Phosphogypsum production process for on-line pH value improvement

Abstract

The application discloses a production process of phosphogypsum with improved pH value online. The process comprises the following steps: filtering and washing the phosphogypsum raw slag after slurry preparation to obtain refined phosphogypsum, then performing three-stage water washing and step-by-step suction filtration, uniformly adding an adjusting agent solution to the surface of the purified phosphogypsum and performing suction filtration, and obtaining the purified phosphogypsum with improved pH value. The flow of the pH adjusting agent liquid and the mass flow of the phosphogypsum are in a chained relationship, and the filtering characteristics of the equipment are used to realize online accurate control of the pH of the phosphogypsum, so that the production raw material meeting the requirements of building gypsum powder, high-strength gypsum powder and cement retarder is obtained. The process is simple in logic and accurate in control, the soluble fluorine salt and phosphate in the purified phosphogypsum are low, the key physical indexes of downstream products are not affected, the amount of water in the phosphogypsum purification process is not increased, and large-scale production can be realized.

Description

Technical Field

[0001] This invention relates to a production process for purifying and raising the pH value of phosphogypsum to prepare building gypsum, α-type high-strength gypsum and cement retarder raw materials, belonging to the field of building materials technology. Background Technology

[0002] The main component of phosphogypsum, a byproduct of wet-process phosphoric acid and phosphate compound fertilizer industry, is CaSO4·2H2O. It also contains harmful impurities such as residual phosphoric acid, sulfuric acid, and organic matter, and is acidic.

[0003] Most water-soluble phosphorus, fluoride, and organic matter impurities can be removed through washing and flotation, generally raising the pH to above 5.0. However, how to precisely raise the pH of purified phosphogypsum online to meet the requirements of large-scale production of building gypsum, α-type high-strength gypsum, and cement retarder is an important research topic.

[0004] GB / T 9776-2022 "Building Gypsum", which came into effect on July 1, 2023, requires building gypsum to have a pH value ≥ 5.0. Therefore, the pH value must be raised to a certain range during the pretreatment stage of phosphogypsum so that the mechanical properties of the building gypsum produced on a large scale meet the standard requirements.

[0005] After the pH value of purified phosphogypsum is increased, it is also suitable for large-scale production of α-type high-strength gypsum and cement retarder. The corresponding product indicators meet the standards and market demands, further verifying the feasibility of the production process of increasing the pH value of phosphogypsum online. Summary of the Invention

[0006] The technical problem to be solved by this invention is that the pH value of phosphogypsum after water washing pretreatment is not accurately increased, and that the pH-increased phosphogypsum does not meet the requirements for large-scale production of building gypsum, α-type high-strength gypsum and cement retarder.

[0007] The technical solution of this invention: a production process for online pH enhancement of phosphogypsum, the specific steps of which are as follows:

[0008] Prepare a pH adjusting solution by adding water to the pH adjusting agent;

[0009] (2) The raw phosphogypsum residue is transferred into the slurry tank via the feeding belt and the loading belt. Water is injected into the tank and stirred evenly to prepare phosphogypsum slurry.

[0010] (3) The phosphogypsum slurry naturally overflows into the filter cloth of the vacuum belt filter, scrapes off the floating organic matter on the upper layer, and is then filtered. The phosphogypsum enters the first washing stage as the vacuum belt filter operates, and refined phosphogypsum is obtained.

[0011] (4) The refined phosphogypsum is washed with three-stage washing water and filtered step by step. The resulting water-washed purified phosphogypsum enters the pH value enhancement stage as the vacuum belt filter is running.

[0012] (5) Add a conditioning agent solution evenly to the surface of the water-washed purified phosphogypsum (the pH conditioning agent solution is automatically adjusted by the feed rate), and filter again to obtain purified phosphogypsum with increased pH value, which falls onto the transfer belt as the vacuum belt filter operates.

[0013] (6) As the conveyor belt operates, the purified phosphogypsum with increased pH value is stored in the stockpile for use as a downstream raw material.

[0014] (7) The various filtrates and filter cloth rinsing water generated in the above process are combined and enter the wastewater treatment system. After treatment, they are used for pH adjustment agent solution preparation, phosphogypsum pulping and rinsing in steps (1), (2) and (4).

[0015] In the above production process, the pH adjuster components and proportions in step (1) are as follows: quicklime with a CaO content of more than 80% accounts for more than 85%, aluminum sulfate accounts for 0.05%~5%, citric acid accounts for 0.05%~5%, and sodium citrate accounts for 0.05%~5%.

[0016] In the above production process, the mass ratio of pH adjuster to water in step (1) is 2% to 10%.

[0017] In the above production process, the pH adjustment agent preparation process in step (1) is divided into two stages: pre-preparation and buffering. A pH adjustment agent preparation tank is used for pre-preparation of pH adjustment agent, and a pH adjustment agent buffer tank is used for buffering pH adjustment agent. The pre-prepared pH adjustment agent is placed in the pH adjustment agent buffer tank for later use. In both stages, a stirring paddle is used to stir the pH adjustment agent to make it uniform.

[0018] In the above production process, in step (2), a variable frequency feeding belt and a variable frequency loading belt are used to ensure that the mass flow rate of the phosphogypsum residue entering the slurry tank is stable, and a loading belt metering scale is used to measure the mass of the phosphogypsum residue carried by the loading belt.

[0019] In the above production process, the free water content of the phosphogypsum residue carried by the feeding belt in step (2) is 15%~20%, and the ratio of water added to the mass of the phosphogypsum residue carried by the feeding belt is 1~3.

[0020] In the above production process, the mass ratio of the three-stage rinsing water to the phosphogypsum residue carried by the feeding belt in step (4) is as follows: 25%~55% for the first stage, 15%~35% for the second stage, and 5%~15% for the third stage.

[0021] In the above production process, the mass ratio of the pH adjuster in step (5) to the phosphogypsum residue carried by the feeding belt in step (2) is 0.01%~0.5%.

[0022] In the above production process, a variable frequency centrifugal pump, a flow meter and a stopcock valve are used in step (5). The relevant signals are interlocked with the relevant signals of the feeding belt metering scale in step (2) to form a DCS interlock. The pH adjustment agent solution in the buffer tank in step (1) is uniformly added to the surface of phosphogypsum through a stainless steel pipe by the variable frequency centrifugal pump.

[0023] In the above production process, the flow rate V(m) of the pH adjuster solution in step (5) is... 3 The functional relationship between / h) and the mass M (kg) of phosphogypsum residue carried by the conveyor belt in step (2) and the free water content ω (%) is: V = 0.049·(MM·ω)

[0024] In the above production process, in step (6), before the pH-enhanced phosphogypsum enters the transfer belt along with the vacuum belt filter, it undergoes primary homogenization via the transfer belt.

[0025] Compared with the prior art, the outstanding advantages of the present invention are as follows:

[0026] This invention effectively removes most organic matter, water-soluble phosphorus, fluorine and other impurities, and can dynamically and automatically adjust the flow rate of pH adjustment solution online according to the quality of phosphogypsum on the feeding belt. The process logic is simple, the pH value control range of phosphogypsum is precise, and it can meet the requirements of large-scale production of building gypsum, α-type high-strength gypsum and cement retarder. The corresponding product indicators meet the standards and market demands. Attached Figure Description

[0027] Figure 1 is a process flow diagram of the present invention. Implementation

[0028] A company uses the process of this invention, and the specific implementation method is as follows:

[0029] 1. Transfer 3000 tons of raw phosphogypsum residue from the phosphogypsum slag yard to the phosphogypsum pretreatment unit and test the residue indicators:

[0030] CaSO4·2H2O content 90.96%;

[0031] Free water content: 15.14%;

[0032] Water-soluble fluoride content: 0.66%;

[0033] Water-soluble phosphorus content: 0.443%;

[0034] Total phosphorus content: 0.98%

[0035] pH value 3.75.

[0036] 2. Set the feeding belt and its operating frequency to 60Hz, and set the phosphogypsum mass flow rate of the feeding belt to 90t / h.

[0037] 3. Based on the mass ratio of phosphogypsum to process water of 1:2, process water is injected into the slurry tank to prepare phosphogypsum slurry.

[0038] IV. Based on the pH adjuster solution flow rate V (m 3 The functional relationship between / h) and the mass M (kg) of phosphogypsum residue carried by the feeding belt and the free water content ω (%) is: V = 0.049·(MM·ω), and a pH adjustment solution is prepared.

[0039] 5. The phosphogypsum slurry naturally overflows into the filter cloth of the vacuum belt filter, where the upper organic matter is scraped off. After undergoing primary washing and tertiary rinsing, it enters the pH adjuster solution nozzle.

[0040] 6. Start the variable frequency centrifugal pump. The pH adjustment agent solution is evenly sprayed from the stainless steel pipe port through the flow meter and stopcock valve onto the surface of the purified phosphogypsum on the filter cloth of the vacuum belt filter. The solution is then homogenized by the conveyor belt to obtain purified phosphogypsum with improved pH value. After being transported to the stockpile to reduce free moisture, it is then transported to the raw material warehouse of the building gypsum plant.

[0041] VII. Testing the pH level after 20 days of storage to purify the phosphogypsum:

[0042] CaSO4·2H2O content: 94.14%;

[0043] Free water content: 14.92%;

[0044] Water-soluble fluoride content: 0.018%;

[0045] Water-soluble phosphorus content: 0.110%;

[0046] Total phosphorus content: 0.67%

[0047] pH value 6.53.

[0048] 8. Testing the performance indicators of building gypsum produced using pH-enhanced purified phosphogypsum:

[0049] Standard viscosity 61.50%;

[0050] Initial setting time: 4 minutes;

[0051] Final setting time: 9 minutes;

[0052] Flexural strength after 2 hours: 3.28 MPa;

[0053] 2h compressive strength 7.40MPa.

[0054] pH value 5.15.

Claims

1. A production process for online pH enhancement of phosphogypsum, characterized in that, Includes the following steps: (1) Prepare a pH adjustment solution by adding water to the pH adjustment agent; (2) The raw phosphogypsum residue is transferred into the slurry tank via a feeding belt and a feeding belt. Water is injected into the tank and stirred evenly to prepare phosphogypsum slurry. (3) The phosphogypsum slurry naturally overflows into the filter cloth of the vacuum belt filter, scrapes off the floating organic matter on the upper layer, and is then filtered. The phosphogypsum enters the first washing stage as the vacuum belt filter operates, and refined phosphogypsum is obtained. (4) The refined phosphogypsum is washed with three-stage washing water and filtered step by step. The resulting water-washed purified phosphogypsum enters the pH value enhancement stage as the vacuum belt filter is running. (5) Add pH adjustment agent solution evenly to the surface of the water-washed purified phosphogypsum and filter again to obtain purified phosphogypsum with increased pH value, which falls onto the transfer belt as the vacuum belt filter operates. (6) As the conveyor belt operates, the purified phosphogypsum with increased pH value enters the stockpile for storage as a downstream raw material. (7) The various filtrates and filter cloth rinsing water generated in the above process are combined and enter the wastewater treatment system. After treatment, they are used for pH adjustment agent solution preparation, phosphogypsum pulping and rinsing in steps (1), (2) and (4); The pH adjuster components and proportions in step (1) are as follows: quicklime with a CaO content of over 80% accounts for over 85%, aluminum sulfate accounts for 0.05%~5%, citric acid accounts for 0.05%~5%, and sodium citrate accounts for 0.05%~5%. The pH adjustment solution preparation process in step (1) is divided into two stages: pre-preparation and buffering. A pH adjustment solution preparation tank is used for pre-preparation of the pH adjustment solution, and a pH adjustment solution buffer tank is used for buffering the pH adjustment solution. The pre-prepared pH adjustment solution is placed in the pH adjustment solution buffer tank for later use. In both stages, a stirring paddle is used to stir the pH adjustment solution to make it uniform. In step (2), a frequency-converting feed belt and a frequency-converting feeding belt are used to ensure that the mass flow rate of the phosphogypsum residue entering the pulping tank is stable, and a feeding belt metering scale is used to measure the mass of the phosphogypsum residue carried by the feeding belt. In step (2), the free moisture content of the phosphogypsum residue carried by the feeding belt is in the range of 15% to 20%, and the ratio of water added to the mass of the phosphogypsum residue carried by the feeding belt is 1 to 3. In step (4), the mass ratio of the three-stage rinsing water to the phosphogypsum residue carried by the feeding belt is as follows: Level 1: 25%~55%, Level 2: 15%~35%, Level 3: 5%~15%; In step (5), a variable frequency centrifugal pump, a flow meter and a stopcock valve are used. The relevant signals are linked with the relevant signals of the feeding belt metering scale in step (2) to form a DCS interlock. The pH adjustment agent solution in the buffer tank in step (1) is evenly added to the surface of phosphogypsum through a stainless steel pipe by the variable frequency centrifugal pump. The functional relationship between the volumetric flow rate V of the pH adjuster solution in step (5) and the mass M of the phosphogypsum residue carried by the conveyor belt in step (2) and the free water content ω (%) is as follows: V =0.049·( M - M · ω ).

2. The production process for online pH enhancement of phosphogypsum according to claim 1, characterized in that, In step (1), the pH adjuster is 2% to 10% of the water mass.

3. The production process for online pH enhancement of phosphogypsum according to claim 1, characterized in that, The mass ratio of the pH adjustment agent solution in step (5) to the phosphogypsum residue carried by the feeding belt in step (2) is 0.01%~0.5%.

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