Method for resource utilization of sludge incineration slag

Abstract

The present application belongs to the technical field of solid waste resource utilization, and particularly relates to a sludge incineration slag resource utilization method. The present application mixes sludge incineration slag, water and acid for acid leaching to obtain an acid leaching solution; the acid leaching solution is adjusted to a pH value of 3-5 by alkali for first alkali treatment to obtain first alkali treatment slag; the first alkali treatment slag is adjusted to a pH value of 11.5-13.5 by alkali for second alkali treatment to obtain a second alkali treatment solution; and the second alkali treatment solution is used as a raw material to prepare a ferric phosphate product and / or a superphosphate product. The present application realizes a high dissolution rate of phosphorus in the sludge incineration slag, thereby effectively realizing resource recycling of phosphorus in the incineration slag waste, and simultaneously obtaining a ferric hydroxide precipitate product and an aluminum hydroxide precipitate product, with low recovery cost, saving consumption of phosphorus ore and other raw materials, and realizing resource utilization of the sludge incineration slag.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid waste resource utilization, and particularly relates to a method for resource utilization of sludge incineration slag. Background Art

[0002] With the acceleration of urbanization in my country, the volume of sewage treatment is increasing dramatically. The production of sludge, a byproduct of sewage treatment, is also increasing. Sludge contains a large number of pathogens, microorganisms, organic matter, and heavy metals. Furthermore, the high concentration of water and organic matter in sludge makes its treatment and disposal difficult. Common mechanical dehydration methods can only reduce the water content to approximately 80%, posing a serious threat to the ecological environment and human health.

[0003] Currently, the most common sludge treatment methods in my country include landfill, land use, composting, and incineration. While sanitary landfill is quick and cost-effective, it occupies a large area and poses high environmental risks to the surrounding environment. Heavy metal issues also limit land use and composting. Therefore, sludge incineration is a key solution for sludge treatment and disposal. Sludge incineration removes organic matter from sludge, ultimately producing slag. Slag is virtually organic-free and stable, and is generally recycled as a building material. Furthermore, because sludge incineration slag contains large amounts of silica and aluminum oxide, similar to clay, it can be used to make unfired bricks and soil conditioners. Processes in Europe and the United States recover phosphorus from slag to produce magnesium ammonium phosphate. However, the recovered magnesium ammonium phosphate is of low purity and high in heavy metals, limiting its disposal options. Consequently, there are no successful examples of this in China.

[0004] In the above-mentioned recycling method, the phosphorus in the sludge incineration slag is not properly recycled, resulting in a waste of resources. Assuming a sludge moisture content of 80%, a slag yield of at least 30% of the sludge dry weight, and phosphorus accounting for 5% to 8% of the slag weight, if my country produces 60 million tons of sludge annually, this would result in 180,000 to 288,000 tons of phosphorus. If this phosphorus is not properly utilized, it will result in a serious waste of resources.

[0005] Prior art CN106430136A discloses a method for recovering phosphorus and removing heavy metals from sludge incineration ash. The method comprises the following steps: obtaining sludge incineration ash from a sludge incineration plant, dissolving heavy metals and phosphorus-containing compounds in the sludge incineration ash into a solution by sulfuric acid dissolution to obtain a mixed solution, and the mixed solution enters a centrifugal separator for solid-liquid separation. The separated residue can be disposed of as general waste; NaOH is added to the supernatant from which the residue is separated to adjust the pH to 8-10, and Na2S is added to form a precipitate with the heavy metals in the supernatant. After centrifugation, the heavy metal precipitate is obtained to achieve the removal of heavy metals; Ca(OH)2 is added to the supernatant from which the heavy metal precipitate is separated and the pH is adjusted to 10-12. Ca(OH)2 is added to the supernatant from which the heavy metal precipitate is removed. 2+ With PO4 in solution 3- A calcium phosphate precipitate forms, and after centrifugation, high-quality calcium phosphate is obtained. The aforementioned method for recovering phosphorus and removing heavy metals from sludge incineration ash suffers from significant technical drawbacks. During implementation, the phosphorus recovery rate is negligible, and even no calcium phosphate is obtained. This method ignores the fact that, in addition to phosphorus and a small amount of heavy metals, sludge incineration ash also contains iron oxide and aluminum oxide (which are present in the raw sludge), at levels far exceeding the phosphorus content. The pH of the dissolution reactor in this method is controlled between 1 and 3, and sulfuric acid dissolution causes aluminum and iron ions to be leached along with the phosphorus and heavy metals. Subsequently, NaOH is added to the supernatant of the separated residue to adjust the pH to 8-10. This causes the iron and aluminum ions to react with phosphate to form iron and aluminum phosphate precipitates, leaving the liquid phase virtually free of phosphorus. This is precisely the reaction process for chemical phosphorus removal in wastewater treatment. The iron and aluminum in the slag hinder the effective recovery of phosphorus. Therefore, the above-mentioned existing technologies are not only unable to achieve the synthesis of calcium phosphate, but also unable to achieve the simultaneous purification and recovery of iron, aluminum and phosphorus. New methods are needed to make breakthroughs. Summary of the Invention

[0006] The object of the present invention is to provide a method for resource utilization of sludge incineration furnace slag. The method provided by the present invention not only fully realizes the recovery and resource utilization of phosphorus in sludge incineration furnace slag, avoids the waste of phosphorus resources in sludge incineration furnace slag, but also simultaneously recovers iron and aluminum elements.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] The present invention provides a method for resource utilization of sludge incineration slag, comprising the following steps:

[0009] (1) mixing sludge incineration furnace slag, water and acid for acid leaching, wherein the acid leaching temperature is ≥30°C to obtain acid leaching liquid and acid leaching residue;

[0010] (2) adjusting the pH value of the acid leaching solution to 3-5 with alkali, performing a first alkali treatment, wherein the temperature of the first alkali treatment is ≥30°C, to obtain a first alkali treatment solution and a first alkali treatment slag, wherein the first alkali treatment slag is a phosphorus-rich solid product;

[0011] (3) adjusting the pH value of the first alkali-treated slag to 11.5-13.5 with alkali, and performing a second alkali treatment, wherein the temperature of the second alkali treatment is ≥30°C, to obtain a second alkali-treated solution and a ferric hydroxide precipitate product;

[0012] (4) After obtaining the second alkaline treatment solution, using the second alkaline treatment solution as a raw material to prepare an iron phosphate product and / or a superphosphate product;

[0013] The preparation method of the ferric phosphate product comprises the following steps:

[0014] The pH value of the second alkaline treatment solution is adjusted to 6.5-7.5 with acid to obtain an aluminum hydroxide precipitate product and a phosphate solution;

[0015] Acidifying the phosphate solution to adjust the pH value to 1-1.5, then adding a divalent iron compound and a hydrogen peroxide solution to mix and perform a first-stage reaction to obtain a first-stage reaction solution;

[0016] The first-stage reaction solution, a surfactant, and a pH adjuster are mixed, and the pH value is adjusted to 1.8-2 to carry out a second-stage reaction to obtain a second-stage reaction solution;

[0017] Aging the second-stage reaction liquid to obtain a solid product;

[0018] Washing the solid product with water until it is neutral to obtain a washed product;

[0019] The washed product is dried and calcined in sequence to obtain the ferric phosphate product;

[0020] The preparation method of the superphosphate product comprises:

[0021] mixing the second alkaline treatment solution and a calcium-containing compound to perform a precipitation reaction to obtain a precipitation reaction solution, wherein the calcium-containing compound includes one or more of calcium hydroxide, calcium chloride, calcium oxide, and calcium sulfate;

[0022] separating the precipitation reaction solution into solid and liquid to obtain a solid phase product and a liquid phase product;

[0023] mixing the solid phase product with sulfuric acid to generate a superphosphate product;

[0024] The pH value of the liquid phase product is adjusted to 6.5-7 by using a pH regulator, and then the solid-liquid separation is performed to obtain an aluminum hydroxide precipitate product, wherein the pH regulator is an acid or carbon dioxide.

[0025] Preferably, in step (1), the acid comprises hydrochloric acid and / or sulfuric acid; the ratio of the mass of the sludge incineration slag to the volume of the water is 1 g: (2-10) mL; the pH value of the acid leaching is 0.5-1.5, and the temperature is 50-100°C;

[0026] The concentration of orthophosphate in the acid leaching solution is 3000-20000 mg / L, the total iron concentration is 2000-15000 mg / L, and the aluminum ion concentration is 2000-15000 mg / L.

[0027] Preferably, the acid leaching directly obtains an initial acid leaching slurry, and after obtaining the initial acid leaching slurry, the initial acid leaching slurry is mixed with a heavy metal scavenger for heavy metal purification to obtain an acid leaching solution and an acid leaching residue, wherein the heavy metal scavenger includes one or more of sodium dimethyldithiocarbamate, sodium diethyldithiocarbamate, sodium ethyl xanthate and sodium ethylenediaminetetraacetate.

[0028] Preferably, in step (1), when the acid is sulfuric acid;

[0029] After obtaining the first alkaline treatment solution, the method further includes: adjusting the pH value of the first alkaline treatment solution to 7.5-8.5 with alkali to obtain an aluminum hydroxide precipitation product and a first post-treatment solution; mixing the first post-treatment solution with calcium oxide for reaction to obtain a first reuse solution and calcium sulfate; and reusing the first reuse solution to step (2) and / or step (3), wherein the calcium sulfate is used as a cement raw material.

[0030] Preferably, in step (1), when the acid is sulfuric acid;

[0031] After obtaining the acid leaching residue, the method further includes neutralizing the acid leaching residue with calcium oxide to a pH value of 6.7-7.5 to obtain a building raw material.

[0032] Preferably, the alkali used in the first alkali treatment or the second alkali treatment is a sodium hydroxide solution, and the mass content of NaOH in the sodium hydroxide solution is 10-30%; the temperature of the first alkali treatment or the second alkali treatment is 50-90°C.

[0033] Preferably, the divalent iron compound includes ferrous salt and / or ferrous oxide, and the acid used in the first-stage reaction is sulfuric acid; the molar ratio of phosphorus in the phosphate solution to iron in the divalent iron compound is ≤1:1, the mass content of H2O2 in the hydrogen peroxide solution is 20~30%, and the molar ratio of H2O2 in the hydrogen peroxide solution to iron in the divalent iron compound is ≥1.1:1, and the temperature of the first-stage reaction is 50~90°C, and the time is 50~60min.

[0034] Preferably, the pH regulator used in the second stage reaction is ammonia water, the surfactant includes cetyl trimethyl ammonium bromide and / or sodium dodecyl benzene sulfonate, the mass percentage of the surfactant to the mass of the divalent iron compound is 1-2%, the temperature of the second stage reaction is 50-90℃, and the time is 30-90min.

[0035] Preferably, the aging temperature is 50-90℃, and the time is 1-12h; the calcination temperature is 600-700℃.

[0036] Preferably, the precipitation reaction time is 30-90min.

[0037] The present invention provides a method for resource utilization of sludge incineration slag, comprising the following steps: (1) mixing sludge incineration slag, water and acid for acid leaching, wherein the acid leaching temperature is ≥30°C, and an acid leaching solution and an acid leaching residue are obtained; (2) adjusting the pH value of the acid leaching solution to 3-5 with alkali, and performing a first alkali treatment, wherein the temperature of the first alkali treatment is ≥30°C, and a first alkali treatment solution and a first alkali treatment residue are obtained, wherein the first alkali treatment residue is a phosphorus-rich solid product; (3) adjusting the pH value of the first alkali treatment residue to 11.5-13.5 with alkali, and performing a second alkali treatment, wherein the temperature of the second alkali treatment is ≥30°C, and a second alkali treatment solution and an iron hydroxide precipitation product are obtained; (4) after obtaining the second alkali treatment solution, using the second alkali treatment solution as a raw material to prepare an iron phosphate product and / or a superphosphate product; the preparation method of the iron phosphate product comprises the following steps: adjusting the pH value of the second alkali treatment solution to 6.5-7.5 with acid, and obtaining an aluminum hydroxide precipitation product and a phosphate solution; adding acid to the phosphate solution to adjust the pH value to 1-1.5, and then A divalent iron compound and a hydrogen peroxide solution are added and mixed to carry out a first-stage reaction to obtain a first-stage reaction liquid; the first-stage reaction liquid, a surfactant and a pH adjuster are mixed, and the pH value is adjusted to 1.8-2 to carry out a second-stage reaction to obtain a second-stage reaction liquid; the second-stage reaction liquid is aged to obtain a solid product; the solid product is washed with water until neutral to obtain a washed product; the washed product is dried and calcined in sequence to obtain the ferric phosphate product; the preparation method of the superphosphate product comprises: mixing the second alkaline treatment liquid and a calcium-containing compound to carry out a precipitation reaction to obtain a precipitation reaction solution, wherein the calcium-containing compound includes one or more of calcium hydroxide, calcium chloride, calcium oxide and calcium sulfate; solid-liquid separation of the precipitation reaction solution to obtain a solid-phase product and a liquid-phase product; mixing the solid-phase product with sulfuric acid to generate a superphosphate product; adjusting the pH value of the liquid-phase product to 6.5-7 with a pH adjuster, and then solid-liquid separation to obtain an aluminum hydroxide precipitation product, wherein the pH adjuster is an acid or carbon dioxide. The method provided by the present invention achieves a higher dissolution rate of phosphorus in sludge incineration slag by reasonably setting the steps and conditions for the recovery and resource utilization of phosphorus in sludge incineration slag, thereby effectively realizing the resource recovery and utilization of phosphorus in incineration slag waste; at the same time, iron and aluminum elements are also recovered simultaneously. The iron phosphate product obtained by the present invention is the main raw material of new energy batteries, and can be used as the positive electrode raw material of the battery after further purification. The superphosphate product obtained by the present invention can be used as a fertilizer, and the heavy metal concentration meets the requirements of standard GB / T20413-2017. At the same time, the method provided by the present invention has low recovery cost, saving the consumption of raw materials such as phosphate rock. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1This is a flow chart of the method for resource utilization of sludge incineration slag provided by the present invention. DETAILED DESCRIPTION

[0039] The present invention provides a method for resource utilization of sludge incineration slag, comprising the following steps:

[0040] (1) mixing sludge incineration furnace slag, water and acid for acid leaching, wherein the acid leaching temperature is ≥30°C to obtain acid leaching liquid and acid leaching residue;

[0041] (2) adjusting the pH value of the acid leaching solution to 3-5 with alkali, performing a first alkali treatment, wherein the temperature of the first alkali treatment is ≥30°C, to obtain a first alkali treatment solution and a first alkali treatment slag, wherein the first alkali treatment slag is a phosphorus-rich solid product;

[0042] (3) adjusting the pH value of the first alkali-treated slag to 11.5-13.5 with alkali, and performing a second alkali treatment, wherein the temperature of the second alkali treatment is ≥30°C, to obtain a second alkali-treated solution and a ferric hydroxide precipitate product;

[0043] (4) After obtaining the second alkaline treatment solution, using the second alkaline treatment solution as a raw material to prepare an iron phosphate product and / or a superphosphate product;

[0044] The preparation method of the ferric phosphate product comprises the following steps:

[0045] The pH value of the second alkaline treatment solution is adjusted to 6.5-7.5 with acid to obtain an aluminum hydroxide precipitate product and a phosphate solution;

[0046] Acidifying the phosphate solution to adjust the pH value to 1-1.5, then adding a divalent iron compound and a hydrogen peroxide solution to mix and perform a first-stage reaction to obtain a first-stage reaction solution;

[0047] The first-stage reaction solution, a surfactant, and a pH adjuster are mixed, and the pH value is adjusted to 1.8-2 to carry out a second-stage reaction to obtain a second-stage reaction solution;

[0048] Aging the second-stage reaction liquid to obtain a solid product;

[0049] Washing the solid product with water until it is neutral to obtain a washed product;

[0050] The washed product is dried and calcined in sequence to obtain the ferric phosphate product;

[0051] The preparation method of the superphosphate product comprises:

[0052] mixing the second alkaline treatment solution and a calcium-containing compound to perform a precipitation reaction to obtain a precipitation reaction solution, wherein the calcium-containing compound includes one or more of calcium hydroxide, calcium chloride, calcium oxide, and calcium sulfate;

[0053] separating the precipitation reaction solution into solid and liquid to obtain a solid phase product and a liquid phase product;

[0054] mixing the solid phase product with sulfuric acid to generate a superphosphate product;

[0055] The pH value of the liquid phase product is adjusted to 6.5-7 by using a pH regulator, and then the solid-liquid separation is performed to obtain an aluminum hydroxide precipitate product, wherein the pH regulator is an acid or carbon dioxide.

[0056] In the present invention, unless otherwise specified, all preparation raw materials / components are commercially available products well known to those skilled in the art.

[0057] The present invention comprises mixing sludge incineration slag, water, and acid for acid leaching, wherein the acid leaching temperature is ≥30°C to obtain an acid leaching solution and acid leaching slag. In the present invention, the sludge incineration slag preferably comprises the following components by weight, expressed as oxides: Na2O 0.6-0.8%, MgO 2-3%, Al2O3 10-12%, SiO2 24-25%, P2O 58-19%, SO3 2-3%, K2O 0.3-0.4%, CaO 9-10%, and Fe2O3 11-12%.

[0058] In an embodiment of the present invention, the sludge incineration slag is composed of oxides, including the following components by mass: Na2O 0.7%, MgO 2.21%, Al2O3 11.0%, SiO2 24.8%, P2O 58.68%, SO3 2.31%, K2O 0.36%, CaO 9.17%, and Fe2O3 11.3%.

[0059] In the present invention, the sludge incineration slag is preferably pretreated prior to acid leaching. The pretreatment preferably includes sequential pulverization and screening. The present invention has no particular requirements for the specific method of pulverization. The screening is preferably performed using a 100-200 mesh screen, and in the embodiment, a 100 mesh screen may be used. The screening is performed using the undersize material.

[0060] In the present invention, the acid preferably includes hydrochloric acid and / or sulfuric acid, more preferably sulfuric acid, which may be concentrated sulfuric acid in the embodiment. The mass fraction of the concentrated sulfuric acid is preferably 98%.

[0061] In the present invention, the mixing of the sludge incineration slag, water, and acid preferably includes: dispersing the sludge incineration slag in water and then adding the acid. The ratio of the mass of the sludge incineration slag to the volume of the water is preferably 1g:(2-10)mL, and in embodiments, it can be 1g:2mL, 1g:5mL, or 1g:6mL. The pH value of the acid leaching is preferably 0.5-1.5, and in embodiments, it can be 1.5, 1.3, 1.45, or 1.2. The temperature of the acid leaching is preferably 50-100°C, and in embodiments, it can be 50°C. The acid leaching time is preferably 50-80 minutes, and in embodiments, it can be 60 minutes.

[0062] In the present invention, the acid leaching directly produces an initial acid leaching slurry. After obtaining the initial acid leaching slurry, the present invention preferably further comprises mixing the initial acid leaching slurry with a heavy metal scavenger for heavy metal purification treatment to produce an acid leaching solution and an acid leaching residue. In the present invention, the heavy metal scavenger preferably comprises one or more of sodium dimethyldithiocarbamate, sodium diethyldithiocarbamate, sodium ethylxanthate, and sodium ethylenediaminetetraacetate. The present invention has no particular requirements for the dosage of the heavy metal scavenger; an amount familiar to those skilled in the art can be used. In the present invention, after the heavy metal purification treatment, a purified acid leaching slurry is directly produced. The heavy metal purification treatment preferably lasts for 15 to 20 minutes.

[0063] The present invention preferably performs solid-liquid separation of the initial acid leaching slurry or the acid leaching purification slurry to obtain the acid leaching liquid and the acid leaching residue. The solid-liquid separation is preferably performed by filtration. The filtration is preferably performed by plate and frame filtration.

[0064] In the present invention, the concentration of orthophosphate in the acid leachate is preferably 3000-20000 mg / L, more preferably 10000-15000 mg / L, and in embodiments, it may be 12502 mg / L, 14050 mg / L, 14300 mg / L, or 20000 mg / L; the total iron concentration is preferably 2000-15000 mg / L, more preferably 7000-10000 mg / L, and in embodiments, it may be 8023 mg / L, 8520 mg / L, or 8560 mg / L; the aluminum ion concentration is preferably 2000-15000 mg / L, more preferably 6000-8000 mg / L, and in embodiments, it may be 7560 mg / L, 6900 mg / L, or 6705 mg / L.

[0065] After obtaining the acid leaching residue, the present invention further comprises neutralizing the acid leaching residue with calcium oxide to a pH value of 6.7 to 7.5, and in an embodiment, 7.0, to obtain a construction raw material. In the present invention, the construction raw material preferably includes cement raw material and / or roadbed soil.

[0066] After obtaining the acid leachate, the present invention uses alkali to adjust the pH value of the acid leachate to 3~5 for the first alkali treatment to obtain a first alkali treatment solution and a first alkali treatment slag. The first alkali treatment slag is a phosphorus-rich solid product. The first alkali treatment slag contains a large amount of aluminum ions and iron ions, which need to be subsequently purified and recycled separately. In the present invention, the alkali used in the first alkali treatment is preferably sodium hydroxide solution. The mass content of the NaOH solution in the sodium hydroxide is preferably 10~30%. The pH value of the first alkali treatment can be 3.5, 4.0 or 5. The temperature of the first alkali treatment is preferably 50~90℃. The time of the first alkali treatment is 20~40min, and in the embodiment it can be 30min. In the present invention, the main chemical reactions in the first alkali treatment process include:

[0067] Fe 3+ +PO4 3- =FePO4↓;

[0068] Al 3+ +PO4 3- =AlPO4↓;

[0069] Fe 3+ +OH - =Fe(OH)3↓;

[0070] Al 3+ +OH - =Al(OH)3↓.

[0071] As can be seen from the above reaction, in the present invention, the phosphorus in the sludge incineration furnace slag is enriched in the first alkali-treated slag through the first alkali-treated slag, thereby obtaining a first alkali-treated slag rich in phosphorus. The present invention adjusts the pH value appropriately through the first alkali treatment, so that the phosphate in the acid leachate is precipitated into the first alkali-treated slag to the maximum extent, thereby obtaining a first alkali-treated slag rich in high phosphorus concentration. In the present invention, by adjusting the pH between 3 and 5.0, the phosphate and iron precipitate the most, and the aluminum partially precipitates. Therefore, the concentration of phosphate in the first alkali-treated slag is relatively high. Subsequently, alkali dissolution can be continued for purification to obtain phosphate. In the present invention, the first alkali-treated slurry is directly obtained after the first alkali treatment. The present invention preferably separates the first alkali-treated slurry into solid and liquid to obtain a first alkali-treated solution and a first alkali-treated slag. The solid-liquid separation is preferably centrifugal separation.

[0072] In the present invention, after obtaining the first alkaline treatment solution, the present invention preferably further comprises: adjusting the pH of the first alkaline treatment solution with an alkali, preferably to 7.5 to 8.5, and performing solid-liquid separation to obtain an aluminum hydroxide precipitate product and a first post-treatment solution. In the present invention, the alkali used for pH adjustment is preferably an aqueous sodium hydroxide solution. The mass content of the aqueous sodium hydroxide solution is preferably 30%. The pH value is preferably 8.0 to 8.5. In the present invention, the aluminum hydroxide precipitate product and the first post-treatment solution are preferably obtained by solid-liquid separation, preferably by plate-and-frame filtration.

[0073] In the present invention, after the first alkali treatment solution is obtained as a first post-treatment solution, the present invention preferably further comprises mixing the first post-treatment solution with calcium oxide to react to obtain a first reuse solution and calcium sulfate. The first reuse solution is reused in the first alkali treatment step and / or the second alkali treatment step. The calcium sulfate is preferably used as a cement raw material.

[0074] In the present invention, when the first alkaline treatment solution is mixed with the first post-treatment solution and calcium oxide, the following chemical reactions mainly occur:

[0075] Na2SO4+CaO+H2O=CaSO4↓+2NaOH;

[0076] Na2CO3+CaO+H2O=CaCO3↓+2NaOH.

[0077] After obtaining the first alkali-treated slag, the present invention uses alkali to adjust the pH value of the first alkali-treated slag to 11.5~13.5 for a second alkali treatment to obtain a second alkali-treated solution and an iron hydroxide precipitate product. In the present invention, the alkali used in the second alkali treatment is preferably a sodium hydroxide solution. The mass content of NaOH in the sodium hydroxide solution is preferably 10~30%. The pH value of the second alkali treatment is preferably 12.5, 13.0 or 13.5. The temperature of the second alkali treatment is preferably 50~90°C. The time of the second alkali treatment is preferably 20~40min, and can be 30min in the embodiment. The second alkali treatment is preferably carried out under stirring. In the present invention, the second alkali treatment process uses alkali to dissolve the aluminum-containing compounds in the first alkali-treated slag, and the precipitate is mainly iron hydroxide, and the second alkali treatment solution is mainly a solution of sodium metaaluminate and sodium phosphate. The main chemical reactions in the second alkali treatment process include:

[0078] Fe(PO4)+3NaOH=Fe(OH)3↓+Na3(PO4);

[0079] Al(PO4)+3NaOH==Al(OH)3↓+Na3(PO4);

[0080] Al(OH)3+NaOH=NaAlO2+2H2O.

[0081] As can be seen from the above reaction, the first alkali-treated slag of the present invention is subjected to alkali dissolution, the purpose of which is to dissolve the aluminum precipitate into the liquid phase to obtain an aluminum phosphate solution and a high concentration of phosphate. In the present invention, the second alkali treatment dissolves the aluminum hydroxide and aluminum phosphate in the first alkali-treated slag into the liquid phase to obtain metaaluminate and phosphate, and the ferric phosphate is dissolved to obtain ferric hydroxide solid and phosphate. The second alkali treatment process purifies the phosphate, creating conditions for the subsequent synthesis of high-purity ferric phosphate, and simultaneously obtaining a high-purity ferric hydroxide precipitate product.

[0082] In the present invention, the second alkali-treated slurry is directly obtained after the second alkali treatment. The present invention preferably separates the second alkali-treated slurry into solid and liquid to obtain a second alkali-treated solution and a ferric hydroxide precipitate product. The solid-liquid separation is preferably performed by plate and frame filtration.

[0083] After obtaining the second alkaline treatment solution, the present invention uses the second alkaline treatment solution as a raw material to prepare an iron phosphate product and / or a superphosphate product.

[0084] In the present invention, the preparation method of the ferric phosphate product comprises the following steps:

[0085] The pH value of the second alkaline treatment solution is adjusted to 6.5-7.5 with acid to obtain an aluminum hydroxide precipitate product and a phosphate solution;

[0086] Acidifying the phosphate solution to adjust the pH value to 1-1.5, then adding a divalent iron compound and a hydrogen peroxide solution to mix and perform a first-stage reaction to obtain a first-stage reaction solution;

[0087] The first-stage reaction solution, a surfactant, and a pH adjuster are mixed, and the pH value is adjusted to 1.8-2 to carry out a second-stage reaction to obtain a second-stage reaction solution;

[0088] Aging the second-stage reaction liquid to obtain a solid product;

[0089] The solid product is washed with water until it becomes neutral;

[0090] The washed product is dried and calcined in sequence to obtain the ferric phosphate product.

[0091] The present invention adjusts the pH of the second alkaline treatment solution to 6.5-7.5 with an acid to obtain an aluminum hydroxide precipitate product and a phosphate solution. The present invention has no particular requirements for the type and concentration of the acid used to adjust the pH of the second alkaline treatment solution. In a specific embodiment of the present invention, the acid is sulfuric acid, specifically concentrated sulfuric acid, with a mass fraction of 98%. The pH in the embodiment can be 6.5 or 7.0. The present invention achieves separation of aluminum ions and phosphate ions by controlling the pH of the second alkaline treatment solution to 6.5-7.5.

[0092] In the present invention, when the acid is sulfuric acid, the main chemical reactions that occur when the pH value of the second alkaline treatment solution is adjusted to 6.5-7.5 with acid are as follows:

[0093] 2NaAlO2+H2SO4+2H2O=2Al(OH)3↓+Na2SO4.

[0094] In the present invention, the solution obtained after the second alkali treatment mainly contains substances such as sodium phosphate and sodium metaaluminate. The pH value of the solution is adjusted by adding sulfuric acid so that the metaaluminate in the solution reacts with hydrogen ions to form aluminum hydroxide precipitation. The reason for adjusting the pH to 6.5-7.5 is that aluminum hydroxide is an amphoteric hydroxide. If the pH is too low, the aluminum hydroxide will dissolve into the solution again; if the pH is too high, the metaaluminate cannot be completely precipitated.

[0095] In the present invention, the phosphate solution is preferably pretreated prior to preparing the ferric phosphate product. The pretreatment preferably includes subjecting the phosphate solution to cationic resin column purification. In the present invention, the cationic resin column purification preferably removes aluminum ions from the phosphate solution. The present invention has no particular requirements for the cationic resin column used in the cationic resin column purification; commercially available products can be used.

[0096] After obtaining a phosphate solution (or a pretreated phosphate solution), the present invention adds acid to the phosphate solution (or pretreated phosphate solution) to adjust the pH to 1.0 to 1.5. A divalent iron compound and a hydrogen peroxide solution are then added and mixed to carry out a first-stage reaction, thereby obtaining a first-stage reaction solution. The purpose of the first-stage reaction is to oxidize ferrous ions to ferric ions to produce a ferric phosphate product. The synthesis of ferric phosphate in the present invention requires acidic conditions. When the pH is above 2.0, the proportion of ferric hydroxide produced by the reaction is high, which affects the purity of the ferric phosphate.

[0097] In the present invention, the divalent iron compound preferably includes ferrous salts and / or ferrous oxide, and in an embodiment, it may be ferrous sulfate. The acid used in the first stage reaction is preferably sulfuric acid, and the sulfuric acid is concentrated sulfuric acid, and the mass fraction of the concentrated sulfuric acid is 98%. The molar ratio of the phosphorus element in the phosphate solution to the iron element in the divalent iron compound is preferably ≤1:1, more preferably 1:1~2, and in an embodiment, it may be 1:1.25 or 1:1. The mass content of the hydrogen peroxide solution is preferably 20~30%, and in an embodiment, it may be 30%. The molar ratio of H2O2 in the hydrogen peroxide solution to the iron element in the divalent iron compound is preferably ≥1.1:1, more preferably 1.1~1.5:1, and in an embodiment, it may be 1.1:1 or 1.5:1. The pH value of the first stage reaction may be 1.0.

[0098] In the present invention, the mixing order is preferably: adding the acid, the divalent iron compound, and the hydrogen peroxide solution to the phosphate solution in sequence. The temperature of the first-stage reaction is preferably 50-90°C, and the time is preferably 50-60 minutes. The first-stage reaction is carried out under stirring.

[0099] After obtaining the first-stage reaction solution, the present invention mixes the first-stage reaction solution, a surfactant, and a pH adjuster, and adjusts the pH value to 1.8 to 2 to carry out the second-stage reaction to obtain the second-stage reaction solution. In the present invention, the purpose of the surfactant is to disperse the particles and reduce the agglomeration of the particles during the formation of ferric phosphate, thereby achieving effective control of the size and appearance of the ferric phosphate.

[0100] In the present invention, the pH adjuster used in the second-stage reaction is preferably aqueous ammonia. There are no specific requirements for the mass concentration of the aqueous ammonia. The surfactant preferably includes cetyltrimethylammonium bromide (CTAB) and / or sodium dodecylbenzenesulfonate (SDBS). The mass percentage of the surfactant to the mass of the ferrous compound is preferably 1-2%, and in embodiments, can be 1.25% or 1.5%. The mixing order is preferably: adding the surfactant and the pH adjuster sequentially to the first-stage reaction solution. The temperature of the second-stage reaction is preferably 50-90°C, and the reaction time is preferably 30-90 minutes. The second-stage reaction is carried out under stirring.

[0101] After obtaining the second-stage reaction liquid, the present invention ages the second-stage reaction liquid to obtain a solid product. In the present invention, the aging temperature is 50~90°C, and the time is preferably 1~12h, and in the embodiment it can be 9h. The present invention can make the iron phosphate crystals grow by controlling the temperature and time of aging. After the aging is completed, the aged liquid is directly obtained. The present invention preferably separates the aged liquid into solid and liquid to obtain the wet solid product. The separation is preferably plate and frame filtration. The present invention preferably dries the wet solid product to obtain the solid product. The drying is preferably carried out in a dryer, and the drying temperature is preferably 90~110°C.

[0102] In the present invention, during the first stage reaction, by controlling the pH value of the first stage, the H2O2 in the divalent iron compound and the hydrogen peroxide solution is fully oxidized to trivalent iron ions. Then, a surfactant is added during the second stage reaction. The surfactant can promote the formation of crystal nuclei of ferric phosphate and provide conditions for the subsequent crystallization of ferric phosphate products. The present invention utilizes ammonia water to adjust the pH of the solution to preferably 1.8 to 2, promotes the formation and growth of ferric phosphate under the appropriate conditions of pH value=1.8 to 2, and obtains an ferric phosphate product. The present invention, through the aging, can further promote the growth of ferric phosphate crystals to obtain an ferric phosphate product with a large specific surface area.

[0103] After obtaining the solid product, the present invention washes the solid product with water until it becomes neutral to obtain a washed product. In the present invention, the washing is preferably performed multiple times.

[0104] After obtaining the washed product, the present invention sequentially dries and calcines the washed product to obtain the ferric phosphate product. In the present invention, the drying is performed in a dryer, and the drying temperature is preferably 80-90°C. The calcination temperature is preferably 600-700°C, and in embodiments, it can be 700°C or 650°C.

[0105] In the present invention, the preparation method of the calcium phosphate product comprises:

[0106] mixing the second alkaline treatment solution and a calcium-containing compound to perform a precipitation reaction to obtain a precipitation reaction solution, wherein the calcium-containing compound includes one or more of calcium hydroxide, calcium chloride, calcium oxide, and calcium sulfate;

[0107] separating the precipitation reaction solution into solid and liquid to obtain a solid phase product and a liquid phase product;

[0108] mixing the solid phase product with sulfuric acid to generate a superphosphate product;

[0109] The pH value of the liquid phase product is adjusted to 6.5-7 with acid or carbon dioxide, and then the solid-liquid separation is performed to obtain an aluminum hydroxide precipitate product.

[0110] The second alkali treatment solution and a calcium-containing compound are mixed to carry out a precipitation reaction in the present application, and a precipitation reaction solution is obtained. The calcium-containing compound includes one or more of calcium hydroxide, calcium chloride, calcium oxide, and calcium sulfate. In the present application, the calcium salt preferably includes calcium chloride. In the present application, the molar ratio of phosphorus in the phosphate solution to calcium in the calcium-containing compound (P:Ca 2+ ) is ≥ 1:1.8, preferably 1:1.8~2, and can be 1:2 in the examples. The time of the precipitation reaction is preferably 30~90 min, and can be 60 min in the examples.

[0111] After the precipitation reaction solution is obtained, the precipitation reaction solution is solid-liquid separated in the present application, and a solid-phase product and a liquid-phase product are obtained. In the present application, the solid-liquid separation is preferably plate-and-frame filtration.

[0112] After the solid-phase product is obtained, the solid-phase product is mixed with sulfuric acid to generate a calcium superphosphate product in the present application. In the present application, the sulfuric acid is preferably concentrated sulfuric acid, and the mass fraction of the concentrated sulfuric acid is preferably 98%. The ratio of the amount of use of the concentrated sulfuric acid to the amount of use of the solid-phase product is preferably (0.6~0.8) mL:4 g, and can be 0.7 mL:1 g in the examples. The mixing is carried out under stirring. After the mixing, the mixture is left to stand and mature, and a calcium superphosphate product is obtained. The time of the standing and maturing is preferably 1~2 days. The calcium superphosphate product is preferably dried, and the temperature of the drying is preferably 85~90℃.

[0113] After the liquid-phase product is obtained, the liquid-phase product is adjusted to a pH value of 6.5~7 with a pH adjuster, and then solid-liquid separated, to obtain an aluminum hydroxide precipitation product in the present application. The pH adjuster is an acid or carbon dioxide. The acid is preferably concentrated sulfuric acid. The solid-liquid separation is preferably plate-and-frame filtration. The solid-phase product obtained by the solid-liquid separation is the aluminum hydroxide precipitation product, and the liquid-phase product obtained is a second post-treatment solution.

[0114] In the present application, when the pH adjuster is concentrated sulfuric acid, after the second post-treatment solution is obtained, the present application preferably further includes mixing the second post-treatment solution with calcium oxide to carry out a reaction, to obtain a second recycled solution and calcium sulfate. The second recycled solution is recycled to the first alkali treatment step and / or the second alkali treatment step. The calcium sulfate is preferably used as a cement raw material.

[0115] In the present application, when the pH adjuster is carbon dioxide, after the second post-treatment solution is obtained, the present application preferably further includes mixing the second post-treatment solution with calcium oxide to carry out a reaction, to obtain a second recycled solution and calcium carbonate. The second recycled solution is recycled to the first alkali treatment step and / or the second alkali treatment step.

[0116] In a specific embodiment of the present invention, when the pH adjuster is concentrated sulfuric acid, after obtaining the second post-treatment solution, the first and second post-treatment solutions are preferably mixed and then subjected to subsequent treatment together. Specifically, the first and second post-treatment solutions are preferably mixed and then reacted with calcium oxide to obtain a third recycled solution and calcium sulfate. The third recycled solution is recycled to the first and / or second alkaline treatment steps. The calcium sulfate is preferably used as a cement raw material.

[0117] The reaction principle of adding sulfuric acid to the solid product to generate superphosphate includes:

[0118] Ca3(PO4)2+2H2SO4+6H2O=Ca(H2PO4)2·2H2O+2CaSO4·2H2O.

[0119] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0120] Example 1:

[0121] This embodiment provides a method for resource utilization of sludge incineration slag, wherein the composition test results of the sludge incineration slag are shown in Table 1, and specifically includes the following steps:

[0122] Table 1 Component test results of sludge incineration slag (wt%)

[0123]

[0124] Crush the sludge incineration slag and pass it through a 100-mesh sieve. Add water to the sieved sludge incineration slag at a solid-liquid ratio of 1g:5mL. Add concentrated sulfuric acid (98% by mass) at 50°C, adjust the pH to 1.3, and react for 60 minutes. Add the heavy metal scavenger sodium dimethyldithiocarbamate and react for 15 minutes. After the reaction is complete, filter through a plate and frame filter. The resulting acid-leached residue is neutralized with calcium oxide to a pH of 7.0 and then used as roadbed soil.

[0125] The acid leaching solution obtained after plate and frame filtration had an orthophosphate concentration of 12502 mg / L, a total iron concentration of 8023 mg / L, and an aluminum ion concentration of 7560 mg / L.

[0126] Add sodium hydroxide aqueous solution to the acid leachate at a concentration of 30%, adjust the pH to 3.5, and maintain the temperature at 50°C. Allow the solution to stabilize at pH 3.5 for 30 minutes. After complete precipitation, dehydrate the solution using a centrifuge. The resulting solid phase is the first alkaline treatment residue, and the liquid phase is the first alkaline treatment solution.

[0127] The first alkali treatment residue is added with 30wt% sodium hydroxide aqueous solution, and stirred to react until the pH value is 12.5 and the temperature is 50°C. The pH value is kept at 12.5 for 30 minutes. Then, the dehydration is performed by plate and frame filtration. The filtrate after dehydration is the second alkali treatment solution, and the solid phase is the iron hydroxide precipitation product, with the purity of 81.2% and the recovery rate of iron element of 80%.

[0128] The second alkali treatment solution is added with concentrated sulfuric acid (mass fraction of 98%) to adjust the pH value to 6.5. The white precipitate and the filtrate (i.e. the phosphate solution) are obtained by plate and frame filtration and dehydration. The white precipitate is aluminum hydroxide, with the purity of 90.5% and the recovery rate of aluminum element of 80%.

[0129] The phosphate solution mainly contains phosphate, sodium ions and sulfate ions. The phosphate solution is passed through a cation resin column. The phosphate solution after purification by the resin is adjusted to pH value of 1.0 by sulfuric acid (mass fraction of 98%), and then ferrous sulfate is added to make n(P:Fe 2+ )=1:1.25. Then, 30wt% hydrogen peroxide aqueous solution is added, with the amount of n(H2O2:Fe 2+ )=1.5:1. The reaction is performed for 60 minutes, with the temperature controlled at 90°C. CTAB is added, with the mass of CTAB controlled at 1.25% of the mass of ferrous sulfate. Ammonia water is added, and the pH value is adjusted to 1.8. The reaction is performed for 90 minutes, with the temperature controlled at 90°C. After the reaction is completed, aging is performed, with the temperature controlled at 90°C and the aging time of 9 hours. The aged solution is subjected to plate and frame filtration.

[0130] The solid obtained by plate and frame filtration is washed with water until the pH value is neutral (7), and then is dried in a drying machine, with the temperature controlled at 90°C.

[0131] The dried substance is calcined, with the calcination temperature controlled at 700°C, to obtain the iron phosphate product.

[0132] The purity of the iron phosphate product is 99.9%, the particle size is 5μm, and the recovery rate of phosphorus element is 79.2%.

[0133] After the first alkali treatment solution is obtained, sodium hydroxide aqueous solution (30wt%) is added to the first alkali treatment solution to adjust the pH value to 8.5. The obtained mixture is subjected to plate and frame filtration to obtain the solid which is aluminum hydroxide and the liquid phase which is the first post-treatment solution. Calcium oxide is added to the first post-treatment solution, and the obtained sodium hydroxide aqueous solution (i.e. the first reused solution) after filtration can be reused. The solid (calcium sulfate) after filtration is used as cement raw material for further resource utilization.

[0134] Example 2:

[0135] This embodiment provides a method for resource utilization of sludge incineration slag, wherein the composition test results of the sludge incineration slag are shown in Table 1, and specifically includes the following steps:

[0136] Pass the sludge incineration slag through a 100-mesh sieve. Add water to the sieved sludge incineration slag at a solid-liquid ratio of 1g:6mL. Add concentrated sulfuric acid (98% by mass) at 50°C, adjust the pH to 1.45, and react for 60 minutes. Add the heavy metal scavenger sodium dimethyldithiocarbamate and react for 15 minutes. After the reaction is complete, filter through a plate and frame filter. The resulting acid-leached residue is neutralized with calcium oxide to a pH of 7.0 and then used as roadbed soil.

[0137] The acid leaching solution obtained after plate and frame filtration had an orthophosphate concentration of 14050 mg / L, a total iron concentration of 8560 mg / L, and an aluminum ion concentration of 6705 mg / L.

[0138] Add sodium hydroxide aqueous solution to the acid leachate at a concentration of 30%, adjust the pH to 4.0, and maintain the temperature at 60°C. Allow the solution to stabilize at pH 4.0 for 30 minutes. After complete precipitation, dehydrate the solution using a centrifuge. The resulting solid phase is the first alkaline treatment residue, and the liquid phase is the first alkaline treatment solution.

[0139] A 30wt% aqueous sodium hydroxide solution was added to the first alkali-treated residue, and the mixture was stirred until the pH reached 13.0 at 60°C. The mixture was stabilized at pH 13.0 for 30 minutes. The residue was then dehydrated using plate and frame filtration. The filtrate formed the second alkali-treated solution, and the solid phase was the precipitated iron hydroxide product with a purity of 80%. The iron recovery rate was 80%.

[0140] Concentrated sulfuric acid (98% by mass) was added to the second alkaline treatment solution to adjust the pH to 7.0. Plate and frame filtration was then performed to obtain a white precipitate and a filtrate (i.e., a phosphate solution). The white precipitate was aluminum hydroxide. The purity of the aluminum hydroxide was 90%, and the recovery rate of aluminum was 80%.

[0141] The main remaining ions in the phosphate solution are phosphate, sodium and sulfate. The phosphate solution is passed through a cationic resin column. After purification by the resin, the pH value of the phosphate solution is adjusted to 1.0 using concentrated sulfuric acid (98% by mass). Then, ferrous sulfate is added to make n(P:Fe 2+ )=1:1, then add 30wt% concentration of hydrogen peroxide aqueous solution, the amount of hydrogen peroxide added is n(H2O2:Fe 2+) = 1.1:1, react for 60 minutes, control the temperature at 90°C, add CTAB, and control the mass of CTAB to 1.5% of the mass of ferrous sulfate. Add ammonia water, stir the reaction, adjust the pH to 1.8, and react for 90 minutes. Control the temperature at 90°C. After the reaction is complete, age the solution at 90°C for 9 hours. The aged solution is then plate-and-frame filtered.

[0142] The solid obtained by plate and frame filtration was washed with water several times until the pH value was 7 (neutral), and then put into the dryer for drying at a controlled temperature of 90°C.

[0143] The dried material is calcined at a temperature of 650° C. to obtain an iron phosphate product.

[0144] The purity of the ferric phosphate product is 99.9%, the particle size is 4μm, and the phosphorus recovery rate is 78.7%.

[0145] After obtaining the first alkaline treatment solution, a 30wt% sodium hydroxide aqueous solution is added to the first alkaline treatment solution to adjust the pH to 8.0. The resulting mixed solution is then plate-and-frame filtered, yielding aluminum hydroxide as a solid and the first post-treatment solution as a liquid. Calcium oxide is added to the first post-treatment solution, and the resulting sodium hydroxide aqueous solution (i.e., the first reuse solution) can be recycled. The solid (calcium sulfate) obtained after filtration is then used as a cement raw material for further resource utilization.

[0146] Example 3:

[0147] This embodiment provides a method for resource utilization of sludge incineration slag, wherein the composition test results of the sludge incineration slag are shown in Table 1, and specifically includes the following steps:

[0148] Pass the sludge incineration slag through a 100-mesh sieve. Add water to the sieved sludge incineration slag at a solid-liquid ratio of 1g:5mL. Add concentrated sulfuric acid (98% by mass) at 50°C, adjust the pH to 1.2, and react for 60 minutes. Add the heavy metal scavenger sodium dimethyldithiocarbamate and react for 15 minutes. After completion, filter the mixture through a plate and frame filter. The resulting acid-leached residue is neutralized with calcium oxide to a pH of 7.0 and then used as roadbed soil.

[0149] The acid leaching solution obtained after plate and frame filtration had an orthophosphate concentration of 14,300 mg / L, a total iron concentration of 8,520 mg / L, and an aluminum ion concentration of 6,900 mg / L.

[0150] Add sodium hydroxide aqueous solution to the acid leachate at a concentration of 30%, adjust the pH to 5.0, and maintain the temperature at 90°C. Allow the solution to stabilize at pH 5.0 for 30 minutes. After precipitation is complete, dehydrate the solution using a centrifuge. The resulting solid phase is the first alkaline treatment residue, and the liquid phase is the first alkaline treatment solution.

[0151] A 30wt% aqueous sodium hydroxide solution was added to the first alkali-treated residue, and the mixture was stirred until the pH reached 13.5 at 90°C. The residue was allowed to stabilize at pH 13.5 for 30 minutes. The residue was then dehydrated using plate and frame filtration. The filtrate formed the second alkali-treated solution, and the solid phase was the ferric hydroxide precipitate.

[0152] Calcium chloride is added to the second alkaline treatment solution so that n(P:Ca 2+ ) = 1:2, react for 60 minutes, and then filter the solution through plate and frame filtration. Concentrated sulfuric acid (98% by mass) is added to the solid obtained through plate and frame filtration, with the ratio of concentrated sulfuric acid to calcium phosphate controlled at 0.7 (mL):1 (g). The mixture is stirred until solidified, then left to mature for 2 days. The resulting product is superphosphate. The clear liquid after plate and frame filtration is adjusted to a pH of 7.0 using concentrated sulfuric acid to produce a white precipitate, which is aluminum hydroxide. Dehydration is then performed through plate and frame filtration again, resulting in the supernatant that serves as the second post-treatment solution.

[0153] After obtaining the first alkaline treatment solution, a sodium hydroxide aqueous solution (30 wt%) was added to the first alkaline treatment solution to adjust the pH to 8.0. The resulting mixed solution was plate-and-frame filtered to obtain aluminum hydroxide as a solid and the first post-treatment solution as a liquid.

[0154] After mixing the first and second post-treatment solutions, calcium oxide is added. The resulting sodium hydroxide solution (the third recycled solution) is filtered and recycled back to the aforementioned process. The solid (calcium sulfate) obtained after filtration is then used as a cement raw material for further resource utilization.

[0155] In this embodiment, the purity of aluminum hydroxide is 89.5%, the purity of ferric hydroxide is 82.3%, the recovery rate of iron is 75.5%, and the recovery rate of aluminum is 75.5%. The phosphorus pentoxide content of the superphosphate product can reach over 12%, and the recovery rate of phosphorus is 79.2%.

[0156] Comparative Example 1:

[0157] This comparative example 1 is substantially the same as Example 2, except that:

[0158] This comparative example provides a method for resource utilization of sludge incineration slag, wherein the composition test results of the sludge incineration slag are shown in Table 1, and specifically comprises the following steps:

[0159] The sludge incineration slag is sieved through a 100-mesh sieve. Water is added to the sieved sludge incineration slag at a solid-liquid ratio of 1 g:6 mL, concentrated sulfuric acid (mass fraction of 98%) is added, and reaction is carried out at room temperature (25°C), the pH value is adjusted to 1.45, reaction is carried out for 60 min, a heavy metal capturing agent sodium dimethyl dithiocarbamate is added, reaction is carried out for 15 min, and after reaction is completed, plate and frame filtration is carried out. The obtained acid leaching residue is neutralized to a pH value of 7.0 by calcium oxide and used as roadbed soil.

[0160] The concentration of orthophosphate in the obtained acid leaching solution after plate and frame filtration is 10050 mg / L, the total iron concentration is 6560 mg / L, and the aluminum ion concentration is 4705 mg / L (the temperature of acid leaching is relatively low, which affects the content of target ions of acid leaching).

[0161] Comparative Example 2

[0162] The comparative example 2 is basically the same as the example 2, and the difference is that:

[0163] Sodium hydroxide solution is added to the acid leaching solution, the concentration of the sodium hydroxide solution is 30%, the pH value is adjusted to 2.5, and reaction is carried out at room temperature (25°C). The pH value is stable at 2.5 for 30 min, and after complete precipitation, dehydration is carried out by using a centrifuge. The obtained solid phase is the first alkali treatment residue, and the liquid phase is the first alkali treatment solution.

[0164] 30wt% sodium hydroxide solution is added to the first alkali treatment residue, stirring reaction is carried out until the pH value is 11.0, and reaction is carried out at room temperature (25°C). The pH value is stable at 11.0 for 30 min. Then, dehydration is carried out by using plate and frame filtration, the obtained filtrate after dehydration is the second alkali treatment solution, and the solid phase is the iron hydroxide precipitation product, and the purity of the iron hydroxide is 42.3%. The iron element recovery rate is 30.8%.

[0165] Concentrated sulfuric acid (mass fraction of 98%) is added to the second alkali treatment solution, the pH value is adjusted to 7.0, and plate and frame filtration is carried out to obtain white precipitate and filtrate (i.e. phosphate solution). The white precipitate is aluminum hydroxide. However, the amount of the white precipitate is too small, and the recovery rate of the aluminum hydroxide is very low, only 10%.

[0166] The main remaining ions in the phosphate solution are phosphate, sodium ions, and sulfate ions. The phosphate solution is passed through a cation resin column, the phosphate solution after purification by the resin is adjusted to a pH value of 1.0 by using concentrated sulfuric acid (mass fraction of 98%), then ferrous sulfate is added so that n(P:Fe 2+ )=1:1.5, then 30wt% concentration hydrogen peroxide aqueous solution is added, and the amount of the hydrogen peroxide is n(H2O2:Fe 2+) = 1.5:1, react for 60 minutes, and control the temperature at 90°C. Add ammonia water, stir the reaction, adjust the pH to 1.8, and react for 90 minutes. The temperature is also controlled at 90°C. After the reaction is completed, age the solution at 90°C for 1.5 hours. The aged solution is then plate-and-frame filtered.

[0167] The solid obtained by plate and frame filtration was washed with water several times until the pH value was 7 (neutral), and then put into the dryer for drying at a controlled temperature of 80°C.

[0168] The resulting iron phosphate had a phosphorus concentration of 150-350 mg / kg and an iron concentration of 200-360 mg / kg. XRD analysis revealed no iron phosphate crystal peaks. Analysis of the resulting material revealed amorphous iron phosphate, which was due to the absence of iron phosphate crystals due to the lack of calcination. The phosphorus recovery rate was 50.2%, which was reduced due to the low pH during the first alkali treatment. Furthermore, the pH value adjusted to 11.0 during the second alkali treatment resulted in a low efficiency in dissolving phosphorus in the slag from the first alkali treatment, ultimately leading to a low iron phosphate recovery rate.

[0169] From the above embodiments, it can be seen that the present invention provides a method for resource utilization of sludge incineration slag. The method provided by the present invention realizes a higher dissolution rate of phosphorus in sludge incineration slag by reasonably setting the steps and conditions for the recovery and resource utilization of phosphorus in sludge incineration slag, thereby effectively realizing the resource recovery and utilization of phosphorus in incineration slag waste, and obtaining iron hydroxide precipitation product and aluminum hydroxide precipitation product. The iron phosphate product obtained by the present invention is the main raw material of new energy batteries, and can be used as the positive electrode raw material of batteries after further purification. At the same time, the cost of recovery of the method provided by the present invention is low, saving the consumption of raw materials such as phosphate rock.

[0170] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for resource utilization of sludge incineration slag, characterized in that: The following steps are involved: (1) mixing sludge incineration furnace slag, water and acid for acid leaching, wherein the acid leaching temperature is ≥30°C to obtain acid leaching liquid and acid leaching residue; (2) adjusting the pH value of the acid leaching solution to 3-5 with alkali, performing a first alkali treatment, wherein the temperature of the first alkali treatment is ≥30°C, to obtain a first alkali treatment solution and a first alkali treatment slag, wherein the first alkali treatment slag is a phosphorus-rich solid product; (3) adjusting the pH value of the first alkali-treated slag to 11.5-13.5 with alkali, and performing a second alkali treatment, wherein the temperature of the second alkali treatment is ≥30°C, to obtain a second alkali-treated solution and a ferric hydroxide precipitate product; (4) adjusting the pH of the second alkaline treatment solution to 6.5-7.5 with an acid to obtain an aluminum hydroxide precipitate product and a phosphate solution; Acidifying the phosphate solution to adjust the pH value to 1-1.5, then adding a divalent iron compound and a hydrogen peroxide solution to mix and perform a first-stage reaction to obtain a first-stage reaction solution; The first-stage reaction solution, a surfactant, and a pH adjuster are mixed, and the pH value is adjusted to 1.8-2 to carry out a second-stage reaction to obtain a second-stage reaction solution; Aging the second-stage reaction liquid to obtain a solid product; Washing the solid product with water until it is neutral to obtain a washed product; The washed product is dried and calcined in sequence to obtain the ferric phosphate product.

2. The method for resource utilization of sludge incineration slag according to claim 1, characterized in that: In step (1), the acid includes hydrochloric acid and / or sulfuric acid; the ratio of the mass of the sludge incineration slag to the volume of the water is 1 g: (2-10) mL; the pH value of the acid leaching is 0.5-1.5, and the temperature is 50-100°C; The concentration of orthophosphate in the acid leaching solution is 3000-20000 mg / L, the total iron concentration is 2000-15000 mg / L, and the aluminum ion concentration is 2000-15000 mg / L.

3. The method for resource utilization of sludge incineration slag according to claim 1, characterized in that: The acid leaching directly obtains an initial acid leaching slurry. After obtaining the initial acid leaching slurry, the initial acid leaching slurry is mixed with a heavy metal scavenger for heavy metal purification to obtain an acid leaching solution and an acid leaching residue. The heavy metal scavenger includes one or more of sodium dimethyldithiocarbamate, sodium diethyldithiocarbamate, sodium ethyl xanthate and sodium ethylenediaminetetraacetate.

4. The method for resource utilization of sludge incineration slag according to claim 1 or 2, characterized in that: In step (1), when the acid is sulfuric acid; After obtaining the first alkaline treatment solution, the method further comprises: adjusting the pH value of the first alkaline treatment solution to 7.5-8.5 with an alkali to obtain an aluminum hydroxide precipitate product and a first post-treatment solution; The first post-treatment solution and calcium oxide are mixed and reacted to obtain a first reuse solution and calcium sulfate; the first reuse solution is reused in step (2) and / or step (3), and the calcium sulfate is used as a cement raw material.

5. The method for resource utilization of sludge incineration slag according to claim 1 or 2, characterized in that: In step (1), when the acid is sulfuric acid; After obtaining the acid leaching residue, the method further includes neutralizing the acid leaching residue with calcium oxide to a pH value of 6.7-7.5 to obtain a building raw material.

6. The method for resource utilization of sludge incineration slag according to claim 1, characterized in that: The alkali used in the first alkali treatment or the second alkali treatment is a sodium hydroxide solution, and the mass content of NaOH in the sodium hydroxide solution is 10-30%; the temperature of the first alkali treatment or the second alkali treatment is 50-90°C.

7. The method for resource utilization of sludge incineration slag according to claim 1, characterized in that: The divalent iron compound includes ferrous salt and / or ferrous oxide, and the acid used in the first-stage reaction is sulfuric acid; the molar ratio of phosphorus in the phosphate solution to iron in the divalent iron compound is ≤1:1, the mass content of H2O2 in the hydrogen peroxide solution is 20-30%, and the molar ratio of H2O2 in the hydrogen peroxide solution to iron in the divalent iron compound is ≥1.1:

1. The temperature of the first-stage reaction is 50-90°C, and the reaction time is 50-60 minutes.

8. The method for resource utilization of sludge incineration slag according to claim 1 or 7, characterized in that: The pH regulator used in the second-stage reaction is ammonia water, the surfactant includes hexadecyltrimethylammonium bromide and / or sodium dodecylbenzenesulfonate, the mass of the surfactant accounts for 1-2% of the mass of the divalent iron compound, the temperature of the second-stage reaction is 50-90°C, and the time is 30-90 minutes.

9. The method for resource utilization of sludge incineration slag according to claim 1, characterized in that: The aging temperature is 50-90° C., and the time is 1-12 hours; the calcination temperature is 600-700° C.

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