Green lightweight dry powder mortar and method for preparing the same

Abstract

The application provides a green light-weight dry powder mortar and a preparation method thereof, which comprises the following steps: drying and crushing and screening coal-fired slag, and dividing the coal-fired slag into first slag, second slag and third slag according to different particle size ranges; and then, according to a preset weight ratio, premixing the weighed first slag, second slag and third slag, and then adding phosphogypsum, steel slag powder, lead-zinc tailing powder, a thickening agent, an air entraining agent and a coagulant, and fully stirring to obtain the green light-weight dry powder mortar. Through the above method, the synergistic effect between the raw materials can be effectively utilized, on the one hand, the problems of fast drying, poor workability, easy cracking and the like of the dry powder mortar can be significantly improved; on the other hand, the dry powder mortar prepared can promote the formation of hydration products, improve the product strength, and effectively solidify heavy metal ions in the actual application process, so that the cheap and difficult-to-treat solid waste material is prepared into the green light-weight dry powder mortar with good mechanical properties, high stability and low apparent density.

Description

Technical Field

[0001] This invention relates to the field of mortar preparation technology, and in particular to a green lightweight dry powder mortar and its preparation method. Background Technology

[0002] Dry-mix mortar is widely used in building construction due to its long shelf life, lack of dust pollution, and ease of application. With the increasing emphasis on carbon reduction and energy conservation in the construction industry, lightweight mortar, which provides energy-saving benefits through thermal insulation, is also gaining popularity. However, the dry apparent density of ordinary dry-mix mortar is around 1750 kg / m³. 3 In addition, insufficient mixing time leads to sagging after application to walls. Furthermore, short open time and susceptibility to cracking are common problems with dry-mix mortar. How to achieve lightweight dry-mix mortar while extending its open time and reducing the risk of cracking remains a pressing issue.

[0003] For example, patent CN106517982A discloses an inorganic thermal insulation and plastering dry powder mortar. The dry powder mortar has the following weight percentages: 50-97% inorganic cementitious material, 3-45% lightweight aggregate, and 0-5% additives. The inorganic cementitious material includes blends of by-product gypsum and natural gypsum, as well as auxiliary materials for the inorganic cementitious material. The lightweight aggregate consists of expanded perlite, vitrified microspheres, or a mixture of both, as well as waste powder generated during the production of expanded perlite or vitrified microspheres. This patent achieves lightweight dry powder mortar by using by-product gypsum from industrial waste as the inorganic cementitious material in the thermal insulation mortar, replacing high-energy-consuming cement products, and by using waste powder as a lightweight filler.

[0004] However, in practical applications, the addition of a large amount of gypsum will result in poor water stability of the mortar after curing. Under long-term rain erosion, the strength will be further reduced, making it difficult to meet the needs of practical applications. At the same time, in order to ensure that the mortar can cure, the mortar with gypsum as the main component actually needs to use calcined gypsum, whose main component is hemihydrate gypsum. Its setting rate is too fast, resulting in a short open time and easy cracking. Furthermore, in order to ensure product performance, the amount of waste micro powder added can only account for 1-5% of the mortar. Not only is the waste utilization rate low, but it also cannot effectively reduce the dry powder density of the mortar. A large amount of expensive expanded perlite or vitrified microspheres still need to be added, resulting in a high overall cost.

[0005] In view of this, it is necessary to design an improved green lightweight dry powder mortar and its preparation method to solve the above problems. Summary of the Invention

[0006] To address the shortcomings of the existing technology, the present invention aims to provide a green lightweight dry mortar and its preparation method. This method involves drying and crushing coal-fired furnace slag into first, second, and third slag particles with different particle sizes. These slag particles are then thoroughly mixed with phosphogypsum, steel slag powder, lead-zinc tailings, and necessary additives. This synergistic effect of the raw materials effectively improves the problems of rapid drying, poor workability, and easy cracking in dry mortar. Furthermore, the resulting dry mortar can effectively solidify heavy metal ions while promoting the formation of hydration products during practical application. This allows for the preparation of a green lightweight dry mortar with good mechanical properties, high stability, and low apparent density from inexpensive and difficult-to-treat solid waste materials.

[0007] To achieve the above objectives, the present invention provides a method for preparing green lightweight dry powder mortar, comprising the following steps:

[0008] S1. Dry the coal-fired furnace slag until the moisture content is less than 0.5%, then crush it to a maximum particle size of ≤4.75mm, screen it and sort it according to the required particle size to obtain the first slag with a particle size of ≤0.15mm, the second slag with a particle size of 0.15~0.6mm, and the third slag with a particle size of 0.6~4.75mm.

[0009] S2. Weigh the first slag, the second slag, and the third slag obtained in step S1 according to the preset weight proportions, and place them in a mixing device for premixing; then add phosphogypsum, steel slag powder, lead-zinc tailings powder, thickener, air-entraining agent, and coagulant according to the preset weight proportions, and stir thoroughly to obtain green lightweight dry powder mortar.

[0010] As a further improvement of the present invention, in step S2, the preset weight fraction is:

[0011] 10-20 parts phosphogypsum, 5-10 parts lead-zinc tailings powder, 1-3 parts steel slag powder, 0.2-0.5 parts thickener, 0.01-0.05 parts air-entraining agent, 0-0.5 parts coagulant, 5-10 parts first furnace slag, 30-60 parts second furnace slag, and 20-40 parts third furnace slag.

[0012] As a further improvement of the present invention, in step S2, the mass fraction of dihydrate gypsum in the phosphogypsum is ≥85%, the mass fraction of phosphate is 0.5% to 2%, and the mass fraction of free fluorine is 0.5% to 2%.

[0013] As a further improvement of the present invention, in step S2, the mass fraction of ZnO in the lead-zinc tailings powder is ≤0.6%, the mass fraction of PbO is ≤0.9%, and the mass fraction of SiO2 is ≥25%.

[0014] As a further improvement of the present invention, in step S2, the mass fraction of CaO in the steel slag powder is ≥35%.

[0015] As a further improvement of the present invention, in step S1, the mass fraction of SiO2 in the coal-fired slag is ≥30%, and the mass fraction of Al2O3 is ≥10%.

[0016] As a further improvement of the present invention, the mass ratio of water added during wet milling in step S3 to water added in step S4 is 1:(0.9-1.1); the wet milling time is 10-20 min.

[0017] As a further improvement of the present invention, in step S2, the thickener is one or more of cellulose ether, polypropylene, and bentonite; the air-entraining agent is one or more of sodium alkyl sulfonate, rosin resin, sodium fatty alcohol sulfonate, and saponin; and the coagulant is one or more of sodium sulfate, quicklime, and water glass.

[0018] To achieve the above objectives, the present invention also provides a green lightweight dry powder mortar, which is prepared by the preparation method described in any of the above technical solutions.

[0019] As a further improvement of the present invention, the green lightweight dry powder mortar is mixed with water at a mass ratio of 100:10 to 15 to obtain the finished mortar.

[0020] As a further improvement of the present invention, the finished mortar has a consistency loss rate of ≤10% over 2 hours, a setting time of 5–8 hours, and an apparent density of ≤1300 kg / m³. 3 The finished mortar, after curing, has a 14-day bond strength ≥ 0.25 MPa and a 28-day compressive strength ≥ 18.8 MPa.

[0021] The beneficial effects of this invention are:

[0022] (1) The method for preparing green lightweight dry powder mortar provided by the present invention involves drying coal slag, crushing and screening it into first slag, second slag and third slag with different particle size ranges, and then fully mixing it with phosphogypsum, steel slag powder, lead-zinc tailings and the required additives. This not only utilizes the porous honeycomb structure inside the coal slag to effectively reduce the density of the mortar, but also enables the coal slag to work synergistically with phosphogypsum, steel slag powder and lead-zinc tailings powder to improve the strength of the mortar. This effectively improves the problems of dry powder mortar drying too quickly, poor workability and easy cracking. In the actual application process, the prepared dry powder mortar can effectively solidify heavy metal ions while promoting the formation of hydration products. Thus, green lightweight dry powder mortar with good mechanical properties, high stability and low apparent density is prepared from inexpensive and difficult-to-treat solid waste materials, which effectively improves the utilization value of solid waste and has high economic and environmental benefits.

[0023] (2) This invention, by simultaneously adding phosphogypsum, steel slag powder, and lead-zinc tailings powder to dry mortar, enables the synergistic effect between phosphogypsum, steel slag powder, and lead-zinc tailings powder during the water mixing process in practical applications. This allows the free phosphate and fluoride ions from the phosphogypsum to combine with the free calcium, lead, and zinc cations from the steel slag powder and lead-zinc tailings, forming stable precipitates. On the one hand, this reduces the retardation effect of phosphate and fluoride ions in the phosphogypsum on the hydration reaction, improving early strength; on the other hand, it solidifies the heavy metal ions in the lead-zinc tailings, reducing the heavy metal hazards of lead-zinc tailings, thus effectively solving the problem that lead-zinc tailings are difficult to utilize effectively due to the presence of harmful heavy metal elements. Furthermore, as the subsequent hydration reaction proceeds, the generated precipitate is encapsulated in the hydration products and cannot dissolve, further ensuring the safety and stability of the green lightweight dry mortar.

[0024] (3) This invention divides coal-fired furnace slag into first slag, second slag, and third slag according to different particle size ranges. The first slag, together with phosphogypsum, steel slag powder, and lead-zinc tailings powder, forms a cementitious material system to solve problems such as rapid drying, short plastic retention time, poor workability, and easy cracking of dry mortar. On the one hand, the phosphate and free fluoride ions in phosphogypsum have a certain inhibitory effect on the hydration reaction, which can greatly reduce the consistency loss of dry mortar. On the other hand, the combined use of phosphogypsum, first slag, and steel slag powder can ensure that the hydration products of the dry mortar provided by this invention contain a large amount of ettringite, which has a certain expansion effect, thereby greatly reducing the shrinkage of dry mortar and thus reducing the risk of shrinkage cracking. Furthermore, the combined use of second and third slag can optimize the aggregate gradation of mortar and improve the quality stability of mortar. At the same time, the dry mortar system can also increase its powder content to a certain extent. The combined effect of the two improves the workability and finishing effect of dry mortar.

[0025] (4) Based on the classification of coal-fired furnace slag into first slag, second slag, and third slag according to different particle size ranges, this invention further incorporates raw materials such as phosphogypsum, steel slag powder, and lead-zinc tailings powder for blending. The resulting dry-mix mortar, when mixed with water, allows the phosphogypsum to release a large amount of calcium and sulfate ions. Simultaneously, the calcium oxide released from the steel slag powder in water creates an alkaline environment and provides an abundant calcium source, working together to form a mortar containing Ca... 2+ SO4 2- and OH - The alkaline environment activates lead-zinc tailings powder and the first furnace slag, promoting the formation of Al in the lead-zinc tailings powder and the first furnace slag. 3+The dissociation of lead-zinc tailings powder and the first slag allows for secondary hydration activity. Simultaneously, the second and third slags, acting as coarse and fine aggregates respectively, provide support for the formed gel system. Under these conditions, phosphogypsum and steel slag powder added in specific proportions can also form Ca... 2+ Excessive environmental factors lead to the release of free Ca. 2+ With SO4 2- This combination promotes the formation of hydrated calcium silicate gel, thereby enabling the continuous hydration of the green lightweight dry powder mortar system and promoting a continuous increase in its compressive strength. The cementitious material system has a high alkalinity in the initial stage of hydration, and the main hydration products are CSH gel and ettringite, which intertwine to form a network, creating a hydration product layer that coats the cementitious material particles. Due to the low content of steel slag powder, the system contains excess Ca... 2+ As the pH gradually decreases, the formation rate of AFt also gradually decreases, and the system gradually becomes more stable. With the extension of the hydration age, the amount of hydration products generated increases, the structure becomes more and more compact, and the strength is further improved; while the unreacted phosphogypsum is gradually encapsulated by the hydration products in the system, so that the mortar after final curing has good physical and mechanical properties and durability. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to specific embodiments.

[0027] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0028] This invention provides a method for preparing green lightweight dry powder mortar, comprising the following steps:

[0029] S1. Dry the coal-fired furnace slag to a moisture content of less than 0.5%, then crush it to a maximum particle size of ≤4.75mm, screen it, and sort it according to the required particle size to obtain the first slag with a particle size of ≤0.15mm, the second slag with a particle size of 0.15~0.6mm, and the third slag with a particle size of 0.6~4.75mm;

[0030] S2. Weigh the first slag, second slag and third slag obtained in step S1 according to the preset weight proportions, and place them in a mixing device for premixing; then add phosphogypsum, steel slag powder, lead-zinc tailings powder, thickener, air-entraining agent and coagulant according to the preset weight proportions, and stir thoroughly to obtain green lightweight dry powder mortar.

[0031] In step S1, the mass fraction of SiO2 in the coal-fired slag is ≥30%, and the mass fraction of Al2O3 is ≥10%.

[0032] In step S2, the preset number of weight parts is:

[0033] The composition includes 10-20 parts phosphogypsum, 5-10 parts lead-zinc tailings powder, 1-3 parts steel slag powder, 0.2-0.5 parts thickener, 0.01-0.05 parts air-entraining agent, 0-0.5 parts coagulant, 5-10 parts first furnace slag, 30-50 parts second furnace slag, and 20-40 parts third furnace slag; the phosphogypsum contains ≥85% dihydrate gypsum, 0.5%-2% phosphate, and 0.5%-2% free fluorine; the steel slag powder contains ≥35% CaO. The powder with a particle size ≤80μm has a mass fraction ≥10%; in the lead-zinc tailings powder, the mass fraction of ZnO is ≤0.6%, the mass fraction of PbO is ≤0.9%, and the mass fraction of SiO2 is ≥25%; in the steel slag powder, the mass fraction of CaO is ≥35%; the thickener is one or more of cellulose ether, polypropylene, and bentonite; the air-entraining agent is one or more of sodium alkyl sulfonate, rosin resin, sodium fatty alcohol sulfonate, and saponins; and the coagulant is one or more of sodium sulfate, quicklime, and water glass.

[0034] This invention also provides a green lightweight dry powder mortar, which is prepared by the preparation method described in any of the above-mentioned technical solutions; the green lightweight dry powder mortar is mixed with water at a mass ratio of 100:10-15 to obtain the finished mortar; the dry powder mortar has a consistency loss rate of ≤10% over 2 hours, a setting time of 5-8 hours, a 14-day bond strength of ≥0.25 MPa, a 28-day compressive strength of ≥18.8 MPa, and an apparent density of ≤1300 kg / m³. 3 The green lightweight dry powder mortar and its preparation method provided by the present invention will be described below with reference to specific embodiments and comparative examples.

[0035] Example 1

[0036] This embodiment provides a method for preparing green lightweight dry powder mortar, including the following steps:

[0037] S1. Dry the coal-fired slag until the moisture content is less than 0.5%, then crush it to a maximum particle size of ≤4.75mm. Then, sieve the crushed coal-fired slag through 100-mesh and 30-mesh screens to obtain the first slag with a particle size of ≤0.15mm, the second slag with a particle size of 0.15~0.6mm (greater than 0.15mm and less than or equal to 0.6mm), and the third slag with a particle size of 0.6~4.75mm (greater than 0.6mm and less than or equal to 4.75mm).

[0038] S2. Weigh the raw materials according to the following weight proportions:

[0039] 15 parts phosphogypsum, 7 parts lead-zinc tailings powder, 2 parts steel slag powder, 0.5 parts thickener, 0.03 parts air-entraining agent, 0.01 parts coagulant, 8 parts first furnace slag, 40 parts second furnace slag, and 30 parts third furnace slag.

[0040] S3. Weigh 8 parts of the first slag, 40 parts of the second slag and 30 parts of the third slag and place them in a mixing device for premixing; then add 15 parts of phosphogypsum, 7 parts of lead-zinc tailings powder, 2 parts of steel slag powder, 0.5 parts of thickener, 0.03 parts of air-entraining agent and 0.01 parts of coagulant, and stir thoroughly until uniformly mixed to obtain green lightweight dry powder mortar.

[0041] In actual construction, the green lightweight dry powder mortar prepared in this embodiment is mixed with water at a mass ratio of 100:13 and then poured into the required location. After standing and curing for the predetermined age, it can meet the requirements for use.

[0042] Specifically, in this embodiment, the coal-fired slag used is the waste residue discharged after coal combustion in coal-fired power plants, industrial and civil boilers, and other equipment, and its chemical composition is shown in Table 1; phosphogypsum is a solid waste generated in the wet-process phosphoric acid process, and its chemical composition is shown in Table 2; lead-zinc tailings powder is obtained by grinding solid waste from the lead-zinc ore beneficiation process, and its chemical composition is shown in Table 3; steel slag powder is obtained by grinding the steel slag remaining after iron extraction from the slag produced in steelmaking, and its chemical composition is shown in Table 4. The mass fraction of powder with a particle size ≥ 80 μm in the above-mentioned phosphogypsum, lead-zinc tailings powder, and steel slag powder is ≤ 10%.

[0043] Table 1 Chemical Composition of Coal-fired Furnace Slag

[0044]

[0045] Table 2 Chemical composition of phosphogypsum

[0046]

[0047] Table 3 Chemical composition of lead-zinc tailings powder

[0048]

[0049]

[0050] Table 4 Chemical Composition of Steel Slag Powder

[0051]

[0052] To test the performance of the green lightweight dry powder mortar prepared in this embodiment, the lightweight dry powder mortar prepared in this embodiment was mixed with water at a mass ratio of 100:13 to obtain a finished mortar. The 2-hour consistency loss rate, setting time, and apparent density of the finished mortar were then tested. Simultaneously, the finished mortar was poured into a mold, allowed to stand for 24 hours, then demolded and cured under standard conditions (20±2℃, humidity ≥90%) until the predetermined age, and the following performance tests were performed:

[0053] Specifically, the 14-day bond strength and 28-day compressive strength of the finished mortar after curing for 14 days and 28 days were tested, respectively. The water stability coefficient and heavy metal release of the finished mortar after curing for 28 days were also tested. The results are shown in Table 5.

[0054] Table 5 Performance parameters of the green lightweight dry powder mortar prepared in Example 1

[0055]

[0056] Examples 2-15 and Comparative Examples 1-6

[0057] Examples 2-15 and Comparative Examples 1-6 each provide a method for preparing green lightweight dry powder mortar. Compared with Example 1, the difference is that the raw material ratio in step S2 is changed. The raw material ratios corresponding to each example and comparative example are shown in Table 6. The remaining steps and parameters are the same as those in Example 1, and will not be repeated here.

[0058] Table 6. Raw material ratios for Examples 2-15 and Comparative Examples 1-6 (unit: parts by weight)

[0059]

[0060]

[0061] The green lightweight dry powder mortars prepared in the above embodiments and comparative examples were tested, and the results are shown in Table 7.

[0062] Table 7 Performance data of Examples 2-15 and Comparative Examples 1-6

[0063]

[0064]

[0065] According to Table 7, comparing Examples 2 and 3, it can be seen that reducing the amount of phosphogypsum in Example 2 reduces its activation effect on lead-zinc tailings and the first slag, leading to a decrease in hydration rate and degree, further reducing the 2-hour consistency loss rate, 14-day bond strength, and 28-day compressive strength of the dry mortar. While increasing the amount of phosphogypsum in Example 3 can increase early hydration and thus increase the 2-hour consistency loss rate, the low content of cementitious materials also reduces the final strength, resulting in a decrease in 14-day bond strength and 28-day compressive strength. Comparing Examples 4 and 5, it can be seen that increasing the amount of lead-zinc tailings increases the apparent density and consistency loss of the mortar, mainly because the density of lead-zinc tailings powder is greater than that of the first slag powder. Simultaneously, lead-zinc tailings help remove phosphate and fluoride ions from the phosphogypsum, accelerating the reaction rate. Comparing Examples 6 and 7, it can be seen that adjusting the amount of steel slag powder results in several problems. If the steel slag powder content is too low, the alkalinity and free calcium ion concentration in the early hydration system will be too low, which is detrimental to the hydration reaction and thus affects the mortar strength. If the steel slag powder content is too high, the alkalinity and free calcium ion concentration in the early hydration system will be high, resulting in a faster early hydration rate. However, excessive calcium ions in the later stages will generate excessive ettringite, causing volume expansion and reducing mortar performance. Comparing Examples 8 and 9, it can be seen that reducing the thickener content leads to a decrease in mortar consistency, while increasing the 2-hour consistency loss. Conversely, increasing the thickener content improves the water retention properties of the mortar but negatively impacts its hardening properties. Comparing Examples 10 and 11, it can be seen that reducing the content of the air-entraining agent leads to a decrease in mortar consistency, a smaller 2-hour consistency loss, and an increase in the mechanical properties of the mortar. Conversely, increasing the content of the air-entraining agent leads to an increase in mortar consistency retention, but a decrease in water retention, resulting in a larger 2-hour consistency loss, and a decrease in mortar strength and apparent density. Comparing Examples 12 and 13, it can be seen that reducing the dosage of the accelerator leads to a decrease in the early hydration rate and a smaller 2-hour consistency loss rate, while having no significant effect on compressive strength. Comparing Examples 14 and 15, it can be seen that reducing the amount of the second slag leads to a larger mortar fineness modulus, poorer mortar workability, and a lower water retention rate, but a certain improvement in 28-day compressive strength. Increasing the amount of the second slag increases the mortar fineness modulus, increases mortar consistency, and reduces the 2-hour consistency loss rate.

[0066] Compared with Example 1, the content of phosphogypsum in Comparative Example 1 was too low, resulting in insufficient activation effect in the mortar system and a significant decrease in the 14-day bond strength and 28-day strength of the mortar. Further testing was conducted on the heavy metal release of the finished mortar prepared in Comparative Example 1 after 28 days of curing, and the results showed that Pb... 2+ The highest concentration was 0.052 mg / L, Zn 2+The highest concentration was 0.055 mg / L, indicating that phosphogypsum has a significant adsorption effect on heavy metals in lead-zinc tailings. However, if the phosphogypsum dosage is too low, it will increase the adsorption of Pb. 2+ and Zn 2+ The leaching rate increased. In Comparative Example 2, the absence of lead-zinc tailings resulted in insufficient adsorption of phosphate and fluoride ions from the phosphogypsum, leading to a slow hydration rate in the mortar and further affecting its strength. In Comparative Example 3, the lack of steel slag powder resulted in insufficient alkalinity and a deficiency of free calcium ions, leading to a very slow hydration reaction and low mortar strength. Further testing was conducted on the heavy metal leaching of the finished mortar from Comparative Example 3 after 28 days of curing. The results showed that Pb... 2+ The highest concentration was 0.035 mg / L, Zn 2+ The highest concentration was 0.041 mg / L, indicating that no steel slag powder was added, which would still increase Pb. 2+ and Zn 2+ The leaching rate is low, mainly because the lack of steel slag components hinders the hydration reaction of the finished mortar, reduces the overall density of the structure, and increases the leaching rate of heavy metal Pb. 2+ and Zn 2+ It is also easier to dissolve. In Comparative Examples 4 and 5, the absence of thickener and air-entraining agent, respectively, resulted in poor initial state and low consistency of the mortar. In Comparative Example 6, the absence of the first slag resulted in excessively low aluminum content in the system, leading to insufficient hydration reaction in the later stages and a reduction in mechanical properties.

[0067] In summary, this invention provides a green lightweight dry mortar and its preparation method. The method involves drying and crushing coal-fired furnace slag, then dividing it into first slag and second slag according to different particle size ranges. The first and second slags are premixed according to preset weight proportions, and then phosphogypsum, steel slag powder, lead-zinc tailings powder, thickener, air-entraining agent, and coagulant are added and thoroughly stirred to obtain the green lightweight dry mortar. Through this method, the invention effectively utilizes the synergistic effect between the raw materials. On the one hand, it significantly improves the problems of rapid drying, poor workability, and easy cracking of dry mortar. On the other hand, the resulting dry mortar promotes the formation of hydration products and improves product strength during practical application, while effectively solidifying heavy metal ions. This transforms inexpensive and difficult-to-treat solid waste materials into green lightweight dry mortar with good mechanical properties, high stability, and low apparent density.

[0068] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing green lightweight dry powder mortar, characterized in that, Includes the following steps: S1. Dry the coal-fired furnace slag until the moisture content is less than 0.5%, then crush it to a maximum particle size of ≤4.75mm, screen it and sort it according to the required particle size to obtain the first slag with a particle size of ≤0.15mm, the second slag with a particle size of 0.15~0.6mm, and the third slag with a particle size of 0.6~4.75mm. S2. Weigh the first slag, the second slag, and the third slag obtained in step S1 according to the preset weight proportions, and place them in a mixing device for premixing; then add phosphogypsum, steel slag powder, lead-zinc tailings powder, thickener, air-entraining agent, and coagulant according to the preset weight proportions, and stir thoroughly to obtain green lightweight dry powder mortar. The preset weight percentage is: 10-20 parts phosphogypsum, 5-10 parts lead-zinc tailings powder, 1-3 parts steel slag powder, 0.2-0.5 parts thickener, 0.01-0.05 parts air-entraining agent, 0-0.5 parts coagulant, 5-10 parts first furnace slag, 30-60 parts second furnace slag, and 20-40 parts third furnace slag. The phosphogypsum contains 0.5% to 2% phosphate by mass and 0.5% to 2% free fluorine by mass.

2. The method for preparing green lightweight dry powder mortar according to claim 1, characterized in that: In step S2, the mass fraction of dihydrate gypsum in the phosphogypsum is ≥85%.

3. The method for preparing green lightweight dry powder mortar according to claim 1, characterized in that: In step S2, the lead-zinc tailings powder contains ZnO with a mass fraction of ≤0.6%, PbO with a mass fraction of ≤0.9%, and SiO2 with a mass fraction of ≥25%.

4. The method for preparing green lightweight dry powder mortar according to claim 1, characterized in that: In step S2, the mass fraction of CaO in the steel slag powder is ≥35%.

5. The method for preparing green lightweight dry powder mortar according to claim 1, characterized in that: In step S1, the mass fraction of SiO2 in the coal-fired slag is ≥30%, and the mass fraction of Al2O3 is ≥10%.

6. The method for preparing green lightweight dry powder mortar according to claim 1, characterized in that: In step S2, the thickener is one or more of cellulose ether, polypropylene, and bentonite; the air-entraining agent is one or more of sodium alkyl sulfonate, rosin resin, sodium fatty alcohol sulfonate, and saponin; and the coagulant is one or more of sodium sulfate, quicklime, and water glass.

7. A green, lightweight dry powder mortar, characterized in that: The green lightweight dry powder mortar is prepared by the preparation method according to any one of claims 1 to 6.

8. A green lightweight mortar, characterized in that: The green lightweight dry powder mortar described in claim 7 is mixed with water at a mass ratio of 100:10~15 to obtain the finished mortar.

9. The green lightweight mortar according to claim 8, characterized in that: The finished mortar has a consistency loss rate of ≤10% over 2 hours, a setting time of 5-8 hours, and an apparent density of ≤1300 kg / m³. 3 The finished mortar, after curing, has a 14-day bond strength ≥ 0.25 MPa and a 28-day compressive strength ≥ 18.8 MPa.

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