A method for combined treatment of converter slag and sludge incineration ash and recovery of phosphorus

Abstract

The present invention discloses a method for the combined treatment and phosphorus recovery of converter slag and sludge incineration ash. The method includes first thoroughly mixing sludge incineration ash with molten converter slag, utilizing the residual heat of the molten slag to reconstruct the mineral phase, cooling the slag to obtain a mixed slag, crushing the mixed slag, and screening it to obtain slag powder. The slag powder is then added to a dilute acid solution for leaching. During the leaching process, the pH is controlled at 1.0 to 4.0, dissolving and separating only the phosphorus-containing mineral phase in the mixed slag, resulting in a phosphorus dissolution rate exceeding 80%. After leaching, the solution is filtered and separated to obtain a leachate and tailings. The tailings primarily contain Fe2O3 and CaO and can be used as a metallurgical raw material. Finally, the pH of the leachate is raised to precipitate phosphate ions, and solid-liquid separation is performed to obtain a phosphate product. This method achieves efficient recovery of phosphorus from converter slag and sludge incineration ash and effective utilization of other components, solving the problem of solid waste resource utilization and having important significance for the sustainable development of the steel and phosphate industries.

Description

Technical Field

[0001] The invention belongs to the field of solid waste resource utilization and chemical technology, and particularly relates to a method for jointly treating converter slag and sludge incineration ash and recovering phosphorus. Background Art

[0002] Phosphate rock is a limited, non-renewable natural resource. To achieve a long-term sustainable supply of phosphorus, developing new phosphorus resources, such as recovering phosphorus from phosphorus-containing industrial solid waste, has become an important research topic.

[0003] Converter slag is a solid waste produced during the steelmaking process, which usually contains 3% P2O5. In addition, CaO, Fe t The total content of beneficial components such as O, MgO, and MnO exceeds 70%, all of which are essential raw materials or fluxes in the steelmaking process. Directly returning converter slag to the smelting process without dephosphorization significantly increases the phosphorus content in the molten iron, increasing the burden of subsequent dephosphorization. The phosphorus in converter slag is primarily concentrated in the dicalcium silicate phase. Therefore, effective separation of the dicalcium silicate phase in the slag is not only essential for phosphorus resource recovery but also crucial for achieving in-plant recycling of converter slag.

[0004] The dicalcium silicate phase in converter slag has a higher solubility in dilute acid solutions. Selective leaching can dissolve the phosphorus-containing dicalcium silicate phase, effectively separating phosphorus from valuable elements such as iron, magnesium, and manganese in the slag. The inventors reported in the papers "Effect of Fe2O3 Mass Fraction on Phosphorus Leaching Separation from Dephosphorized Steel Slag" and "Acid-leaching Separation of Phosphorus from the BOF Slag Modified with Al2O3" that increasing the Fe2O3 and Al2O3 contents in converter slag is beneficial to the leaching of the dicalcium silicate phase. Therefore, in order to improve the separation efficiency of phosphorus in converter slag and reduce processing costs, the Fe2O3 and Al2O3 contents in the slag can be increased. However, there is currently no economically feasible method to increase the Fe2O3 and Al2O3 contents in converter slag and effectively separate the dicalcium silicate phase.

[0005] Sludge incineration ash is the product obtained by calcining the separated sludge after treating wastewater using a chemical precipitation method (adding iron, aluminum, and calcium salts). Sludge incineration ash contains a large amount of metal phosphates, such as iron phosphate, aluminum phosphate, and calcium phosphate, with a P2O5 content ranging from 10.0% to 25.7%. Therefore, sludge incineration ash is a solid waste rich in elements such as phosphorus, iron, and aluminum, and is also a potential phosphorus resource. The separation and recovery of phosphorus from sludge incineration ash has long been a research focus. For example, patent CN105772484A discloses a technology for harmless treatment of municipal sludge incineration ash and a method for recovering phosphorus compounds. Patent CN111440011A discloses a method for preparing phosphate fertilizer from municipal sludge. These methods all use acid hydrolysis. However, since sludge incineration ash contains a large amount of insoluble iron phosphate and aluminum phosphate, a large amount of acid is consumed during the acid leaching process, and elements such as iron and aluminum are difficult to effectively recycle. Furthermore, these methods all involve multiple leaching and precipitation steps, resulting in complex process flows and high processing costs, which limits their industrial application. Summary of the Invention

[0006] In order to overcome the defects of the above-mentioned prior art, the purpose of the present invention is to provide a method for the joint treatment and phosphorus recovery of converter slag and sludge incineration ash, which reconstructs the mineral phases of the two solid wastes, promotes the efficient and selective extraction of phosphorus, and effectively recovers elements such as iron, magnesium, and aluminum in converter slag and sludge incineration ash, which is of great significance for promoting the large-scale and resource utilization of solid waste.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides a method for the combined treatment of converter slag and sludge incineration ash and recovery of phosphorus:

[0008] First, the sludge incineration ash is fully mixed with the molten converter slag, and the mineral phase is reconstructed using the waste heat of the slag. After the slag is cooled, a mixed slag is obtained, which is then crushed and sieved to obtain slag powder.

[0009] Then, the slag powder is added to a dilute acid solution for leaching. During the leaching process, the pH value is controlled so that only the phosphorus-containing mineral phase in the mixed slag is dissolved and separated. After leaching, the solution is filtered and separated to obtain a leachate and tailings. The tailings can be used as a metallurgical raw material.

[0010] Finally, the pH of the leachate is increased to precipitate phosphate ions, and a phosphate product is obtained after solid-liquid separation.

[0011] In the above technical solution, further, the temperature of the molten converter slag should be above 1450°C, and the mass ratio of sludge incineration ash to molten converter slag should be lower than 1:2.

[0012] Furthermore, after the sludge incineration ash is fully mixed with the molten converter slag, the slag is oxidized by injecting air or oxygen, and the heat released by the oxidation is helpful for the reconstruction of the mineral phase.

[0013] Furthermore, during the slag cooling process, the cooling rate is controlled to be lower than 20°C / min.

[0014] Furthermore, the mixed slag is crushed into slag powder with a particle size of less than 0.5 mm, and the mass ratio of the slag powder to the dilute acid solution during leaching is less than 1:10.

[0015] Furthermore, the leaching process is carried out under normal temperature and pressure conditions, the pH value is controlled to be 1.0-4.0, the selected dilute acid solution is hydrochloric acid or nitric acid solution, and the leaching time is 10-90 minutes.

[0016] Furthermore, an alkaline substance is added to increase the pH value of the leachate to 6.0-9.0 to precipitate phosphate ions, and the added alkaline substance is calcium oxide, calcium hydroxide or sodium hydroxide.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The present invention proposes a new method for simultaneously recovering phosphorus from converter slag and sludge incineration ash with high efficiency and low cost. The two solid wastes are resource coupled and mineral phase reconstructed, so that phosphorus is enriched in the easily soluble dicalcium silicate phase, thereby improving the phosphorus recovery rate. The tailings after phosphorus extraction can be used as metallurgical raw materials, realizing high added value utilization of the two solid wastes.

[0019] (2) The present invention utilizes the waste heat and chemical heat of molten converter slag to reconstruct the mineral phase, does not require an additional heat source, and has low energy consumption. The leaching process is carried out under weakly acidic conditions, has low equipment requirements, high production efficiency, and low cost.

[0020] (3) The present invention utilizes acid leaching to treat the mixed slag, which can leach out most of the phosphorus in the slag while leaving elements such as iron, manganese, and magnesium at very low solubility rates, achieving an ideal separation effect. The residue, primarily composed of valuable components such as Fe2O3 and CaO, can be used as a metallurgical raw material. A phosphate product can be recovered from the leachate and used as a fertilizer, thus resolving the shortage of phosphate rock and saving a significant amount of mineral resources.

[0021] (4) The present invention uses cheap acid and alkali as leaching agent and pH regulator respectively, without the need for other raw materials and additives. This technology can turn two types of solid waste into "treasures", has good application prospects, and can bring significant economic and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a process flow chart for the combined treatment of converter slag and sludge incineration ash and phosphorus recovery according to the present invention;

[0023] Figure 2This is an electron microscope picture of the mixed slag after the converter slag and sludge incineration ash treatment in the embodiment;

[0024] Figure 3 The bar graph of the dissolution rate of the main elements in the mixed slag in the embodiment;

[0025] Figure 4 The following is a photo of the phosphate product recovered in the examples. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to specific examples, but the present invention is not limited in any way. To avoid redundancy, the raw materials in the following examples are all commercially available products unless otherwise specified, and the methods used are all conventional methods unless otherwise specified.

[0027] A method for combined treatment of converter slag and sludge incineration ash and recovery of phosphorus:

[0028] First, the sludge incineration ash is fully mixed with the molten converter slag, and the mineral phase is reconstructed using the waste heat of the slag. After the slag is cooled, a mixed slag is obtained, which is then crushed and sieved to obtain slag powder.

[0029] Then, the slag powder is added to a dilute acid solution for leaching. During the leaching process, the pH value is controlled so that only the phosphorus-containing mineral phase in the mixed slag is dissolved and separated. After leaching, the solution is filtered and separated to obtain a leachate and tailings.

[0030] Finally, the pH of the leachate is increased to precipitate phosphate ions, and a phosphate product is obtained after solid-liquid separation.

[0031] Example

[0032] The process flow of the method for combined treatment of converter slag and sludge incineration ash and recovery of phosphorus of the present invention is as follows: Figure 1 shown.

[0033] The converter slag used in the examples was sourced from the converter workshop of a domestic steel mill, and the sludge incineration ash was sourced from a domestic sewage treatment plant. First, two groups of 100g of converter slag were placed in high-purity magnesium oxide crucibles and heated to 1550°C in a high-temperature resistance furnace to form molten slag. Then, 25g and 42g of sludge incineration ash were added to the slag, respectively. The slag was kept at this temperature for 30 minutes and heated to melt in an atmospheric atmosphere, equivalent to injecting air or oxygen for oxidation in actual production. The slag was then cooled to room temperature at a cooling rate of 10°C / min to obtain two mixed slags. The two mixed slags were crushed and ground through a 300-mesh sieve, and the chemical composition and mineral phase composition of the two mixed slags were analyzed using XRF and SEM.

[0034] Table 1 Chemical composition of the two mixed slags in the embodiment (mass fraction / %)

[0035]

[0036] Table 1 shows the chemical composition of the two mixed slags. The P2O5 content in the mixed slag 1 with 25g of sludge incineration ash added is 5.7%, and the P2O5 content in the mixed slag 2 with 42g of sludge incineration ash added is 7.1%.

[0037] Figure 2 The electron microscope images of the two mixed slags are shown in Figure 2. The two mixed slags are mainly composed of dicalcium silicate, magnesia-ferrous silicate phase and magnesia-ferrous spinel phase.

[0038] 6g of slag powder was added to 300mL of dilute hydrochloric acid solution for leaching, and the solution was mechanically stirred. The leaching process was carried out at room temperature, and dilute hydrochloric acid solution was added to the solution using a peristaltic pump to maintain the solution pH at 2.0. After 90 minutes of reaction, the solution was filtered to separate the tailings and leachate.

[0039] The mass concentration of each element in the leachate was determined by ICP-OES, and the leaching rate of the main elements in the two mixed slags was calculated. The results are as follows: Figure 3 As shown in the figure, at pH 2.0, the phosphorus dissolution rates in the two mixed slags were 83% and 88%, respectively. Almost all silicon was dissolved and separated, while the leaching rates of iron and aluminum were extremely low, achieving ideal selective leaching. The results show that most of the dicalcium silicate phase in the mixed slag was dissolved, while the magnesian spinel phase was retained in the residue, achieving effective phosphorus separation.

[0040] The chemical composition of the tailings after leaching the two mixed slags was analyzed by XRF, as shown in Table 2. The tailings are mainly composed of valuable components such as Fe2O3, MgO, and Al2O3, with a very low P2O5 content. Therefore, the tailings after leaching can be returned to the smelting process as a metallurgical raw material for reuse.

[0041] Table 2 Chemical composition of tailings after leaching of two mixed slags in the embodiment (mass fraction / %)

[0042]

[0043] The content of P2O5 in mixed slag 2 is high, and its leaching solution contains a large amount of Ca 2+ A saturated solution of Ca(OH)2 was added to the leachate to raise its pH value, and the solution was stirred with a stirring paddle. As the pH value increased, a white precipitate gradually formed in the solution. When the pH value increased to 7.5, a large amount of precipitate was produced.

[0044] After the solution was allowed to stand for a period of time, it was centrifuged and a white precipitate was extracted. The concentration of phosphorus in the remaining leachate was extremely low, indicating that most of the phosphate ions formed precipitates in the neutral solution, achieving effective recovery of phosphorus.

[0045] After the recovered white precipitate is dried, a phosphate product is obtained. Table 4 shows the chemical composition of the phosphate product. The phosphate is mainly composed of CaO, SiO2 and P2O5, of which the P2O5 content is 22.4% and has a high citric acid solubility, and the SiO2 content is 32.7%, which mainly exists in the form of amorphous silica gel. Therefore, the phosphate product can be used as a fertilizer. Through this process, more than 80% of the phosphorus in the converter slag and sludge incineration ash is effectively recovered, and the following is obtained: Figure 4 Phosphate products shown.

[0046] Table 3 Chemical composition of the phosphate product obtained in the embodiment (mass fraction / %)

[0047]

[0048] In summary, the present invention provides a method for the combined treatment of converter slag and sewage sludge incineration ash for phosphorus recovery. First, the sludge incineration ash and molten converter slag are reconstituted into a mineral phase. Then, the phosphorus in the mixed slag is separated by acid leaching. Phosphates are then precipitated and separated from the leachate. This method can achieve resourceful utilization of phosphorus-containing solid waste.

[0049] Anyone skilled in the art will be able to utilize the above-disclosed technical content to make many possible changes and modifications to the technical solution of the present invention, or to modify it into equivalent embodiments with equivalent changes, without departing from the scope of the technical solution of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention that do not depart from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for combined treatment of converter slag and sludge incineration ash and recovery of phosphorus, characterized by: First, the sludge incineration ash is fully mixed with the molten converter slag, and the mineral phase is reconstructed using the waste heat of the slag. After the slag is cooled, a mixed slag is obtained, which is then crushed and sieved to obtain slag powder. Then, the slag powder is added to a dilute acid solution for leaching. During the leaching process, the pH value is controlled to dissolve and separate the phosphorus-containing mineral phase in the mixed slag. After leaching, the solution is filtered and separated to obtain a leachate and tailings. The leaching process is carried out under normal temperature and pressure conditions, the pH value is controlled to be 1.0-4.0, the dilute acid solution selected is hydrochloric acid or nitric acid solution, and the leaching time is 10-90 min; Finally, the pH of the leachate is increased to precipitate phosphate ions, and a phosphate product is obtained after solid-liquid separation.

2. The method according to claim 1, wherein The temperature of the molten converter slag is above 1450° C., and the mass ratio of the sludge incineration ash to the molten converter slag is less than 1:

2.

3. The method according to claim 1, characterized in that After the sludge incineration ash is fully mixed with the molten converter slag, the slag is oxidized by injecting air or oxygen.

4. The method according to claim 1, wherein During the slag cooling process, the cooling rate is controlled to be lower than 20℃ / min.

5. The method according to claim 1, wherein The mixed slag is crushed into slag powder with a particle size of less than 0.5 mm, and the mass ratio of the slag powder to the dilute acid solution is less than 1:10 during leaching.

6. The method according to claim 1, characterized in that An alkaline substance is added to increase the pH value of the leachate to 6.0-9.0 to precipitate phosphate ions; the added alkaline substance is calcium oxide, calcium hydroxide or sodium hydroxide.

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