Magnesium phosphate cement paste based on low-temperature calcined phosphate tailings and preparation method thereof

Abstract

The invention discloses magnesium phosphate cement paste based on low-temperature calcined phosphate tailings and a preparation method of the magnesium phosphate cement paste, and relates to the technical field of magnesium phosphate cement materials. Uniformly mixing soluble phosphate, low-temperature calcined phosphate tailings, light calcined magnesia and a delayed coagulation substance to obtain a mixed dry material; adding the calculated water reducing agent into water, and fully and uniformly mixing for later use; the mixed dry material and the water reducing agent mixed solution are mixed, magnesium phosphate cement paste is obtained, the dry material mixing time is not less than 1 min, and the stirring time is not less than 150 s when the mixed solution is added. The phosphate tailings are used for replacing dead-burnt magnesium oxide, so that a large amount of consumption of the existing accumulated phosphate tailings can be realized, the value of the phosphate tailings is improved, effective elements in the phosphate tailings are fully utilized, cyclic utilization of resources is realized, meanwhile, the manufacturing cost of the magnesium phosphate cement can be remarkably reduced, and impurities such as silicon and aluminum in the phosphate tailings possibly form a compact structure; the acid corrosion resistance and the salt corrosion resistance of MPC are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium phosphate cement materials, and particularly relates to a magnesium phosphate cement paste based on low-temperature calcined phosphorus tailings and a preparation method thereof. Background Art

[0002] Magnesium phosphate cement (MPC) is a non-fired configured cement formed by mixing calcined MgO, soluble phosphate and retarder in a certain proportion. Calcined MgO and soluble phosphate rapidly generate the hydration product struvite (MgKPO4·6H2O) through an acid-base neutralization reaction, and the paste rapidly sets and hardens. Struvite wraps the excessive calcined MgO in the MPC system, thus forming an MPC specimen with relatively high strength. Compared with traditional Portland cement, MPC has a series of advantages such as rapid hardening and early strength, good fluidity, small volume deformation, high bonding strength, low alkalinity and good biocompatibility, and has broad application prospects in fields such as emergency engineering repair and construction, rapid reinforcement, nuclear waste solidification, 3D printing, etc.

[0003] Calcined MgO, as the magnesia component, is the most used and important raw material for preparing MPC, and its properties are the key to preparing MPC with good performance. MgO mainly exists in magnesite, dolomite in the earth's crust and seawater. Among them, calcining magnesite is one of the most important ways to prepare calcined MgO at present. CN115448688A discloses a low exothermic magnesium phosphate cement paste and a preparation method thereof, which uses calcined magnesium oxide, magnesium phosphate, phosphate and retarder to prepare the magnesium phosphate cement paste. The sintering temperature of the calcined magnesium oxide is greater than 1350°C, and the magnesium phosphate is sintered from magnesium hydroxide and magnesium hydrogen phosphate trihydrate. The exploitation and processing of traditional MgO sources such as magnesite not only consume natural resources, but may also cause damage to the environment, and the preparation process has high energy consumption. Finding an alternative magnesium source is the fastest way to reduce the cost and improve the green benefit of magnesium phosphate cement at present.

[0004] As a flotation product of phosphate ore, phosphorus tailings contain a large amount of magnesium elements and have the potential to be used as raw materials for MPC. By calcining phosphorus tailings, the magnesium elements therein can be activated and transformed into active MgO, which can then be used to prepare magnesium phosphate cement. This can not only realize the resource utilization of phosphorus tailings, reduce their environmental pollution, but also reduce the production cost of MPC and improve economic benefits.

[0005] CN109020467A discloses a casting material of activated phosphorus tailings. By calcining phosphorus tailings at a high temperature of 1000 °C, the main components of the phosphorus tailings after high-temperature calcination are calcium oxide and magnesium oxide. The phosphorus tailings after high-temperature calcination are used to replace dead-burned magnesia. Although it reduces the consumption of natural resources in the preparation process of dead-burned magnesia and reduces the production cost, high-temperature calcination still has the problem of high energy consumption. The CaO and MgO after high-temperature calcination are over-sintered, and the reaction activity is reduced. In the reaction process, inert α-Al2O3 or periclase is easily generated, resulting in a low 3d compressive strength and making it difficult to meet the requirements of materials with rapid hardening for projects such as road emergency repair and rapid reinforcement. Summary of the Invention

[0006] The purpose of the present invention is to provide a magnesium phosphate cement paste based on low-temperature calcined phosphorus tailings and its preparation method, so as to solve the problem of high energy consumption existing in the prior art during the preparation process.

[0007] To solve the above technical problems, the present invention adopts the following technical solutions: A magnesium phosphate cement paste based on low-temperature calcined phosphorus tailings, comprising the following raw materials in parts by weight:

[0008]

[0009] A further technical solution is that the soluble phosphate is at least one of potassium dihydrogen phosphate and ammonium dihydrogen phosphate, and the purity of the soluble phosphate is ≥ 99%.

[0010] A further technical solution is that the low-temperature calcined phosphorus tailings are obtained by calcining phosphorus tailings at 700 - 780 °C for 2 - 5 h. The content of magnesium oxide in the low-temperature calcined phosphorus tailings is ≥ 18%, calcium exists in the form of calcium carbonate, and the content of calcium carbonate is ≥ 60%.

[0011] A further technical solution is that the phosphorus tailings are filter-pressed tailings treated by a flotation process. The content of P2O5 in the phosphorus tailings is 7 - 10%, the content of CaO is 30 - 35%, the content of MgO is 20 - 25%, the content of SiO2 is 5 - 10%, the content of Fe2O3 is 0.5 - 1%, the content of Al2O3 is 0.5 - 1%, and the density is 2.5 - 3.1 t / m 3 , and the water content is ≤ 15%.

[0012] A further technical solution is that the content of magnesium oxide in the lightly burned magnesia is ≥ 90%.

[0013] A further technical solution is that the setting retarder is at least one of borax and boric acid.

[0014] A further technical solution is that the dosage of the water reducer is calculated according to the following formula:

[0015] W 减水剂= (K * (W / C) n * S / η 减水剂 ) * (1 + α * T) * (1 - β * R 缓凝剂 )

[0016] Wherein, W 减水剂 is the addition amount of water reducing agent; K is the material characteristic coefficient; W / C is the water-cement ratio, and its value range is 0.22 to 0.30; n is the fluidity index, which takes the value of 1.0 when it is a polycarboxylate-based water reducing agent and 1.5 when it is a naphthalene-based water reducing agent; S is the slump flow; η 减水剂 is the water reducing agent efficiency coefficient, which takes the value of 2.0 when it is a polycarboxylate-based water reducing agent and 1.0 when it is a naphthalene-based water reducing agent; α is the temperature correction coefficient, and its value range is 0.01 to 0.03 / °C; T is the difference between the ambient temperature and the reference temperature, and the reference temperature is 25°C; β is the retarder interference coefficient; R 缓凝剂 is the addition amount of retarder.

[0017] A further technical solution is that the material characteristic coefficient K = K0 * k MgO * k 磷酸盐 ,

[0018] where K0 has a value range of 0.6 to 0.8; k MgO is the characteristic coefficient of magnesium oxide and is 0.6 to 0.7, k 磷酸盐 is the characteristic coefficient of potassium dihydrogen phosphate and is 1.1 to 1.2, k 磷酸盐 is the characteristic coefficient of ammonium dihydrogen phosphate and is 1.0.

[0019] A further technical solution is that β = reduction amount of water reducing agent demand / addition amount of boric acid, and its value is 0.2.

[0020] A further technical solution is the preparation method of the magnesium phosphate cement paste based on low-temperature calcined phosphorus tailings, which includes the following steps:

[0021] 1) Mix soluble phosphate, low-temperature calcined phosphorus tailings, lightly burned magnesium oxide, and retarder substances evenly to obtain a mixed dry material;

[0022] 2) Add the calculated water reducing agent to water, mix evenly, and set aside;

[0023] 3) Mix the mixed dry material with the water reducing agent mixture to obtain magnesium phosphate cement paste. The dry material mixing time in step 1) is not less than 1 min, and when adding the mixture in step 2), the stirring time is not less than 150 s.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] 1. Using the solid waste phosphorous tailings in the phosphorous ore flotation process as raw materials, calcining the phosphorous tailings at a relatively low temperature to obtain magnesium oxide while separating the calcium and magnesium elements in the tailings. On the one hand, calcining at a relatively low temperature not only saves energy, but the magnesium oxide obtained during the calcination process has slightly higher activity than the dead-burned magnesium oxide, which is conducive to quickly achieving the acid-base neutralization reaction between phosphate and magnesium oxide in the case of more impurities in the tailings, achieving the purpose of rapid hardening and early strength of the cement. On the other hand, calcining at a relatively low temperature has little effect on the calcium carbonate in the tailings, making the calcium exist in the form of calcium carbonate. During the later process of improving the cement strength, the calcium carbonate particles, as the aggregate of the cement, quickly cover the hydrate crystals struvite formed during the hardening process of magnesium phosphate cement on their surface, further enhancing its strength.

[0026] 2. The water reducer adsorbs on the surfaces of MgO and phosphorous tailings particles, reducing the friction between particles and preventing agglomeration, thereby improving the fluidity of the slurry. At the same time, when the water content is low, it can reduce the porosity in the cement and improve the cement density. The water reducer also promotes the uniform growth of struvite crystals by uniformly dispersing the reactants and reducing defects. The setting time of magnesium phosphate cement is also adjusted by adding a water reducer, thereby extending the operable window period. The dosage of the water reducer is calculated through formulas composed of water-cement ratio W / C, fluidity S, temperature T, setting retarder dosage, etc., making the dosage of the water reducer more accurate and also making the strength of the obtained neat cement material reach the optimum.

[0027] 3. The magnesium phosphate cement paste based on low-temperature calcined phosphorous tailings provided by the present invention uses phosphorous tailings to replace dead-burned magnesium oxide, which can not only consume a large amount of existing stacked phosphorous tailings, enhance the value of phosphorous tailings itself, make full use of the effective elements therein, and realize the recycling of resources, but also significantly reduce the production cost of magnesium phosphate cement. Compared with the production of traditional silicates, it can reduce carbon emissions by 30 - 50%. Impurities such as silicon and aluminum in the phosphorous tailings may form a dense structure, enhancing the acid and salt erosion resistance of MPC.

[0028] 4. The material composition ratio of the present invention is simple and reasonable, and the process is simple. Compared with the magnesium phosphate cement prepared from dead-burned magnesium oxide, its unconfined compressive strength and flexural strength are not much different. On the premise of realizing the comprehensive utilization of tailings, the production cost of magnesium phosphate cement is reduced as much as possible. The rapid hardening characteristic of magnesium phosphate cement combined with the low cost of phosphorous tailings can be widely used for the emergency repair of roads, bridges, and airport runways. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is the process flow chart of the embodiment of the present invention.

[0030] Figure 2 It is the detection process of the setting time and fluidity of the present invention.

[0031] Figure 3 It is the physical display diagram in Example 1.

[0032] Figure 4 It is the XRD analysis diagram of the low-temperature calcined phosphorus tailings in Example 1.

[0033] Figure 5 It is the XRD analysis diagram of the cement specimen prepared from the magnesium phosphate cement paste. Detailed implementation manners

[0034] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0035] In the following examples, the phosphorus tailings are taken from a flotation plant in Yunnan, and its components are shown in Table 1. It is calcined at a certain temperature for 3 hours. The calcined phosphorus tailings are slightly whiter than the original tailings and are grayish-white powdery solids, and its components are shown in Table 2. As the calcination temperature rises, below 780 °C, the contents of magnesium oxide and calcium oxide (present in the form of calcium carbonate) in the tailings are both steadily increasing. When it exceeds 780 °C, the calcium oxide content suddenly rises, and at this time, calcium carbonate begins to decompose into calcium oxide and carbon dioxide.

[0036] Table 1 Components of a certain phosphorus tailings in Yunnan (unit: wt.%)

[0037] Component <![CDATA[P2O5]]> CaO MgO <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> <![CDATA[SiO2]]> Ni As Cu Pb Zn Cr Content 7.62 32.32 14.76 0.53 0.78 7.12 0.00057 0.00129 0.00055 0.0095 0.0096 0.0023

[0038] Table 2 Main components in phosphorus tailings at different calcination temperatures (unit: wt.%)

[0039]

[0040] Example 1

[0041] Provide a method for preparing magnesium phosphate cement paste by low-temperature calcination of phosphorus tailings, which includes the following raw materials by mass: 60 parts of low-temperature calcined phosphorus tailings, 32 parts of soluble phosphate (analytical pure potassium dihydrogen phosphate), 8 parts of lightly burned magnesium oxide, 1 part of retarder (boric acid), and 23 parts of water.

[0042] In the calculation of the dosage of the water reducer, the material characteristic coefficient K is K = 0.6 * 0.65 * 1.1 = 0.468; W / C is the water-cement ratio of 0.23; n takes the value of 1.2; S is the slump flow of 156 mm; η 减水剂 is the water reducer efficiency coefficient of 2; at room temperature of 25 °C, α * T is 0; β is the retarder interference coefficient of 0.2; R 缓凝剂 is the dosage of the retarder of 1. Then W 减水剂 =(K * (W / C)n *S / η 减水剂 )*(1 + α*T)*(1 - β*R 缓凝剂 )=(0.468 * 0.23 1.2 * 0.156 / 2)*(1 + 0)*(1 - 0.2 * 1)=0.50%, The dosage of water - reducing agent is 0.50% of the mass of the mixed dry materials.

[0043] Method for preparing magnesium phosphate cement based on low - temperature calcined phosphorus tailings, comprising the following steps:

[0044] Mix the above - mentioned soluble phosphate, low - temperature calcined phosphorus tailings, light - burned magnesia, and setting retarder evenly. The mixing time of the dry materials is 30 s. Add the polycarboxylate water - reducing agent to the aqueous solution and mix evenly. Set aside. Mix the mixed dry materials with the water - reducing agent mixture, and stir for 3 - 5 min to obtain magnesium phosphate cement paste. After injecting it into the mold, cure it at room temperature (25 °C) for 1 h and then demold for testing.

[0045] Performance testing:

[0046] (1) Test the compressive strength of the test blocks prepared from the magnesium phosphate cement material of this example according to the "Test Method for Strength of Cement Mortar (ISO Method)" (GB / T 17671 - 1999).

[0047] (2) Test the setting time of the magnesium phosphate cement material of this example according to the "Test Regulations for Cement and Cement Concrete in Highway Engineering" (JTG 3420 - 2020).

[0048] (3) Immerse the cement finished product that has reached the specified time period in ethanol sufficiently, and then perform low - temperature drying treatment for XRD test analysis.

[0049] Example 2

[0050] The second embodiment of the present invention provides a method for preparing magnesium phosphate cement paste from low - temperature calcined phosphorus tailings. The raw materials include, by mass: 59 parts of dry - based calcined phosphorus tailings, 33 parts of soluble phosphate (analytical - grade potassium dihydrogen phosphate), 8 parts of light - burned magnesia, 1 part of setting retarder (boric acid), and 24 parts of water.

[0051] In the calculation of the dosage of the water - reducing agent, the material characteristic coefficient K is K = 0.6 * 0.65 * 1.1 = 0.468; W / C is the water - cement ratio of 0.24; n takes the value of 1.2; S is the slump flow of 174 mm; η 减水剂 is the water - reducing agent efficiency coefficient of 2; at room temperature of 25 °C, α*T is 0; β is the setting retarder interference coefficient of 0.2; R 缓凝剂 is the dosage of the setting retarder of 1. Then W 减水剂 =(K*(W / C) n *S / η减水剂 )*(1 + α*T)*(1 - β*R 缓凝剂 ) = (0.468 * 0.24 1.2 * 0.174 / 2)*(1 + 0)*(1 - 0.2 * 1) = 0.59%, and the dosage of water reducer is 0.59% of the mixed dry materials.

[0052] The same method as in Example 1 above is used to test the performance indexes of the magnesium phosphate cement material prepared in this example.

[0053] Example 3

[0054] Example 3 of the present invention provides a method for preparing magnesium phosphate cement paste by low-temperature calcination of phosphorus tailings, which includes the following raw materials by mass: 62 parts of calcined phosphorus tailings dry basis, 28 parts of soluble phosphate (analytical pure potassium dihydrogen phosphate), 10 parts of light-burned magnesia, 0.5 part of setting retarder (boric acid), and 22 parts of water.

[0055] In the calculation of the dosage of water reducer, the material characteristic coefficient K = 0.6 * 0.65 * 1.1 = 0.468; W / C is the water-cement ratio of 0.22; n takes the value of 1.2; S is the slump flow of 143 mm; η 减水剂 is the water reducer efficiency coefficient of 2; at room temperature of 25 °C, α*T is 0; β is the setting retarder interference coefficient of 0.2; R 缓凝剂 is the dosage of the setting retarder of 0.5. Then W 减水剂 = (K * (W / C) n * S / η 减水剂 )*(1 + α*T)*(1 - β*R 缓凝剂 ) = (0.468 * 0.22 1.2 * 0.143 / 2)*(1 + 0)*(1 - 0.2 * 0.5) = 0.44%, and the dosage of water reducer is 0.44% of the mixed dry materials.

[0056] The same method as in Example 1 above is used to test the performance indexes of the magnesium phosphate cement material prepared in this example.

[0057] Example 4

[0058] Example 4 of the present invention provides a method for preparing magnesium phosphate cement paste by low-temperature calcination of phosphorus tailings, which includes the following raw materials by mass: 65 parts of calcined phosphorus tailings dry basis, 23 parts of soluble phosphate (analytical pure potassium dihydrogen phosphate), 11 parts of light-burned magnesia, 1.5 parts of setting retarder (boric acid), and 25 parts of water.

[0059] In the calculation of the dosage of water reducer, the material characteristic coefficient K = 0.6 * 0.65 * 1.1 = 0.468; W / C is the water-cement ratio of 0.25; n takes the value of 1.2; S is the slump flow of 184 mm; η减水剂 The water-reducing agent efficiency coefficient is 2; at room temperature of 25°C, α*T is 0; β is the retarding agent interference coefficient of 0.2; R 缓凝剂 is the dosage of the retarding agent of 1.5. Then W 减水剂 =(K*(W / C) n *S / η 减水剂 )*(1 + α*T)*(1 - β*R 缓凝剂 )=(0.468*0.25 1.2 *0.184 / 2)*(1 + 0)*(1 - 0.2*1.5)=0.65%, and the addition amount of the water-reducing agent is 0.65% of the mixed dry materials.

[0060] The same method as in Example 1 above is used to test the various performance indicators of the magnesium phosphate cement material prepared in this example.

[0061] Example 5

[0062] Example 5 of the present invention provides a method for preparing magnesium phosphate cement paste by low-temperature calcination of phosphorus tailings, which includes the following raw materials by mass: 56 parts of calcined phosphorus tailings dry basis, 30.5 parts of soluble phosphate (analytical pure potassium dihydrogen phosphate), 13.5 parts of lightly calcined magnesium oxide, 0.5 part of retarding substance (boric acid), and 23 parts of water.

[0063] In the calculation of the dosage of the water-reducing agent, the material characteristic coefficient K is K = 0.6*0.65*1.1 = 0.468; W / C is the water-cement ratio of 0.23; n takes the value of 1.2; S is the slump flow of 165 mm; η 减水剂 is the water-reducing agent efficiency coefficient of 2; at room temperature of 25°C, α*T is 0; β is the retarding agent interference coefficient of 0.2; R 缓凝剂 is the dosage of the retarding agent of 0.5. Then W 减水剂 =(K*(W / C) n *S / η 减水剂 )*(1 + α*T)*(1 - β*R 缓凝剂 )=(0.468*0.23 1.2 *0.165 / 2)*(1 + 0)*(1 - 0.2*0.5)=0.53%, and the addition amount of the water-reducing agent is 0.53% of the mixed dry materials.

[0064] The same method as in Example 1 above is used to test the various performance indicators of the magnesium phosphate cement material prepared in this example.

[0065] Example 6

[0066] Example 6 of the present invention provides a method for preparing magnesium phosphate cement paste by low-temperature calcination of phosphorus tailings, which comprises the following raw materials by mass: 56 parts of dry calcined phosphorus tailings, 30.5 parts of soluble phosphate (analytical pure potassium dihydrogen phosphate), 13.5 parts of lightly calcined magnesium oxide, 1 part of retarder (boric acid), and 25 parts of water.

[0067] In the calculation of the dosage of water-reducing agent, the material characteristic coefficient K is K = 0.6 * 0.65 * 1.1 = 0.468; W / C is the water-cement ratio of 0.25; n is taken as 1.2; S is the slump flow of 187 mm; η 减水剂 is the water-reducing agent efficiency coefficient of 2; at room temperature of 25 °C, α*T is 0; β is the retarder interference coefficient of 0.2; R 缓凝剂 is the dosage of retarder of 1. Then W 减水剂 = (K * (W / C) n * S / η 减水剂 ) * (1 + α*T) * (1 - β*R 缓凝剂 ) = (0.468 * 0.25 1.2 * 0.187 / 2) * (1 + 0) * (1 - 0.2 * 1) = 0.66%, and the addition amount of water-reducing agent is 0.66% of the mixed dry materials.

[0068] The same method as in Example 1 above was used to test the performance indexes of the magnesium phosphate cement material prepared in this example.

[0069] Example 7

[0070] Example 7 of the present invention provides a method for preparing magnesium phosphate cement paste by low-temperature calcination of phosphorus tailings, which comprises the following raw materials by mass: 56 parts of dry calcined phosphorus tailings, 30.5 parts of soluble phosphate (analytical pure potassium dihydrogen phosphate), 13.5 parts of lightly calcined magnesium oxide, 1.5 parts of retarder (boric acid), and 27 parts of water.

[0071] In the calculation of the dosage of water-reducing agent, the material characteristic coefficient K is K = 0.6 * 0.65 * 1.1 = 0.468; W / C is the water-cement ratio of 0.27; n is taken as 1.2; S is the slump flow of 195 mm; η 减水剂 is the water-reducing agent efficiency coefficient of 2; at room temperature of 25 °C, α*T is 0; β is the retarder interference coefficient of 0.2; R 缓凝剂 is the dosage of retarder of 1.5. Then W 减水剂 = (K * (W / C) n * S / η 减水剂 ) * (1 + α*T) * (1 - β*R 缓凝剂 ) = (0.468 * 0.27 1.2 * 0.195 / 2) * (1 + 0) * (1 - 0.2 * 1.5) = 0.75%, and the addition amount of water-reducing agent is 0.75% of the mixed dry materials.

[0072] The same method as that in the above-mentioned Example 1 was used to test the performance indexes of the magnesium phosphate cement material prepared in this example.

[0073] Comparative Example 1

[0074] Comparative Example 1 of the present invention provides a method for preparing magnesium phosphate cement paste by calcining phosphorus tailings at low temperature, which includes the following raw materials by mass: 59 parts of dry calcined phosphorus tailings, 33 parts of soluble phosphate (analytical pure potassium dihydrogen phosphate), 8 parts of lightly burned magnesium oxide, 1.5 parts of setting retarder (boric acid), and 25 parts of water. No water reducing agent is added in this comparative example.

[0075] The same method as that in the above-mentioned Example 1 was used to test the performance indexes of the magnesium phosphate cement material prepared in this example.

[0076] Comparative Example 2

[0077] Comparative Example 2 of the present invention provides a method for preparing magnesium phosphate cement paste by calcining phosphorus tailings at low temperature, which includes the following raw materials by mass: 56 parts of dry calcined phosphorus tailings, 30.5 parts of soluble phosphate (analytical pure potassium dihydrogen phosphate), 13.5 parts of lightly burned magnesium oxide, 1 part of setting retarder (boric acid), and 25 parts of water. No water reducing agent is added in this comparative example.

[0078] The same method as that in the above-mentioned Example 1 was used to test the performance indexes of the magnesium phosphate cement material prepared in this example. The test analysis results are shown in Table 3.

[0079] Table 3 Test results of each example and comparative example

[0080]

[0081] As can be seen from Table 3, in different examples, changing the phosphorus-magnesium ratio, water-cement ratio, setting retarder, and dosage of water reducing agent will all affect the performance of the phosphorus tailings-based magnesium phosphate cement. Adding 56 parts of calcined phosphorus tailings, 30.5 parts of potassium dihydrogen phosphate, and 13.5 parts of lightly burned magnesium oxide, the 2h strength of the tailings-based magnesium phosphate cement reaches more than 25MPa, and the 1d strength reaches more than 40MPa. The addition of both the setting retarder and the water reducing agent will affect the setting time of the cement in this experiment.

[0082] Appendix Figure Four is the XRD analysis diagram of the calcined phosphorus tailings. The main substances present are active magnesium oxide and calcium carbonate as the filling aggregate, and there are no peaks of substances such as calcium oxide. Selecting a reasonable calcination temperature to generate the required substances to achieve the separation of calcium and magnesium components is one of the innovation points of the patent. Appendix Figure FiveIt is the product phase of tailings-based cement, and the main substance is potassium magnesium phosphate, which conforms to the crystal form of magnesium phosphate cement. At the same time, MgKPO4·6H2O is one of the important indicators for the formation of cement strength. At the same time, there is also calcium carbonate filling the aggregate and unreacted magnesium oxide in the peak shape, which verifies the rationality of the calcination temperature of tailings again.

[0083] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A magnesium phosphate cement paste based on low-temperature calcined phosphate tailings, characterized in that: The invention comprises the following raw materials in parts by weight:

2. The magnesium phosphate cement paste based on low-temperature calcined phosphate tailings according to claim 1, characterized in that: The soluble phosphate is at least one of potassium dihydrogen phosphate and ammonium dihydrogen phosphate, and the purity of the soluble phosphate is ≥99%.

3. The magnesium phosphate cement paste based on low-temperature calcined phosphate tailings according to claim 1, characterized in that: The low-temperature calcined phosphate tailings are prepared by calcining the phosphate tailings at 700-780° C. for 2-5 hours. The magnesium oxide content in the low-temperature calcined phosphate tailings is ≥18%, and the calcium exists in the form of calcium carbonate, with the calcium carbonate content being ≥60%.

4. The magnesium phosphate cement paste based on low-temperature calcined phosphate tailings according to claim 3, characterized in that: The phosphate tailings are filter press tailings after flotation process treatment, and the content of P2O5 in the phosphate tailings is 7-10%, the content of CaO is 30-35%, the content of MgO is 20-25%, the content of SiO2 is 5-10%, the content of Fe2O3 is 0.5-1%, the content of Al2O3 is 0.5-1%, and the density is 2.5-3.1t / m 3 , moisture content ≤15%.

5. The magnesium phosphate cement paste based on low-temperature calcined phosphate tailings according to claim 1, characterized in that: The magnesium oxide content in the light-burned magnesium oxide is ≥90%.

6. The magnesium phosphate cement paste based on low-temperature calcined phosphate tailings according to claim 1, characterized in that: The retarding substance is at least one of borax and boric acid.

7. The magnesium phosphate cement paste based on low-temperature calcined phosphate tailings according to claim 1, characterized in that: The amount of water reducing agent is calculated according to the following formula: W 减水剂 =(K*(W / C) n *S / n 减水剂 )*(1+α*T)*(1-β*R 缓凝剂 ) Among them, W 减水剂 is the amount of water reducer added; K is the material property coefficient; W / C is the water-cement ratio, ranging from 0.22 to 0.30; n is the fluidity index, which is 1.0 for polycarboxylic acid water reducer and 1.5 for naphthalene water reducer; S is the slump fluidity; η 减水剂 is the water reducer efficiency coefficient, which is 2.0 for polycarboxylic acid water reducer and 1.0 for naphthalene water reducer; α is the temperature correction coefficient, which ranges from 0.01 to 0.03 / ℃; T is the difference between the ambient temperature and the reference temperature, and the reference temperature is 25℃; β is the retarder interference coefficient; R 缓凝剂 is the dosage of retarder.

8. The magnesium phosphate cement paste based on low-temperature calcined phosphate tailings according to claim 7, characterized in that: The material characteristic coefficient K=K0*k MgO *k 磷酸盐 , The value range of K0 is 0.6~0.8; MgO The characteristic coefficient of magnesium oxide is 0.6 to 0.7, k 磷酸盐 The characteristic coefficient of potassium dihydrogen phosphate is 1.1 to 1.2, k 磷酸盐 The characteristic coefficient of diammonium phosphate is 1.

0.

9. The magnesium phosphate cement paste based on low-temperature calcined phosphate tailings according to claim 7, characterized in that: The β=reduction in water reducing agent demand / boric acid dosage, with a value of 0.

2.

10. A method for preparing magnesium phosphate cement paste based on low-temperature calcined phosphate tailings as claimed in any one of claims 1 to 8, characterized in that: The steps include: 1) mixing soluble phosphate, low-temperature calcined phosphate tailings, light-burned magnesium oxide and retarding material uniformly to obtain a mixed dry material; 2) Add the calculated water reducer to water, mix thoroughly and set aside; 3) Mixing the mixed dry materials with the water reducing agent mixed liquid to obtain magnesium phosphate cement slurry, the mixing time of the dry materials in step 1) is not less than 1 minute, and when adding the mixed liquid in step 2), the stirring time is not less than 150 seconds.

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