3 mm and used as biological calcium magnesium carbonate.

[0051] After testing and statistics, the active calcium oxide in the decalcified and demagnified steel slag is reduced from 12% to 2%, and the active magnesium oxide is reduced from 5.7% to 2.3%, meeting the requirements of Class II sand in "Construction Sand" (GB / T 14684); 353 kg of biological calcium magnesium carbonate can be by-produced per ton of steel slag treated.

[0052] Figure 2 This is the transfer process of active calcium and magnesium in steel slag. After the steel slag enters the culture water body, the active calcium and magnesium are gradually dissolved in ionic form, and the ionic calcium and magnesium ions can provide calcium / magnesium sources for microalgae growth. These dissolved calcium and magnesium ions, together with the ammonia nitrogen and inorganic salts in the concentrated saline wastewater, enter the shellfish through the food chain. In addition, these dissolved calcium and magnesium also act as a medium to induce CO2 to enter the water phase as a carbon source. Finally, the active calcium and magnesium in the steel slag are converted into calcium carbonate in the shells and become biological calcium sources.

[0053] Example 2

[0054] A method for inducing CO2 to improve the soundness of steel slag through microalgae cultivation. The steel slag is collected from an inland steel plant in Shandong, and its composition is shown in Sample 2 in Table 1 # The method for improving the soundness of steel slag by microalgae cultivation combines the following steps Figure 1 as follows

[0055] S1. Crushing and screening of steel slag: Crush and screen the steel slag to obtain steel slag particles with a particle size of 2.0 mm

[0056] S2. Preparation of steel slag slurry: Add concentrated salt wastewater with a concentration of 4.5 g / L to the steel slag particles and stir to obtain a steel slag slurry with a solid concentration of 2.5 g / L

[0057] S3. Microalgae cultivation and carbon reaction: Place the steel slag slurry in a microalgae cultivator, and the algal species is diatom. Pass in CO2 gas and stir. The CO2 input volume is 20 L / min·m 2 , the induced carbonization time is 48 h, and the Reynolds number Re of the steel slag slurry in the reactor cross-section is 200. After solid-liquid separation, a microalgae suspension with a biomass of 15 g / L is obtained

[0058] S4. Utilization of decalcified and demagnified steel slag: The decalcified and demagnified steel slag is used as manufactured sand

[0059] S5. Utilization of microalgae suspension: The microalgae suspension is used to culture razor clams and tilapia

[0060] S6. Utilization of shells: Filter out the remaining shells through a filter screen with a pore size of 25 mm and use them as biological calcium magnesium carbonate

[0061] After testing and statistics, the active calcium oxide in the decalcified and demagnified steel slag is reduced from 11.7% to 1.6%, and the active magnesium oxide is reduced from 6.1% to 2.1%, meeting the requirements of Class I sand in "Construction Sand" (GB / T 14684); 406 kg of biological calcium magnesium carbonate can be by-produced per ton of steel slag treated

[0062] Example 3

[0063] A method for inducing CO2 to improve the soundness of steel slag through microalgae cultivation. The steel slag is collected from an inland steel plant in Hebei, and its composition is shown in Sample 3 in Table 1 # The method for improving the soundness of steel slag by microalgae cultivation combines the following steps Figure 1 as follows

[0064] S1. Crushing and screening of steel slag: Crush and screen the steel slag to obtain steel slag particles with a particle size of 4.75 mm

[0065] S2. Preparation of steel slag slurry: Add concentrated salt wastewater with a concentration of 9 g / L to steel slag particles and stir to obtain a steel slag slurry with a solid concentration of 5 g / L.

[0066] S3. Microalgae cultivation and carbonation reaction: Place the steel slag slurry in a microalgae cultivator, and the algal species is cyanobacteria. Introduce CO2 gas and stir. The CO2 input amount is 35 L / min·m 2 , the induced carbonation time is 8 h, and the Reynolds number Re of the steel slag slurry at the reactor cross-section is 3000. After solid-liquid separation, a microalgae suspension with a biomass of 35 g / L is obtained.

[0067] S4. Utilization of decalcified and demagnified steel slag: The decalcified and demagnified steel slag is used as manufactured sand.

[0068] S5. Utilization of microalgae suspension: Use the microalgae suspension to cultivate oysters and groupers.

[0069] S6. Utilization of shells: Filter out the remaining shells through a filter screen with a pore size of 50 mm and use them as biological calcium magnesium carbonate.

[0070] After testing and statistics, the active calcium oxide in the decalcified and demagnified steel slag is reduced from 13.6% to 3.1%, and the active magnesium oxide is reduced from 5.3% to 1.52%, meeting the requirements of Class II sand in "Construction Sand" (GB / T 14684); 462 kg of biological calcium magnesium carbonate can be by-produced per ton of steel slag treated.

[0071] Example 4

[0072] A method for improving the soundness of steel slag by inducing CO2 through microalgae cultivation. The steel slag is collected from a coastal steel plant in Hebei and its composition is as shown in Sample 4 in Table 1. The method for improving the soundness of steel slag by microalgae cultivation combines # the following steps: Figure 1

[0073] S1. Crushing and screening of steel slag: Crush and screen the steel slag to obtain steel slag particles with a particle size of 1.0 mm.

[0074] S2. Preparation of steel slag slurry: Add concentrated salt wastewater with a concentration of 2.0 g / L to steel slag particles and stir to obtain a steel slag slurry with a solid concentration of 1 g / L.

[0075] S3. Microalgae cultivation and carbonation reaction: Place the steel slag slurry in a microalgae cultivator, and the algal species is diatom. Introduce CO2 gas and stir. The CO2 input amount is 5 L / min·m 2 , the induced carbonation time is 24 h, and the Reynolds number Re of the steel slag slurry at the reactor cross-section is 1000. After solid-liquid separation, a microalgae suspension with a biomass of 10 g / L is obtained.

[0076] S4. Utilization of decalcified and demagnified steel slag: The decalcified and demagnified steel slag is used as manufactured sand.​

[0077] S5. Utilization of microalgae suspension: The microalgae suspension is used for cultivating Meretrix meretrix and Epinephelus coioides.

[0078] S6. Utilization of shells: The remaining shells are filtered out through a filter screen with a pore size of 10 mm and used as biological calcium magnesium carbonate.

[0079] After testing and statistics, the active calcium oxide in the decalcified and de-magnesium steel slag is reduced from 10.71% to 1.85%, and the active magnesium oxide is reduced from 5.91% to 2.19%, meeting the requirements of Class I sand in "Construction Sand" (GB / T 14684); 651 kg of biological calcium magnesium carbonate can be by-produced per ton of steel slag treated.

[0080] Example 5

[0081] A method for improving the soundness of steel slag by inducing CO2 through microalgae cultivation. The steel slag is taken from a steel plant in Liaoning, and the composition is as shown in Sample 5 in Table 1. The method for improving the soundness of steel slag by microalgae cultivation combines the following steps: # as shown. Figure 1 The following steps:

[0082] S1. Crushing and screening of steel slag: The steel slag is crushed and screened to obtain steel slag particles with a particle size of 0.5 mm.

[0083] S2. Preparation of steel slag slurry: Concentrated salt wastewater with a concentration of 1.0 g / L is added to the steel slag particles, and the mixture is stirred to obtain a steel slag slurry with a solid concentration of 0.5 g / L.

[0084] S3. Microalgae cultivation and carbonation reaction: The steel slag slurry is placed in a microalgae cultivator, and the algal species are dinoflagellates and green algae. CO2 gas is introduced and stirred, the CO2 introduction rate is 5 L / min·m 2 , the induced carbonation time is 72 h, and the Reynolds number Re of the steel slag slurry at the reactor cross-section is 5500. After solid-liquid separation, a microalgae suspension with a biomass of 5 g / L is obtained.

[0085] S4. Utilization of decalcified and de-magnesium steel slag: The decalcified and de-magnesium steel slag is used as manufactured sand.

[0086] S5. Utilization of microalgae suspension: The microalgae suspension is used for cultivating razor clams and tilapia.

[0087] S6. Utilization of shells: The remaining shells are filtered out through a filter screen with a pore size of 5 mm and used as biological calcium magnesium carbonate.

[0088] After testing and statistics, the active calcium oxide in the decalcified and de-magnesium steel slag is reduced from 10.91% to 1.26%, and the active magnesium oxide is reduced from 4.64% to 1.72%, meeting the requirements of Class I sand in "Construction Sand" (GB / T 14684); 395 kg of biological calcium magnesium carbonate can be by-produced per ton of steel slag treated.

[0089] Example 6

[0090] A method for inducing CO2 to improve the soundness of steel slag through microalgae cultivation. The steel slag is collected from a steel plant in Inner Mongolia Autonomous Region, and the composition is as shown in Sample 6 in Table 1. # The method for improving the soundness of steel slag by microalgae cultivation combines Figure 1 the following steps:

[0091] S1. Crushing and screening of steel slag: The steel slag is crushed and screened to obtain steel slag particles with a particle size of 3.0 mm.

[0092] S2. Preparation of steel slag slurry: Concentrated salt wastewater with a concentration of 7.0 g / L is added to the steel slag particles, and stirred to obtain a steel slag slurry with a solid concentration of 2.5 g / L.

[0093] S3. Microalgae cultivation and carbonation reaction: The steel slag slurry is placed in a microalgae cultivator, and the algal species is dinoflagellate. CO2 gas is introduced and stirred, the CO2 introduction amount is 20 L / min·m 2 , the induced carbonation time is 24 h, and the Reynolds number Re of the steel slag slurry in the reactor cross-section is 800. After solid-liquid separation, a microalgae suspension with a biomass of 25 g / L is obtained.

[0094] S4. Utilization of decalcified and demagnified steel slag: The decalcified and demagnified steel slag is used as manufactured sand.

[0095] S5. Utilization of microalgae suspension: The microalgae suspension is used for cultivating sea mussels and groupers.

[0096] S6. Utilization of shells: The remaining shells are filtered out through a filter screen with a pore size of 30 mm and used as biological calcium magnesium carbonate.

[0097] After testing and statistics, the active calcium oxide in the decalcified and demagnified steel slag is reduced from 10.62% to 1.32%, and the active magnesium oxide is reduced from 3.12% to 1.27%, meeting the requirements of Class I sand in "Construction Sand" (GB / T 14684); 527 kg of biological calcium magnesium carbonate can be by-produced per ton of steel slag treated.

[0098] Comparative Example 1

[0099] A method for inducing CO2 to improve the soundness of steel slag through microalgae cultivation. Compared with Example 6, the crushing particle size of the steel slag in S1 is 13 mm, and other conditions are the same as those in Example 6.

[0100] Due to the relatively coarse particle size of steel slag, the active calcium and magnesium inside the particles cannot be fully removed. The active calcium oxide in the de - calcium - magnesium steel slag decreases from 10.62% to 9.16%, and the active magnesium oxide decreases from 3.12% to 1.97%, not meeting the requirements of "Construction Sand" (GB / T 14684), so it cannot be used as manufactured sand. Since the proportion of active calcium and magnesium on the surface of steel slag particles is low, 213 kg of bio - calcium magnesium carbonate can be by - produced per ton of steel slag treated.

[0101] Comparative Example 2

[0102] A method for inducing CO₂ to improve the soundness of steel slag through micro - algae cultivation. Compared with Example 6, the crushing particle size of S1 steel slag is 0.1 mm, and other conditions are the same as those in Example 6.

[0103] Due to the relatively fine particle size of steel slag, the de - calcium - magnesium steel slag exists in the form of fine mud. The active calcium oxide in the de - calcium - magnesium steel slag decreases from 10.62% to 10.34%, and the active magnesium oxide decreases from 3.12% to 2.31%, not meeting the particle size requirements of "Construction Sand" (GB / T 14684), so it cannot be used as manufactured sand. However, because the particle size is relatively fine and the biological reaction is sufficient, 692 kg of bio - calcium magnesium carbonate can be by - produced per ton of steel slag treated.

[0104] Comparative Example 3

[0105] A method for inducing CO₂ to improve the soundness of steel slag through micro - algae cultivation. Compared with Example 6, the solid concentration of S2 steel slag slurry is 800 g / L, and other conditions are the same as those in Example 6.

[0106] Due to the high concentration of steel slag slurry, the solid concentration in the aqueous phase of the cultivator is too high, unable to meet the fluidity requirements of the cultivation device; and the light transmittance of the aqueous phase is insufficient, restricting the growth of micro - algae and the biological process is not complete, so manufactured sand that meets the requirements of "Construction Sand" (GB / T 14684) cannot be obtained. Due to the too high solid concentration, the micro - algae suspension cannot be separated for fish and shellfish research and development, and no bio - calcium magnesium carbonate product is obtained.

[0107] Comparative Example 4

[0108] A method for inducing CO₂ to improve the soundness of steel slag through micro - algae cultivation. Compared with Example 6, the solid concentration of S2 steel slag slurry is 0.1 g / L, and other conditions are the same as those in Example 6.

[0109] Since the concentration of steel slag slurry is low, it meets the quality requirements of Class Ⅰ sand in "Construction Sand" (GB / T 14684), but the treatment volume of manufactured sand is only 0.21% of that in Example 6; because the particle size is relatively fine and the biological reaction is sufficient, 713 kg of bio - calcium magnesium carbonate can be by - produced per ton of steel slag treated. However, due to the low treatment volume of the device, the actual output of bio - calcium magnesium carbonate collected is only 0.09% of that in Example 6.

[0110] The above embodiments cover the upper limits, lower limits, and intermediate values of parameters such as the particle size of steel slag particles, the concentration of concentrated salt wastewater, the solid concentration of the steel slag slurry, the biomass of the microalgae suspension, and the pore size of the filter screen in the claims, verifying the feasibility and wide applicability of the present invention.

[0111] The present invention provides a method for improving the soundness of steel slag by inducing CO2 through microalgae cultivation. By using a simple biological process, the reactive calcium magnesium carbonate in the steel slag is converted into biological calcium magnesium carbonate, and the decalcified and demagnified steel slag can be used as fine aggregate for concrete. It can solve the technical defects in the prior art of steel slag reuse technology, such as high cost, low utilization rate, complex preparation process, difficult operation, long process, and low efficiency. It has a wide range of applications, a simple process flow, low cost and high efficiency in the utilization method, and is conducive to large-scale industrial production and popularization.

[0112] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for inducing the improvement of the soundness of steel slag by microalgae cultivation, characterized in that, The specific steps are as follows: S1. Steel slag crushing and screening: Crush and screen the steel slag to obtain steel slag particles; S2. Preparation of steel slag slurry: Add concentrated salt wastewater to the steel slag particles and stir to obtain steel slag slurry; S3. Microalgae cultivation and carbonation reaction: Place the steel slag slurry in a microalgae cultivator, introduce CO2 gas and stir, and use microorganisms to induce carbonation reaction. Then, perform solid-liquid separation to obtain de-calcium and magnesium steel slag precipitate and microalgae suspension; S4. Utilization of de-calcium and magnesium steel slag: Use the de-calcium and magnesium steel slag as manufactured sand, and the de-calcium and magnesium steel slag meets the standards of Class II sand or above in "Construction Sand" (GB / T 14684); S5. Utilization of microalgae suspension: Use the microalgae suspension to cultivate shellfish and economic fish; S6. Utilization of shells: Filter out the shells remaining after being eaten by economic fish through a filter screen and use them as biological calcium magnesium carbonate.

2. The method for inducing the improvement of the soundness of steel slag by CO2 through microalgae cultivation according to claim 1, characterized in that The steel slag in S1 is converter steel slag, and the particle size of the steel slag particles is 0.3 - 4.75 mm, preferably 0.5 - 2.5 mm.

3. The method for inducing the improvement of the soundness of steel slag by CO2 through microalgae cultivation according to claim 1, wherein The concentrated salt wastewater in S2 is the concentrated brine produced by membrane method treatment in municipal, iron and steel, chemical, non-ferrous, and power industrial sectors, with a concentration of 3.5 - 9 g / L, preferably 4 - 6 g / L.

4. The method for inducing the improvement of the soundness of steel slag by microalgae cultivation according to claim 1, wherein The solid concentration in the steel slag slurry in S2 is 0.5 - 5 g / L, preferably 1 - 2.5 g / L.

5. The method for inducing the improvement of the soundness of steel slag by microalgae cultivation according to claim 1, characterized in that, The algal species in S3 is selected from one or a combination of several of green algae, brown algae, red algae, dinoflagellates, diatoms, and cyanobacteria.

6. The method for inducing the improvement of the soundness of steel slag by CO2 through microalgae cultivation according to claim 1, characterized in that After placing the steel slag slurry in the microalgae cultivator in S3, the amount of CO2 introduced into the microalgae cultivator is 2-35 L / min·m 2 , so that the Reynolds number Re of the steel slag slurry at the reactor cross-section is 20-5500.

7. The method for inducing the improvement of the soundness of steel slag by CO2 through microalgae cultivation according to claim 1, characterized in that, The biomass of the microalgae suspension in S3 is 0.5 - 35 g / L, preferably 10 - 35 g / L.

8. The method for inducing the improvement of the soundness of steel slag by microalgae cultivation according to claim 1, characterized in that, The shellfish in S5 is selected from at least one of Ruditapes philippinarum, Perna viridis, Tegillarca granosa, Crassostrea gigas, Ostrea gigas, Mactra veneriformis, Chlamys farreri, Ostrea rivularis, Anadara subcrenata, Sinonovacula constricta, Corbicula fluminea, Solen grandis, and Meretrix meretrix.

9. The method for inducing the improvement of the soundness of steel slag by CO2 through microalgae cultivation according to claim 1, characterized in that, The economic fish in S5 are the edible fish and ornamental fish that can eat shellfish, and the edible fish are selected from at least one of Epinephelus spp., Oreochromis niloticus, and Paralichthys olivaceus.

10. The method for inducing the improvement of the soundness of steel slag by CO2 through microalgae cultivation according to claim 1, characterized in that, The aperture of the filter screen in S6 is 0.3 - 50 mm, preferably 0.3 - 4.75 mm.

Images