A method for resource utilization of alkali residue through in-situ stirring and ex-situ dewatering and solidification

Abstract

This invention provides a method for the resource utilization of alkali slag through in-situ stirring and ex-situ dehydration and consolidation, belonging to the technical field of comprehensive treatment and resource utilization of industrial solid waste. The method provided by this invention includes the following steps: 1) Dechlorination stage: In the alkali slag tank, incremental wet slag is used to flush the existing stock, and fly ash is added and stirred in-situ to obtain mixed wet slag; 2) Solid-liquid separation stage: a) After treating the foundation outside the alkali slag tank, concrete flooring is poured, anti-corrosion coating is applied, fiberglass grating is laid, and geotextile bags with permeable pipes fixed at the bottom are laid in sequence; b) The mixed wet slag obtained in step 1) is pumped into the geotextile bags with permeable pipes fixed at the bottom for dehydration, thus obtaining solid and liquid substances. Based on the high moisture content of alkali slag, this invention adopts ex-situ overhead measures to implement solid-liquid separation of the mixture by gravity. Through separation, solid and liquid are disposed of separately, achieving the purpose of harmless treatment and comprehensive resource utilization of alkali slag.

Description

Technical Field

[0001] This invention belongs to the field of industrial solid waste comprehensive treatment and resource utilization technology, and in particular relates to a method for the resource utilization of alkaline residue through in-situ stirring and ex-situ dehydration and consolidation. Background Technology

[0002] Currently, the treatment of alkali residue produced by the ammonia-soda process remains a global challenge. The difficulties in treating alkali residue lie in its high moisture content, high pH value, and small amounts of heavy metals. Existing technologies still employ plate and frame filter presses and acid washing processes to treat alkali residue. These technologies only address the moisture content issue, providing a temporary solution rather than a permanent one. Furthermore, the acid washing process introduces secondary pollution problems and suffers from drawbacks such as high cost, high energy consumption, long cycle time, and complex procedures. Summary of the Invention

[0003] In view of this, the purpose of this invention is to provide a method for the resource utilization of alkali residue through in-situ stirring and ex-situ dehydration and consolidation. Based on the high moisture content characteristic of alkali residue, this invention adopts in-situ mixing and ex-situ dehydration measures to achieve solid-liquid separation of the alkali residue mixture. Through solid-liquid separation, solids and liquids are disposed of separately, achieving the goal of harmless and comprehensive resource utilization of the alkali residue. The method provided by this invention is relatively simple to operate and easy to implement.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for the resource utilization of alkaline residue through in-situ stirring, ex-situ dehydration, and consolidation, comprising the following steps: 1) Chlorine reduction stage: In the alkali slag tank, the existing amount is flushed with incremental wet slag and fly ash is added and stirred in situ to obtain mixed wet slag; 2) Solid-liquid separation stage: a. After treating the foundation outside the alkali slag pond, the concrete floor is poured, anti-corrosion coating is applied, fiberglass grating is laid, and geotextile bags with bottom-fixed permeable pipes are laid in sequence. b) Pump the mixed wet slag obtained in step 1) into a geotextile bag with a fixed permeable pipe at the bottom for dewatering, thus obtaining solid and liquid substances.

[0005] Preferably, it also includes: filling the geotextile bags with the bottom fixed permeable pipes with water and stacking them alternately, that is, laying them up alternately and stacking them layer by layer.

[0006] Preferably, it also includes: laying slope protection bags and planting greenery along the outer edge of the alternately stacked geotextile bags, or erecting sunshade nets on the alternately stacked geotextile bags.

[0007] Preferably, the method also includes repeatedly rinsing the alternately stacked geotextile bags with natural rainfall or artificial precipitation to obtain solids with reduced water-soluble harmful media.

[0008] Preferably, the mass ratio of the incremental wet slag to fly ash is 7-9:1-3.

[0009] Preferably, the mass ratio of the incremental wet slag to fly ash is 8:2.

[0010] Preferably, the stirring time is 2 to 6 hours.

[0011] Preferably, the stirring time is 3 to 5 hours.

[0012] The present invention also provides a method for the resource utilization of alkaline residue by in-situ stirring and ex-situ dehydration and consolidation, which yields solid material that can be used as engineering soil for backfilling.

[0013] The present invention also provides a method for the resource utilization of alkaline residue by in-situ stirring and ex-situ dehydration and consolidation, the solid-liquid separation stage of which can be applied in the leaching of improved saline-alkali soil.

[0014] This invention addresses the treatment of alkaline sludge by employing an in-situ mixing and stirring process within a treatment tank, followed by off-site dewatering. Specifically, fly ash is added to the treatment tank, and repeated stirring solidifies chloride ions and heavy metals. The solidified sludge is then pumped to an off-site geotextile bag for gravity-fed filtration and dewatering. The alkaline sludge is then suspended above a fiberglass grating, allowing the waste liquid to flow downwards into a drainage ditch and collect in a collection well, achieving solid-liquid separation. Attached Figure Description

[0015] Figure 1 This is a diagram showing the amount of alkali residue in Example 1; Figure 2 This is a schematic diagram of the operation platform for the alkali sludge dechlorination technology in Example 1; Figure 3 This is a schematic diagram of the overhead solid-liquid separation technology outside the alkali residue tank in Example 1; Figure 4 This is a process flow diagram for treating alkaline residue in Example 1. Detailed Implementation

[0016] This invention provides a method for the resource utilization of alkaline residue through in-situ stirring, ex-situ dehydration, and consolidation, comprising the following steps: 1) Chlorine reduction stage: In the alkali slag tank, the existing amount is flushed with incremental wet slag and fly ash is added and stirred in situ to obtain mixed wet slag; 2) Solid-liquid separation stage: a. After treating the foundation outside the alkali slag pond, the concrete floor is poured, anti-corrosion coating is applied, fiberglass grating is laid, and geotextile bags with bottom-fixed permeable pipes are laid in sequence. b) Pump the mixed wet slag obtained in step 1) into a geotextile bag with a fixed permeable pipe at the bottom for dewatering, thus obtaining solid and liquid substances.

[0017] In this invention, the alkaline residue (referred to as "white mud") produced by the ammonia-soda process is mainly composed of calcium salts. Its high chlorine content and high water content (60-80%) are key bottlenecks restricting its resource utilization.

[0018] The chemical composition (main mass fraction) of the alkaline residue described in this invention is as follows: Calcium carbonate (CaCO3): 40-65%. Skeletal component.

[0019] Calcium chloride (CaCl2): 4-13%. Highly hygroscopic, and a major source of chloride ions.

[0020] Calcium hydroxide [Ca(OH)2]: 4-11%. The main substance providing alkalinity.

[0021] Sodium chloride (NaCl): 4-11%. A soluble salt and one of the sources of chloride ions.

[0022] Calcium sulfate (CaSO4): 2-15%. Participates in hydration reactions.

[0023] Other: Contains small amounts of MgO (3-12%), SiO2 (1-11%), and Al2O3 (1-3%).

[0024] The alkaline residue solution is strongly alkaline, with a pH value between 10 and 12.

[0025] The fly ash used in this invention can be sourced from conventional products in the field. The purpose of adding fly ash in this invention is to increase the solidification strength of the solid by chemically reacting chloride ions and a small amount of heavy metals.

[0026] In this invention, the main purpose of mixing fly ash into the slag pool is to address the issues of consolidating chloride ions to lower the pH value and consolidating a small amount of heavy metals.

[0027] In this invention, it is preferable to use wet slag with high water content to flush out the stock, which can significantly reduce water consumption.

[0028] In this invention, it is preferable to dilute the wet slag with water at a mass ratio of 9:1 according to the actual site conditions. This facilitates in-situ mixing in the slag pool, avoids the use of large mixers and other equipment, reduces energy consumption and increases efficiency. In-situ mixing of large volumes of wet slag is much more efficient than using a mixer.

[0029] In this invention, the preferred mass ratio of wet slag to fly ash is 8:2, and it is preferred to mix and stir simultaneously for 3 to 5 hours.

[0030] In this invention, the dry mass ratio of the alkali residue to fly ash is preferably 7:3.

[0031] In this invention, the purpose of adding fly ash to the alkali slag and stirring is to fully generate a chemical reaction during the stirring process; the stirring time is directly proportional to the effect of consolidating chloride ions; to increase the degree of consolidation after engineering geotechnical work; and to effectively limit the possibility of alkali slag absorbing water and swelling again.

[0032] In this invention, the combination of alkali residue and fly ash, along with a well-coordinated construction method, creates a technological closure, which has significant advantages.

[0033] In this invention, it is preferable to mix and stir alkali slag and fly ash, using the alkali slag to activate the fly ash; the two are the best "golden combination." In the resource utilization of alkali slag, fly ash can play a role in activating the chemical reaction that strengthens the curing. Fly ash itself has very low activity, and alkali slag acts as an activator. Its high alkalinity and chloride salts act like a "catalyst," disrupting the stable glassy structure of fly ash, prompting it to release its internal medium and recombine and solidify. Alkali slag provides a calcium source and an alkaline environment, while fly ash provides active aluminum and silicon ions. The reaction generates "Friedel salts," which "lock" chloride ions in the form of mineral crystals through a chemical reaction, solidifying them within the gel and greatly reducing the risk of leaching. During the chemical reaction, heavy metals are physically adsorbed and chemically bonded, and hydration reactions generate "geopolymers" such as CSH gel and NASH gel. Like glue, these bind loose particles together, fixing conventional heavy metal ions within the generated gel structure, effectively improving the strength of the mixture.

[0034] In this invention, the foundation outside the alkali slag pond is preferably backfilled with a deficit, and the method of backfilling the deficit adopts the technology of reinforcing the under-consolidated layer in the authorized patent with publication number CN113684815B.

[0035] In this invention, the consolidation settlement is very large and the backfill volume is large. The method of filling the backfill first when the volume is insufficient saves the amount of work in subsequent processes.

[0036] After the foundation is treated according to the present invention, the post-construction parameter f ak With a strength of ≥200kPa and Es≥28MPa, after consolidation, no harmful media will seep into the ground and pollute groundwater resources; the excavation of the water collection well foundation pit can be carried out without support, saving time and money, and ensuring construction safety; pollutants have an additional layer of consolidation protection.

[0037] In this invention, the concrete floor is preferably poured with a 1% slope, and the ground is pre-sloped to facilitate wastewater flowing into the drainage ditch and collecting in the collection well. The wastewater is treated separately.

[0038] In this invention, all concrete surfaces must be coated with anti-corrosion paint to protect the concrete structure from corrosion.

[0039] In this invention, the fiberglass grating is preferably laid in 2 to 3 layers to elevate all materials and facilitate rapid wastewater discharge.

[0040] In this invention, the laying of geotextile bags involves filling geotextile bags with fluid materials because soft materials are easy to fill, have a large volume, good permeability, are easy to stack, and can be preloaded.

[0041] In this invention, it is preferable to fix a permeable pipe at the bottom of the geotextile bag, preferably at a Φ50@1000 ratio, and then fill the bag with fluid material in batches. This allows for simultaneous filling and drainage of wastewater under its own weight, effectively shortening the drainage consolidation cycle; and the pre-fixing of the permeable pipe prevents drifting when soft materials are filled.

[0042] In this invention, it is preferable to fill the tube bags in batches until they are full; while filling and discharging wastewater, the filling capacity of the tube bags is increased.

[0043] This invention employs gravity-based pressure filtration, which reduces energy consumption, optimizes the process, and yields significant results.

[0044] In this invention, it is preferable to stack the tubes and bags alternately, that is, after the tubes and bags are filled, they are arranged alternately upwards, layer by layer, so that the permeable pipes are alternately placed between the two. When the permeable pipes are under force, they will deform downwards in the gaps, which facilitates the depressurization and discharge of wastewater. The layered stacking results in the effect of self-weight filtration. The residual water-soluble harmful media are repeatedly washed away by natural rainfall or artificial precipitation.

[0045] In this invention, it is preferable to lay slope protection bags, that is, to fully cover the outer edge; due to their large size and long disposal cycle, the bag material is easily aged due to the influence of ultraviolet rays; the protection bags themselves carry plant seeds, which will germinate and regreen when it rains, increasing the appearance of the storage yard.

[0046] In this invention, because the geotextile bags are made of polypropylene, they are prone to aging and becoming brittle under the influence of ultraviolet radiation and high temperatures. Therefore, slope protection and vegetation bags need to be laid along the outer edge to provide cooling and protection with greenery. Considering the impact of high temperatures in summer, sunshade nets need to be erected for cooling.

[0047] In this invention, natural rainfall is preferred for rinsing, and repeated rinsing is used to remove residual water-soluble harmful media. Whether it is natural rainfall or artificial precipitation, repeated rinsing reduces the amount of residual water-soluble harmful media, thus meeting environmental protection requirements.

[0048] This invention focuses on solving the problem of high pH value until it drops to 6-8, and after solidification, it meets the requirements of national environmental protection standards.

[0049] This invention completes in-situ stirring in the slag pool and then transports it to another location, relying on gravity for filtration, thus solving the problems of high water content and residual water-soluble harmful media.

[0050] The present invention also provides the application of the solid material obtained by the above-mentioned method of in-situ stirring and ex-situ dehydration and consolidation for resource utilization of alkali residue in the preparation of engineering soil.

[0051] In this invention, the soil is preferably prepared as engineering soil. Based on the authorized patent CN113684815B, if the construction period is greater than 4 months and the treatment depth of under-consolidated soil is less than 20m, the post-construction parameters can reach f. ak =500-800kPa, Es≥38-45MPa, these parameters can meet any engineering and environmental protection requirements.

[0052] In this invention, the moisture content of the engineering soil is preferably 40-60%, and the authorized patented construction method has the function of in-situ water squeezing and consolidation.

[0053] In addition to engineering soil, the solid material of this invention can be mixed with materials such as slag to achieve a solidification effect that is twice as effective as possible, depending on the high performance requirements of the final product or the presence of special pollutants.

[0054] The present invention also provides a method for the resource utilization of alkaline residue by in-situ stirring and ex-situ dehydration and consolidation, the solid-liquid separation stage of which can be applied in the leaching of improved saline-alkali soil.

[0055] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0056] Example 1 The ammonia-soda process for producing alkali uses limestone, sodium chloride, ammonia, and additives as raw materials to produce soda ash, baking soda, baking soda-based daily chemical products, and marine products. It discharges massive amounts of alkali residue, creating the "white sea" phenomenon. Figure 1 .

[0057] Alkali residue is a white paste, commonly known as white mud. Its chemical composition is mainly non-toxic inorganic compounds. It is characterized by small particle size, large pores, and strong alkalinity (pH: 10-12) in aqueous solution. The particles are usually negatively charged and have sol properties.

[0058] The main chemical elements of alkali residue are Ca, Cl, Mg, Na, Si, and Al. The main chemical components are CaCO3, CaCl2, NaCl, Ca(OH)2, CaSO4, Mg(OH)2, SiO2, Al2O3, and some other salts and water-insoluble substances. The mass fraction of the chemical components of alkali residue is shown in Table 1.

[0059] Table 1

[0060] This invention treats alkaline residue by employing an in-situ mixing method within the tank followed by ex-situ dewatering outside the tank (see flowchart). Figure 4 ),as follows: In the alkaline slag tank, the following method is used: incremental flushing of the existing stock → water dilution → mixing with fly ash → conveying the liquid mixed wet slag to the geotextile bag outside the site using a pipeline pump. Because the alkali residue in the pool has a very high water content, the personal safety of construction workers must be ensured during operation. During the operation, red life jackets and safety helmets must be worn to prevent safety hazards. Since the residue pool is white and vast, working in the vicinity for a long time can easily lead to snow blindness, so sunglasses must be worn for protection. Large-volume foam blocks should be laid around the mixing work area. A lightweight, corrosion-resistant structural material should be installed on top of the foam blocks, followed by a fiberglass grating or bamboo raft. A guardrail should be erected around the perimeter for ease of manual operation and safety. (See attached image.) Figure 2 (Legend: 1-mixing tank; 2-alkali residue tank surface; 3-foam block; 4-fixture; 5-component; 6-walkway slab; 7-guardrail; 8-progressive ramp; 9-dam) Outside the alkali slag pond, to prevent the leakage of harmful waste liquid and damage to groundwater resources, the post-construction parameters of the foundation treatment must meet the following requirements: f ak ≥200kPa, compression modulus Es≥28MPa → Excavate the foundation pit for the water collection tank → Pour concrete for the water collection tank and ground → Slope the ground at a 1% gradient towards the drainage ditch → Apply anti-corrosion coating to all concrete surfaces → Lay 1-3 layers of fiberglass grating on the ground → Fix rigid permeable pipes wrapped with filter cloth to the bottom of the geotextile bags radially at Φ50@1000 to increase permeability → Lay the geotextile bags on the grating → Fill and stack them sequentially → Lay slope protection greening bags along the outer edge and plant greenery, see Figure 3 (Legend: 1-Drainage ditch; 2-Fiberglass grating; 3-Geotextile bag; 4-Slope protection bag; 5-Greenery; 6-Rigid permeable pipe) The effects achieved are as follows: 1. By mixing in fly ash, the pH value is reduced, and chloride ions and heavy metals are solidified; 2. By using the self-weight filtration of the alkaline residue mixture, the moisture content is reduced; 3. By using natural rainfall or artificial spraying, the water-soluble media remaining in the mixture are repeatedly washed and filtered by self-weight, flowing from top to bottom through the permeable pipe, from the bottom of the grid into the drainage ditch, and finally into the collection tank.

[0061] The engineering soil prepared by the above method was applied to the third fully intelligent wharf project in Tianjin, covering an area of ​​1 million square meters. 2 The massive amount of alkali residue comes from the Tianjin Alkali Plant.

[0062] This project utilizes the applicant's authorized invention patent ZL20211095126.1 (CN113684815B) "A Method for Solid-Liquid Separation of High-Moisture-Content Soft Materials" for technical support. The project involves pre-filling the site with engineering soil prepared according to this invention, without any added materials. After dynamic consolidation, the post-construction parameters include: characteristic value f of the foundation bearing capacity.ak >200KPa, compression modulus Es>28MPa, far exceeding national standards and design requirements.

[0063] The mixture is subjected to external dynamic consolidation based on its strength, resulting in high post-processing parameters, with a chloride ion consolidation rate of >98%, a pH value of <8, no leaching risk, and compliance with environmental protection requirements.

[0064] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for the resource utilization of alkaline residue through in-situ stirring, ex-situ dehydration, and consolidation, comprising the following steps: 1) Chlorine reduction stage: In the alkali slag tank, the existing amount is flushed with incremental wet slag and fly ash is added and stirred in situ to obtain mixed wet slag; 2) Solid-liquid separation stage: a. After treating the foundation outside the alkali slag pond, the concrete floor is poured, anti-corrosion coating is applied, fiberglass grating is laid, and geotextile bags with bottom-fixed permeable pipes are laid in sequence. b) Pump the mixed wet slag obtained in step 1) into a geotextile bag with a fixed permeable pipe at the bottom for dewatering, thus obtaining solid and liquid substances.

2. The method for resource utilization of alkaline residue through in-situ stirring and ex-situ dehydration and consolidation as described in claim 1, characterized in that, It also includes the following steps: After filling the geotextile bags with the bottom permeable pipes as described in step 2), stack them alternately, that is, lay them up alternately, layer by layer.

3. The method for resource utilization of alkaline residue through in-situ stirring and ex-situ dehydration and consolidation as described in claim 2, characterized in that, It also includes the following steps: Slope protection bags can be laid along the outer edge of the alternately stacked geotextile bags and planted with greenery, or sunshade nets can be erected on the alternately stacked geotextile bags.

4. The method for resource utilization of alkaline residue through in-situ stirring and ex-situ dehydration and consolidation as described in claim 2, characterized in that, It also includes the following steps: By repeatedly rinsing alternatingly stacked geotextile bags with natural rainfall or artificial precipitation, solids with reduced water-soluble harmful media are obtained.

5. The method for resource utilization of alkaline residue through in-situ stirring and ex-situ dehydration and consolidation as described in claim 1, characterized in that, In step 1), the mass ratio of incremental wet slag to fly ash is 7-9:1-3.

6. The method for resource utilization of alkaline residue through in-situ stirring and ex-situ dehydration and consolidation as described in claim 1, characterized in that, In step 1), the mass ratio of incremental wet slag to fly ash is 8:

2.

7. The method for resource utilization of alkaline residue through in-situ stirring and ex-situ dehydration and consolidation as described in claim 1, characterized in that, The stirring time in step 1) is 2 to 6 hours.

8. The method for resource utilization of alkaline residue through in-situ stirring, ex-situ dehydration, or consolidation as described in claim 1, characterized in that... The stirring time in step 1) is 3 to 5 hours.

9. The solid material obtained by the method of in-situ stirring and ex-situ dehydration and consolidation of alkaline slag according to any one of claims 1 to 8 is used as engineering soil for backfilling.

10. The method for resource utilization of alkaline residue by in-situ stirring and ex-situ dehydration and consolidation as described in any one of claims 1 to 8 can be applied in the leaching of improved saline-alkali soil during the solid-liquid separation stage.

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