Method for recycling converter steel slag

Abstract

The invention discloses a method for recycling converter steel slag, which comprises the following steps of: mixing high-alkalinity steel slag with multi-source solid waste to react according to different alkalinity of converter hot-state steel slag, so as to obtain phosphorus-free slag, high-chlorine slag and ferrophosphorus slag which are in a solid solution state and are mutually layered; and then the components can be respectively circulated to corresponding working procedures of steel production for absorption. The low-alkalinity steel slag is subjected to cooling, crushing and acid leaching, the obtained iron slag is returned to be sintered for absorption, and the leachate is subjected to micro-electrolysis, oxidation and precipitation treatment and then is respectively recovered to obtain iron phosphate and calcium chloride products, so that zero discharge of wastewater is realized. According to the method, the steel slag is subjected to quality-divided treatment according to different alkalinity of the converter hot steel slag, so that the harmless treatment effect of the steel slag is improved, the discharge amount of the steel slag is greatly reduced, the method is environment-friendly and low in treatment cost, and synergistic efficient treatment of different steel slag, steel mill solid waste and waste acid is realized through a simple and easy-to-operate process; waste gas emission is little, no waste water is discharged, the required raw materials are solid wastes generated in the iron and steel industry, the overall treatment cost is low, and the method is environment-friendly.

Description

Technical Field

[0001] This invention relates to the treatment of steel slag, specifically to a method for recycling converter steel slag, belonging to the field of comprehensive treatment technology for steel slag and solid waste. 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. Summary of the Invention

[0005] To address the problems of poor dephosphorization, large emissions of waste gas, and large amounts of wastewater in existing steel slag treatment technologies, this invention provides a method for recycling converter steel slag. Based on the different alkalinities of the hot converter steel slag, the high-alkalinity steel slag is mixed and reacted with multi-source solid waste to obtain solid-solution, stratified, phosphorus-free slag, high-chloride slag, and ferrophosphate slag. These can then be recycled to the corresponding processes in steel production for disposal. The low-alkalinity steel slag is cooled, crushed, and acid-leached, and the resulting iron slag is returned to sintering for disposal. The leachate is then treated through micro-electrolysis, oxidation, and precipitation to recover ferric phosphate and calcium chloride products, thus achieving zero wastewater discharge. This invention achieves efficient treatment of different types of steel slag through a simple and easy-to-operate process, with low waste gas emissions, zero wastewater discharge, and all required raw materials being solid waste generated in the steel industry. The overall treatment cost is low, and it is environmentally friendly.

[0006] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows: A method for recycling converter steel slag, 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.

[0007] 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.

[0008] 3) After cooling and crushing the low-alkali hot steel slag, it 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.

[0009] 4) The leachate obtained in step 3) is subjected to iron-carbon micro-electrolysis and oxidation treatment in sequence, followed by solid-liquid separation to obtain iron phosphate and waste liquid. Calcium agent is added to the waste liquid for neutralization and precipitation reaction. After solid-liquid separation, the resulting filtrate is dried to obtain calcium chloride.

[0010] Preferably, in step 3), the low-alkali hot steel slag is cooled with air to obtain high-temperature hot air. The high-temperature hot air is then used to obtain medium-temperature gas by utilizing its waste heat. The medium-temperature gas is then circulated to step 4) and used as drying hot air to obtain low-temperature waste gas. The low-temperature waste gas is then circulated to step 3) and combined with air to be used as cooling air for the low-alkali hot steel slag.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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%.

[0015] 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.

[0016] 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.

[0017] 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%.

[0018] 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%.

[0019] 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%.

[0020] Preferably, in step 2), the phosphorus content in the upper layer material is no higher than 0.5%, more preferably no higher than 0.3%, and even more preferably no higher than 0.2%.

[0021] 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 more preferably not less than 0.7%.

[0022] Preferably, in step 2), the lower layer material is recycled and mixed multiple times (e.g., 3 to 8 times) before being discharged for disposal.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] Preferably, in step 4), the duration of iron-carbon micro-electrolysis is not less than 10 minutes, and more preferably 20 to 60 minutes.

[0028] Preferably, in step 4), the oxidation treatment involves reacting with hydrogen peroxide for 10-60 minutes, more preferably 15-45 minutes. The amount added is 0.5-2 g / L, more preferably 0.8-1.5 g / L.

[0029] Preferably, in step 4), the calcium agent is calcium oxide and / or calcium hydroxide, and the amount added is 2~12 g / L, preferably 3~8 g / L. The drying is spray drying.

[0030] In this invention, 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 steel slag. Therefore, this invention addresses the fluctuations in steel slag composition by performing a quality-based treatment, that is, by detecting the basicity of the steel slag and classifying it according to its different basicities (basicity R=CaO / SiO2). This invention addresses the issue of high-alkali and low-alkali hot steel slag. The high-alkali hot steel slag is mixed with various solid wastes to produce stratified, phosphorus-free slag, high-chlorine slag, and ferrophosphate slag, which can then be recycled to their respective steel production processes. The low-alkali hot steel slag is cooled, crushed, and acid-leached, with the resulting iron slag returned to sintering for disposal. The leachate is then treated through micro-electrolysis, oxidation, and precipitation to recover ferric phosphate and calcium chloride products, achieving zero wastewater discharge. In other words, this invention achieves the recycling and disposal of steel slag through differentiated treatment, while also enabling the synergistic disposal of other solid wastes from steel plants, thus achieving the technical objective of treating waste with waste.

[0031] In this invention, steel slag typically contains about 2-5% phosphorus, and direct recycling of it 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 large amounts of forced draft and generate large quantities 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.

[0032] In this invention, reformed multi-source solid waste is mixed with high-alkali hot steel slag. The reducing agents 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 ash from converters). The exothermic effect of the combustion of elemental Zn and Al in the solid waste can be used to achieve self-heating of the entire steel slag treatment, thereby avoiding the low-temperature solidification of phosphorus in the steel slag due to the endothermic reduction.

[0033] 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.

[0034] In this invention, the dephosphorization of converter steel slag generally needs to be controlled at a high alkalinity. Comprehensive treatment of multi-source solid waste with high-alkalinity hot steel slag can further increase the alkalinity of the steel slag. After dephosphorization by reduction, the increased alkalinity is beneficial for the subsequent recycling of the steel slag. In this invention, the alkalinity of the high-alkalinity hot steel slag is greater than 1.5 (preferably greater than 1.8, more preferably greater than 2.0).

[0035] In this invention, the treatment of low-alkali hot steel slag (after phosphorus-free slag is smelted in a circulating converter, the basicity of the steel slag gradually decreases, resulting in low-alkali steel slag. Generally, to maintain the basicity in the furnace, a large amount of alkali needs to be added, resulting in an increasing amount of slag. In addition, after multiple cycles of phosphorus-free slag circulation, when the basicity of the steel slag decreases to a certain level, it needs to be discharged externally, i.e., discharged slag) mainly involves recovering elements such as phosphorus, iron, and chlorine. Since low-alkali hot steel slag contains elemental iron, when the temperature of low-alkali hot steel slag is high (e.g., >1400℃), direct water cooling may pose a risk of hydrogen precipitation due to iron displacement from water, potentially leading to an explosion. However, if it is first naturally cooled to about 800~1000℃ before water cooling, the water cooling will form 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 utilizes compressed air as the cooling medium to cool the low-alkali hot steel slag through counter-current heat exchange. The entire cooling process is dry, avoiding the formation of high-strength steel slag and wastewater, and ensuring high-quality thermal energy. The high-temperature gas used for heat recovery can be used for waste heat power generation, and the resulting low-temperature gas (400~500℃) is used for subsequent wastewater treatment, reducing overall treatment costs and achieving full utilization of thermal energy.

[0036] In this invention, phosphorus in the cooled, low-alkali hot steel slag exists primarily in solid solution form, while iron exists as FeO and metallic iron. Phosphorus in the dust (from the mixed reaction of high-alkali hot steel slag and multi-source solid waste) exists primarily as P2O5, with virtually no iron. By using waste acid from within the steel plant (such as acidic wastewater from cold rolling), and controlling the leaching pH to approximately 1-4 (preferably 2-4, for example 2.5-3.5), phosphorus dissolution in the steel slag (containing phosphorus dust) can be achieved. Simultaneously, the high-chlorine slag generated during the recycling process of the high-alkali hot steel slag is leached along with the slag, which allows for centralized disposal of chlorine and full recovery of phosphorus from the high-chlorine slag.

[0037] In this invention, it should be noted that the iron-containing slag obtained after leaching with waste acid can be directly returned to sintering for disposal, thereby achieving the recycling of solid slag. The leaching solution mainly contains calcium, phosphorus, chlorine, and iron, and is acidic. Based on the characteristics of this leaching solution, this invention sequentially processes it through iron-carbon micro-electrolysis, oxidation, neutralization precipitation, and spray drying, allowing phosphorus to be recovered as ferric phosphate and chlorine as calcium chloride, thus achieving zero wastewater discharge.

[0038] In this invention, the process flow is roughly as follows: 1) The converter steel slag discharged from the converter is subjected to hot testing to detect the basicity of the steel slag. When the basicity is high (e.g., exceeding 2.0), the steel slag proceeds to the subsequent step 2); when the basicity is low (e.g., below 1.5), the steel slag proceeds to the subsequent step 6); 2) A certain amount of multi-source solid waste (a mixture composed of coal gangue, carbon powder, blast furnace bag ash, aluminum ash, sintering ash, converter secondary ash, etc. in different proportions) is added to the high-alkali hot steel slag discharged from the converter, and the mixture is stirred thoroughly to react and obtain a layered mixed solid solution; 3) The gases generated during the reaction process are collected centrally and generally filtered out using a ceramic membrane before being discharged. The dust obtained after the ceramic membrane filtration can participate in the subsequent acid leaching treatment step. 4) After the reaction in step 2), the slag pot is tilted at a certain angle to facilitate two-stage slag removal treatment of the mixed solid solution in the slag pot: the upper slag in the first stage generally accounts for about 60-85% of the solid solution, which is phosphorus-free slag and can be directly returned to the next converter for recycling; the middle slag in the second stage generally accounts for about 3-25% of the solid solution, which is high-chloride slag and can be directly returned to sintering for recycling or enter the subsequent acid leaching treatment step. 5) The remaining lower slag after step 4) is used to mix and react with the slag in the next converter. After generally 3-8 cycles, it can be discharged. 6) The low-alkali hot steel slag obtained in step 1) is directly countercurrent cooled with compressed air, with the cooling rate controlled at 30~100℃ / min, preferably cooled to less than 100℃; 7) The high-temperature hot gas generated during the cooling process is collected and used for waste heat power generation, and the medium-temperature gas obtained after power generation is used for subsequent applications; 8) The cooled solid obtained in step 6) is ball-milled and crushed. The crushed solid, together with the dust obtained in step 3) and the high-chlorine slag obtained in step 4), is mixed with waste acid from the steel plant (such as acidic wastewater from cold rolling) for leaching reaction. After reacting for a period of time, the mixed solution is filtered, and the resulting iron slag can be returned to sintering for disposal. The leachate obtained is used for subsequent treatment; 9) The leachate obtained in step 8) is passed through an iron-carbon reactor, and hydrogen peroxide is slowly added. After reacting for a period of time, the mixed solution is filtered to obtain high-purity iron phosphate as a solid. The filtrate obtained is used for subsequent treatment; 10) The filtrate obtained in step 9) is alkali-adjusted with calcium oxide or calcium hydroxide and precipitated and separated. The supernatant is pumped into a spray dryer to recover high-purity calcium chloride; 11) The heat source used for spray drying in step 10) is the medium-temperature gas obtained in step 7). The low-temperature exhaust gas after passing through the spray dryer is returned to step 6) as a cooling medium for cooling the steel slag.

[0039] Compared with the prior art, the beneficial technical effects of the present invention are as follows: 1. This invention classifies steel slag according to its different alkalinity in hot converter slag, thereby improving the harmless treatment effect of steel slag, significantly reducing the amount of steel slag discharged, and is environmentally friendly with low disposal costs.

[0040] 2. This invention presents a novel approach to co-processing high-alkali hot steel slag with specific solid waste, thereby achieving synergistic dephosphorization of steel slag and solid waste disposal. The resulting reaction products have different melting points, making them easy to separate and greatly avoiding the accumulation and enrichment of harmful elements in solid waste. It achieves low-cost enrichment of phosphorus in steel slag and significantly reduces the amount of steel slag discharged. In particular, the resulting phosphorus-free slag has high calorific value and can be recycled for converter smelting, thus saving energy. Compared with existing reduction gasification dephosphorization, it has better dephosphorization effect, lower waste gas emissions and no wastewater discharge. In addition, the process is simpler, more stable, and has lower input costs.

[0041] 3: This invention cools and recovers the waste heat of low-alkali hot steel slag before co-treating it with waste acid, achieving resource utilization without generating waste. By adopting dry cooling, the mineral phase morphology in low-alkali hot steel slag can be well controlled, while improving the recovery and utilization of heat energy. Through coupled cascade utilization of heat energy, the sensible heat of the slag can be fully recovered. Attached Figure Description

[0042] Figure 1 This is a schematic flowchart of the method for recycling converter steel slag according to the present invention. Detailed Implementation

[0043] 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

[0044] 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 h, 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 returned to the sintering batching process.

[0045] 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

[0046] The basicity of a batch of hot steel slag discharged from a converter was found to be approximately 1.4, with a mass of approximately 1000 kg and a temperature of approximately 1600℃. The hot steel slag was then cooled using counter-current heat exchange with compressed air, reducing its temperature to approximately 80℃. The resulting hot air was then transported to a waste heat power generation unit for waste heat utilization, yielding medium-temperature hot air at approximately 300℃. The cooled steel slag was then ground and crushed to 1-2 mm, and then 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 to obtain iron slag and leachate. The iron slag was recycled as sintering material, and the leachate underwent further treatment.

[0047] First, the leachate obtained above is transported to an iron-carbon micro-electrolysis device and reacted for 25 minutes. Then, hydrogen peroxide (0.8 g / L) is added to the leachate after micro-electrolysis for oxidation reaction for 35 minutes. After the reaction is completed, the solution is filtered, and the resulting filter residue is washed and dried to obtain iron phosphate product (purity of approximately 99%). Calcium oxide (5 g / L) is added to the obtained filtrate for neutralization and precipitation reaction. After the reaction is completed, the solution is filtered (the filter residue is returned to sintering for disposal). The obtained filtrate is transported to a spray drying device and spray-dried with medium-temperature hot gas at approximately 300°C to obtain calcium chloride product (purity of 99%) and low-temperature waste gas. The low-temperature waste gas is recycled and used as a cooling medium for hot steel slag. Example 3

[0048] Example 2 was repeated, except that the dust and high-chlorine slag obtained in Example 1 were mixed evenly with the crushed steel slag in Example 2 and then mixed together with cold-rolled acidic wastewater with a pH of about 3 for leaching reaction (solid-liquid mass ratio of 1:5). 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.

[0049] First, the leachate obtained above is transported to an iron-carbon micro-electrolysis device and reacted for 25 minutes. Then, hydrogen peroxide (1.0 g / L) is added to the leachate after micro-electrolysis and the oxidation reaction is carried out for 35 minutes. After the reaction is completed, the product is filtered. The resulting filter residue is washed and dried to obtain iron phosphate product (purity of 99%). Calcium oxide (8 g / L) is added to the obtained filtrate for neutralization and precipitation reaction. After the reaction is completed, the product is filtered. The obtained filtrate is transported to a spray drying device and spray-dried with medium-temperature hot gas at a temperature of approximately 300°C to obtain calcium chloride product (purity of 99%) and low-temperature waste gas. The low-temperature waste gas is recycled and used as a cooling medium for hot steel slag. Example 4

[0050] 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

[0051] 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

[0052] 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

[0053] 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

[0054] 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

[0055] 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

[0056] 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

[0057] 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.

[0058] Table 1: Comparison of parameters between Examples 4-11 and Example 1: Example 12

[0059] 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

[0060] 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

[0061] 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

[0062] 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

[0063] 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

[0064] 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.

[0065] Table 2: A comparison of parameters between Examples 12-17 and Example 1:

[0066] Comparative Example 1 Repeat Example 1, except that all multi-source solid waste is replaced with coal gangue.

[0067] Comparative Example 2 Repeat Example 1, except that all the multi-source solid waste is replaced with carbon powder.

[0068] Comparative Example 3 Repeat Example 1, except that all the multi-source solid waste is replaced with blast furnace bag ash.

[0069] Comparative Example 4 Repeat Example 1, except that all the multi-source solid waste is replaced with aluminum ash.

[0070] Comparative Example 5 Repeat Example 1, except that all the multi-source solid waste is replaced with sintered ash.

[0071] Comparative Example 6 Repeat Example 1, except that all multi-source solid waste is replaced with secondary ash from converters.

[0072] Table 3: A comparison of various parameters between Comparative Examples 1-6 and Example 1:

[0073] 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 recycling converter steel slag, 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 and crushing the low-alkali hot steel slag, it is mixed with waste acid for leaching reaction. After the reaction is completed, solid-liquid separation is carried out to obtain iron slag and leachate. The iron slag is recycled as sintering material and the leachate is further processed. 4) The leachate obtained in step 3) is subjected to iron-carbon micro-electrolysis and oxidation treatment in sequence, and then solid-liquid separation is performed to obtain iron phosphate and waste liquid; calcium agent is added to the waste liquid to carry out neutralization and precipitation reaction, and after solid-liquid separation, the obtained filtrate is dried to obtain calcium chloride; Preferably, in step 3), the low-alkali hot steel slag is cooled with air to obtain high-temperature hot air. The high-temperature hot air is then used to obtain medium-temperature gas by utilizing its waste heat. The medium-temperature gas is then circulated to step 4) and used as drying hot air to obtain low-temperature waste gas. The low-temperature waste gas is then circulated to step 3) and combined with air to be used as cooling air for the low-alkali hot steel slag.

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: 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.

5. The method according to any one of claims 1-4, characterized in that: 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.

6. The method according to any one of claims 1-5, 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%.

7. The method according to any one of claims 1-6, characterized in that: In step 2), the phosphorus content in the upper layer material is no higher than 0.5%, preferably no higher than 0.3%, more preferably no higher than 0.2%; 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 (e.g., 3 to 8 times) before being discharged for disposal.

8. The method according to any one of claims 1-7, 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, 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.

9. The method according to any one of claims 1-8, 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.

10. The method according to any one of claims 1-9, characterized in that: In step 4), the duration of iron-carbon micro-electrolysis is not less than 10 minutes, preferably 20-60 minutes; and / or In step 4), the oxidation treatment involves reacting with hydrogen peroxide for 10-60 minutes, preferably 15-45 minutes; the amount added is 0.5-2 g / L, preferably 0.8-1.5 g / L; and / or In step 4), the calcium agent is calcium oxide and / or calcium hydroxide, and the amount added is 2~12 g / L, preferably 3~8 g / L; the drying is spray drying.

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