Comprehensive treatment method for steel slag cooperating with steel mill solid waste and acid wastewater

Abstract

The invention discloses a comprehensive treatment method for steel slag cooperating with steel mill solid waste and acidic wastewater, which is characterized in that according to different alkalinity of converter hot steel slag, the converter hot steel slag is subjected to quality-divided treatment and is respectively coupled with the steel mill solid waste and the acidic wastewater to implement comprehensive treatment, so that low-cost treatment of the steel slag, other solid waste of the steel mill and the acidic wastewater is realized; the method has the advantages of simple operation, no discharge of three wastes, substantial reduction of the discharge amount of steel slag, realization of resource treatment of waste water and solid wastes, obvious full recycling of steel slag, low overall operation cost, simple operation, convenient process treatment, environmental protection and the like.

Description

Technical Field

[0001] This invention relates to the treatment of solid waste and wastewater from steel plants, specifically to a method for the integrated treatment of steel slag, steel plant solid waste, and acidic wastewater, belonging to the technical field of integrated treatment of steel slag, solid waste, and waste acid. Background Technology

[0002] my country has a massive steel slag discharge, with annual increases exceeding 100 million tons. Currently, steel slag disposal mainly focuses on cement production, which suffers from low added value and low utilization rate (only about 40%). With the revision of GB175-2023 "General Portland Cement," it is clearly stipulated that from June 1, 2024, steel slag will no longer be allowed as a blending material in general Portland cement. The proper disposal of steel slag has become a major bottleneck for the green and sustainable development of my country's steel industry.

[0003] Steel slag is rich in iron resources, with iron oxides accounting for 15-25%. However, it also contains a large amount of phosphorus, a harmful element in steel materials, which limits its internal recycling potential. If steel slag dephosphorization technology can be developed to overcome the constraints of internal steel slag recycling, steel slag emissions can be greatly reduced, eliminating the need for building material production and achieving source reduction and resource recycling.

[0004] Regarding steel slag dephosphorization technology, Chinese patent CN117778669A discloses "A Method for Gasification Dephosphorization of Converter Final Slag and Recycling of Dephosphorized Slag." This method involves adding a carbonaceous dephosphorizing agent to the converter slag for gasification dephosphorization, and the dephosphorized slag can be recycled back to the sintering process. This method can effectively remove phosphorus and achieve steel slag recycling; however, it suffers from poor dephosphorization effect and inadequate slag-phosphorus separation in practical applications. Chinese patent CN110184399A discloses "A Steel Slag Treatment Method Using a Two-Step Oxidative Desulfurization and Reduction Dephosphorization Process," in which dephosphorization employs gas-based reduction dephosphorization, utilizing a mixture of CO and CO2 to convert phosphorus into phosphorus gas for removal. This method has a good dephosphorization effect, reaching 80%; however, the phosphorus gas produced is highly toxic, posing a risk of personnel poisoning and explosion of the mixed gas. Chinese patent CN110526745A discloses "A method for separating phosphorus from dephosphorized steel slag and preparing phosphate fertilizer". The method first oxidizes the dephosphorized steel slag in a molten state, then cools it and crushes and leaches it to obtain low-phosphorus residue and phosphorus-containing leachate. This method can achieve effective removal and recovery of phosphorus to a certain extent, but the amount of steel slag is large, the amount of by-product wastewater generated is too large, and the disposal cost is high.

[0005] Meanwhile, steel plants produce large amounts of waste acid and wastewater, such as acidic wastewater from cold rolling and wet desulfurization wastewater from sintering. Direct treatment of these wastes is costly. For example, Chinese patent CN110436671A, "A Zero-Discharge Treatment Method and System for Sintering Wet Desulfurization Wastewater," addresses the issue of ammonia nitrogen and magnesium ions in wet desulfurization wastewater by adding phosphoric acid to the solution. This converts ammonia nitrogen into magnesium ammonium phosphate precipitate, thus removing the ammonia nitrogen. However, this method suffers from drawbacks: phosphate is expensive, the precipitate is fine, and it requires a large amount of coagulant aid and a large settling tank. Summary of the Invention

[0006] To address the problems of poor dephosphorization, large emissions of waste gas, and high disposal costs caused by separately treating steel slag, solid waste, and acidic wastewater from steel plants in existing technologies, this invention provides a method for the integrated treatment of steel slag, steel plant solid waste, and acidic wastewater. This method involves treating hot converter steel slag separately based on its alkalinity and then coupling the treatment of steel plant solid waste and acidic wastewater. This achieves low-cost treatment of steel slag, other steel plant solid waste, and acidic wastewater, while minimizing the discharge of these three pollutants. Furthermore, it enables the resource utilization of valuable elements in the solid waste and wastewater. The method is characterized by its simple operation, convenient process, and environmental friendliness.

[0007] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows: A method for the integrated treatment of steel slag, steel plant solid waste, and acidic wastewater, the method comprising: 1) The steel slag discharged from the converter is classified into high-alkali hot steel slag and low-alkali hot steel slag according to its basicity.

[0008] 2) Add multi-source solid waste to high-alkali hot steel slag for a mixing reaction, resulting in a mixed solid solution. Collect the upper layer of the mixed solid solution and recycle it as converter feed. Collect the middle layer of the mixed solid solution and recycle it to step 3) to mix with waste acid for a leaching reaction. Collect the lower layer of the mixed solid solution and add it to the high-alkali hot steel slag for a recyclable mixing reaction. Collect the dust generated during the mixing reaction and recycle it to step 3) to mix with waste acid for a leaching reaction.

[0009] 3) After cooling, crushing and magnetic separation of low-alkali hot steel slag, magnetic iron (which can be directly smelted in blast furnace) and phosphorus-containing slag are obtained. The phosphorus-containing slag is mixed with waste acid for leaching reaction. After the reaction is completed, solid-liquid separation is performed to obtain iron slag and leachate. The iron slag is recycled as sintering material and the leachate is further processed.

[0010] 4) The leachate obtained in step 3) is mixed with wet desulfurization wastewater to obtain mixed waste liquid. A deweighting agent and an oxidant are added to the mixed waste liquid for deweighting and oxidation treatment. After treatment, solid-liquid separation is performed to obtain waste residue and waste liquid. The waste residue is recycled as sintering material, and the waste liquid is further treated.

[0011] 5) Add calcium to the waste liquid obtained in step 4) for a first alkali adjustment and precipitation treatment. After solid-liquid separation, struvite precipitate and a high-calcium solution are obtained. Continue adding calcium to the high-calcium solution for a second alkali adjustment and precipitation treatment. After solid-liquid separation, calcium phosphate residue and a high-salt filtrate are obtained. The calcium phosphate residue is recycled to step 3) and mixed with waste acid for a leaching reaction. The high-salt filtrate is then subjected to resource recovery treatment to obtain calcium salts.

[0012] Preferably, in step 1), the basicity of the high-alkali hot steel slag is greater than 1.5, more preferably greater than 1.8, and even more preferably greater than 2.0.

[0013] Preferably, in step 1), the basicity of the low-alkali hot steel slag is not higher than 2.0, more preferably not higher than 1.8, and even more preferably not higher than 1.5.

[0014] Preferably, in step 2), the multi-source solid waste is a mixed solid waste composed of coal gangue, waste carbon powder, blast furnace bag ash, aluminum ash, sintering ash, and converter secondary ash.

[0015] Preferably, in step 2), the amount of multi-source solid waste added is 5-20% of the total mass of high-alkali hot steel slag, preferably 5-18%, and more preferably 7-15%.

[0016] Preferably, in step 2), the multi-source solid waste includes: 10-40 wt% coal gangue, 5-30 wt% waste carbon powder, 5-25 wt% blast furnace bag ash, 15-40 wt% aluminum ash, 3-15 wt% sintering ash, and 2-15 wt% converter secondary ash, preferably 15-30 wt% coal gangue, 10-25 wt% waste carbon powder, 10-20 wt% blast furnace bag ash, 20-35 wt% aluminum ash, 5-12 wt% sintering ash, and 5-12 wt% converter secondary ash.

[0017] Preferably, in step 2), the reaction is a stirring reaction, and the stirring reaction time is 0.2~2h, preferably 0.3~1.5h, and more preferably 0.4~1h.

[0018] Preferably, in step 2), the upper layer material accounts for 60-85% of the total mass of the mixed solid solution, more preferably 65-80%, and even more preferably 70-75%.

[0019] Preferably, in step 2), the intermediate layer material accounts for 3-25% of the total mass of the mixed solid solution, more preferably 5-20%, and even more preferably 10-15%.

[0020] Preferably, in step 2), the lower layer material accounts for 1 to 20% of the total mass of the mixed solid solution, more preferably 3 to 18%, and even more preferably 5 to 15%.

[0021] Preferably, in step 2), the phosphorus content in the upper layer material is not higher than 0.5%, more preferably not higher than 0.3%, and even more preferably not higher than 0.1%.

[0022] Preferably, in step 2), the chlorine content in the intermediate layer material is not less than 0.3%, more preferably not less than 0.5%, and even more preferably not less than 0.7%.

[0023] Preferably, in step 2), the lower layer material is recycled and mixed multiple times (preferably 3 to 8 times) before being discharged for disposal.

[0024] Preferably, in step 3), the cooling is to cool the low-alkali hot steel slag to below 150°C, preferably to below 120°C, and more preferably to below 100°C.

[0025] Preferably, in step 3), the cooling method is countercurrent heat exchange cooling using compressed air. The cooling rate is 30~100℃ / min, preferably 40~80℃ / min, and more preferably 50~70℃ / min.

[0026] Preferably, in step 3), the compressed air cools the low-alkali hot steel slag to obtain high-temperature hot air, and the high-temperature hot air is used to obtain low-temperature gas by utilizing the waste heat, and the low-temperature gas is circulated back to step 3) as the cooling air for the low-alkali hot steel slag.

[0027] Preferably, in step 3), the crushing involves grinding the cooled steel slag to a particle size of less than 2 mm, preferably less than 1 mm.

[0028] Preferably, in step 3), the pH of the leaching reaction is 1-4.5, more preferably 2-4. The duration of the leaching reaction is 0.5-10 h, more preferably 1-8 h. The solid-liquid mass ratio of the leaching reaction is 1:3-30, more preferably 1:5-20.

[0029] Preferably, in step 4), the volume ratio of the leachate to the wet desulfurization wastewater is 1~5:1, more preferably 1.5~4:1.

[0030] Preferably, in step 4), the sludge remover is sodium sulfide or a sludge remover (preferably a xanthate ester sludge remover or a dithiocarbamate sludge remover), and the amount added is 0.05~2g / L, preferably 0.1~1g / L.

[0031] Preferably, in step 4), the oxidation to hydrogen peroxide is carried out at an amount of 0.05~0.8 g / L, more preferably 0.1~0.5 g / L.

[0032] Preferably, in step 5), the calcium agent is calcium oxide and / or calcium hydroxide.

[0033] Preferably, in step 5), the amount of calcium agent added during the first alkali-adjusting precipitation treatment is such that the pH of the waste liquid is 8-9.5, preferably 8.5-9. During the second alkali-adjusting precipitation treatment, the amount of calcium agent added is such that the pH of the high-calcium solution is 9.5-11, preferably 10-10.5.

[0034] In this invention, addressing the shortcomings of existing steel slag treatment technologies and based on the analysis and research of steel slag characteristics, this invention proposes a new approach to achieve comprehensive and efficient treatment of steel slag, other solid wastes from steel plants, and acidic wastewater. This approach involves the separate treatment of hot converter steel slag and its integration with the comprehensive resource utilization of other solid wastes and acidic wastewater from steel plants. While achieving near-complete recycling of steel slag, this approach also realizes the resource utilization of valuable elements in steel slag, other solid wastes from steel plants, and acidic wastewater. Simultaneously, there is virtually no discharge of the three wastes (waste gas, wastewater, and solid waste). The overall process is simple and easy to operate, essentially achieving the goal of treating waste with waste. It has low treatment costs and is environmentally friendly, and is expected to provide a new research direction for energy conservation and emission reduction in steel plants.

[0035] In this invention, it should be noted that the main mineral phases in converter steel slag are 2CaO·SiO2, 3CaO·SiO2, calcium magnesium olivine, and RO phase (FeO-MgO-MnO-Al2O3), as well as metallic iron, free calcium oxide, and magnesium oxide, etc. Their composition ratio changes with the recycling of the steel slag. Therefore, this invention addresses the compositional fluctuations of the steel slag by performing a graded treatment. Specifically, by detecting the alkalinity of the steel slag, it is divided into high-alkali hot-state steel slag and low-alkali hot-state steel slag according to its alkalinity (alkalinity R=CaO / SiO2). The high-alkali hot-state steel slag is then mixed with multi-source solid waste for further processing. The resulting solid-solution, stratified, phosphorus-free slag, high-chlorine slag, and ferrophosphate slag can be recycled to their respective steel production processes for disposal. The low-alkali hot steel slag is separated into magnetic iron through cooling, crushing, and magnetic separation. The remaining phosphorus-containing slag is acid-leached to obtain iron slag, which is then returned to sintering for disposal. The leachate from the acid leaching is homogenized with wet desulfurization wastewater, followed by gravimetric and oxidation treatments to obtain waste residue and waste liquid. The resulting waste liquid undergoes two-stage alkali adjustment and precipitation treatment to obtain struvite, calcium phosphate slag, and high-salt filtrate. The calcium phosphate slag can be recycled for acid leaching, and the high-salt filtrate can be recovered to obtain calcium salts. In other words, this invention achieves the recycling and disposal of steel slag through its differentiated treatment, while also enabling the synergistic disposal and resource recovery of other solid wastes and acidic wastewater from steel plants, thus achieving the technical objective of treating waste with waste.

[0036] In this invention, converter steel slag typically contains about 2-5% phosphorus. Direct recycling of this slag would adversely affect the converter. Since phosphorus in steel slag mainly exists as a Ca3(PO4)2 solid solution, reducing it to elemental phosphorus or phosphorus gas is a prerequisite for its removal. However, considering that converting all the phosphorus into phosphorus gas would require a large amount of blasting and generate a large amount of toxic phosphorus gas, posing a safety hazard, this invention addresses this issue by reforming the solid waste from steel slag and other processes, then mixing it with high-alkali hot steel slag. This results in the formation of phosphorus-free slag, high-chloride slag, and phosphorus-iron slag with significantly different and easily separable components from the high-alkali hot steel slag and multi-source solid waste. These three slag phases can then be disposed of within the steel production process, achieving low-cost disposal of steel slag and multi-source solid waste.

[0037] In this invention, reformed multi-source solid waste is mixed and reacted with high-alkali hot steel slag. The reducing substances in the multi-source solid waste (such as the carbonaceous matter contained in coal gangue, carbon powder, and blast furnace bag ash) are used to convert most of the phosphorus in the high-alkali hot steel slag into elemental phosphorus and a small amount of phosphorus gas at low cost. The main reaction process involved is Ca3(PO4)2(s) + 5C(s) = 3CaO(s) + P2(g) + 5CO(g). Simultaneously, the obtained elemental phosphorus undergoes an alloying reaction with the iron inherent in the high-alkali hot steel slag and the iron in the multi-source solid waste (such as blast furnace bag ash, sintering ash, and converter secondary ash) under high-temperature conditions, transforming it into a stable phosphorus-iron phase. Furthermore, it should be noted that if carbon or biomass is simply used to reduce the phosphorus in the high-alkali hot steel slag, the reduction process is endothermic, which can cause the high-alkali hot steel slag to solidify during the reaction. In this invention, the multi-source solid waste also contains a considerable amount of Zn and Al (generally from aluminum ash and secondary converter ash). The exothermic effect of the combustion of elemental Zn and Al in the solid waste can be utilized to achieve self-heating of the entire steel slag treatment process, thereby avoiding low-temperature solidification of phosphorus in the steel slag due to the endothermic effect of reduction. It should be noted that dephosphorization of converter steel slag generally needs to be controlled at high alkalinity. The comprehensive treatment of multi-source solid waste with high-alkalinity hot steel slag can further increase the alkalinity of the steel slag. After the alkalinity is increased, the subsequent dephosphorization process facilitates the recycling of the steel slag.

[0038] In this invention, after the high-alkali hot steel slag is mixed and reacted with multi-source solid waste, it will stratify according to its melting point and density. The upper layer is mainly CaO-SiO2-MgO-Al2O3 slag (i.e., phosphorus-free slag), generally accounting for more than 60% of the total slag. This part of the slag can be directly used as a slagging agent in the next converter, realizing the recycling of high-alkali hot steel slag. The middle layer is mainly a eutectic mixture containing chlorine and fluorine (i.e., high-chlorine slag), generally accounting for about 3-25% of the total slag. It originates from the fluorine and chloride salts carried in the added solid waste, which react with calcium, iron, etc. during the dephosphorization of the steel slag. The lower layer is mainly ferrophosphorus (i.e., ferrophosphorus slag), generally accounting for about 1-20% of the total slag. When the phosphorus content is not high, it can be used for the recycling reaction of the slag in the next converter. Since the three slag phases have significantly different densities, a slag skimmer can be used to separate the reacted steel slag. In other words, based on the different melting points of the three slag phases, this invention achieves the recycling and consumption of high-alkali hot steel slag on the one hand, and the enrichment and separation of phosphorus in steel slag on the other hand, and further achieves the selective separation and open-circuit disposal of harmful elements in solid waste.

[0039] In this invention, the treatment of low-alkali hot steel slag mainly involves the recovery of elements such as phosphorus, iron, and chlorine. Since low-alkali hot steel slag contains elemental iron, direct water cooling at high temperatures (e.g., >1400℃) poses a risk of hydrogen evolution and explosion due to iron displacement from water. While naturally cooling it to approximately 800-1000℃ before water cooling can lead to the formation of calcium ferrite and RO phases, which have high hardness (Mohs hardness 5-7), increasing wear and energy consumption in subsequent treatment processes. Therefore, this invention uses compressed air as the cooling medium, employing countercurrent heat exchange to cool the low-alkali hot steel slag. Furthermore, the entire cooling process is dry cooling, avoiding the formation of high-strength steel slag and wastewater, and ensuring high-quality thermal energy. The high-temperature gas generated during the cooling process can be used for waste heat power generation, and the low-temperature gas generated after waste heat power generation can be used for subsequent wastewater treatment or recycled as a cooling medium for low-alkali hot steel slag, thereby reducing the overall disposal cost and realizing the full utilization of thermal energy.

[0040] In this invention, phosphorus in the cooled low-alkali hot steel slag mainly exists in solid solution form, while iron exists in the form of FeO and metallic iron. Phosphorus in the dust (from the mixed reaction of high-alkali hot steel slag and multi-source solid waste) mainly exists in the form of P2O5, with virtually no iron. Magnetic iron in the cooled low-alkali hot steel slag can be separated through crushing and magnetic separation. The phosphorus-containing slag after separating the magnetic iron can then be leached with waste acid from the steel plant (such as acidic wastewater from cold rolling), controlling the leaching pH to around 1-4 (preferably 2-4, for example, 2.5-3.5). Simultaneously, the high-chlorine slag generated during the recycling of the high-alkali hot steel slag is leached along with the slag, achieving both centralized chlorine disposal and full recovery of phosphorus from the high-chlorine slag. It should be noted that the iron-containing slag obtained after the waste acid leaching reaction can be directly returned to sintering for disposal, thus achieving the recycling of solid slag. The leachate solution mainly contains calcium, phosphorus, chloride, and iron, and is acidic. Based on the characteristics of this leachate, particularly its phosphorus and calcium content, this invention mixes it with wet desulfurization wastewater. Utilizing the ammonia nitrogen and magnesium in the wet desulfurization wastewater, a two-stage alkali-adjusting precipitation treatment is performed. Under low alkalinity, phosphorus is converted into high-purity magnesium ammonium phosphate (struvite crystals) precipitate. Unreacted phosphate ions are converted into a mixed precipitate of calcium phosphate and magnesium ammonium phosphate under high alkalinity. This precipitate is then returned to the acid dissolution process for phosphorus recycling, achieving high-value recovery. The resulting solution is primarily composed of calcium chloride, which can be used in subsequent resource recovery processes (e.g., spray drying with low-temperature waste gas from waste heat power generation to recover calcium chloride products).

[0041] In this invention, the process flow specifically includes: 1) Hot testing of the converter steel slag discharged from the converter to detect the alkalinity of the steel slag. When the alkalinity is high (e.g., exceeding 2.0), the steel slag enters the subsequent step 2); when the alkalinity is low (e.g., below 1.5), the steel slag enters the subsequent step 3); 2) Hot slag circulation: 2-1) Adding a certain amount of multi-source solid waste composed of coal gangue, carbon powder, blast furnace bag ash, aluminum ash, sintering ash, converter secondary ash, etc. in different proportions to the high-alkali hot steel slag obtained in step 1), and stirring and reacting thoroughly; 2-2) Collecting the gas generated during the reaction process, for example, by using a ceramic membrane for interception and then discharging it. The dust obtained after the ceramic membrane interception can enter the subsequent acid leaching treatment step; 2-3) After the reaction in step 2-1), tilting the slag pot at a certain angle and treating the solid solution in the slag pot with two-stage slag removal. One stage of slag, comprising approximately 60-85% of the solid solution, is phosphorus-free slag and can be directly returned to the next converter for disposal. The second stage of slag, comprising approximately 3-25% of the solid solution, is high-chlorine slag and can be directly returned to sintering for disposal or proceed to the subsequent acid leaching treatment step. 2-4) The slag remaining after step 2-3) is used for mixing and reaction with the slag from the next converter. For example, after 3-8 cycles, the wastewater is discharged externally; 3) Co-treatment and resource recovery of wastewater: 3-1) The low-alkali hot steel slag obtained in step 1) is directly countercurrent cooled with compressed air, preferably with a cooling rate of 30-100℃ / min and cooled to less than 100℃; 3-2) The high-temperature hot gas generated during the cooling process is collected and used for waste heat power generation. The low-temperature gas obtained after power generation can be used for subsequent wastewater treatment or recycled for the cooling treatment of low-alkali hot steel slag; 3-3) The cooled solid steel slag obtained in step 3-1) is ball-milled and crushed. The crushed solid is magnetically separated to remove magnetic iron and then mixed with the dust obtained in step 2-2) and the high-chlorine slag obtained in step 2-3) and leached with waste acid from the steel plant, and reacted for a period of time. Time, then filter the mixed solution. The resulting iron slag can be returned to sintering for disposal, and the resulting solution is used for subsequent treatment; 3-4) Mix the solution obtained in step 3-3) with the wet desulfurization wastewater of the steel plant. After mixing, add the desludge remover and oxidant in sequence, and then perform precipitation and filtration. The resulting waste residue can be returned to sintering for recycling and disposal, and the supernatant waste liquid is obtained; 3-5) The supernatant waste liquid obtained in step 3-4) is subjected to two-stage alkali adjustment precipitation with calcium oxide or calcium hydroxide. The first stage controls the pH to 8~9.5, and the second stage controls the pH to 9.5~11, to obtain struvite precipitate and calcium phosphate slag precipitate, respectively; 3-6) The solution obtained after separation and precipitation in step 3-5) is mainly used for subsequent resource recovery, such as evaporation and concentration to recover calcium chloride product.

[0042] Compared with the prior art, the beneficial technical effects of the present invention are as follows: 1. This invention classifies hot steel slag into different grades based on their alkalinity. High-alkalinity hot steel slag is combined with specific steel plant solid waste for co-processing to achieve dephosphorization and co-disposal of steel slag. Low-alkalinity hot steel slag is coupled with acidic wastewater from the steel plant for co-processing to achieve resource utilization of both steel slag and wastewater. By classifying steel slag and co-processing it with solid waste and then coupling it with acidic wastewater treatment, the harmless treatment effect of steel slag is improved, the amount of steel slag discharged is significantly reduced, and the invention is environmentally friendly and has low disposal costs.

[0043] 2. This invention mixes high-alkali hot steel slag with specific solid waste to produce reaction products with different melting points, which are easy to separate and greatly avoid the accumulation and enrichment of harmful elements in solid waste. It achieves low-cost enrichment of phosphorus in steel slag and can significantly reduce the amount of steel slag discharged. In particular, the resulting phosphorus-free slag has high calorific value and can be recycled for converter smelting, thereby saving energy. Compared with the existing reduction gasification dephosphorization, the dephosphorization effect is better, the waste gas emission is smaller and there is no wastewater discharge. In addition, the process is simpler, more stable and has lower input costs.

[0044] 3. This invention involves cooling and recovering waste heat from low-alkali hot steel slag and separating magnetic iron, then sequentially coupling these slags with various acidic wastewaters for treatment. This significantly reduces the amount of steel slag discharged and achieves resource-based wastewater treatment, while generating virtually no waste gas, wastewater, or solid waste, thus achieving green production. Furthermore, by employing dry cooling, the mineral phase morphology in the low-alkali hot steel slag can be effectively controlled, while simultaneously improving heat recovery and utilization. Through coupled, cascaded utilization of heat energy, the full recovery of sensible heat from the steel slag is achieved. Attached Figure Description

[0045] Figure 1 This is a flowchart of the method for the integrated treatment of steel slag, steel plant solid waste, and acidic wastewater according to the present invention. Detailed Implementation

[0046] The technical solution of the present invention will be illustrated below with examples. The scope of protection sought by the present invention includes, but is not limited to, the following embodiments. Example 1

[0047] The basicity of a batch of hot steel slag discharged from a converter was detected to be approximately 2.3, with a mass of approximately 1000 kg and a temperature of approximately 1600℃. This hot steel slag was then placed in a slag pot and 150 kg of multi-source solid waste (a mixture of 20 parts coal gangue, 20 parts waste carbon powder, 15 parts blast furnace bag ash, 25 parts aluminum ash, 10 parts sintering ash, and 10 parts converter secondary ash) was added. The mixture was then stirred and reacted for 0.5 hours, resulting in a mixed solid solution. The gases generated during the reaction were intercepted using a ceramic membrane before being discharged. The dust collected after the ceramic membrane was used for future reference (it can be returned to the sintering batching process).

[0048] The slag pot is tilted, and approximately 76% of the slag material from the upper layer of the mixed solid solution is collected as phosphorus-free slag (phosphorus content approximately 0.18%, dephosphorization rate approximately 94.38%) and recycled as converter feed. Approximately 10% of the slag material from the middle layer of the mixed solid solution is collected as high-chlorine slag (chlorine content approximately 0.82%) for later use. The remaining lower layer of the mixed solid solution is collected as ferrophosphate slag and added to hot steel slag for recycling and reaction with multi-source solid waste. The resulting ferrophosphate slag is recycled four times before being discharged (approximately 161 kg discharged). Example 2

[0049] The basicity of a batch of hot steel slag discharged from a converter was found to be approximately 1.2, with a mass of approximately 1000 kg and a temperature of approximately 1600℃. The hot steel slag was then cooled using countercurrent heat exchange with compressed air, reducing its temperature to approximately 85℃. The resulting hot air was then transported to a waste heat power generation unit for waste heat utilization, yielding low-temperature gas at approximately 120℃. The cooled steel slag was then ground and crushed to <25mm and subjected to magnetic separation to obtain magnetic iron (iron content approximately 90%, which can be returned to the blast furnace for smelting) and phosphorus-containing slag. The phosphorus-containing slag was then ground to 1-2mm and mixed with cold-rolling acidic wastewater (pH approximately 3) at a solid-liquid mass ratio of 1:5 for leaching. After the reaction, the mixture was filtered, and the resulting iron slag was recycled as sintering material. The resulting leachate underwent further treatment.

[0050] The leachate obtained above was mixed and homogenized with wet desulfurization wastewater at a volume ratio of 3:1. Sodium sulfide (0.3 g / L) was then added to the homogenized wastewater mixture and reacted for 20 minutes. Hydrogen peroxide (0.2 g / L) was then added and reacted for another 20 minutes. After the reaction was completed, the mixture was filtered to obtain waste residue and waste liquid. The waste residue was recycled as sintering material. Calcium oxide was added to the waste liquid to adjust the pH to about 9.0 for precipitation. After the reaction was completed, the mixture was filtered to obtain struvite precipitate (i.e., magnesium ammonium phosphate, with a purity of about 99%) and a high-calcium solution. Calcium oxide was added to the high-calcium solution to adjust the pH to about 11 for precipitation. After the reaction was completed, the mixture was filtered to obtain calcium phosphate slag and high-salt filtrate. The calcium phosphate slag was returned to be mixed with cold-rolling acidic wastewater for leaching and disposal. The high-salt filtrate was sent to a spray drying unit for spray drying to recover calcium chloride product (with a purity of about 99%). Example 3

[0051] Example 2 was repeated, except that the dust and high-chlorine slag obtained in Example 1 were mixed evenly with the phosphorus-containing slag and calcium phosphate slag in Example 2, and then mixed together with cold-rolled acidic wastewater with a pH of about 3 for leaching reaction. After the reaction was completed, the mixture was filtered and the resulting iron slag was recycled as sintering material for disposal. The resulting leachate was then subjected to further treatment.

[0052] The leachate obtained above was mixed and homogenized with wet desulfurization wastewater at a volume ratio of 4:1. Sodium sulfide (0.6 g / L) was then added to the homogenized wastewater mixture and reacted for 20 min. Hydrogen peroxide (0.4 g / L) was then added and reacted for another 20 min. After the reaction was completed, the mixture was filtered to obtain waste residue and waste liquid. The waste residue was recycled as sintering material. Calcium oxide was added to the waste liquid to adjust the pH to approximately 9.0 for precipitation. After the reaction was completed, the mixture was filtered to obtain struvite precipitate and a high-calcium solution. Calcium oxide was then added to the high-calcium solution to adjust the pH to approximately 11 for precipitation. After the reaction was completed, the mixture was filtered to obtain calcium phosphate slag and high-salt filtrate. The calcium phosphate slag was returned to be mixed with cold-rolling acidic wastewater for leaching and disposal. The high-salt filtrate was sent to a spray drying unit for spray drying to recover calcium chloride product (purity approximately 99%). Example 4

[0053] Example 1 was repeated, except that the multi-source solid waste was obtained by uniformly mixing 30 parts of coal gangue, 10 parts of waste carbon powder, 15 parts of blast furnace bag ash, 25 parts of aluminum ash, 10 parts of sintering ash, and 10 parts of converter secondary ash. Example 5

[0054] Example 1 was repeated, except that the multi-source solid waste was obtained by uniformly mixing 20 parts of coal gangue, 25 parts of waste carbon powder, 10 parts of blast furnace bag ash, 25 parts of aluminum ash, 10 parts of sintering ash, and 10 parts of converter secondary ash. Example 6

[0055] Example 1 was repeated, except that the multi-source solid waste was obtained by uniformly mixing 20 parts of coal gangue, 20 parts of waste carbon powder, 10 parts of blast furnace bag ash, 30 parts of aluminum ash, 10 parts of sintering ash, and 10 parts of converter secondary ash. Example 7

[0056] Example 1 was repeated, except that the multi-source solid waste was obtained by uniformly mixing 20 parts of coal gangue, 20 parts of waste carbon powder, 15 parts of blast furnace bag ash, 30 parts of aluminum ash, 5 parts of sintering ash, and 10 parts of converter secondary ash. Example 8

[0057] Example 1 was repeated, except that the multi-source solid waste was obtained by uniformly mixing 25 parts of coal gangue, 20 parts of waste carbon powder, 15 parts of blast furnace bag ash, 25 parts of aluminum ash, 5 parts of sintering ash, and 10 parts of converter secondary ash. Example 9

[0058] Example 1 was repeated, except that the multi-source solid waste was obtained by uniformly mixing 20 parts of coal gangue, 25 parts of waste carbon powder, 15 parts of blast furnace bag ash, 25 parts of aluminum ash, 10 parts of sintering ash, and 5 parts of converter secondary ash. Example 10

[0059] Example 1 was repeated, except that the multi-source solid waste was obtained by uniformly mixing 20 parts of coal gangue, 25 parts of waste carbon powder, 15 parts of blast furnace bag ash, 20 parts of aluminum ash, 10 parts of sintering ash, and 10 parts of converter secondary ash. Example 11

[0060] Example 1 was repeated, except that the multi-source solid waste was obtained by uniformly mixing 20 parts of coal gangue, 15 parts of waste carbon powder, 20 parts of blast furnace bag ash, 25 parts of aluminum ash, 10 parts of sintering ash, and 10 parts of converter secondary ash.

[0061] Table 1: Comparison of parameters between Examples 4-11 and Example 1: Example 12

[0062] Example 1 was repeated, except that the multi-source solid waste was obtained by uniformly mixing 10 parts of coal gangue, 23 parts of waste carbon powder, 17 parts of blast furnace bag ash, 28 parts of aluminum ash, 11 parts of sintering ash, and 11 parts of converter secondary ash. Example 13

[0063] Example 1 was repeated, except that the multi-source solid waste was obtained by uniformly mixing 24 parts of coal gangue, 5 parts of waste carbon powder, 18 parts of blast furnace bag ash, 29 parts of aluminum ash, 12 parts of sintering ash, and 12 parts of converter secondary ash. Example 14

[0064] Example 1 was repeated, except that the multi-source solid waste was obtained by uniformly mixing 22.5 parts of coal gangue, 22.5 parts of waste carbon powder, 5 parts of blast furnace bag ash, 28 parts of aluminum ash, 11 parts of sintering ash, and 11 parts of converter secondary ash. Example 15

[0065] Example 1 was repeated, except that the multi-source solid waste was obtained by uniformly mixing 23 parts of coal gangue, 23 parts of waste carbon powder, 17 parts of blast furnace bag ash, 15 parts of aluminum ash, 11 parts of sintering ash, and 11 parts of converter secondary ash. Example 16

[0066] Example 1 was repeated, except that the multi-source solid waste was obtained by uniformly mixing 21.5 parts of coal gangue, 21.5 parts of waste carbon powder, 16 parts of blast furnace bag ash, 27 parts of aluminum ash, 3 parts of sintering ash, and 11 parts of converter secondary ash. Example 17

[0067] Example 1 was repeated, except that the multi-source solid waste was obtained by uniformly mixing 22 parts of coal gangue, 22 parts of waste carbon powder, 16 parts of blast furnace bag ash, 27 parts of aluminum ash, 11 parts of sintering ash, and 2 parts of converter secondary ash.

[0068] Table 2: A comparison of parameters between Examples 12-17 and Example 1:

[0069] Comparative Example 1 Repeat Example 1, except that all multi-source solid waste is replaced with coal gangue.

[0070] Comparative Example 2 Repeat Example 1, except that all the multi-source solid waste is replaced with carbon powder.

[0071] Comparative Example 3 Repeat Example 1, except that all the multi-source solid waste is replaced with blast furnace bag ash.

[0072] Comparative Example 4 Repeat Example 1, except that all the multi-source solid waste is replaced with aluminum ash.

[0073] Comparative Example 5 Repeat Example 1, except that all the multi-source solid waste is replaced with sintered ash.

[0074] Comparative Example 6 Repeat Example 1, except that all multi-source solid waste is replaced with secondary ash from converters.

[0075] Table 3: A comparison of various parameters between Comparative Examples 1-6 and Example 1:

[0076] As can be clearly seen from Table 3, after the composition of multi-source solid waste changed significantly, its synergistic treatment effect with steel slag deteriorated significantly, mainly manifested in a significant decrease in dephosphorization rate and a significant increase in the amount of slag discharged.

Claims

1. A method for the integrated treatment of steel slag, steel plant solid waste, and acidic wastewater, characterized in that: The method includes: 1) The steel slag discharged from the converter is classified into high-alkali hot steel slag and low-alkali hot steel slag according to its basicity; 2) Add multi-source solid waste to high-alkali hot steel slag for mixing and reaction. After the reaction is completed, a mixed solid solution is obtained. Collect the upper layer of the mixed solid solution and recycle it as converter feed. Collect the middle layer of the mixed solid solution and recycle it to step 3) to mix with waste acid for leaching reaction. Collect the lower layer of the mixed solid solution and add it to high-alkali hot steel slag for mixing and reaction. Collect the dust generated during the mixing reaction and recycle it to step 3) to mix with waste acid for leaching reaction. 3) After cooling, crushing and magnetic separation of low-alkali hot steel slag, magnetic iron and phosphorus-containing slag are obtained. The phosphorus-containing slag is mixed with waste acid for leaching reaction. After the reaction is completed, solid-liquid separation is performed to obtain iron slag and leachate. The iron slag is recycled as sintering material and the leachate is further processed. 4) Mix the leachate obtained in step 3) with wet desulfurization wastewater to obtain mixed waste liquid. Add a desizing agent and an oxidant to the mixed waste liquid for desizing and oxidation treatment. After the treatment is completed, perform solid-liquid separation to obtain waste residue and waste liquid. Use the waste residue as sintering material for recycling and disposal, and carry out subsequent treatment of the waste liquid. 5) Add calcium agent to the waste liquid obtained in step 4) for a first alkali adjustment and precipitation treatment. After solid-liquid separation, struvite precipitate and high-calcium solution are obtained. Continue to add calcium agent to the high-calcium solution for a second alkali adjustment and precipitation treatment. After solid-liquid separation, calcium phosphate residue and high-salt filtrate are obtained. The calcium phosphate residue is recycled to step 3) and mixed with waste acid for leaching reaction. The high-salt filtrate is treated for resource recovery to obtain calcium salt.

2. The method according to claim 1, characterized in that: In step 1), the basicity of the high-alkali hot steel slag is greater than 1.5, preferably greater than 1.8, and more preferably greater than 2.0; and / or In step 1), the basicity of the low-alkali hot steel slag is not higher than 2.0, preferably not higher than 1.8, and more preferably not higher than 1.

5.

3. The method according to claim 1 or 2, characterized in that: In step 2), the multi-source solid waste is a mixed solid waste composed of coal gangue, waste carbon powder, blast furnace bag ash, aluminum ash, sintering ash, and converter secondary ash; Preferably, the amount of multi-source solid waste added is 5-20% of the total mass of high-alkali hot steel slag, more preferably 5-18%, and even more preferably 7-15%.

4. The method according to any one of claims 1-3, characterized in that: In step 2), the multi-source solid waste includes: 10-40 wt% coal gangue, 5-30 wt% waste carbon powder, 5-25 wt% blast furnace bag ash, 15-40 wt% aluminum ash, 3-15 wt% sintering ash, and 2-15 wt% converter secondary ash, preferably 15-30 wt% coal gangue, 10-25 wt% waste carbon powder, 10-20 wt% blast furnace bag ash, 20-35 wt% aluminum ash, 5-12 wt% sintering ash, and 5-12 wt% converter secondary ash; Preferably, in step 2), the reaction is a stirring reaction, and the stirring reaction time is 0.2~2h, preferably 0.3~1.5h, and more preferably 0.4~1h.

5. The method according to any one of claims 1-4, characterized in that: In step 2), the upper layer material accounts for 60-85% of the total mass of the mixed solid solution, preferably 65-80%, more preferably 70-75%; and / or In step 2), the intermediate layer accounts for 3-25% of the total mass of the mixed solid solution, preferably 5-20%, more preferably 10-15%; and / or In step 2), the lower layer material accounts for 1 to 20% of the total mass of the mixed solid solution, preferably 3 to 18%, and more preferably 5 to 15%.

6. The method according to any one of claims 1-5, characterized in that: In step 2), the phosphorus content in the upper layer material is no more than 0.5%, preferably no more than 0.3%, more preferably no more than 0.1%; and / or In step 2), the chlorine content in the intermediate layer material is not less than 0.3%, preferably not less than 0.5%, and more preferably not less than 0.7%. Preferably, in step 2), the lower layer material is recycled and mixed multiple times (preferably 3 to 8 times) before being discharged for disposal.

7. The method according to any one of claims 1-6, characterized in that: In step 3), the cooling is to cool the low-alkali hot steel slag to below 150°C, preferably to below 120°C, and more preferably to below 100°C; Preferably, in step 3), the cooling method is countercurrent heat exchange cooling using compressed air; the cooling rate is 30~100℃ / min, preferably 40~80℃ / min, and more preferably 50~70℃ / min. Preferably, in step 3), the compressed air cools the low-alkali hot steel slag to obtain high-temperature hot air, and the high-temperature hot air is used to obtain low-temperature gas by utilizing the waste heat, and the low-temperature gas is circulated back to step 3) as the cooling air for the low-alkali hot steel slag.

8. The method according to any one of claims 1-7, characterized in that: In step 3), the crushing involves grinding the cooled steel slag to a particle size of less than 2 mm, preferably less than 1 mm; and / or In step 3), the pH of the leaching reaction is 1 to 4.5, preferably 2 to 4; the duration of the leaching reaction is 0.5 to 10 h, preferably 1 to 8 h; and the solid-liquid mass ratio of the leaching reaction is 1:3 to 30, preferably 1:5 to 20.

9. The method according to any one of claims 1-8, characterized in that: In step 4), the mixing volume ratio of the leachate to the wet desulfurization wastewater is 1~5:1, preferably 1.5~4:1; and / or In step 4), the sludge removal agent is sodium sulfide or a sludge trap, and its addition amount is 0.05~2 g / L, preferably 0.1~1 g / L; and / or In step 4), the oxidation is performed to produce hydrogen peroxide, and the amount added is 0.05~0.8g / L, preferably 0.1~0.5g / L.

10. The method according to any one of claims 1-9, characterized in that: In step 5), the calcium agent is calcium oxide and / or calcium hydroxide; Preferably, during the first alkali-adjusting precipitation treatment, the amount of calcium agent added is such that the pH of the waste liquid is 8-9.5, preferably 8.5-9; during the second alkali-adjusting precipitation treatment, the amount of calcium agent added is such that the pH of the high-calcium solution is 9.5-11, preferably 10-10.5.

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