Phosphogypsum reverse-direct flotation coupling synchronous impurity removing and whitening process

Abstract

The invention belongs to the technical field of ardealite solid waste treatment, and particularly relates to an ardealite reverse-direct flotation coupling synchronous impurity removing and whitening process. The process comprises the following steps: mixing and stirring ardealite and water to obtain ore pulp; after sufficient stirring, adding a flotation reagent A into the ore pulp, continuously stirring at a high speed, aerating, carrying out reverse flotation, scraping bubbles until the bubbles are white, and taking a product in a tank as rough concentrate ore pulp; adding a flotation reagent B into the rough concentrate pulp, continuously stirring at a high speed, adding a certain amount of foaming agent, continuously stirring at a high speed, aerating, carrying out direct flotation, and scraping bubbles until floating gypsum does not exist, so as to obtain a foam product; and filtering and drying the foam product to obtain a concentrate product. After'one-reverse and one-positive 'flotation, the whiteness and the purity of CaSO4. 2H2O are greatly improved, the SiO2 content, the organic matter content and the fluorine ion content are greatly reduced, and the problems that an existing ardealite treatment process is single in impurity removal capacity, common in removal effect, long in process line, large in agent dosage and high in cost are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of phosphogypsum solid waste treatment, and in particular relates to a phosphogypsum reverse-positive flotation coupling synchronous impurity removal and whitening process. Background Art

[0002] Phosphoric acid is one of the important strategic basic raw materials. Phosphogypsum is the main by-product in the production process of phosphoric acid. According to statistics, the world will add 200 to 300 million tons of phosphogypsum every year, and the cumulative stockpile has exceeded 7 billion tons, but only about 15% is recycled or used at a low value. The remaining 85% of untreated phosphogypsum is usually stored in the open air or landfilled, which not only occupies land, but also easily causes serious environmental problems. It is also a waste of Ca and O resources. The high content (more than 85%) of CaSO4·2H2O in phosphogypsum makes it have the potential to be used as an auxiliary alternative resource in many industries such as cement retarders, gypsum building materials and roadbed fillers. However, the use of phosphogypsum as an auxiliary resource is severely restricted by its whiteness, high impurity content and complex impurity composition (such as SiO2, organic matter and fluoride ions).

[0003] The comprehensive utilization of phosphogypsum is the only way to promote the comprehensive utilization of resources and green development of the phosphorus chemical industry. At the same time, as a misplaced resource, it is necessary to improve its resource utilization rate and reduce pressure and empower phosphorus chemical enterprises. At present, pretreatment methods mainly include physical, chemical and physical-chemical composite processes, such as water washing, chemical conversion, extraction, flotation and calcination. Among them, flotation is widely used because of its low reagent cost, simple operation, easy scale and automatic application. It can be specifically divided into positive flotation, reverse flotation, positive and reverse flotation, double reverse flotation and multi-stage composite flotation. However, single flotation has problems such as single impurity removal performance, general removal effect and limited increase in CaSO4·2H2O purity. The multi-stage composite process has problems such as long process line, large amount of reagents and high cost. CN202211037009.0 discloses a method for purifying and whitening phosphogypsum, using trihydroxy polyammonium collector and sodium dodecylbenzene sulfonate as reverse flotation and forward flotation reagents, respectively, and adopting a one-reverse three-forward flotation process to purify and whiten phosphogypsum, and obtain a concentrate with a CaSO4·2H2O content of 96.17% and a SiO2 content of 0.57%, but there are problems such as long process and high reagent cost. Lai Jingyi et al. used kerosene and dodecylamine as reverse flotation and forward flotation reagents, respectively, and adopted a one-reverse three-forward flotation process to decolorize and purify phosphogypsum, and obtained a concentrate with a whiteness of 60.80% and a CaSO4·2H2O content of 99.32% (Nonferrous Metals (Ore Dressing Part), 2024, (07): 85-92), but there are problems such as large reagent dosage, long process, single impurity type removal, and small increase in whiteness. CN202211307197.4 discloses a phosphogypsum reverse flotation whitening and impurity removal agent and its preparation method and process method, and adopts a composite collector to whiten and remove impurities from phosphogypsum through a two-stage reverse flotation process, and obtains a concentrate with a whiteness of 63%, a CaSO4·2H2O content of 93%, and a SiO2 content of 2.1%. However, there are complex collector configurations, low organic matter removal rates, and unobvious improvements in CaSO4·2H2O content, which affect the back-end building material utilization. Therefore, the development of a phosphogypsum impurity removal and whitening process with a short process, simple operation, and the ability to simultaneously remove organic matter, SiO2, fluoride ions and other impurities, and simultaneously achieve a significant increase in concentrate whiteness and CaSO4·2H2O content, is of great significance for building a resource-saving and environmentally friendly society and helping to build an ecological civilization. Summary of the invention

[0004] In view of the shortcomings in the prior art, the purpose of the present invention is to provide a reverse-forward flotation coupled synchronous impurity removal and whitening process for phosphogypsum, so as to solve the problems of the existing phosphogypsum impurity removal and whitening process, such as single impurity removal capacity, general removal effect, limited improvement in CaSO4·2H2O purity, long process line, large amount of reagents used and high cost.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A phosphogypsum reverse-forward flotation coupled synchronous impurity removal and whitening process, comprising the following steps:

[0007] (1) mixing phosphogypsum and water to obtain a slurry of a certain proportion, and stirring at a high speed for a period of time;

[0008] (2) After sufficient stirring, a certain amount of flotation reagent A is added to the pulp, and high-speed stirring is continued for a period of time, followed by aeration for reverse flotation, and the foam is scraped until it turns white. The product obtained in the tank is a coarse concentrate pulp;

[0009] (3) adding a certain amount of flotation agent B to the coarse concentrate slurry obtained in step (2), continuing high-speed stirring for a certain period of time, adding a certain amount of frother, continuing high-speed stirring for a certain period of time, aerating for positive flotation, scraping bubbles until there is no floating gypsum, and obtaining a foam product;

[0010] (4) filtering the obtained foam product and drying it to obtain a concentrate product.

[0011] Preferably, in step (1), the concentration of the slurry is 20-40 wt%.

[0012] Preferably, in step (1), the speed of the high-speed stirring is 1500-2500 rpm and the time is 3-9 min.

[0013] Preferably, in step (2), the flotation agent A is one or more of dodecyl bis(hydroxyethyl)methylammonium chloride, tetradecyl bis(hydroxyethyl)methylammonium chloride, hexadecyl bis(hydroxyethyl)methylammonium chloride, and octadecyl bis(hydroxyethyl)methylammonium chloride.

[0014] Preferably, in step (2), the amount of flotation agent A used is 150-450 g / ton of phosphogypsum.

[0015] Preferably, in step (2), the speed of the high-speed stirring is 1500 to 2500 rpm, and the time of the high-speed stirring is 2 to 4 min.

[0016] Preferably, in step (2), the aeration rate is 0.15-0.30 m 3 / h.

[0017] Preferably, in step (2), the reverse flotation temperature is 5-40°C; more preferably, the temperature is 25°C.

[0018] Preferably, in step (3), the amount of flotation agent B used is 30-90 L / ton of phosphogypsum.

[0019] Preferably, in step (3), the flotation agent B is prepared by weighing an appropriate amount of one or more of dodecylamine, tetradecylamine, hexadecylamine and octadecylamine, adding 37 wt % hydrochloric acid at a mass ratio of 1:1, and after sufficient reaction, adding water to prepare a mother liquor with a concentration of 5 g / L.

[0020] Preferably, in step (3), after the flotation agent B is added, the high-speed stirring speed is 1500-2500 rpm and the time is 2-4 min.

[0021] Preferably, in step (3), the temperature of positive flotation is room temperature.

[0022] Preferably, in step (3), the foaming agent is 4-methyl-2-pentanol (MIBC), and the amount used is 150 to 450 g per ton of phosphogypsum.

[0023] Preferably, in step (3), after the foaming agent is added, the high-speed stirring speed is 1500 to 2500 rpm and the time is 2 to 4 minutes.

[0024] Preferably, in step (3), the aeration rate is 0.15 to 0.30 m 3 / h.

[0025] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0026] (1) The reagent used in the reverse flotation step of the present invention has strong collection and selection performance, can simultaneously achieve the removal of organic matter, SiO2, and fluoride ions, conforms to the principle of "floating less and suppressing more", and can greatly improve the whiteness and CaSO4·2H2O content of the phosphogypsum concentrate; it also has good foaming performance, low reagent dosage, and good defoaming performance.

[0027] (2) In the present invention, the reagent used in the reverse flotation step contains a hydroxyethyl group, which can increase the hydrogen bonding ability between the silicate mineral and the electrostatic interaction between the mineral and the reagent; the reagent has good stability, especially being able to be in a stable liquid state at low temperatures, and can be used for separation operations at 5 to 40°C.

[0028] (3) The simultaneous impurity removal and whitening process of the present invention, comparing the various indicators of the products obtained by adjusting the pH value of Comparative Examples 1-7 with the various indicators of the products obtained by not adjusting the pH value of Examples 1-5, the overall effect is similar. Therefore, compared with the prior art, the present invention does not need to use a pharmaceutical agent to adjust the pH value, which can greatly reduce production costs and avoid pollution caused by pharmaceutical agents.

[0029] (4) In step 1 of the present invention, when the concentration of the phosphogypsum slurry is lower than 20wt%, the processing volume per unit time is small and the processing cost is high; when the phosphogypsum slurry is greater than 40wt%, the whiteness increase of the phosphogypsum concentrate slows down, the SiO2 removal performance deteriorates, and the energy consumption and equipment damage rate are greatly increased.

[0030] In step 2, when the flotation reagent A is lower than 150g / t, the removal effect of impurities such as organic matter, SiO2 and fluoride ions is poor, and the increase in the whiteness of the phosphogypsum concentrate and the purity of CaSO4·2H2O is limited; when the flotation reagent A is higher than 450g / t, the removal effect of impurities such as organic matter, SiO2 and fluoride ions is not much different, and the whiteness of the phosphogypsum concentrate and the purity of CaSO4·2H2O remain almost unchanged, but continuing to increase the dosage of the reagent will increase the production cost.

[0031] In step 3, when the flotation reagent B is less than 150g / t (based on the amount of dodecylamine added when preparing the flotation reagent B), all gypsum cannot be floated out, resulting in a low final concentrate yield; when the flotation reagent B is higher than 450g / t (based on the amount of dodecylamine added when preparing the flotation reagent B), the probability of impurities such as SiO2 and phosphate ore floating out will increase, resulting in a decrease in the whiteness of the final phosphogypsum concentrate and the purity of CaSO4·2H2O. At the same time, excessive addition of flotation reagent B will increase production costs.

[0032] (5) Compared with the commonly used "one reverse and three positive" and multi-stage positive flotation process in the prior art, the "one reverse and one positive" double flotation process provided by the present invention has a shorter process and can simultaneously remove organic matter, SiO2 and fluoride ion impurities.

[0033] (6) In the present invention, the positive flotation step can greatly reduce the SiO2 content in the concentrate, and the entire flotation process does not require the pH of the slurry to be adjusted, which is low in cost and easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic diagram of the operation process of a reverse-forward flotation coupled synchronous impurity removal and whitening process for phosphogypsum of the present invention;

[0035] Figure 2 The pictures are the pictures at the beginning (a) and the end (b) of the scraping of bubbles in the reverse flotation step in Example 1;

[0036] Figure 3 The pictures are the pictures at the beginning (a) and the end (b) of the frothing scraping in the positive flotation step in Example 1;

[0037] Figure 4 From left to right in the figure are pictures of phosphogypsum slag, the concentrate product of Example 1, the concentrate product of Comparative Example 1-2 and the concentrate product of Comparative Example 1-3. DETAILED DESCRIPTION

[0038] The following non-limiting embodiments may enable a person skilled in the art to more fully understand the present invention, but do not limit the present invention in any way. The preferred embodiments of the present invention are described in detail in conjunction with the accompanying drawings, wherein the accompanying drawings are used to illustrate the principles of the present invention and are not used to limit the scope of protection of the present invention.

[0039] The test methods described in the examples are conventional methods unless otherwise specified; the reverse flotation and forward flotation reagents, other reagents and materials are commercially available unless otherwise specified.

[0040] The basic parameters of the flotation machine used in the following examples are: XFD-IV single-tank flotation machine, specification: 1L, power: 120w, spindle speed parameter: 0-2800r / min, aeration flowmeter working range: 0-0.40m 3 / h.

[0041] The colored impurities such as flotation agent, ore mud, apatite and pyrite attached to the surface of phosphogypsum are important factors affecting its whiteness. The present invention promotes the shedding of colored impurities by high-speed stirring and slurry mixing. After the flotation agent A is added, the hydroxyethyl and quaternary ammonium salt C4N contained in it + Under the combined influence of the hydrogen bond and electrostatic action of the group, it quickly combines with the impurity ions, improves the surface hydrophobicity of the impurity ions, and promotes flotation separation. Under high-speed stirring conditions, it fully interacts with impurities such as organic matter, SiO2, and fluoride ions, promotes the synchronous removal of impurity ions, and effectively achieves the removal and whitening of phosphogypsum. In the positive flotation process, the cationic flotation agent B is easily adsorbed with the gypsum with negative surface charge under the action of electrostatics, changes the hydrophobicity of the gypsum surface, and then improves its floatability, realizes the further separation of impurities such as SiO2 and phosphate ore in the phosphogypsum rough concentrate, and greatly reduces the content of SiO2. Compared with the prior art, the process of the present invention is short, easy to operate, and low in cost. It can effectively achieve the synchronous removal of impurities such as organic matter, SiO2 and fluoride ions, and significantly improve the whiteness of the phosphogypsum concentrate and the purity of CaSO4·2H2O, which meets the requirements of the first-class building material gypsum in the national standard GB / T 23456-2018 "Phosphogypsum".

[0042] Example 1

[0043] A phosphogypsum reverse-forward flotation coupled synchronous impurity removal and whitening process, the process flow chart is as follows Figure 1 As shown, the following steps are included:

[0044] The phosphogypsum used in this embodiment comes from Hubei Xingfa Mining Company, has a natural pH of about 2.5, a whiteness of 30.89%, a CaSO4·2H2O purity of 88.21%, an organic matter content of 0.74wt%, a fluoride ion content of 0.329wt%, and a SiO2 content of 6.20wt%.

[0045] Table 1 Chemical components and contents of phosphogypsum

[0046] Element pH Whiteness <![CDATA[CaSO4·2H2O]]> Organic matter Fluoride ion <![CDATA[SiO2]]> content ～2.5 30.89 88.21 0.74 0.329 6.20

[0047] Step (1), 300 g of phosphogypsum was mixed with water to obtain a slurry with a concentration of 30 wt % (pH value was 2.48), and stirred at 2000 rpm for 6 min;

[0048] Step (2): After stirring, add flotation agent A (dodecyl bis(hydroxyethyl)methylammonium chloride) to the slurry at a dosage of 300 g per ton of phosphogypsum, continue stirring at 2000 rpm for 3 min, and then aerate (0.2 m 3 / h air) for reverse flotation, scraping the foam until it turns white, and the product obtained in the tank is coarse concentrate pulp; reverse flotation is completed at 25°C.

[0049] Step (3), add flotation reagent B (dodecylamine hydrochloride solution) to the coarse concentrate slurry obtained in step (2) at a ratio of 30L per ton of phosphogypsum, continue stirring at 2000rpm for 3min, add foaming agent 4-methyl-2-pentanol (MIBC) at a ratio of 150g per ton of phosphogypsum, continue stirring at 2000rpm for 3min, and then aerate (0.2m 3 / h air) for positive flotation, scrape the foam until there is no floating gypsum, and obtain the foam product. The positive flotation is completed at 25℃.

[0050] The preparation method of the dodecylamine hydrochloride solution is as follows: weigh 5g of dodecylamine, add 37wt% hydrochloric acid at a mass ratio of 1:1, and after sufficient reaction, add water to prepare a mother liquor with a concentration of 5g / L (the concentration is calculated based on the amount of dodecylamine, that is, 5g of dodecylamine / 1L of mother liquor volume = 5g / L).

[0051] Step (4), filtering the foam product obtained in step (3) and drying it at 45°C to obtain a final concentrate product.

[0052] Test results: The yield of the concentrate product is 68.74%, the whiteness is 61.33%, the purity of CaSO4·2H2O in the concentrate product is 97.07%, the organic matter content is 0.25wt%, the fluoride ion content is 0.029wt%, and the SiO2 content is 1.69wt%.

[0053] Comparative Example 1-1

[0054] The phosphogypsum was treated according to the process of Example 1, except that no flotation reagent A and no flotation reagent B were added in the flotation process of steps (2) and (3), and only water washing was performed. The other process conditions were the same as those of Example 1.

[0055] Test results: The yield of the obtained product is 96.40%, the whiteness is 38.33%, the CaSO4·2H2O purity is 89.08%, the organic matter content is 0.68wt%, the fluoride ion content is 0.215wt%, and the SiO2 content is 5.82wt%.

[0056] Comparative Example 1-2

[0057] The phosphogypsum was treated according to the process of Example 1, except that the amount of flotation agent A in the reverse flotation process of step (2) was 300 g / ton of phosphogypsum, and no flotation agent B was added in the forward flotation process of step (3). The other process conditions were the same as those of Example 1.

[0058] Test results: The yield of the obtained product is 75.81%, the whiteness is 59.95%, the CaSO4·2H2O purity is 93.19%, the organic matter content is 0.32wt%, the fluoride ion content is 0.038wt%, and the SiO2 content is 2.92wt%.

[0059] Comparative Examples 1-3

[0060] The phosphogypsum was treated according to the process of Example 1, except that no flotation agent A was added in the reverse flotation process of step (2), and the amount of flotation agent B used in the forward flotation process of step (3) was 30 L / ton of phosphogypsum. Other process conditions were the same as those of Example 1.

[0061] Test results: The yield of the obtained product is 77.59%, the whiteness is 41.47%, the CaSO4·2H2O purity is 91.25%, the organic matter content is 0.61wt%, the fluoride ion content is 0.224wt%, and the SiO2 content is 3.75wt%.

[0062] Comparative Examples 1-4

[0063] The phosphogypsum treatment was carried out according to the process of Example 1, except that the positive flotation process in step (3) was omitted. The other process conditions were the same as those in Example 1.

[0064] Test results: The yield of the obtained product is 75.22%, the whiteness is 59.67%, the CaSO4·2H2O purity is 92.98%, the organic matter content is 0.36wt%, the fluoride ion content is 0.039wt%, and the SiO2 content is 3.01wt%.

[0065] Comparative Examples 1-5

[0066] The phosphogypsum treatment was carried out according to the process of Example 1, except that the reverse flotation process in step (2) was omitted. The other process conditions were the same as those in Example 1.

[0067] Test results: The yield of the obtained product is 78.10%, the whiteness is 40.86%, the CaSO4·2H2O purity is 91.01%, the organic matter content is 0.62wt%, the fluoride ion content is 0.231wt%, and the SiO2 content is 3.83wt%.

[0068] Comparative Examples 1-6

[0069] The phosphogypsum was treated according to the process of Example 1, except that the amount of flotation reagent A in the reverse flotation process of step (2) was 600 g / ton of phosphogypsum, and the amount of flotation reagent B in the forward flotation process of step (3) was 120 L / ton of phosphogypsum. Other process conditions were the same as those of Example 1.

[0070] Test results: The yield of the obtained product is 65.94%, the whiteness is 63.28%, the CaSO4·2H2O purity is 97.69%, the organic matter content is 0.27wt%, the fluoride ion content is 0.015wt%, and the SiO2 content is 1.49wt%.

[0071] By comparing the test results of Example 1 and Comparative Examples 1-1, 1-2, 1-3, 1-4, 1-5 and 1-6, it can be seen that water washing alone has little effect on the desiliconization, impurity removal and whitening of phosphogypsum; using flotation agent A only in the reverse flotation process can remove organic matter, fluoride ions and part of SiO2 impurities, and significantly improve the whiteness of the product and its CaSO4·2H2O purity, but the removal of SiO2 is poor; using flotation agent B only in the forward flotation process, although the impurity removal effect, product whiteness and its CaSO4·2H2O purity are better than those of Comparative Example 1-1 with water washing alone, the overall effect is poor, and the gap with the product of Example 1 is obvious.

[0072] Example 2

[0073] The phosphogypsum was treated according to the process of Example 1, except that the amount of flotation agent A used in the reverse flotation process of step (2) was 150 g per ton of phosphogypsum. Other process conditions were the same as those of Example 1.

[0074] Test results: The yield of the concentrate product obtained is 70.33%, the whiteness is 58.16%, the CaSO4·2H2O purity is 96.01%, the organic matter content is 0.22wt%, the fluoride ion content is 0.031wt%, and the SiO2 content is 2.12wt%.

[0075] Example 3

[0076] The phosphogypsum was treated according to the process of Example 1, except that the amount of the reverse flotation agent A in the reverse flotation process of step (2) was 150 g per ton of phosphogypsum, and the amount of the flotation agent B in the forward flotation process of step (3) was 60 L per ton of phosphogypsum. The other process conditions were the same as those of Example 1.

[0077] Test results: The yield of the obtained product is 76.33%, the whiteness is 57.39%, the CaSO4·2H2O purity is 95.52%, the organic matter content is 0.30wt%, the fluoride ion content is 0.041wt%, and the SiO2 content is 2.29wt%.

[0078] Example 4

[0079] The phosphogypsum treatment was carried out according to the process of Example 1, except that 90 L of flotation agent B was added per ton of phosphogypsum in the positive flotation process of step (3). Other process conditions were the same as those of Example 1.

[0080] Test results: The yield of the obtained concentrate product is 75.71%, the whiteness is 58.86%, the CaSO4·2H2O purity is 96.36%, the organic matter content is 0.38wt%, the fluoride ion content is 0.031wt%, and the SiO2 content is 1.90wt%.

[0081] Example 5

[0082] The phosphogypsum was treated according to the process of Example 1, except that the amount of the reverse flotation agent A in the reverse flotation process of step (2) was 450 g per ton of phosphogypsum, and the amount of the flotation agent B in the forward flotation process of step (3) was 90 L per ton of phosphogypsum. The other process conditions were the same as those of Example 1.

[0083] Test results: The yield of the obtained product is 74.54%, the whiteness is 61.08%, the CaSO4·2H2O purity is 96.74%, the organic matter content is 0.43wt%, the fluoride ion content is 0.027wt%, and the SiO2 content is 1.84wt%.

[0084] By comparing the product test results of Example 1, Example 2, Example 3, Example 4 and Example 5, it can be seen that the amount of flotation agent A has an important influence on the removal of impurities such as organic matter, SiO2 and fluoride ions, the improvement of whiteness and CaSO4·2H2O purity, especially the removal of SiO2. The amount of flotation agent B has an important influence on the yield of the final concentrate. With the increase of the amount of flotation agent B, the yield of the final concentrate will increase, but at the same time, it is accompanied by the increase of the content of impurities such as organic matter, SiO2 and fluoride ions in the phosphogypsum concentrate.

[0085]

[0086] Comparative Examples 1-7

[0087] The phosphogypsum was treated according to the process of Example 1, except that 1 mol / L hydrochloric acid was added to the slurry obtained in step (1) before adding flotation agent A during the reverse flotation process of step (2) to adjust the pH value to 1.5. The other process conditions were the same as those of Example 1.

[0088] Test results: The yield of the obtained product is 72.25%, the whiteness is 62.16%, the CaSO4·2H2O purity is 95.97%, the organic matter content is 0.23wt%, the fluoride ion content is 0.024wt%, and the SiO2 content is 1.57wt%.

[0089] By comparing the test results of the products of Examples 1-5 and Comparative Examples 1-7, it can be seen that, for the process of the present invention, the various indices of the products obtained by adjusting the pH value in Comparative Examples 1-7 are similar to the various indices of the products obtained by not adjusting the pH value in Examples 1-5. Therefore, the process of the present invention does not require adjusting the pH value, which can greatly reduce the production cost and avoid pollution caused by the agent selected for adjusting the pH value.

[0090] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A phosphogypsum reverse-forward flotation coupled synchronous impurity removal and whitening process, comprising the following steps: (1) mixing phosphogypsum and water to obtain a slurry with a concentration of 20 to 40 wt%, and stirring at a high speed; (2) After sufficient stirring, add flotation agent A to the pulp, continue high-speed stirring and aeration for reverse flotation, scrape the foam until the foam is white, and the product obtained in the tank is a coarse concentrate pulp; (3) adding flotation agent B to the coarse concentrate slurry obtained in step (2), adding a frother after continuing high-speed stirring, aerating after continuing high-speed stirring for positive flotation, scraping the foam until there is no floating gypsum, and obtaining a foam product; (4) filtering the obtained foam product and drying it to obtain a concentrate product.

2. The phosphogypsum reverse-forward flotation coupled synchronous impurity removal and whitening process according to claim 1, characterized in that: In the step (1), the speed of the high-speed stirring is 1500 to 2500 rpm and the time is 3 to 9 minutes.

3. The phosphogypsum reverse-forward flotation coupled synchronous impurity removal and whitening process according to claim 1, characterized in that: In the step (2), the flotation agent A is one or more of dodecyl bis(hydroxyethyl)methylammonium chloride, tetradecyl bis(hydroxyethyl)methylammonium chloride, hexadecyl bis(hydroxyethyl)methylammonium chloride, and octadecyl bis(hydroxyethyl)methylammonium chloride; preferably, in the step (2), the amount of the flotation agent A is 150-450 g / ton of phosphogypsum.

4. The phosphogypsum reverse-forward flotation coupled synchronous impurity removal and whitening process according to claim 1, characterized in that: In step (2), the speed of the high-speed stirring is 1500-2500 rpm, and the time is 2-4 min; preferably, in step (2), the aeration rate is 0.15-0.30 m 3 / h.

5. The phosphogypsum reverse-forward flotation coupled synchronous impurity removal and whitening process according to claim 1, characterized in that: In step (3), the amount of flotation agent B is 30-90 L / ton of phosphogypsum.

6. The phosphogypsum reverse-forward flotation coupled synchronous impurity removal and whitening process according to claim 1, characterized in that: In step (3), the flotation agent B is prepared by weighing an appropriate amount of one or more of dodecylamine, tetradecylamine, hexadecylamine and octadecylamine, adding 37wt% hydrochloric acid at a mass ratio of 1:1, and adding water to prepare a mother liquor after sufficient reaction; preferably, the concentration of the mother liquor is 5g / L; preferably, in step (3), after the flotation agent B is added, the high-speed stirring speed is 1500-2500rpm and the time is 2-4min.

7. The phosphogypsum reverse-forward flotation coupled synchronous impurity removal and whitening process according to claim 1, characterized in that: In the step (3), the foaming agent is 4-methyl-2-pentanol, and its dosage is 150-450 g / ton of phosphogypsum; preferably, in the step (3), after the foaming agent is added, the high-speed stirring speed is 1500-2500 rpm and the time is 2-4 min.

8. The phosphogypsum reverse-forward flotation coupled synchronous impurity removal and whitening process according to claim 1, characterized in that: In step (3), the aeration rate is 0.15-0.30 m 3 / h.

9. The phosphogypsum reverse-forward flotation coupled synchronous impurity removal and whitening process according to claim 1, characterized in that: In the step (2), the reverse flotation temperature is 5-40°C, preferably, the temperature is 25°C.

Images