A treatment method for soda residue by the ammonia-soda process

Abstract

The present invention relates to a method for treating soda residue by the ammonia-soda process, belonging to the technical field of environmental protection and comprehensive utilization of solid waste. The method includes three steps: conversion crystallization, flotation separation, and evaporation for salt precipitation; conversion crystallization: reacting soda residue with sulfuric acid to form calcium sulfate; flotation separation: separating calcium sulfate from silicate impurities by flotation; evaporation for salt precipitation or adjusting the pH value to meet the discharge standard: evaporation for salt precipitation is to evaporate the salt-containing liquid phase, and by controlling the evaporation amount, sodium salts and magnesium salts are precipitated at different stages. The present invention completely decomposes soda residue through mineral separation technology, eliminates the environmental protection and safety problems of soda residue, and at the same time obtains high-value-added products such as calcium sulfate, sodium chloride, and magnesium chloride, generating considerable economic benefits and providing a new method for treating soda residue.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental protection and comprehensive utilization of solid waste, and in particular relates to a method for comprehensive utilization of waste residues in the production of soda ash using an ammonia-soda process. Background Art

[0002] Alkali residue is waste residue with calcium salts and magnesium salts such as CaCO3, CaSO4, CaCl2, Mg(OH)2 as main components, and also contains silicate components such as SiO2. Alkali residue solution is alkaline, with a pH value of about 10. The alkali residue has a very fine particle size, which makes the alkali residue have a large specific surface area and a high water content, making it difficult to store and handle.

[0003] At present, there is no economical and effective method for treating alkali residue in the world. Most of the known technologies adopt the method of transporting waste liquid to the slag yard, allowing the alkali residue to settle naturally, and then piling it up for storage. Because the solid particles of alkali residue are very small, with an average particle size of 10μm, it has been determined that when the alkali residue settles naturally to 80% of the water content, it will no longer continue to settle. Therefore, this treatment method occupies a large amount of land, and as the height of the slag yard increases, it also creates huge safety and environmental risks.

[0004] In order to solve the problem of alkali residue, various methods for comprehensive utilization and treatment of alkali residue are disclosed in the prior art. For example, the patent with publication number CN140151A discloses a method for making engineering soil using alkali residue; the patent with publication number CN102092972A discloses a method for synthesizing cement clinker, auxiliary materials and cement using soda ash waste residue and ammonia evaporation waste liquid; the patent with publication number CN103664242A discloses a method for preparing potash fertilizer using alkali residue; the patent with publication number CN107555462A discloses the comprehensive utilization and recovery of alkali residue to prepare precipitated barium sulfate, light calcium carbonate, agricultural grade ammonium chloride or industrial crude salt sodium chloride. The patent with publication number CN108483461A discloses a method for recycling alkali residue in soda ash production, which significantly reduces the alkali residue generated in the soda ash production process.

[0005] The basic ideas for recycling and treating alkali residue based on the existing technologies are: 1. harmless treatment followed by stacking and burying. However, with the progress of production, the alkali residue will continue to accumulate, which will eventually have a huge impact on the environment and safety; 2. recovering the effective ingredients in the alkali residue. However, this method cannot completely treat the alkali residue, and may even make the remaining part of the alkali residue more difficult to treat due to the introduction of other ingredients; 3. chemical treatment into a specific product, but it is often limited to a single use and a small amount, making it difficult to expand the scale. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for treating waste residues produced by the production of soda ash by the ammonia-soda process in view of the deficiencies in the prior art. The method adopts the technology of mineral separation to completely decompose the alkali residues, which is environmentally friendly, safe, and can also generate greater economic benefits.

[0007] The technical problem to be solved by the present invention is achieved through the following technical solutions. The present invention is a method for treating ammonia-soda process alkali residue, and the method includes three steps: conversion crystallization, flotation separation, and evaporation for salt precipitation;

[0008] Conversion crystallization: reacting alkali residue with sulfuric acid to generate calcium sulfate;

[0009] Flotation separation: separating calcium sulfate from silicate impurities by flotation;

[0010] Evaporation for salt precipitation or adjusting pH value to meet the discharge standard:

[0011] Evaporation for salt precipitation is to evaporate the salt-containing liquid phase, and by controlling the evaporation amount, sodium salts and magnesium salts are precipitated in different stages;

[0012] Adjusting pH value to meet the discharge standard is to adjust the pH value of the liquid phase obtained by flotation separation and then discharge it up to the standard.

[0013] For the method for treating ammonia-soda process alkali residue according to the present invention, the preferred technical solution is that during conversion crystallization: the reaction temperature is 10~40°C, the reaction time is 2~6 hours, and the pH value of the liquid phase in the reactor is 1.0~6.0.

[0014] For the method for treating ammonia-soda process alkali residue according to the present invention, the preferred technical solution is that positive flotation process is adopted for flotation separation, and calcium sulfate is enriched in the foam product.

[0015] For the method for treating ammonia-soda process alkali residue according to the present invention, the preferred technical solution is that the steps are specifically as follows:

[0016] ① Conversion crystallization: The alkali residue enters the grinding mill and is ground to a particle size finer than 100 mesh. If the particle size of the alkali residue is uniform and finer than 100 mesh, this operation is omitted; the ground slurry is fed into the reaction crystallizer, and sulfuric acid is added to control the pH value of the liquid phase in the reaction crystallizer between 1.0 and 6.0;

[0017] ② Flotation separation: The slurry discharged from the reaction crystallizer enters the stirring tank, the flotation regulator enters the stirring tank, the flotation collector enters the stirring tank, and the slurry is adjusted for 1~20 minutes, and then the slurry enters the flotation machine for flotation. The foam product is the calcium sulfate product, and the product in the tank is the silicate tailings; the foam product is filtered and dehydrated, the solid phase is the calcium sulfate product, and the liquid phase enters the evaporation for salt precipitation section; the product in the tank is filtered and dehydrated, the solid phase is the silicate tailings, and the liquid phase enters the evaporation for salt precipitation section;

[0018] ③Evaporation and salt precipitation: The liquid phase in the flotation separation section flows into the collection tank. After evaporating a certain amount of water, sodium chloride begins to precipitate. Before the magnesium salt precipitates after continuous evaporation, solid-liquid separation is carried out to obtain sodium chloride products; the liquid phase is further evaporated, and magnesium salts precipitate until old brine is obtained or finally dried; magnesium chloride products, magnesium sulfate products or a mixture of both are obtained.

[0019] The further preferred technical solution steps are as follows:

[0020] ①Conversion and crystallization: Wet grinding of ore, with the discharge concentration of 10 - 40%, controlling the flow rate into the reactor, sulfuric acid enters the reactor at a concentration of 10 - 50%, and the dosage is 80 - 100% of the amount of alkali residue. Control the residence time of the material in the reactor for 2 - 8 hours, the reaction temperature is 10 - 40 °C, and the pH value of the slurry in the crystallizer is 1.0 - 6.0;

[0021] ②Flotation separation: The slurry from the reactor enters the agitation tank for pulp conditioning, the flotation regulator enters the agitation tank for pulp conditioning, and the flotation collector enters the agitation tank for pulp conditioning. After pulp conditioning for 1 - 20 minutes, the pulp enters the flotation machine for one rough selection and 1 - 4 fine selections. The foam product is calcium sulfate dihydrate, and the product in the cell is silicate tailings. After solid-liquid separation, calcium sulfate dihydrate, tailings and salt-containing liquid phase are obtained (the grade of calcium sulfate dihydrate is not less than 95%);

[0022] ③Evaporation and salt precipitation: The salt-containing liquid phase enters the evaporation pond. When the liquid phase concentration reaches 15 - 30%, magnesium sulfate products are precipitated. After continuous evaporation, old brine is obtained, and magnesium chloride products, magnesium sulfate products or a mixture of both are obtained after drying.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] Through the method of mineral separation, the present invention completely decomposes the alkali residue, eliminates the environmental and safety hazards of the alkali residue, and at the same time obtains calcium sulfate products, sodium chloride products, magnesium chloride products and a small amount of silicate tailings. Calcium sulfate, sodium chloride and magnesium chloride are all products with high added value. The silicate tailings have no environmental and safety hazards and can be used as raw materials in the construction industry, such as cement, etc.

[0025] The method of the present invention controls the particle size of calcium sulfate crystals by reacting the alkali residue with sulfuric acid, solving the problem of difficult dehydration due to too fine particle size; solves the problem of separating calcium sulfate from silicate impurities by flotation; and realizes the stage precipitation of water-soluble salts by controlling the evaporation water volume, solving the problem of separating soluble salts such as sodium chloride, magnesium chloride and magnesium sulfate.

[0026] The present invention treats the alkali residue by adopting the technology of mineral separation, completely decomposes the alkali residue, meets the requirements of environmental protection and safety, and at the same time generates considerable economic benefits. It meets the requirements of environmental protection and safety, obtains products with high added value, and provides a new method for treating alkali residue. Description of the Drawings

[0027] Figure 1 This is the process flow diagram of the present invention. Detailed implementation manners

[0028] The following further describes the specific technical solutions of the present invention to facilitate the further understanding of the present invention by those skilled in the art, without constituting a limitation to its rights.

[0029] Example 1, referring to Figure 1 , a treatment method for ammonia-soda process alkali residue:

[0030] A certain alkali residue, with the main components being: calcium carbonate 60%, gypsum dihydrate 10%, magnesium hydroxide 10%, acid-insoluble substances 10%. The treatment method steps are as follows:

[0031] ① In the conversion and crystallization section, wet grinding is carried out, the discharge concentration is 25%, the flow rate is controlled to enter the reactor, sulfuric acid enters the reactor at a concentration of 10%, the dosage is 85% of the alkali residue amount, the residence time of the material in the reactor is controlled for 3 hours, the reaction temperature is 25 °C, and the pH value of the slurry in the crystallizer is 3.5;

[0032] ② In the flotation separation section, the slurry from the reactor enters the agitation tank for pulp adjustment, the flotation regulator enters the agitation tank for pulp adjustment, the flotation collector enters the agitation tank for pulp adjustment, the pulp is adjusted for 2 minutes, the pulp enters the flotation machine, one rough selection and two fine selections are carried out. The foam product is gypsum dihydrate, the product in the tank is silicate tailings, and after solid-liquid separation, gypsum dihydrate, tailings and salt-containing liquid phase are obtained. The content of gypsum dihydrate in the concentrate is not less than 95%, the yield is 105%, and the tailing yield is 15%.

[0033] ③ In the evaporation and salt precipitation section, the salt-containing liquid phase enters the evaporation pond. When the liquid phase concentration reaches 25%, magnesium sulfate product is precipitated. Continuing evaporation gives old brine, and after evaporation to dryness, crude magnesium sulfate product is obtained. The main component of the magnesium sulfate product is epsom salt (MgSO4·7H2O), and the yield is 70%.

[0034] Example 2, referring to Figure 1 , a treatment method for ammonia-soda process alkali residue:

[0035] A certain alkali residue, with the main components being: CaCO3 45%, Mg(OH)2 10%, CaO 6%, CaSO4 6%, CaCl2 10%, NaCl 15%, acid-insoluble substances 12%,

[0036] ① In the conversion and crystallization section, wet grinding is carried out, the discharge concentration is 25%, the flow rate is controlled to enter the reactor, sulfuric acid enters the reactor at a concentration of 15%, the dosage is 85% of the alkali residue amount, the residence time of the material in the reactor is controlled for 3 hours, the reaction temperature is 25 °C, and the pH value of the slurry in the crystallizer is 3.5;

[0037] ② Flotation separation section: The reactor slurry enters the agitation tank for pulp conditioning. The flotation regulator enters the agitation tank for pulp conditioning. The flotation collector enters the agitation tank for pulp conditioning. After 3 minutes of pulp conditioning, the slurry enters the flotation machine for one rough selection and two fine selections. The foam product is the concentrate, mainly composed of calcium sulfate dihydrate. The product in the cell is the tailings, mainly composed of silicate. After solid-liquid separation, calcium sulfate dihydrate, tailings, and salt-containing liquid phase are obtained. The grade of calcium sulfate dihydrate in the concentrate is not less than 95%, the yield is 110%, and the yield of the tailings is 18%.

[0038] ③ Evaporation and salt precipitation section: The salt-containing liquid phase enters the evaporation pond. When the liquid phase concentration reaches 15%, sodium chloride product is precipitated, and the yield is 20%. When the evaporation continues until the liquid phase concentration reaches 20%, magnesium chloride product is precipitated. Continuing evaporation yields mother liquor, and drying gives crude magnesium chloride product. The main components of the magnesium chloride product are bischofite and epsomite (MgCl2·6H2O and MgSO4·7H2O), and the yield is 60%.

[0039] Example 3, referring to Figure 1 , the treatment method of ammonia-soda process alkali residue:

[0040] A certain alkali residue, the main components are: CaCO3 45%, Mg(OH)2 10%, CaO 6%, CaSO4 6%, CaCl2 10%, NaCl 15%, acid-insoluble matter 12%.

[0041] ① Conversion and crystallization section: Wet grinding, the discharge concentration is 10%, and it is controlled to flow into the reactor. Sulfuric acid enters the reactor at a concentration of 15%, and the dosage is 85% of the alkali residue amount. The residence time of the material in the reactor is controlled for 3 hours, the reaction temperature is 25 °C, and the pH value of the slurry in the crystallizer is 3.5.

[0042] ② Flotation separation section: The reactor slurry enters the agitation tank for pulp conditioning. The flotation regulator enters the agitation tank for pulp conditioning. The flotation collector enters the agitation tank for pulp conditioning. After 3 minutes of pulp conditioning, the slurry enters the flotation machine for one rough selection and two fine selections. The foam product is the concentrate, mainly composed of calcium sulfate dihydrate. The product in the cell is the tailings, mainly composed of silicate. After solid-liquid separation, calcium sulfate dihydrate, tailings, and salt-containing liquid phase are obtained. The grade of calcium sulfate dihydrate in the concentrate is not less than 95%, the yield is 110%, and the yield of the tailings is 18%.

[0043] ③ When the concentration of the salt-containing liquid phase is 3%, sodium carbonate is added to adjust the pH value to 6.0 - 8.0, and the ion content in the water meets the national environmental protection requirements and can be directly discharged.

Claims

1. A method for treating soda residue by the ammonia-soda process, characterized in that: The method includes three steps: conversion crystallization, flotation separation, and evaporation for salt precipitation; Conversion crystallization: It is the reaction of alkali residue with sulfuric acid to generate calcium sulfate; Flotation separation: It is to separate calcium sulfate from silicate impurities by flotation; Evaporation for salt precipitation or adjusting pH value to meet the discharge standard: Evaporation for salt precipitation is to evaporate the salt-containing liquid phase, and through controlling the evaporation amount, sodium salts and magnesium salts are precipitated at different stages; Adjusting pH value to meet the discharge standard means that when the concentration of the salt-containing liquid phase is lower than 5%, the pH value of the liquid phase obtained from flotation separation is adjusted and then discharged up to the standard.

2. The treatment method of ammonia-soda process alkali residue according to claim 1, wherein During conversion crystallization: the reaction temperature is 10 - 40 °C, the reaction time is 2 - 6 hours, and the pH value of the liquid phase in the reactor is 1.0 - 6.

0.

3. The treatment method of ammonia-soda process alkali residue according to claim 1, characterized in that, Positive flotation process is adopted for flotation separation, and calcium sulfate is concentrated in the foam product.

4. The treatment method of ammonia-soda process alkali residue according to claim 1, characterized in that, The steps are as follows: ① Conversion crystallization: The alkali residue enters the grinding mill and is ground to a particle size finer than 100 mesh. If the particle size of the alkali residue is uniform and finer than 100 mesh, this operation can be omitted; the ground slurry is fed into the reaction crystallizer, and sulfuric acid is added to control the pH value of the liquid phase in the reaction crystallizer between 1.0 and 6.0; ② Flotation separation: The slurry discharged from the reaction crystallizer enters the stirring tank, the flotation regulator enters the stirring tank, the flotation collector enters the stirring tank, and the slurry is adjusted for 1 - 20 minutes. Then the slurry enters the flotation machine for flotation. The foam product is the calcium sulfate product, and the product in the tank is the silicate tailings; the foam product is filtered and dewatered, the solid phase is the calcium sulfate product, and the liquid phase enters the evaporation for salt precipitation section; the product in the tank is filtered and dewatered, the solid phase is the silicate tailings, and the liquid phase enters the evaporation for salt precipitation section; ③ Evaporation for salt precipitation: The liquid phase in the flotation separation section converges to the collection tank. After evaporating a certain amount of water, sodium chloride starts to precipitate. Before the magnesium salt precipitates, solid-liquid separation is carried out to obtain the sodium chloride product; the liquid phase is further evaporated, and the magnesium salt precipitates until old brine is obtained or finally evaporated to dryness; magnesium chloride product, magnesium sulfate product or a mixture of both are obtained.

5. The treatment method of ammonia-soda process alkali residue according to claim 4, characterized in that, The specific steps are as follows: ① Conversion crystallization: Wet grinding, the discharge concentration is 10 - 40%, the flow rate is controlled to enter the reactor, sulfuric acid enters the reactor at a concentration of 10 - 50%, and the dosage is 80 - 100% of the alkali residue amount. The residence time of the material in the reactor is controlled for 2 - 8 hours, the reaction temperature is 10 - 40 °C, and the pH value of the slurry in the crystallizer is 1.0 - 6.0; ② Flotation separation: The slurry from the reactor enters the stirring tank for slurry adjustment, the flotation regulator enters the stirring tank for slurry adjustment, the flotation collector enters the stirring tank for slurry adjustment, and the slurry is adjusted for 1 - 20 minutes. Then the slurry enters the flotation machine for one rough selection and 1 - 4 fine selections. The foam product is calcium sulfate dihydrate, the product in the tank is the silicate tailings. After solid-liquid separation, calcium sulfate dihydrate, tailings and salt-containing liquid phase are obtained; ③ Evaporation for salt precipitation: The salt-containing liquid phase enters the evaporation pond. When the liquid phase concentration reaches 15 - 30%, products are precipitated. Continuing evaporation gives old brine, and evaporating to dryness gives magnesium chloride product, magnesium sulfate product or a mixture of both.

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