A method for solidifying chromium in coal gasification ash and the resulting low-chromium-migration, high-content coal gasification ash-based cementitious backfill material.

Abstract

This invention discloses a method for solidifying chromium in coal gasification ash and the resulting low-chromium-migration, high-content coal gasification ash-based cemented backfill material, relating to the fields of solid waste resource utilization and heavy metal solidification technology. The solidification method includes mixing coal gasification ash with gangue, steel slag, cementing material, and water to prepare a low-chromium-migration, high-content coal gasification ash-based cemented backfill material, thereby solidifying the chromium in the coal gasification ash. The raw materials for the cementing material include slag and an alkali activator. The low-chromium-migration, high-content coal gasification ash-based cemented backfill material prepared by this solidification method exhibits strong chromium solidification capacity, low cost, high utilization rate of coal-based solid waste, and significant comprehensive benefits.

Description

Technical Field

[0001] This invention relates to the fields of solid waste resource utilization and heavy metal solidification technology, and in particular to a method for solidifying chromium in coal gasification ash and slag, and the resulting low-chromium-migration, high-volume coal gasification ash-based cementitious backfill material. Background Technology

[0002] Currently, in the field of clean coal utilization, coal gasification technology is widely promoted due to its ability to efficiently and cleanly utilize coal resources. However, the associated coal gasification ash has a complex chemical composition, easily inducing heavy metal pollution. Chromium, especially highly toxic hexavalent chromium, has extremely high solubility and mobility. If it leaks into soil or water bodies, it will spread rapidly, posing a serious threat to ecosystems and human health. Traditional coal gasification ash treatment methods have poor chromium solidification stability, making it difficult to curb chromium diffusion. Therefore, how to effectively and stably solidify chromium in coal gasification ash is a major problem currently faced. Summary of the Invention

[0003] The purpose of this invention is to provide a method for solidifying chromium in coal gasification ash and a low-chromium-migration, high-volume coal gasification ash-based cementitious backfill material. This invention uses steel slag and mineral slag as solidification materials for chromium in coal gasification ash. By adding an alkaline activator to activate the coal gasification ash, steel slag, and mineral slag, the invention achieves effective and stable solidification of chromium in the coal gasification ash.

[0004] To achieve the above objectives, the present invention provides the following solution:

[0005] One of the technical solutions of the present invention is a method for solidifying chromium in coal gasification ash, wherein coal gasification ash is mixed with gangue, steel slag, cementing material and water to prepare a low-chromium-migration, high-volume coal gasification ash-based cementitious filling material, so as to achieve solidification of chromium in coal gasification ash.

[0006] The raw materials for the cementitious material include slag and alkali activator.

[0007] This invention utilizes gangue, steel slag, and cementing materials to solidify chromium in coal gasification ash. The alkaline oxides in the steel slag neutralize the acidity of the coal gasification ash, thereby promoting chromium precipitation. Gangue possesses certain physical adsorption properties, enabling the adsorption and fixation of chromium-containing substances. Simultaneously, under the activation of an alkaline activator, the gangue, slag, and steel slag in the cementing materials form a relatively stable cementitious phase, further solidifying the chromium. The synergistic effect of gangue, steel slag, and cementing materials effectively solidifies chromium in coal gasification ash, significantly reducing the migration of chromium in the resulting high-volume coal gasification ash-based cemented backfill material.

[0008] Furthermore, steel slag, ore slag, and gangue are all bulk industrial solid wastes, which not only occupy land resources but also have adverse effects on the ecological environment. This invention utilizes steel slag, ore slag, and gangue to solidify the chromium element in coal gasification ash, thereby obtaining a high-performance cemented backfill material and realizing the resource utilization of industrial solid waste.

[0009] Furthermore, the coal gasification ash residue includes coarse coal gasification ash residue and fine coal gasification ash residue.

[0010] Furthermore, the mass ratio of the coarse coal gasification ash residue, fine coal gasification ash residue, gangue, steel slag, and cementing material is 12–20:6–10:3–5:1–3:3–6. The mass of the coarse and fine coal gasification ash residues is expressed as dry matter content.

[0011] Furthermore, the mass concentration of the solid component in the low-chromium-migration, high-volume coal gasification ash-based cementitious backfill material is 50-60%.

[0012] The third technical solution of the present invention: a low-chromium-migration, high-volume coal gasification ash-based cementitious backfill material, the raw materials of which include coarse coal gasification ash, fine coal gasification ash, gangue, steel slag and cementing materials in a mass ratio of 12-20:6-10:3-5:1-3:3-6, as well as water;

[0013] The mass concentration of the solid component in the low-chromium-migration, high-volume coal gasification ash-based cementitious filling material is 50-60%.

[0014] The mass of coarse and fine coal gasification ash residue is measured by solid content. Therefore, the amount of water used needs to be adjusted based on the moisture content of the coarse and fine coal gasification ash residue and the mass concentration of the solid components in the desired cemented backfill material. Since the coarse and fine coal gasification ash residues contain a large amount of water, the water content in these residues must be deducted when determining the water amount based on the desired mass concentration of the solid components in the cemented backfill material.

[0015] Furthermore, the raw materials of the cementitious material include mechanically activated coal gasification ash slag, mineral slag, and alkali activator in a mass ratio of 1-3:1-3:1-3.

[0016] Furthermore, the coarse slag from the coal gasification ash has a particle size of 0.15–2 mm, excluding 0.15 mm, and is used as one of the aggregates in the filling material.

[0017] Coal gasification ash coarse slag is formed by inorganic mineral slag flowing into the bottom of the gasifier and cooling into particles. It has a variety of shapes, a glassy luster on the surface, low carbon content, and is mainly composed of crystalline minerals.

[0018] Furthermore, the fine slag from the coal gasification ash has a particle size ≤0.15mm, which can fill the voids in the material and accelerate the hydration of the cementitious material.

[0019] The fine ash residue from coal gasification is a fine particle separated from the syngas during subsequent gas purification. It is mostly in powder form, has a high carbon content, and is mainly composed of amorphous glass.

[0020] Coarse coal gasification ash and fine coal gasification ash are two types of solid waste with different morphologies, sizes, and compositions, produced in different parts of the gasifier during the coal gasification process.

[0021] Furthermore, the mechanically activated coal gasification ash coarse slag is obtained by ball milling the dried coal gasification ash coarse slag (dried to a moisture content ≤1%) to D. 50 =10~18 micrometers and D 90 =38-58 micrometers.

[0022] Mechanical activation enhances the pozzolanic effect by disrupting the dense structure of the glass and exposing the amorphous aluminosilicate active components in the coarse slag.

[0023] Furthermore, the raw materials for the alkaline activator include water glass, NaOH, and water in a mass ratio of 8-12:1-3:6-10.

[0024] Furthermore, the modulus of the water glass is 3.3.

[0025] Furthermore, the particle size of the gangue is 2-5 mm, excluding 2 mm.

[0026] Furthermore, the preparation steps of the low-chromium-migration, high-dosage coal gasification ash-based cementitious backfill material specifically include (flowchart shown in the figure). Figure 1 As shown):

[0027] S1. Use a crusher to crush the gangue and screen out gangue with a particle size of 2-5mm (excluding 2mm);

[0028] S2. After drying some of the coarse coal gasification ash residue to a moisture content ≤1%, the dried coarse coal gasification ash residue is ball-milled to D using a ball mill. 50 =10~18 micrometers, D 90 =38~58 micrometers, to obtain mechanically activated coal gasification ash coarse slag (referred to as mechanically activated coarse slag);

[0029] S3. Mix water glass, NaOH and water evenly to obtain an alkaline activator;

[0030] S4. Mix mechanically activated coarse slag, slag, alkali activator and a small amount of water evenly to obtain cementitious material;

[0031] S5. Mix the cementitious material, steel slag, coarse coal gasification ash residue, fine coal gasification ash residue, gangue, and water (the amount of water is based on the slurry quality, i.e., the mass concentration of the solid components is 50-60%. When calculating the amount of water, the moisture contained in the coarse and fine coal gasification ash residues must be excluded). Stir until a uniform state is obtained to obtain a low-chromium migration, high-volume coal gasification ash-based cementitious filling material.

[0032] The third technical solution of the present invention: the application of a method for solidifying chromium in the above-mentioned coal gasification ash residue in the resource utilization of solid waste or the solidification of heavy metals.

[0033] This invention proposes using alkali activator-activated mechanically activated coal gasification ash as a cementing material, and coal gangue with a particle size of 2-5 mm and coarse coal gasification ash with a particle size of 0.15-2 mm as aggregates to prepare a cemented filling material. This method effectively and stably solidifies the chromium element in the coal gasification ash, aiming to provide a method for the combined solidification of chromium element in a high-volume coal gasification ash-based cemented filling material for the resource utilization of solid waste and the solidification of heavy metals.

[0034] The present invention discloses the following technical effects:

[0035] The method for solidifying chromium in coal gasification ash provided by this invention has the following advantages compared with existing methods for treating chromium in coal gasification ash:

[0036] (1) Using steel slag and blast furnace slag as solidification materials for chromium in coal gasification ash, the activity of coal gasification ash, steel slag and blast furnace slag is activated by adding alkali activator, so as to effectively and stably solidify the chromium in coal gasification ash.

[0037] (2) Mechanical activation is used to destroy the glassy structure in coal gasification ash and release active ions. Then, an alkaline activator is used to generate a geopolymer gel through a condensation reaction, which physically solidifies the chromium element. The highly toxic hexavalent chromium is reduced to almost non-toxic trivalent chromium by reducing substances such as low-valent iron in steel slag. In an alkaline environment, it easily forms insoluble hydroxides, which further reduces its mobility and toxicity. At the same time, the porous structure and large specific surface area of ​​coal gasification ash, steel slag, and gangue can capture hexavalent chromium through physical adsorption or electrostatic action, thus achieving stable solidification of the chromium element.

[0038] (3) It enables the large-scale utilization of solid waste, which is both economically feasible and environmentally friendly;

[0039] (4) Using alkaline activators to activate the activity of coal gasification ash, steel slag and slag can replace cement, reduce energy consumption and carbon emissions, and reduce the cost of backfill materials. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 This is a schematic diagram of the preparation process of the low-chromium-migration, high-dosage coal gasification ash-based cementitious backfill material of the present invention.

[0042] Figure 2 The relationship between different steel slag contents, cementitious material contents and uniaxial compressive strength of cemented filling material specimens was investigated.

[0043] Figure 3 The relationship between different steel slag and cementitious material dosages and the concentration of hexavalent chromium in the leachate of cemented filling material specimens was investigated. Detailed Implementation

[0044] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0045] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0046] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0047] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0048] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0049] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0050] In the following embodiments, comparative examples and test examples of the present invention, if room temperature is involved, it specifically refers to 20-30°C.

[0051] In the following embodiments, comparative examples, and test examples of this invention, the term "number of parts" specifically refers to "parts by mass".

[0052] Unless otherwise specified, all raw materials used in the following embodiments, comparative examples, and test examples of this invention are commercially available products. Specifically, the coarse coal gasification ash has a particle size of 0.15–2 mm (excluding 0.15 mm), a moisture content of 58%, and a hexavalent chromium content of 105.32 mg / kg; the fine coal gasification ash has a particle size ≤0.15 mm, a moisture content of 63%, and a hexavalent chromium content of 218.34 mg / kg; the cement is P·O 42.5 cement; the gangue is coal gangue; the slag is S95 grade slag; and the steel slag contains 11.35 wt% FeO, 40.92 wt% CaO, and 12.37 wt% MFe.

[0053] The amount of water added in the following examples and comparative examples is adjusted according to the moisture content of the coarse and fine coal gasification ash residues and the desired slurry concentration.

[0054] Example 1

[0055] A method for solidifying chromium in coal gasification ash residue, comprising the following steps:

[0056] S1. Use a crusher to crush the gangue and screen out gangue particles with a particle size of 2-5mm (excluding 2mm).

[0057] S2. Mechanically activate the coarse coal gasification ash residue. Specifically, dry the coarse coal gasification ash residue to a moisture content ≤1% and then ball-mill it to D. 50 =10 micrometers, D 90 =38 micrometers, yielding mechanically activated coarse slag.

[0058] S3. Mix 10 parts of 3.3-mold water glass, 2 parts of NaOH and 8 parts of water evenly to obtain an alkaline activator.

[0059] S4. Mix 2 parts of mechanically activated coarse slag, 2 parts of slag, 2 parts of alkali activator and 2 parts of water evenly to obtain a cementitious material.

[0060] S5. Mix 3 parts cementitious material, 1 part steel slag, 16 parts coarse coal gasification ash, 8 parts fine coal gasification ash, 4 parts gangue particles, and water (the amount of water is based on a slurry mass concentration of 60%, and the water content in the coarse and fine coal gasification ash must be excluded when calculating the amount of water). Stir until uniform (stirring time not less than 4 minutes) to obtain a low-chromium migration, high-volume coal gasification ash-based cementitious filling material, so as to solidify the chromium element in the coal gasification ash.

[0061] Example 2

[0062] A method for solidifying chromium in coal gasification ash residue, comprising the following steps:

[0063] S1. Use a crusher to crush the gangue and screen out gangue particles with a particle size of 2-5mm (excluding 2mm).

[0064] S2. Mechanically activate the coarse coal gasification ash residue. Specifically, dry the coarse coal gasification ash residue to a moisture content ≤1% and then ball-mill it to D. 50 =10 micrometers, D 90 =38 micrometers, yielding mechanically activated coarse slag.

[0065] S3. Mix 10 parts of 3.3-mold water glass, 2 parts of NaOH and 8 parts of water evenly to obtain an alkaline activator.

[0066] S4. Mix 2 parts of mechanically activated coarse slag, 2 parts of slag, 2 parts of alkali activator and 2 parts of water evenly to obtain a cementitious material.

[0067] S5. Mix 4.5 parts of cementitious material, 1 part of steel slag, 16 parts of coarse coal gasification ash residue, 8 parts of fine coal gasification ash residue, 4 parts of gangue particles and water (the amount of water is based on the mass concentration of the slurry being 60%), and stir until uniform (stirring time not less than 4 minutes) to obtain a low-chromium migration, high-volume coal gasification ash-based cementitious filling material, so as to solidify the chromium element in the coal gasification ash residue.

[0068] Example 3

[0069] A method for solidifying chromium in coal gasification ash residue, comprising the following steps:

[0070] S1. Use a crusher to crush the gangue and screen out gangue particles with a particle size of 2-5mm (excluding 2mm).

[0071] S2. Mechanically activate the coarse coal gasification ash residue. Specifically, dry the coarse coal gasification ash residue to a moisture content of less than 1% and then ball-mill it to D. 50 =10 micrometers, D 90 =38 micrometers, yielding mechanically activated coarse slag.

[0072] S3. Mix 10 parts of 3.3-mold water glass, 2 parts of NaOH and 8 parts of water evenly to obtain an alkaline activator.

[0073] S4. Mix 2 parts of mechanically activated coarse slag, 2 parts of slag, 2 parts of alkali activator and 2 parts of water evenly to obtain a cementitious material.

[0074] S5. Mix 6 parts of cementitious material, 1 part of steel slag, 16 parts of coarse coal gasification ash residue, 8 parts of fine coal gasification ash residue, 4 parts of gangue particles and water (the amount of water is based on the mass concentration of the slurry being 60%), and stir until uniform (stirring time not less than 4 minutes) to obtain a low-chromium migration, high-volume coal gasification ash-based cementitious filling material, so as to solidify the chromium element in the coal gasification ash residue.

[0075] Example 4

[0076] A method for solidifying chromium in coal gasification ash residue, comprising the following steps:

[0077] S1. Use a crusher to crush the gangue and screen out gangue particles with a particle size of 2-5mm (excluding 2mm).

[0078] S2. Mechanically activate the coarse coal gasification ash residue. Specifically, dry the coarse coal gasification ash residue to a moisture content ≤1% and then ball-mill it to D. 50 =10 micrometers, D 90 =38 micrometers, yielding mechanically activated coarse slag.

[0079] S3. Mix 10 parts of 3.3-mold water glass, 2 parts of NaOH and 8 parts of water evenly to obtain an alkaline activator.

[0080] S4. Mix 2 parts of mechanically activated coarse slag, 2 parts of slag, 2 parts of alkali activator and 2 parts of water evenly to obtain a cementitious material.

[0081] S5. Mix 3 parts cementitious material, 2 parts steel slag, 16 parts coarse coal gasification ash residue, 8 parts fine coal gasification ash residue, 4 parts gangue particles and water (the amount of water is based on the mass concentration of the slurry being 60%), and stir until uniform (stirring time not less than 4 minutes) to obtain a low-chromium migration, high-volume coal gasification ash-based cementitious filling material, so as to solidify the chromium element in the coal gasification ash residue.

[0082] Example 5

[0083] A method for solidifying chromium in coal gasification ash residue, comprising the following steps:

[0084] S1. Use a crusher to crush the gangue and screen out gangue particles with a particle size of 2-5mm (excluding 2mm).

[0085] S2. Mechanically activate the coarse coal gasification ash residue. Specifically, dry the coarse coal gasification ash residue to a moisture content ≤1% and then ball-mill it to D. 50 =10 micrometers, D 90 =38 micrometers, yielding mechanically activated coarse slag.

[0086] S3. Mix 10 parts of 3.3-mold water glass, 2 parts of NaOH and 8 parts of water evenly to obtain an alkaline activator.

[0087] S4. Mix 2 parts of mechanically activated coarse slag, 2 parts of slag, 2 parts of alkali activator and 2 parts of water evenly to obtain a cementitious material.

[0088] S5. Mix 4.5 parts of cementitious material, 2 parts of steel slag, 16 parts of coarse coal gasification ash residue, 8 parts of fine coal gasification ash residue, 4 parts of gangue particles and water (the amount of water is based on the mass concentration of the slurry being 60%), and stir until uniform (stirring time not less than 4 minutes) to obtain a low-chromium-migration, high-volume coal gasification ash-based cementitious filling material, so as to solidify the chromium element in the coal gasification ash residue.

[0089] Example 6

[0090] A method for solidifying chromium in coal gasification ash residue, comprising the following steps:

[0091] S1. Use a crusher to crush the gangue and screen out gangue particles with a particle size of 2-5mm (excluding 2mm).

[0092] S2. Mechanically activate the coarse coal gasification ash residue. Specifically, dry the coarse coal gasification ash residue to a moisture content ≤1% and then ball-mill it to D. 50 =10 micrometers, D 90 =38 micrometers, yielding mechanically activated coarse slag.

[0093] S3. Mix 10 parts of 3.3-mold water glass, 2 parts of NaOH and 8 parts of water evenly to obtain an alkaline activator.

[0094] S4. Mix 2 parts of mechanically activated coarse slag, 2 parts of slag, 2 parts of alkali activator and 2 parts of water evenly to obtain a cementitious material.

[0095] S5. Mix 6 parts of cementitious material, 2 parts of steel slag, 16 parts of coarse coal gasification ash residue, 8 parts of fine coal gasification ash residue, 4 parts of gangue particles and water (the amount of water is based on the mass concentration of the slurry being 60%), and stir until uniform (stirring time not less than 4 minutes) to obtain a low-chromium migration, high-volume coal gasification ash-based cementitious filling material, so as to solidify the chromium element in the coal gasification ash residue.

[0096] Example 7

[0097] A method for solidifying chromium in coal gasification ash residue, comprising the following steps:

[0098] S1. Use a crusher to crush the gangue and screen out gangue particles with a particle size of 2-5mm (excluding 2mm).

[0099] S2. Mechanically activate the coarse coal gasification ash residue. Specifically, dry the coarse coal gasification ash residue to a moisture content ≤1% and then ball-mill it to D. 50 =10 micrometers, D 90 =38 micrometers, yielding mechanically activated coarse slag.

[0100] S3. Mix 10 parts of 3.3-mold water glass, 2 parts of NaOH and 8 parts of water evenly to obtain an alkaline activator.

[0101] S4. Mix 2 parts of mechanically activated coarse slag, 2 parts of slag, 2 parts of alkali activator and 2 parts of water evenly to obtain a cementitious material.

[0102] S5. Mix 3 parts cementitious material, 3 parts steel slag, 16 parts coarse coal gasification ash residue, 8 parts fine coal gasification ash residue, 4 parts gangue particles and water (the amount of water is based on the mass concentration of the slurry being 60%), and stir until uniform (stirring time not less than 4 minutes) to obtain a low-chromium migration, high-volume coal gasification ash-based cementitious filling material, so as to solidify the chromium element in the coal gasification ash residue.

[0103] Example 8

[0104] A method for solidifying chromium in coal gasification ash residue, comprising the following steps:

[0105] S1. Use a crusher to crush the gangue and screen out gangue particles with a particle size of 2-5mm (excluding 2mm).

[0106] S2. Mechanically activate the coarse coal gasification ash residue. Specifically, dry the coarse coal gasification ash residue to a moisture content ≤1% and then ball-mill it to D. 50 =10 micrometers, D 90 =38 micrometers, yielding mechanically activated coarse slag.

[0107] S3. Mix 10 parts of 3.3-mold water glass, 2 parts of NaOH and 8 parts of water evenly to obtain an alkaline activator.

[0108] S4. Mix 2 parts of mechanically activated coarse slag, 2 parts of slag, 2 parts of alkali activator and 2 parts of water evenly to obtain a cementitious material.

[0109] S5. Mix 4.5 parts of cementitious material, 3 parts of steel slag, 16 parts of coarse coal gasification ash residue, 8 parts of fine coal gasification ash residue, 4 parts of gangue particles and water (the amount of water is based on the mass concentration of the slurry being 60%), and stir until uniform (stirring time not less than 4 minutes) to obtain a low-chromium migration, high-volume coal gasification ash-based cementitious filling material, so as to solidify the chromium element in the coal gasification ash residue.

[0110] Example 9

[0111] A method for solidifying chromium in coal gasification ash residue, comprising the following steps:

[0112] S1. Use a crusher to crush the gangue and screen out gangue particles with a particle size of 2-5mm (excluding 2mm).

[0113] S2. Mechanically activate the coarse coal gasification ash residue. Specifically, dry the coarse coal gasification ash residue to a moisture content ≤1% and then ball-mill it to D. 50 =10 micrometers, D 90 =38 micrometers, yielding mechanically activated coarse slag.

[0114] S3. Mix 10 parts of 3.3-mold water glass, 2 parts of NaOH and 8 parts of water evenly to obtain an alkaline activator.

[0115] S4. Mix 2 parts of mechanically activated coarse slag, 2 parts of slag, 2 parts of alkali activator and 2 parts of water evenly to obtain a cementitious material.

[0116] S5. Mix 6 parts of cementitious material, 3 parts of steel slag, 16 parts of coarse coal gasification ash, 8 parts of fine coal gasification ash, 4 parts of gangue particles and water (the amount of water is based on the mass concentration of the slurry being 60%), and stir until uniform (stirring time not less than 4 minutes) to obtain a low-chromium migration, high-volume coal gasification ash-based cementitious filling material, so as to solidify the chromium element in the coal gasification ash.

[0117] Comparative Example 1

[0118] A method for solidifying chromium in coal gasification ash residue, comprising the following steps:

[0119] S1. Use a crusher to crush the gangue and screen out gangue particles with a particle size of 2-5mm (excluding 2mm).

[0120] S2. Mechanically activate the coarse coal gasification ash residue. Specifically, dry the coarse coal gasification ash residue to a moisture content ≤1% and then ball-mill it to D. 50 =10 micrometers, D 90 =38 micrometers, yielding mechanically activated coarse slag.

[0121] S3. Mix 2 parts of mechanically activated coarse slag, 2 parts of slag and 2 parts of water evenly to obtain a cementitious material.

[0122] S4. Mix 3 parts of cementitious material, 1 part of steel slag, 16 parts of coarse coal gasification ash, 8 parts of fine coal gasification ash, 4 parts of gangue particles and water (the amount of water is based on the mass concentration of the slurry being 60%), and stir until uniform (stirring time is not less than 4 minutes) to obtain a high-volume coal gasification ash-based cementitious filling material.

[0123] Comparative Example 2

[0124] A method for solidifying chromium in coal gasification ash residue, comprising the following steps:

[0125] S1. Use a crusher to crush the gangue and screen out gangue particles with a particle size of 2-5mm (excluding 2mm).

[0126] S2. Mix 3 parts cement (P·O 42.5 cement), 1 part steel slag, 16 parts coarse coal gasification ash residue, 8 parts fine coal gasification ash residue, 4 parts gangue and water (the amount of water is based on the mass concentration of the slurry being 60%), and stir until uniform (stirring time not less than 4 minutes) to obtain a high-volume coal gasification ash residue-based cementitious backfill material.

[0127] Comparative Example 3

[0128] A method for solidifying chromium in coal gasification ash residue, comprising the following steps:

[0129] S1. Use a crusher to crush the gangue and screen out gangue particles with a particle size of 2-5mm (excluding 2mm).

[0130] S2. Mechanically activate the coarse coal gasification ash residue. Specifically, dry the coarse coal gasification ash residue to a moisture content ≤1% and then ball-mill it to D. 50 =10 micrometers, D 90 =38 micrometers, yielding mechanically activated coarse slag.

[0131] S3. Mix 10 parts of 3.3-mold water glass, 2 parts of NaOH and 8 parts of water evenly to obtain an alkaline activator.

[0132] S4. Mix 2 parts of mechanically activated coarse slag, 2 parts of slag, 2 parts of alkali activator and 2 parts of water evenly to obtain a cementitious material.

[0133] S5. Mix 3 parts of cementitious material, 16 parts of coarse coal gasification ash residue, 8 parts of fine coal gasification ash residue, 4 parts of gangue particles and water (the amount of water is based on the mass concentration of the slurry being 60%), and stir until uniform (stirring time is not less than 4 minutes) to obtain a high-volume coal gasification ash residue-based cementitious filling material.

[0134] Test Example 1

[0135] Chromium migration rate and compressive strength were tested on the high-volume coal gasification ash-based cementitious backfill materials prepared in each embodiment and comparative example. Specifically, the cementitious backfill material was poured into a 70.7mm×70.7mm×70.7mm triple mold with silicone oil applied to the inside, placed on a vibrator and vibrated for 30 seconds. After 24 hours, it was demolded and placed in a curing chamber at 20℃ and 95% humidity for 7 days to obtain the specimen. The migration of hexavalent chromium in the specimen was tested by the alkaline digestion method. Specifically, the specimen was immersed in a 0.28M Na2CO3 / 0.5M NaOH mixed solution at 90-95℃ for 60 minutes to allow the chromium to migrate. 6+ The chromium was stable and not reduced, and the concentration of hexavalent chromium in the leachate was determined spectrophotometrically using diphenylcarbazide. Uniaxial compressive strength was tested using a WAW-2000D microcomputer-controlled electro-hydraulic servo rock pressure testing system at a loading rate of 0.35 mm / min. The test results are shown in Table 1 and... Figure 2-3 As shown.

[0136] Table 1

[0137] Example 1 1.97 2.47 Example 2 2.11 2.36 Example 3 2.15 2.31 Example 4 2.03 2.25 Example 5 2.14 2.17 Example 6 2.19 2.12 Example 7 2.06 2.16 Example 8 2.16 2.09 Example 9 2.21 2.04 Comparative Example 1 1.31 3.56 Comparative Example 2 1.84 3.19 Comparative Example 3 1.69 5.23

[0138] The relationship between different steel slag contents, cementitious material contents, and uniaxial compressive strength of cemented filling material specimens in Examples 1-9 is as follows: Figure 2 As shown.

[0139] The relationship between different steel slag dosages, cementitious material dosages, and the concentration of hexavalent chromium in the leachate of cementitious filling material specimens in Examples 1-9 is as follows: Figure 3 As shown.

[0140] Comparative analysis of the test data of Comparative Example 1 and Example 1 shows that Comparative Example 1, which did not add an alkali activator to the cementitious material, has poor bonding ability due to insufficient activity of the cementitious material, and its strength and detoxification ability are far lower than those of Example 1. Comparative analysis of the test data of Comparative Example 2 and Example 1 shows that Comparative Example 2, which added cement (using cement to replace the cementitious material in Example 1), has slightly lower strength and detoxification ability than Example 1. This may be because the gel structure formed by the alkali-activated slag is more dense and can effectively solidify chromium ions. Comparative analysis of the test data of Comparative Example 3 and Example 1 shows that Comparative Example 3, which did not add steel slag, has slightly lower strength than Example 1 and the worst detoxification ability. This may be because the steel slag contains a large amount of low-valence metals, which can form a stable chromite spinel phase, which can effectively solidify chromium ions. Comparing the test data of Examples 1-9, it was found that as the steel slag content increased, the compressive strength of the specimens continuously increased, while the concentration of hexavalent chromium in the leachate continuously decreased and gradually approached a certain value. Similarly, as the concentration of cementitious material increased, the compressive strength of the specimens continuously increased, and the concentration of hexavalent chromium in the leachate after detoxification continuously decreased. This indicates that both the steel slag and cementitious material content have a positive effect on the compressive strength and chromium fixation capacity of the material, but the effect of steel slag on chromium fixation capacity is more significant, while the effect of cementitious material on compressive strength is more significant. The concentration of hexavalent chromium in the leachate of a mixed sample with a ratio of 2:1 of coarse coal gasification slag (dried and sieved) and fine coal gasification slag (dried and sieved) was measured to be 25.61 mg / L. Therefore, the hexavalent chromium fixation rate of the cemented filling material of this invention is higher than 90% and meets the leaching toxicity identification standard value.

[0141] The low-chromium-migration, high-dosage coal gasification ash-based cemented backfill material of this invention exhibits remarkable mechanical properties and outstanding chromium fixation capabilities. It effectively solves the problems of poor chromium stability and large-volume solid waste utilization in traditional coal gasification ash treatment methods, providing a new method and material for coal-based solid waste utilization and heavy metal solidification.

[0142] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for solidifying chromium in coal gasification ash, characterized in that, Coal gasification ash is mixed with gangue, steel slag, cementing materials and water to prepare a low-chromium-migration, high-volume coal gasification ash-based cementitious filling material, so as to solidify the chromium element in the coal gasification ash. The raw materials for the cementitious material are mechanically activated coal gasification ash, coarse slag, and alkali activator in a mass ratio of 1-3:1-3:1-3. The coal gasification ash residue is composed of coarse coal gasification ash residue and fine coal gasification ash residue. The mass ratio of the coarse coal gasification ash residue, fine coal gasification ash residue, gangue, steel slag, and cementing material is 12-20:6-10:3-5:1-3:3-6; The mechanically activated coal gasification ash coarse slag is obtained by ball milling the dried coal gasification ash coarse slag to D. 50 =10~18 micrometers and D 90 =38-58 micrometers; The raw materials for the alkaline activator are water glass, NaOH, and water in a mass ratio of 8-12:1-3:6-10; The coarse ash residue from the coal gasification process has a particle size of 0.15–2 mm, excluding 0.15 mm. The particle size of the fine ash residue from coal gasification is ≤0.15mm; The particle size of the gangue is 2-5 mm, excluding 2 mm.

2. The curing method as described in claim 1, characterized in that, The mass concentration of solid components in the low-chromium-migration, high-volume coal gasification ash-based cementitious backfill material is 50-60%.

3. A low-chromium-migration, high-volume coal gasification ash-based cementitious backfill material, characterized in that, The raw materials are coarse coal gasification ash residue, fine coal gasification ash residue, gangue, steel slag, and cementing materials in a mass ratio of 12-20:6-10:3-5:1-3:3-6, as well as water; The mass concentration of the solid component in the low-chromium-migration, high-volume coal gasification ash-based cementitious filling material is 50-60%. The raw materials for the cementitious material are mechanically activated coal gasification ash, coarse slag, and alkali activator in a mass ratio of 1-3:1-3:1-3. The mechanically activated coal gasification ash coarse slag is obtained by ball milling the dried coal gasification ash coarse slag to D. 50 =10~18 micrometers and D 90 =38-58 micrometers; The raw materials for the alkaline activator are water glass, NaOH, and water in a mass ratio of 8-12:1-3:6-10; The coarse ash residue from the coal gasification process has a particle size of 0.15–2 mm, excluding 0.15 mm. The particle size of the fine ash residue from coal gasification is ≤0.15mm; The particle size of the gangue is 2-5 mm, excluding 2 mm.

4. The application of a method for solidifying chromium in coal gasification ash as described in any one of claims 1-2 in the resource utilization of solid waste or the solidification of heavy metals.

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