Preparation method of cemented filling body based on phosphogypsum pretreatment

Abstract

The invention discloses a cemented filling body preparation method based on phosphogypsum pretreatment, and particularly relates to the technical field of phosphogypsum application. The method comprises the following steps: selecting phosphogypsum subjected to sufficient filter pressing in a phosphoric acid production process; taking NaOH, adding a small amount of deionized water to dissolve, cooling to room temperature, and adding deionized water to dilute the NaOH solution; adding an APAM flocculating agent into deionized water to prepare an APAM solution; mixing ardealite with the diluted NaOH solution, and adding an APAM solution to realize separation of supernate and high-concentration ardealite slurry; after standing is finished, calcium hydroxide is added to adjust the pH of supernate to be alkalescent, and then the supernate is subjected to filtering, drying and flotation processes; and adding a certain amount of deionized water and ordinary Portland cement, and uniformly stirring to obtain the required homogeneous cemented filling slurry. By adopting the technical scheme of the invention, the problem that the phosphogypsum in the existing cemented filling body pollutes underground water is solved, and the application prospect of the phosphogypsum in the filling field is further widened.

Description

Technical Field

[0001] The present invention relates to the technical field of phosphogypsum application, and in particular to a method for preparing a cementing filling body based on phosphogypsum pretreatment. Background Art

[0002] Phosphogypsum is produced during the production of phosphoric acid. As a major industrial solid waste, phosphogypsum is difficult to be effectively utilized due to its high pollution. At present, the main application of phosphogypsum is as a filling aggregate. It is added with a certain amount of ordinary Portland cement and mixed with water to form a cementing filling body that meets the strength requirements, so that the cementing filling body can be used to treat the underground goaf. This method solves the problems of phosphogypsum storage and goaf collapse to a certain extent, but the phosphogypsum in the cementing filling body may cause serious pollution to the groundwater after entering the goaf. Therefore, pre-treatment of phosphogypsum to reduce the content of harmful substances in phosphogypsum and meet the strength design requirements of the cementing filling body is the bottleneck in the field of phosphogypsum filling.

[0003] At present, the main focus of phosphogypsum in the filling field is to add other materials to prepare a cemented filling body, so as to use the prepared cemented filling body to treat the goaf. For example, a Chinese invention patent (patent publication number is CN108516713A) discloses a pretreatment and application method of phosphogypsum; phosphogypsum, heavy calcium and water are mixed and slurried to obtain phosphogypsum slurry, and then the phosphogypsum slurry is subjected to aging pretreatment, which can improve the performance of the obtained pretreated phosphogypsum and enhance its strength in the application field of filling aggregate. Another example is a Chinese invention patent (publication number is CN100476162C) discloses a method for filling phosphogypsum in underground goafs to form a solidified filling body, in which cement, fly ash and phosphogypsum are mixed in a specific proportion, and then the additive sodium sulfate is added to prepare and improve the strength of the filling body. Regarding the above-mentioned related technical solutions, although phosphogypsum can be mixed with cement to form a phosphogypsum filling body with a certain strength before pretreatment, the soluble F element in the cementing filling body will leach out of the standard under long-term immersion in groundwater, which poses a potential risk of groundwater environmental pollution and is difficult to be used directly for filling. Therefore, it is urgent to develop a risk-free or low-risk cementing filling body that can be directly used for filling goaf areas. Summary of the invention

[0004] The present invention aims to provide a method for preparing a cementing filling body based on phosphogypsum pretreatment, which solves the problem of groundwater contamination caused by the presence of phosphogypsum in the existing cementing filling body.

[0005] In order to achieve the above object, the technical solution of the present invention is as follows: A method for preparing a cemented filling body based on phosphogypsum pretreatment comprises the following steps:

[0006] S1. Select phosphogypsum that has been fully filtered during the phosphoric acid production process, and use a rapid moisture detector to test the moisture content of the phosphogypsum for later use;

[0007] S2. Pour some NaOH flakes into a beaker, add a small amount of deionized water to dissolve, cool to room temperature and transfer the cooled NaOH solution to a volumetric flask, add a certain amount of deionized water to dilute the NaOH solution to 0.5-1.0 mol / L;

[0008] S3, taking some granular APAM flocculants, adding deionized water and using a magnetic stirrer to prepare an APAM solution with a mass fraction of 0.5‰;

[0009] S4, mixing the phosphogypsum of step S1 with the diluted NaOH solution of step S2 at a certain solid-liquid ratio, and stirring the mixture uniformly at a speed of 200 r / min for 15-20 min, and then adding the APAM solution of step S3 to accelerate the flocculation, sedimentation and concentration of the phosphogypsum, and separating the supernatant from the high-concentration phosphogypsum slurry after standing for 5-10 min;

[0010] S5. After standing, a certain proportion of calcium hydroxide is added to adjust the pH of the supernatant to a weak alkaline state, and the supernatant is filtered, dried, and subjected to a flotation process to convert the fluorine element in the supernatant into calcium fluoride, thereby realizing the recovery of the F element in the supernatant;

[0011] S6. After testing the moisture content of the high-concentration phosphogypsum slurry, add a certain amount of deionized water and 42.5-grade ordinary Portland cement and stir evenly to obtain the required homogeneous cementitious filling slurry.

[0012] Principle and effect of the technical solution: This solution uses phosphogypsum, a solid waste generated during the preparation of phosphoric acid, as the original filling aggregate. After pretreatment with low-concentration NaOH and polyaluminium chloride (APAM), the soluble F element in the phosphogypsum is removed and used as the filling aggregate. It is then mixed with ordinary Portland cement, clean water and the like to form a homogeneous cemented filling body. Among them, the F element in the supernatant after NaOH alkaline washing is recycled in the form of calcium fluoride. At the same time, the soluble F content in phosphogypsum can be greatly reduced by the combined pretreatment of NaOH and APAM. While realizing the comprehensive utilization of phosphogypsum and the management of underground goaf areas, it further broadens the application prospects of phosphogypsum in the filling field.

[0013] Furthermore, in step S1, the moisture content of the phosphogypsum after sufficient pressure filtration is generally about 20%;

[0014] By means of the above device, the water in the phosphogypsum is included in the liquid part when calculating the solid-liquid ratio.

[0015] Furthermore, in step S2, the amount of NaOH used is 15%-20% of the total mass of phosphogypsum; the reaction temperature is 21-25°C, and the reaction time is 10 minutes.

[0016] Through the above arrangement, the active fluoride on the surface of the phosphogypsum is dissolved in the liquid phase through sufficient alkali washing, thereby smoothly removing the fluoride.

[0017] Furthermore, in step S3, the amount of APAM used is 2‰-4‰ of the total mass of phosphogypsum.

[0018] The above arrangement is conducive to the solid-liquid separation of the phosphogypsum slurry.

[0019] Furthermore, in step S4, the solid-liquid ratio is 1:1-1:2.

[0020] Through the above settings, the amount of water added is adjusted. If the water is too little, the alkaline washing will be inadequate, and if the water is too much, the subsequent water treatment system capacity will be too high. This solution adopts this ratio to ensure sufficient washing while reducing the subsequent process requirements as much as possible.

[0021] Furthermore, in step S5, the pH range of the weak alkalinity is 7-9.

[0022] Through the above settings, the alkalinity requirements of the hydration system are met.

[0023] Furthermore, in step S6, the mass fractions of the components in the homogenous filling slurry are: 3-5 parts of NaOH, 20 parts of phosphogypsum, and 3-5 parts of cement.

[0024] Through the above arrangement, the residual acid contained in the phosphogypsum can be neutralized.

[0025] Furthermore, in step S6, the mass concentration of the homogeneous cementitious filling slurry is 60%-66%, and the density is 2.2-2.5 g / cm 3 .

[0026] Through the above arrangement, the filling slurry conveying requirements are met.

[0027] Furthermore, the method also includes: S7, conducting uniaxial compressive strength tests on the test blocks 3 days, 7 days and 28 days after the homogeneous cementitious filling slurry is molded, taking 3 blocks at each age and taking the average value as the compressive strength of the test blocks at that age.

[0028] Compared with the prior art, this solution has the following beneficial effects:

[0029] 1. This scheme provides a method for preparing a cemented filling body based on phosphogypsum pretreatment, which can use the phosphogypsum produced in the phosphorus chemical industry to fill the goaf, reduce the waste of land resources and contribute to environmental sustainability.

[0030] 2. This scheme provides a method for preparing a cemented filling body based on the pretreatment of phosphogypsum. The solid waste phosphogypsum produced in the phosphorus chemical process is used as a filling aggregate. After being pretreated with NaOH and APAM, a certain amount of ordinary Portland cement is added to form a homogeneous cemented filling body. This method can not only improve the comprehensive utilization rate of phosphogypsum waste, reduce the surface stockpile of phosphogypsum, avoid the problem of wasting precious land resources, and contribute to environmental sustainable development, but also use the prepared homogeneous cemented filling slurry to treat the underground goaf and further improve the safety of the recovery operation.

[0031] 3. This scheme provides a method for preparing a cementing filling body based on the pretreatment of phosphogypsum. After the phosphogypsum is pretreated with NaOH and APAM, a certain amount of calcium hydroxide is added to the supernatant to allow the F element present to be recovered and utilized in the form of calcium fluoride. This can not only reduce the content of harmful substances in the phosphogypsum, but also minimize the potential pollution risk of the phosphogypsum filling body to the mine groundwater environment, and at the same time convert the F leaching pollution of the phosphogypsum into the recovery and utilization of the harmful element F. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below through specific embodiments:

[0033] Example 1

[0034] A method for preparing a cemented filling body based on phosphogypsum pretreatment comprises the following steps:

[0035] S1. Select phosphogypsum with a certain moisture content after sufficient filtration during the phosphoric acid production process, and use a rapid moisture detector to test the moisture content of the phosphogypsum for later use. Crush and screen it, and then use a ball mill to grind it to a particle size of less than 3-5mm. The pH value of the phosphogypsum is 2-4; the main chemical components of phosphogypsum are SiO 2 , CaO and SO 3 etc., the particle size distribution is d 10 =3.52μm, d 30 =18.14μm, d 50 =42.93μm, d 60 =45.97μm, Cu=13.06.

[0036] S2. Pour some NaOH flakes into a beaker, and add a small amount of deionized water to dissolve it. Cool it to room temperature and transfer the cooled NaOH solution to a volumetric flask, add a certain amount of deionized water to dilute the NaOH solution to 0.5-1.0 mol / L; use the diluted NaOH solution to pre-treat the phosphogypsum by alkali washing in a certain proportion, the amount of NaOH is 15%-20% of the total mass of the phosphogypsum, the reaction temperature is 21-25°C, and the reaction time is 10 minutes. Through sufficient alkali washing, the active fluoride on the surface of the phosphogypsum is dissolved in the liquid phase, thereby smoothly removing the fluoride.

[0037] S3. In order to achieve solid-liquid separation of the phosphogypsum slurry, take some granular APAM flocculants, add deionized water and use a magnetic stirrer to prepare an APAM solution with a mass fraction of 0.5‰. Add the APAM solution to the mixed slurry of step S2 in a certain proportion and let it stand for 5-10 minutes. In this step, the amount of APAM used is 2‰-4‰ of the total mass of the phosphogypsum.

[0038] S4. The phosphogypsum of step S1 is mixed with the diluted NaOH solution of step S2 at a certain solid-liquid ratio. In this embodiment, the solid-liquid ratio is 1:1-1:2, and the mixed solution is uniformly stirred at a speed of 200 r / min for 15-20 min, and then the APAM solution of step S3 is added to accelerate the flocculation, sedimentation and concentration of the phosphogypsum. After standing for 5-10 min, the supernatant and the high-concentration phosphogypsum slurry are separated.

[0039] S5. After standing, a certain proportion of calcium hydroxide is added to adjust the pH of the supernatant to weak alkalinity. In order to meet the alkalinity requirements of the filling slurry hydration, the weak alkalinity pH range in this step is 7-9; the supernatant is filtered, dried, floated, etc. to convert the fluorine element in the supernatant into calcium fluoride, thereby realizing the recovery of the F element in the supernatant.

[0040] S6. After testing the moisture content of the high-concentration phosphogypsum slurry, add a certain amount of deionized water and 42.5-grade ordinary Portland cement, and stir evenly to obtain the required homogeneous cementitious filling slurry. In order to meet the concentration, fluidity, and viscosity pipeline transportation requirements of the filling slurry, in this embodiment, the mass fraction of each component in the homogeneous filling slurry is: 4 parts of NaOH, 20 parts of phosphogypsum, 4 parts of cement, and 0.04 parts of APAM. Clean water is added to form a homogeneous filling slurry with a mass concentration of 63% and a density of 2.4 g / cm 3 .

[0041] S7. Carry out uniaxial compressive strength tests on the filling body specimens 3 days, 7 days and 28 days after the filling slurry is molded. Take 3 specimens at each age and take the average value as the compressive strength of the filling body at that age.

[0042] S8. According to the "Solid Waste Leaching Toxicity Leaching Method Reversal Method" (GB 5086.1-1997), the broken test blocks after 28-day compressive strength test were processed to obtain the leachate, and then the fluoride leaching amount of the 28-day phosphogypsum filling body was measured according to the "Determination of Fluoride in Water Quality Ion Selective Electrode Method" (GB / T 7484-1987).

[0043] Example 2

[0044] The difference between this embodiment and embodiment 1 is that in this embodiment, the mass fraction of each component in the homogeneous filling slurry is: 3 parts of NaOH, 20 parts of phosphogypsum, 3 parts of cement, 0.04 parts of APAM, and clean water is added to form a homogeneous filling slurry with a mass concentration of 60% and a density of 2.2 g / cm 3 .

[0045] Example 3

[0046] The difference between this embodiment and embodiment 1 is that in this embodiment, the mass fraction of each component in the homogeneous filling slurry is: 5 parts of NaOH, 20 parts of phosphogypsum, 5 parts of cement, and 0.04 parts of APAM. Clean water is added to form a homogeneous filling slurry with a mass concentration of 66% and a density of 2.5 g / cm 3 .

[0047] Example 4

[0048] The difference between this embodiment and embodiment 1 is that in this embodiment, the mass fraction of each component in the homogeneous filling slurry is: 4 parts of NaOH, 20 parts of phosphogypsum, 4 parts of cement, and 0.06 parts of APAM. Clean water is added to form a homogeneous filling slurry with a mass concentration of 63% and a density of 2.4 g / cm 3 .

[0049] Example 5

[0050] The difference between this embodiment and embodiment 1 is that: in this embodiment, the mass composition of the homogeneous filling slurry is: 4 parts of NaOH, 20 parts of phosphogypsum, 4 parts of cement, and 0.08 parts of APAM. Clean water is added to form a homogeneous filling slurry with a mass concentration of 63% and a density of 2.4 g / cm 3 .

[0051] Comparative Example 1

[0052] The difference between this embodiment and embodiment 1 is that in this embodiment, NaOH is not added to the homogeneous filling slurry for pretreatment, and other steps remain unchanged. The final filling slurry is composed of 20 parts of phosphogypsum, 4 parts of cement, and 0.04 parts of APAM by weight. Clean water is added to form a homogeneous filling slurry with a mass concentration of 63% and a density of 2.4 g / cm 3 .

[0053] Comparative Example 2

[0054] The difference between this embodiment and embodiment 1 is that in this embodiment, NaOH is not added to the homogeneous filling slurry for pretreatment, and other steps remain unchanged. The final filling slurry is composed of 20 parts of phosphogypsum, 5 parts of cement, and 0.04 parts of APAM by weight. Clean water is added to form a homogeneous filling slurry with a mass concentration of 66% and a density of 2.5 g / cm 3 .

[0055] Comparative Example 3

[0056] The difference between this embodiment and embodiment 1 is that in this embodiment, no NaOH is added to the homogeneous filling slurry for pretreatment, and no APAM solution is added. The other steps remain unchanged. The final filling slurry is composed of 20 parts of phosphogypsum and 4 parts of cement. Clean water is added to form a homogeneous filling slurry with a mass concentration of 63% and a density of 2.4 g / cm 3 .

[0057] The samples in Comparative Examples 1-3 and Examples 1-5 were subjected to compressive strength tests at different ages and F leaching statistics at 28 days, and the results are as follows:

[0058]

[0059] As can be seen from the above table, by comparing the test results of the embodiments and the comparative examples, after the phosphogypsum in the cemented filling body is pretreated with NaOH, the strength of each age is increased, and the amount of F leaching is greatly reduced; and from comparative examples 1 and 2, it can be found that when the phosphogypsum is pretreated with different weight portions of NaOH, the strength of the filling body at each age is slightly enhanced, indicating that NaOH plays a positive role in the growth of the filling body strength. At the same time, it can be found from comparative example 3 that when different weight portions of APAM are added to the homogeneous filling slurry, the strength of the filling body at each age is slightly enhanced, and the amount of F leaching is reduced, indicating that APAM has a positive effect on the strength growth of the filling body and the control of F leaching. In addition, considering the groundwater Class IV standard (GB / T 14848-2017) and the quality requirements and costs of phosphate filling bodies, Examples 1 and 2 have obvious economic advantages under the premise of meeting groundwater pollution and filling body quality.

[0060] The above are only embodiments of the present invention, and the common knowledge such as the known specific structures and / or characteristics in the scheme are not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing a cemented filling body based on phosphogypsum pretreatment, characterized in that: The steps include: S1. Select phosphogypsum that has been fully filtered during the phosphoric acid production process, and use a rapid moisture detector to test the moisture content of the phosphogypsum for later use; S2. Pour some NaOH flakes into a beaker, add a small amount of deionized water to dissolve, cool to room temperature and transfer the cooled NaOH solution to a volumetric flask, add a certain amount of deionized water to dilute the NaOH solution to 0.5-1.0 mol / L; S3, taking some granular APAM flocculants, adding deionized water and using a magnetic stirrer to prepare an APAM solution with a mass fraction of 0.5‰; S4, mixing the phosphogypsum of step S1 with the diluted NaOH solution of step S2 at a certain solid-liquid ratio, and stirring the mixture uniformly at a speed of 200 r / min for 15-20 min, and then adding the APAM solution of step S3 to accelerate the flocculation, sedimentation and concentration of the phosphogypsum, and separating the supernatant from the high-concentration phosphogypsum slurry after standing for 5-10 min; S5. After standing, a certain proportion of calcium hydroxide is added to adjust the pH of the supernatant to a weak alkaline state, and the supernatant is filtered, dried, and subjected to a flotation process to convert the fluorine element in the supernatant into calcium fluoride, thereby realizing the recovery of the F element in the supernatant; S6. After testing the moisture content of the high-concentration phosphogypsum slurry, add a certain amount of deionized water and 42.5-grade ordinary Portland cement and stir evenly to obtain the required homogeneous cementitious filling slurry.

2. A method for preparing a cemented filling body based on phosphogypsum pretreatment according to claim 1, characterized in that: In step S1, the moisture content of the phosphogypsum after sufficient pressure filtration is generally about 20%.

3. A method for preparing a cemented filling body based on phosphogypsum pretreatment according to claim 1, characterized in that: In step S2, the amount of NaOH used is 15%-20% of the total mass of phosphogypsum; the reaction temperature is 21-25°C, and the reaction time is 10 minutes.

4. The method for preparing a cemented filling body based on phosphogypsum pretreatment according to claim 1, characterized in that: In step S3, the amount of APAM used is 2‰-4‰ of the total mass of phosphogypsum.

5. The method for preparing a cemented filling body based on phosphogypsum pretreatment according to claim 1, characterized in that: In step S4, the solid-liquid ratio is 1:1-1:

2.

6. The method for preparing a cemented filling body based on phosphogypsum pretreatment according to claim 1, characterized in that: In step S5, the weakly alkaline pH range is 7-9.

7. The method for preparing a cemented filling body based on phosphogypsum pretreatment according to claim 1, characterized in that: In step S6, the mass components of the additives in the production process of the homogeneous cementitious filling slurry are: 3-5 parts of NaOH, 20 parts of phosphogypsum, and 3-5 parts of cement.

8. The method for preparing a cemented filling body based on phosphogypsum pretreatment according to claim 7, characterized in that: In step S6, the mass concentration of the homogeneous cementitious filling slurry is 60%-66%, and the density is 2.2-2.5g / cm 3 .

9. A method for preparing a cemented filling body based on phosphogypsum pretreatment according to any one of claims 1 to 8, characterized in that: The method also includes: S7, conducting uniaxial compressive strength tests on the test blocks 3 days, 7 days and 28 days after the homogeneous cementitious filling slurry is molded, taking 3 blocks at each age and taking the average value as the compressive strength of the test blocks at that age.

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