A method for evaluating the effect of eutectic phosphorus on gypsum gelling properties

Abstract

The present invention provides an evaluation method for the effect of eutectic phosphorus on the gelling properties of gypsum, characterized in that the evaluation method comprises: (a) providing at least two types of gypsum, and then independently mixing them with water to obtain a slurry of standard consistency, and measuring the setting time thereof; (b) sequentially molding the slurry of standard consistency obtained in step (a), and testing its strength after standing; the gypsum is a gypsum powder containing only eutectic phosphorus. The evaluation method for the effect of eutectic phosphorus on the gelling properties of gypsum provided by the present invention accurately studies the effect of eutectic phosphorus on the gelling properties of gypsum by using gypsum powder containing only eutectic phosphorus and having the same crystal appearance and particle size.

Description

Technical Field

[0001] The invention belongs to the technical field of comprehensive utilization of gypsum, and relates to a method for evaluating the influence of phosphorus-containing impurities on gypsum performance, and in particular to a method for evaluating the influence of eutectic phosphorus on the gelling properties of gypsum. Background Art

[0002] Phosphogypsum (mainly composed of CaSO4·2H2O) is a byproduct discharged during the wet phosphoric acid process. The phosphorus impurities in it are divided into soluble phosphorus, insoluble phosphorus and eutectic phosphorus, of which eutectic phosphorus refers to the phosphorus in the CaSO4·2H2O crystal lattice. Since CaHPO4·2H2O and CaSO4·2H2O have very similar unit cell parameters, during the wet phosphoric acid process, the crystallization of CaSO4·2H2O will be accompanied by a small amount of CaHPO4·2H2O entering its crystal lattice, and this part of phosphorus is therefore called eutectic phosphorus in phosphogypsum.

[0003] Relevant scholars in this field have always believed that eutectic phosphorus, like soluble phosphorus, can have a certain impact on the gelling properties of phosphogypsum, but no scholar has yet provided clear evidence to prove this conclusion.

[0004] CN 113607668A discloses a method for testing the content of eutectic phosphorus in phosphogypsum, and CN 113402185A discloses a method for separating and treating eutectic phosphorus in phosphogypsum, but neither of them mentions the degree of influence of eutectic phosphorus on the gelling properties of gypsum. Peng Jiahui et al. mentioned the study on the influence of eutectic phosphorus on the gelling properties of gypsum (see Organic matter, eutectic phosphorus in phosphogypsum and its influence on performance [J], Journal of Building Materials, 2003, 6(3): 221-226). Peng Jiahui et al. studied the influence of eutectic phosphorus content on the gelling properties of gypsum by mixing CaHPO4·2H2O and CaSO4·2H2O in a supersaturated solution of phosphoric acid and calcium ions.

[0005] Li Mei et al. also studied the effect of eutectic phosphorus on the cementing properties of gypsum (see "Research on Factors Affecting the Quality of Phosphogypsum and Its Resource Utilization as Building Materials" for details). They studied the effect of eutectic phosphorus content on the cementing properties of gypsum by mixing CaHPO4·2H2O and CaSO4·2H2O in a supersaturated solution of phosphoric acid and calcium ions.

[0006] The above research process has the following problems: first, it cannot be guaranteed that all CaHPO4·2H2O can enter the crystal lattice of CaSO4·2H2O; second, CaHPO4·2H2O is not the only phosphorus impurity present in this system, but also other forms of phosphorus impurities (such as insoluble phosphorus), which will affect the cementing properties of gypsum. Therefore, it is impossible to determine whether the difference in the cementing properties of gypsum is caused by CaHPO4·2H2O.

[0007] In addition, the crystal morphology and particle size of CaHPO4·2H2O will also have a certain influence on the mechanical properties of the prepared β-hemihydrate gypsum powder.

[0008] Therefore, it is necessary to provide several calcium sulfate dihydrates containing only eutectic phosphorus and having similar crystal morphology and particle size, so as to accurately study the effect of eutectic phosphorus on the cementitious properties of gypsum. Summary of the invention

[0009] The object of the present invention is to provide an evaluation method for the influence of eutectic phosphorus on the gelling properties of gypsum, wherein the evaluation method accurately studies the influence of eutectic phosphorus on the gelling properties of gypsum by using gypsum powder containing only eutectic phosphorus and having the same crystal appearance and particle size.

[0010] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0011] The present invention provides a method for evaluating the influence of eutectic phosphorus on the gelling properties of gypsum, the evaluation method comprising:

[0012] (a) providing at least two kinds of gypsum, and then mixing them with water separately to obtain slurry of standard consistency, and measuring the setting time thereof;

[0013] (b) forming the slurry of standard consistency obtained in step (a) in sequence, allowing it to stand, and then testing its strength;

[0014] The gypsum is gypsum powder containing only eutectic phosphorus.

[0015] The present invention uses gypsum powder containing only eutectic phosphorus as an experimental object to measure the physical properties (setting time and strength) of the gypsum, so as to accurately determine the influence of the eutectic phosphorus on the gelling properties of the gypsum.

[0016] Preferably, the gypsum in step (a) has the same crystal appearance and particle size.

[0017] Preferably, the gypsum in step (a) has different eutectic phosphorus contents.

[0018] The molding of the present invention is to invert the slurry of standard consistency obtained in step (a) into a 40mm×40mm×160mm triple test mold for molding.

[0019] Preferably, the standing time in step (b) is 1.8-2.3 h, for example, 1.8 h, 1.9 h, 2 h, 2.1 h, 2.2 h or 2.3 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0020] Since the crystal morphology and particle size of gypsum have a certain influence on the mechanical properties of hemihydrate gypsum powder, the present invention limits the research object (gypsum) to have the same crystal appearance and particle size to ensure accurate determination of the effect of eutectic phosphorus on the gelling properties of gypsum.

[0021] Preferably, the method for preparing the gypsum powder containing only eutectic phosphorus comprises the following steps:

[0022] (1) mixing a sulfate solution and a phosphate solution, heating, and then adding an acid solution until the pH value is 1-3 to obtain a mixed solution;

[0023] (2) stirring and mixing the calcium salt solution and the mixed solution obtained in step (1), filtering, washing with water and calcining in sequence after the reaction to obtain the gypsum powder containing only eutectic phosphorus.

[0024] The present invention selects sulfate solution, phosphate solution and calcium salt solution as the main reaction system, and controls the pH value of the reaction system so that all phosphorus in the solution is converted into HPO4 2- form exists, so that in Ca 2+ 、SO4 2- Under supersaturation conditions, it can maximize the interaction with Ca 2+ 、SO4 2- A continuous solid solution is formed, namely Ca(HPO4-SO4). Under this condition, there will be no insoluble phosphorus (Ca3(PO4)2, Ca 10 (PO4)6(OH)2, etc.) are produced, while soluble phosphorus, soluble Na salts, etc. can be removed by water washing. Therefore, only eutectic phosphorus, an impurity, exists in the final prepared calcium sulfate dihydrate.

[0025] The present invention limits the pH value of the reaction system to 1-3 because the phosphate radical exists in different forms under different pH conditions: mainly PO4 3- 、HPO4 2- 、H2PO4 - When the solution pH is between 1 and 3, phosphate is converted to HPO4. 2- In the form of 2+ When the pH value of the solution is higher than 3, phosphate may exist in PO4 3- form, when there is Ca in the solution 2+ When Ca 10 (PO4)6(OH)2 crystals (this is the insoluble phosphorus outside the crystal lattice); when the pH value of the solution is lower than 1, the phosphate radical is basically in the form of H2PO4 - and H3PO4. When there is Ca in the solution2+ No crystals will be generated.

[0026] Since CaHPO4·2H2O and CaSO4·2H2O have very similar lattice parameters, they can easily form a solid solution, that is, CaHPO4·2H2O will enter the lattice of CaSO4·2H2O to form eutectic phosphorus. When the pH is higher than 3, insoluble phosphorus will be produced along with the crystallization of calcium sulfate; when the pH value is lower than 1, only soluble phosphorus exists, and there is no eutectic phosphorus crystallization. At this time, the crystallized calcium sulfate only contains washable soluble phosphorus. Therefore, choosing a pH value between 1-3 can accurately control the presence of only eutectic phosphorus as an impurity in phosphogypsum.

[0027] Preferably, the sulfate solution in step (1) comprises Na2SO4 solution and / or K2SO4 solution.

[0028] Preferably, the concentration of the sulfate solution in step (1) is 0.1-5 mol / L, for example, 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L or 5 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0029] Preferably, the phosphate solution in step (1) comprises any one of Na2HPO4 solution, NaH2PO4 solution, Na3PO4 solution, K2HPO4 solution, KH2PO4 solution or K3PO4 solution, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of Na2HPO4 solution, NaH2PO4 solution and Na3PO4 solution, a combination of K2HPO4 solution, KH2PO4 solution and K3PO4 solution, or a combination of Na2HPO4 solution and K2HPO4 solution, a combination of NaH2PO4 solution and KH2PO4 solution, or a combination of Na3PO4 solution and K3PO4 solution.

[0030] Preferably, the concentration of the phosphate solution in step (1) is 0.1-5 mol / L, for example, 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L or 5 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] Preferably, the molar ratio of the sulfate solution to the phosphate solution in step (1) is 1-3, for example, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8 or 3, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0032] The concentrations of the sulfate solution and the phosphate solution of the present invention are both 0.1-5 mol / L. If the concentration is too low, the crystal nucleation growth rate of calcium sulfate and calcium hydrogen phosphate will be slowed down, and the crystal will become larger. However, if the concentration is too slow, the efficiency will be affected. If the concentration is too high, the crystal nucleation growth rate of calcium sulfate and calcium hydrogen phosphate will be slowed down, and the crystal will become fine. On the one hand, it may affect the formation of the solid solution, and on the other hand, it will affect the strength and other properties of the subsequent products. If the strength is very low, it will affect the judgment of the influence of eutectic phosphorus on its performance.

[0033] Preferably, the heating temperature in step (1) is 20-60°C, for example, it can be 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C or 60°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0034] Preferably, the acid solution in step (1) comprises hydrochloric acid and / or nitric acid.

[0035] Preferably, the calcium salt solution in step (2) includes CaCl2 solution and / or Ca(NO3)2 solution.

[0036] Preferably, the concentration of the calcium salt solution in step (2) is 0.1-5 mol / L, for example, 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L or 5 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0037] Preferably, the stirring rate of the stirring and mixing in step (2) is 100-500 r / min, for example, it can be 100 r / min, 150 r / min, 200 r / min, 250 r / min, 300 r / min, 350 r / min, 400 r / min, 450 r / min or 500 r / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0038] Preferably, the reaction time of step (2) is 1-24 h, for example, it can be 1 h, 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h or 24 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0039] Preferably, the reaction in step (2) is accompanied by continuous stirring.

[0040] Preferably, the calcination temperature in step (2) is 120-170°C, for example, it can be 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C or 170°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0041] Preferably, the calcination time in step (2) is 4-6 h, for example, 4 h, 4.4 h, 4.8 h, 5.2 h, 5.6 h or 6 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0042] Preferably, the stirring and mixing in step (2) comprises: adding the calcium salt dropwise at a uniform rate into the mixed solution obtained in step (1) during the stirring process.

[0043] Preferably, the uniform dripping rate is 0.001-1 mL / s, for example, it can be 0.001 mL / s, 0.01 mL / s, 0.1 mL / s, 0.2 mL / s, 0.3 mL / s, 0.4 mL / s, 0.5 mL / s, 0.6 mL / s, 0.7 mL / s, 0.8 mL / s, 0.9 mL / s or 1 mL / s, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0044] Preferably, the uniform dripping method includes shower-style uniform dripping.

[0045] The present invention enables the crystals to grow evenly by dropping the calcium salt into the mixed solution at a uniform speed, thereby ensuring that the eutectic phosphorus content entering the calcium sulfate crystals is relatively uniform.

[0046] As a preferred technical solution of the present invention, the method for preparing gypsum powder containing only eutectic phosphorus according to the present invention comprises the following steps:

[0047] (1) mixing 0.1-5 mol / L sulfate solution and 0.1-5 mol / L phosphate solution in a molar ratio of 0.1-10, heating to 20-60° C., and then adding hydrochloric acid and / or nitric acid to a pH value of 1-3 to obtain a mixed solution;

[0048] (2) stirring and mixing the calcium salt solution with a concentration of 0.1-5 mol / L and the mixed solution obtained in step (1) at a stirring rate of 100-500 r / min, reacting for 1-24 hours, filtering and washing with water, and then calcining at a temperature of 120-170° C. for 4-6 hours to obtain the gypsum powder containing only eutectic phosphorus;

[0049] The stirring and mixing comprises: during the stirring process, adding the calcium salt dropwise at a rate of 0.001-1 mL / s into the mixed solution obtained in step (1) in a shower-like uniform speed.

[0050] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] (1) The gypsum powder containing only eutectic phosphorus provided by the present invention controls the pH value of the reaction system so that the prepared calcium sulfate dihydrate contains only one impurity, eutectic phosphorus. The preparation method is simple, the conditions are mild, and it is easy to industrialize production;

[0053] (2) The method for evaluating the effect of eutectic phosphorus on the gelling properties of gypsum provided by the present invention accurately studies the effect of eutectic phosphorus on the gelling properties of gypsum by using gypsum powder containing only eutectic phosphorus and having the same crystal appearance and particle size. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 A schematic diagram of the crystal morphology of gypsum powder containing only eutectic phosphorus provided in Example 1 of the present invention;

[0055] Figure 2 A schematic diagram of the crystal morphology of gypsum powder containing only eutectic phosphorus provided in Example 2 of the present invention;

[0056] Figure 3 A schematic diagram of the crystal morphology of gypsum powder containing only eutectic phosphorus provided in Example 3 of the present invention;

[0057] Figure 4 XRD results of gypsum powder containing only eutectic phosphorus provided in Examples 1-3 of the present invention;

[0058] Figure 5 The particle size distribution diagram of the gypsum powder containing only eutectic phosphorus provided in Examples 1-3 of the present invention. DETAILED DESCRIPTION

[0059] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0060] Example 1

[0061] This embodiment provides a gypsum powder containing only eutectic phosphorus. The preparation method of the gypsum powder containing only eutectic phosphorus comprises the following steps:

[0062] (1) mixing 1 mol / L Na2SO4 solution and 1 mol / L Na2HPO4 solution in a molar ratio of 1:0, heating to 60° C., and adding hydrochloric acid until the pH value is 3 to obtain a mixed solution;

[0063] (2) stirring a CaCl2 solution having a concentration of 1 mol / L and the mixed solution obtained in step (1) at a stirring rate of 300 r / min, reacting for 1 h, filtering and washing with water, and then calcining at 155° C. for 5 h to obtain the gypsum powder containing only eutectic phosphorus;

[0064] The stirring and mixing comprises: during the stirring process, adding the calcium salt dropwise at a rate of 0.1 mL / s into the mixed solution obtained in step (1) in a shower-like uniform speed.

[0065] The crystal morphology schematic diagram of the gypsum powder containing only eutectic phosphorus provided in this embodiment is as follows Figure 1 shown.

[0066] Example 2

[0067] This embodiment provides a gypsum powder containing only eutectic phosphorus. The preparation method of the gypsum powder containing only eutectic phosphorus is different from that of Embodiment 1 only in that the molar ratio in step (1) is changed to 3:1 in this embodiment.

[0068] The crystal morphology schematic diagram of the gypsum powder containing only eutectic phosphorus provided in this embodiment is as follows Figure 2 shown.

[0069] Example 3

[0070] This embodiment provides a gypsum powder containing only eutectic phosphorus. The preparation method of the gypsum powder containing only eutectic phosphorus is different from that of Embodiment 1 only in that the molar ratio in step (1) is changed to 2:1 in this embodiment.

[0071] The crystal morphology schematic diagram of the gypsum powder containing only eutectic phosphorus provided in this embodiment is as follows Figure 3 shown.

[0072] The XRD results of the gypsum powder containing only eutectic phosphorus provided in Examples 1-3 are as follows: Figure 4As shown; the particle size distribution diagram of the gypsum powder containing only eutectic phosphorus provided in Examples 1-3 is as follows Figure 5 shown.

[0073] Depend on Figure 1-Figure 5 It can be seen that the crystal appearance and particle size of the gypsum powder provided in Examples 1-3 are consistent, which meets the requirements for evaluating the effect of eutectic phosphorus on the gelling properties of gypsum.

[0074] The gypsum powder containing only eutectic phosphorus provided in Examples 1-3 was tested for gelling properties, and the specific process is as follows:

[0075] (1) The gypsum powder containing only eutectic phosphorus provided in Examples 1-3 was mixed with water separately to obtain a slurry of standard consistency, and the setting time thereof was measured;

[0076] (b) After the slurry solidified in step (a) is allowed to stand, its strength is tested.

[0077] The setting time and strength structure are shown in Table 1.

[0078] Table 1

[0079]

[0080] It can be seen from Table 1 that with the increase of eutectic phosphorus content, the setting time of gypsum hydration is prolonged and the strength is reduced. This proves that eutectic phosphorus has a certain negative impact on the gelling properties of gypsum.

[0081] In summary, the method for evaluating the effect of eutectic phosphorus on the gelling properties of gypsum provided by the present invention accurately studies the effect of eutectic phosphorus on the gelling properties of gypsum by using gypsum powder containing only eutectic phosphorus and having the same crystal appearance and particle size.

[0082] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A method for evaluating the effect of eutectic phosphorus on the gelling properties of gypsum, characterized in that: The evaluation methods include: (a) providing at least two kinds of gypsum, and then mixing them with water separately to obtain slurry of standard consistency, and measuring the setting time thereof; (b) forming the slurry of standard consistency obtained in step (a) in sequence, allowing it to stand, and then testing its strength; The gypsum is a gypsum powder containing only eutectic phosphorus, and the preparation method thereof comprises the following steps: (1) mixing a sulfate solution and a phosphate solution, heating and then adding an acid solution until the pH value is 1-3 to obtain a mixed solution; (2) stirring and mixing the calcium salt solution and the mixed solution obtained in step (1), filtering, washing with water and calcining in sequence after the reaction to obtain the gypsum powder containing only eutectic phosphorus; In step (1), the concentration of the sulfate solution is 0.1-5 mol / L, the concentration of the phosphate solution is 0.1-5 mol / L, the molar ratio of the sulfate solution to the phosphate solution is 1-3, and the heating temperature is 20-60° C.; The concentration of the calcium salt solution in step (2) is 0.1-5 mol / L, and the reaction time is 1-24 h.

2. The method for evaluating the effect of eutectic phosphorus on gypsum gelling properties according to claim 1, characterized in that: The gypsum in step (a) has the same crystal appearance and particle size.

3. The method for evaluating the effect of eutectic phosphorus on gypsum gelling properties according to claim 1, characterized in that: The gypsum in step (a) has different eutectic phosphorus contents.

4. The method for evaluating the effect of eutectic phosphorus on gypsum gelling properties according to claim 1, characterized in that: The standing time in step (b) is 1.8-2.3h.

5. The method for evaluating the effect of eutectic phosphorus on gypsum gelling properties according to claim 1, characterized in that: The sulfate solution described in step (1) includes Na2SO4 solution and / or K2SO4 solution.

6. The method for evaluating the effect of eutectic phosphorus on gypsum gelling properties according to claim 1, characterized in that: The phosphate solution described in step (1) includes any one of Na2HPO4 solution, NaH2PO4 solution, Na3PO4 solution, K2HPO4 solution, KH2PO4 solution or K3PO4 solution, or a combination of at least two thereof.

7. The method for evaluating the effect of eutectic phosphorus on gypsum gelling properties according to claim 1, characterized in that: The acid solution in step (1) includes hydrochloric acid and / or nitric acid.

8. The method for evaluating the effect of eutectic phosphorus on gypsum gelling properties according to claim 1, characterized in that: The calcium salt solution in step (2) includes CaCl2 solution and / or Ca(NO3)2 solution.

9. The method for evaluating the effect of eutectic phosphorus on gypsum gelling properties according to claim 1, characterized in that: The stirring rate of the stirring and mixing in step (2) is 100-500r / min.

10. The method for evaluating the effect of eutectic phosphorus on gypsum gelling properties according to claim 1, characterized in that: The reaction in step (2) is accompanied by continuous stirring.

11. The method for evaluating the effect of eutectic phosphorus on gypsum gelling properties according to claim 1, characterized in that: The calcination temperature in step (2) is 120-170°C.

12. The method for evaluating the effect of eutectic phosphorus on gypsum gelling properties according to claim 1, characterized in that: The calcination time in step (2) is 4-6 hours.

13. The method for evaluating the effect of eutectic phosphorus on gypsum gelling properties according to claim 1, characterized in that: The stirring and mixing in step (2) comprises: adding the calcium salt dropwise at a uniform speed into the mixed solution obtained in step (1) during the stirring process.

14. The method for evaluating the effect of eutectic phosphorus on gypsum gelling properties according to claim 13, characterized in that: The uniform dripping rate is 0.001-1 mL / s.

15. The method for evaluating the effect of eutectic phosphorus on gypsum gelling properties according to claim 13, characterized in that: The uniform dripping method includes shower-style uniform dripping.

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