A kind of preparation method of phosphogypsum

Abstract

The present application relates to the technical field of phosphogypsum production, and specifically discloses a method for preparing phosphogypsum, comprising the following steps: step (1), feeding the phosphogypsum quantitatively into a drying device by a feeder for preliminary drying at 150-180°C for 5-25 minutes to reduce the moisture in the phosphogypsum; step (2), sending the preliminarily dried phosphogypsum into a ball mill for grinding, and sieving the ground phosphogypsum powder through a sieve with a mesh diameter of 5-150 μm; step (3), sending the phosphogypsum powder into a calcining furnace through a conveyor belt for calcination to obtain relatively pure phosphogypsum. The purpose of this patent is to solve the problem of phosphogypsum agglomeration when removing impurities from calcined phosphogypsum.

Description

Technical Field

[0001] The invention relates to the technical field of phosphogypsum production, and in particular to a method for preparing phosphogypsum. Background Art

[0002] There are two main types of phosphogypsum: gray-black and gray-white. The particle diameter is generally 5 to 50 μm, and the crystal water content is 20% to 25%. Phosphogypsum is a solid waste produced in the wet phosphoric acid process. Its main component is calcium sulfate dihydrate (CaSO4·2H2O). The composition of phosphogypsum is relatively complex. In addition to calcium sulfate, there are also incompletely decomposed phosphate ore, residual phosphoric acid, fluoride, acid insoluble matter, organic matter, etc. The types of impurities in phosphogypsum are divided into two categories according to their solubility: soluble and insoluble. Among them, soluble impurities, on the one hand, can easily enter the surrounding water and soil after dissolving in water, endangering the surrounding environment. On the other hand, when phosphogypsum is used to prepare gypsum products, it is easy to have an adverse effect on the performance of the product. Insoluble impurities have little effect on the performance of phosphogypsum products and are usually harmless components. The four types of impurities with greater impact in phosphogypsum are soluble phosphorus, eutectic phosphorus, soluble fluorine and organic matter.

[0003] When phosphoric acid is produced by wet process, 4.5~5 tons of phosphogypsum will be produced for every ton of phosphoric acid produced. However, the four types of impurities with great influence in phosphogypsum make it impossible to directly use the phosphogypsum produced by wet process to produce phosphoric acid. Therefore, the key and prerequisite for its resource utilization is to effectively remove the harm of soluble impurities in phosphogypsum to its performance. At present, the main methods for eliminating impurities in phosphogypsum include chemical treatment, water washing, flotation, ball milling, aging, screening, high-temperature calcination and flash burning. Among them, high-temperature calcination is the most effective method for removing eutectic phosphorus impurities in phosphogypsum. In addition, organic matter and soluble fluoride ions will be converted into gas and volatilized under high temperature conditions, thereby eliminating the adverse effects of organic matter and soluble fluoride on phosphogypsum. However, there may be agglomerated phosphogypsum in the phosphogypsum slag. During the feeding process, the agglomerated phosphogypsum may enter the drying and calcination stage through grates and belts. In the process of drying and calcining the phosphogypsum, the agglomerated phosphogypsum will have an outer layer over-burned and an inner layer under-burned, resulting in uneven calcination of gypsum powder and failure to completely remove impurities in the phosphogypsum. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a method for preparing phosphogypsum, aiming to solve the problem of phosphogypsum agglomeration during calcination and impurity removal.

[0005] In order to solve the above problems, the technical solution adopted by the present invention is:

[0006] A method for preparing phosphogypsum comprises the following steps:

[0007] Step (1), feeding the phosphogypsum into a drying device in a quantitative manner through a feeder, and performing preliminary drying at 150-180° C. for 5-25 minutes to reduce the moisture in the phosphogypsum;

[0008] Step (2), feeding the preliminarily dried phosphogypsum into a ball mill for grinding, and sieving the ground phosphogypsum powder through a sieve with a mesh size of 5-150 μm;

[0009] Step (3), the phosphogypsum powder is conveyed into a calcining furnace via a conveyor belt for calcination to obtain relatively pure phosphogypsum.

[0010] The principles of this solution are:

[0011] The phosphogypsum is quantitatively fed into a drying device for drying, and then the dried phosphogypsum is sent to a ball mill for grinding, the phosphogypsum is ground into powder, and a screen is set at the outlet of the ball mill to transfer the phosphogypsum powder that can pass the screen to a calcining furnace for calcining. Because the phosphogypsum is dried before grinding and calcining, the phosphogypsum sent to the ball mill and the calcining furnace carries very little moisture, which will cause the phosphogypsum powder to adhere to the inner wall of the calcining furnace during calcination and will not cause agglomeration. At the same time, the phosphogypsum will not adhere to the inner wall of the ball mill during grinding.

[0012] The beneficial effects of this program are:

[0013] 1. Dry the phosphogypsum before grinding and calcining to reduce the moisture carried by the phosphogypsum, so that the phosphogypsum will not adhere to the inner wall of the ball mill and calcining furnace during grinding and calcining, and will not form lumps;

[0014] 2. Grind the phosphogypsum into powder using a ball mill and transfer it to a calcining furnace for calcination to remove eutectic phosphorus impurities, soluble fluoride ions and organic matter in the phosphogypsum.

[0015] Preferred solution 1: As a further optimization of the basic solution, the phosphogypsum that fails to pass through the filter in step (2) is sent to the ball mill again for secondary grinding, and then sieved, and the above steps are repeated until all the phosphogypsum can pass through the sieve and enter step (3). The phosphogypsum powder after grinding in the ball mill is sieved by setting a sieve, and the phosphogypsum that cannot pass through the sieve holes is sent back to the ball mill for secondary grinding, so as to ensure that the particle size of the phosphogypsum powder transmitted to the calcining furnace is consistent, and ensure that the phosphogypsum powder obtained after calcination at the same time does not contain impurities.

[0016] Preferred solution 2: As a further optimization of the basic solution, the structure of the calcining furnace used in the step (3) is as follows: the calcining furnace is vertically fixed on the frame, a through hole is opened in the middle of the side wall of the calcining furnace, a ventilation duct for introducing hot air flow is installed in the through hole, and a screw conveyor is vertically fixedly installed at the bottom of the calcining furnace, the screw shaft of the screw conveyor is hollow, and the screw shaft passes through the panel of the frame and is fixedly connected to the output shaft of the motor and driven by the motor.

[0017] By installing a screw conveyor in the calcining furnace and driving the screw conveyor to rotate through a motor, the phosphogypsum powder fed into the calcining furnace is continuously conveyed from bottom to top, so that the phosphogypsum powder is in direct contact with the hot air flow fed from the ventilation duct, thereby removing impurities in the phosphogypsum powder, and at the same time improving the calcination efficiency and shortening the calcination time; the spiral shaft of the screw conveyor is set to a hollow state with openings at both ends, so that the hot air flow introduced into the calcining furnace can be discharged, and the ventilation duct is passed into the calcining furnace to form an upward air flow, so that the phosphogypsum powder is in a suspended state in the calcining furnace, and the contact area between the phosphogypsum powder and the hot air flow is large, and the calcination is uniform. At the same time, centrifugal force is formed during the rotation of the screw conveying mechanism, so that the phosphogypsum powder expands outward, thereby preventing the phosphogypsum powder from being discharged from the spiral shaft in the middle of the calcining furnace.

[0018] Preferred solution three: As a further optimization of the optimized solution two, a one-way air outlet valve is fixedly installed in the cavity of the spiral shaft to ensure that the outside wind cannot blow into the calcining furnace and affect the temperature and phosphogypsum powder in the calcining furnace.

[0019] Preferred solution 4: As a further optimization of preferred solution 2, the spiral blades at both ends of the screw conveyor are larger than other spiral blades. Because the hot air flows into the calcining furnace, it generates wind force on the phosphogypsum powder, so that the phosphogypsum powder on the screw conveyor diffuses toward the side wall of the calcining furnace and falls down. After the phosphogypsum falls, it needs to be lifted up by the spiral blade at the bottom. Therefore, the spiral blade at the bottom is larger than the other spiral blades, and the spiral blade at the top needs to prevent the phosphogypsum powder from falling out of the opening of the spiral shaft as much as possible. Therefore, the spiral blade at the top is also larger than the other spiral blades.

[0020] Preferred solution 5: As a further optimization of the preferred solution 3, the speed of the motor is 60-120 r / min. By controlling the speed of the motor, the speed of the screw conveyor is controlled to ensure that the screw conveyor transfers the phosphogypsum powder in the calcining furnace to the ventilation duct multiple times during the calcining time, so that the phosphogypsum powder continuously exchanges heat with the hot air flow, so as to achieve the purpose of removing impurities in the phosphogypsum powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1A schematic diagram of a main view of a calcining furnace for a method for preparing phosphogypsum provided by the present invention;

[0022] Figure 2 A schematic diagram of the main view of a calcining furnace in operation for a method for preparing phosphogypsum provided by the present invention;

[0023] Figure 3 A calcining furnace for a method for preparing phosphogypsum provided by the present invention Figure 1 An enlarged schematic diagram of area A in FIG.

[0024] The reference numerals in the drawings of the specification include:

[0025] Calcination furnace 101 , spiral shaft 102 , spiral blade 103 , feed port 104 , air outlet 105 , one-way air outlet valve 106 , auxiliary block 107 , support rod 108 , air inlet 109 , valve 110 , frame 201 , panel 202 , motor 301 , ventilation duct 401 . DETAILED DESCRIPTION

[0026] The following is further described in detail through specific implementation methods:

[0027] Example:

[0028] A method for preparing phosphogypsum comprises the following steps:

[0029] Step (1), feeding the phosphogypsum into a drying device in a quantitative manner through a feeder, and performing preliminary drying at 150-180° C. for 5-25 minutes to reduce the moisture in the phosphogypsum;

[0030] Step (2), feeding the preliminarily dried phosphogypsum into a ball mill for grinding, and sieving the ground phosphogypsum powder through a sieve with a mesh size of 5-150 μm;

[0031] The phosphogypsum that fails to pass through the filter in step (2) is sent to the ball mill again for secondary grinding, and then sieved, and the above steps are repeated until all the phosphogypsum can pass through the sieve and enter step (3);

[0032] Step (3), the phosphogypsum powder is conveyed into a calcining furnace via a conveyor belt for calcination to obtain relatively pure phosphogypsum.

[0033] like Figure 1-2As shown, the structure of the calcining furnace 101 used in step (3) is as follows: the calcining furnace 101 is fixedly mounted on a frame 201, the frame 201 is fixed to the ground, a through hole is opened on the side wall of the bottom end of the calcining furnace 101, and a feed port 104 is fixedly installed in the through hole, the feed port 104 is connected to a transmission mechanism between the ball mill and the calcining furnace 101, the transmission mechanism delivers the phosphogypsum powder to the feed port 104, a valve 110 is fixedly installed at the feed port 104, and whether the calcining furnace 101 is in a closed state is controlled by controlling the opening and closing of the valve 110, a through hole is opened in the middle of the side wall of the calcining furnace 101, and a ventilation duct 401 for introducing hot air flow is fixedly installed in the through hole, a screw feeder is fixedly installed at the bottom end of the calcining furnace 101, and the central axis of the screw feeder coincides with the central axis of the calcining furnace 101. The screw shaft 102 of the screw feeder is combined, and is set to a hollow state with openings at both ends, and the screw shaft 102 extends out of the calcining furnace 101 and passes through the panel 202 of the frame 201, and an air outlet 105 is provided on the side wall of the screw shaft 102 extending out of the panel 202 of the frame 201, and the end of the screw shaft 102 extending out of the panel 202 of the frame 201 is fixedly connected to the auxiliary block 107, and a rotating support rod 108 is fixedly connected to the lower surface of the auxiliary block 107, and the rotating support rod 108 is fixedly connected to the output shaft of the motor 301, and the motor 301 is fixedly installed on the ground, and a one-way air outlet valve 106 is fixedly installed in the cavity of the screw shaft 102 above the air outlet 105, and the one-way air outlet valve 106 only allows the gas in the calcining furnace 101 to be discharged from the calcining furnace 101, and does not allow external air to enter the calcining furnace 101. The screw conveyor lifts the phosphogypsum powder by rotating blades to transport the phosphogypsum powder. When the hot air flows into the calcining furnace 101 to calcine the phosphogypsum powder, the phosphogypsum powder will be diffused outward by the centrifugal force of the screw conveyor. At the same time, it will be suspended in the upper part of the calcining furnace 101 by the upward hot air flow. The phosphogypsum powder is simultaneously subjected to the centrifugal force toward the side wall of the calcining furnace and the upward force of the hot air flow. Therefore, the phosphogypsum powder will diffuse obliquely upward toward the side wall of the calcining furnace and then fall into the calcining furnace 101. At the bottom, the spiral blade 103 at the lowest end of the screw conveyor sends the phosphogypsum powder to the upper side for heat exchange with the hot air flow again to realize calcination of the phosphogypsum powder. At the same time, the phosphogypsum is in powder state, which can increase the contact area between the phosphogypsum powder and the hot air flow, thereby increasing the calcination rate of the phosphogypsum powder. In addition, by setting the lowest spiral blade 103 to be larger than other spiral blades 103, it can be ensured that the phosphogypsum powder that falls on the bottom of the calcining furnace 101 can be transported up for calcination and impurity removal.

[0034] It can be imagined that in order to ensure that there is no deviation when the motor 301 drives the screw conveyor to rotate, the motor 301 is fixed on the central axis of the screw shaft 102, and an auxiliary block 107 is fixed to the end of the screw shaft 102 extending from the motor 301 panel 202. The auxiliary block 107 is a solid block, and a support rod 108 is fixed on the lower surface of the auxiliary block 107. The support rod 108 is fixedly connected to the output shaft of the motor 301 to make the center line of the motor 301 coincide with the extension line of the central axis of the screw shaft 102, thereby ensuring that there is no deviation when the motor 301 drives the screw shaft 102 to rotate.

[0035] In this embodiment, the speed of the motor is 60-120 r / min. By controlling the speed of the motor, the speed of the screw conveyor is controlled to ensure that the screw conveyor transfers the phosphogypsum powder in the calcining furnace to the ventilation duct multiple times during the calcining time, so that the phosphogypsum powder is continuously heat-exchanged with the hot air flow, so as to achieve the purpose of removing impurities in the phosphogypsum powder.

[0036] The heating device of the hot air flow can be a hot air furnace, which heats the air and then passes it into the calcining furnace 101 to calcine the phosphogypsum powder. The air outlet of the hot air furnace has a temperature of 260°C-460°C, which is sufficient to calcine the phosphogypsum powder. At the same time, the gas discharged from the air outlet 105 can be passed into the hot air furnace again for repeated use.

[0037] In this embodiment, a discharge port can be opened at the bottom of the calcining furnace. The discharge port is not marked in the figure. During the calcination of the phosphogypsum powder, the discharge port is always in a closed state. After the calcination of the Lin Zhigao powder is completed, the hot air is stopped from entering the calcining furnace and the screw conveyor is turned off. The discharge port is opened, and the calcined phosphogypsum powder is discharged from the discharge port, and then the next batch of phosphogypsum powder is calcined.

[0038] In this embodiment, the dried and polished phosphogypsum powder is fed into the calcining furnace 101 from the feed port 104 through a transmission mechanism. After the phosphogypsum powder that is quantitatively fed into the drying device and then dried and polished into powder is transmitted, the valve 110 at the feed port is closed, and then the motor 301 is started to drive the screw conveyor, and a hot air flow is introduced at the same time. In the process of the screw conveyor conveying the phosphogypsum powder upward, the hot air flow calcines the phosphogypsum powder at a high temperature, and the phosphogypsum powder diffuses toward the side wall of the calcining furnace under the action of the centrifugal force of the screw shaft 102. At the same time, the phosphogypsum powder is suspended upward under the action of the upward hot air flow. The phosphogypsum powder is simultaneously subjected to the centrifugal force in the direction of the calcining furnace side wall and the upward force of the hot air flow. Therefore, the phosphogypsum powder will diffuse obliquely upward in the direction of the calcining furnace side wall, and then fall to the bottom of the calcining furnace 101. Then the spiral blade 103 conveys the phosphogypsum powder along the screw conveyor again, and the hot air flow in the ventilation duct 401 calcines the phosphogypsum powder again. The calcination is repeated continuously during the calcination time, which improves the calcination efficiency and shortens the calcination time. When calcining in the calcining furnace 101, the hot air flow is continuously introduced into the calcining furnace 101, the air pressure in the calcining furnace 101 increases, and the screw shaft 102 of the screw conveyor is set to a hollow state with openings at both ends so that the gas in the calcining furnace 101 can be discharged.

[0039] Before the phosphogypsum powder is conveyed to the ball mill for grinding, the phosphogypsum is first dried so that the phosphogypsum conveyed to the ball mill and the subsequent calcining furnace 101 contains very little moisture and will not clump or adhere to the inner wall of the ball mill or the calcining furnace 101.

[0040] The above is only an embodiment of the present invention, and the common knowledge such as the known specific structure and characteristics in the scheme is 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 phosphogypsum, characterized in that: The steps include: Step (1), feeding the phosphogypsum into a drying device in a quantitative manner through a feeder, and performing preliminary drying at 150-180° C. for 5-25 minutes to reduce the moisture in the phosphogypsum; Step (2), feeding the preliminarily dried phosphogypsum into a ball mill for grinding, and sieving the ground phosphogypsum powder through a sieve with a mesh size of 5-150 μm; Step (3), the phosphogypsum powder is conveyed into a calcining furnace via a conveyor belt for calcination to obtain relatively pure phosphogypsum; The phosphogypsum that fails to pass through the filter in step (2) is sent to the ball mill again for secondary grinding, and then sieved, and the above steps are repeated until all the phosphogypsum can pass through the sieve and enter step (3); The calcining furnace used in step (3) has the following structure: the calcining furnace is vertically fixed on a frame, a through hole is provided in the middle of the side wall of the calcining furnace, a ventilation duct for introducing hot air flow is installed in the through hole; a through hole is provided on the side wall at the bottom end of the calcining furnace, a feed port is fixedly installed in the through hole, and the feed port is connected to a transmission mechanism between the ball mill and the calcining furnace; A screw conveyor is fixedly installed at the bottom end of the calcining furnace, the central axis of the screw conveyor coincides with the central axis of the calcining furnace, and the screw shaft of the screw conveyor is set to be a hollow state with both ends open; the screw shaft of the screw conveyor passes through the panel of the frame and is fixedly connected to the output shaft of the motor and is driven by the motor; An air outlet is provided on the side wall of the spiral shaft of the panel extending out of the frame, and a one-way air outlet valve is fixedly installed in the cavity of the spiral shaft above the air outlet; The motor is fixed on the central axis of the screw shaft, an auxiliary block is fixed on the lower end of the screw shaft, the auxiliary block is a solid block, a support rod is fixed on the lower surface of the auxiliary block, the support rod is fixedly connected to the output shaft of the motor, the center line of the motor coincides with the extension line of the central axis of the screw shaft, so that the motor drives the screw conveyor to rotate without deviation; The spiral blades at both ends of the screw conveyor are larger than other spiral blades; The rotation speed of the motor is 60-120 r / min.

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