Ardealite reverse-direct flotation desilicication and impurity removal combined process

Abstract

The invention relates to the technical field of phosphorus chemical solid waste treatment, and particularly discloses a reverse-direct flotation desilicication and impurity removal combined process for phosphogypsum. According to the process, C12-18 alkyl dimethyl ethyl benzyl ammonium chloride is used as a reverse flotation reagent, a mixture of R-NH2 or hydrochloride thereof and R-OSO3Na according to a certain proportion is used as a direct flotation reagent, R in the direct flotation reagent is alkyl and is the same as the alkyl in the reverse flotation reagent, and through the one-reverse-one-direct flotation process, the content of the R in the reverse flotation reagent is reduced, and the content of the R in the reverse flotation reagent is reduced. And various impurities such as silicon, organic matters and fluorine in the phosphogypsum can be synchronously removed. After flotation, the yield of concentrate can reach 75%, the grade of CaSO4. 2H2O is 97.7% or above, and the desilicication rate reaches 75% or above. The method is simple in process, efficient and low in cost.

Description

Technical Field

[0001] The invention relates to the technical field of phosphorus chemical solid waste treatment, and specifically discloses a combined process for reverse-positive flotation desiliconization and impurity removal of phosphogypsum. Background Art

[0002] Phosphogypsum is a by-product produced during the production of wet-process phosphoric acid. Usually, 4.5 to 5.5 tons of phosphogypsum are produced for every ton of phosphoric acid produced. According to statistics, the cumulative stockpile of phosphogypsum in China has reached about 600 million tons, and it is expected that the total stockpile will increase to about twice the current size in the next 5 to 20 years. At present, the comprehensive utilization rate of phosphogypsum worldwide is about 40%, and most of it is still handled by open-air stockpiling. This storage method not only occupies a large amount of land resources and brings potential geological safety hazards, but also because phosphogypsum contains a large amount of soluble phosphorus, fluorine, heavy metals and other harmful impurities, it is very easy to dissolve during long-term storage, causing serious pollution to the surrounding soil and water.

[0003] CaSO in phosphogypsum 4 ·2H 2 O content exceeds 80%, which is a renewable resource with development potential. However, phosphogypsum also contains a certain amount of SiO 2 , organic matter, residual phosphoric acid, fluoride, incompletely decomposed phosphate rock and acid insoluble matter, among which SiO 2 and organic matter have a particularly significant impact on its resource utilization. 2 The presence of organic matter will affect the thermal decomposition process of PG, and the presence of organic matter will seriously reduce the strength and whiteness of PG products. At present, phosphogypsum is mainly used in low value-added fields such as cement, chemical raw materials, soil conditioner and roadbed construction. Therefore, in order to realize the wide application of phosphogypsum in high value-added fields, it is necessary to effectively remove SiO through pretreatment technologies such as flotation. 2 , organic matter, fluoride and other impurities, thereby improving the purity and whiteness of phosphogypsum, and promoting its large-scale and high-value utilization.

[0004] In response to this problem, domestic and foreign researchers have conducted a lot of research on the pretreatment of PG. Common pretreatment methods include chemical conversion, calcination, ball milling, water washing and flotation. Among them, the flotation technology based on the difference in hydrophobicity of different mineral surfaces for separation and purification is considered to be an environmentally friendly and efficient separation technology because of its advantages such as good selectivity and low reagent cost. It has been widely used in the purification and separation of various minerals. For example, CN 113695085A discloses a method for purifying and harmless treatment of phosphogypsum. The method uses benzyl quaternary ammonium salt, non-polar oil and alcohol as a combined collector. Through a one-step reverse flotation process, the concentrate CaSO 4 ·2H 2O grade is increased to 95.7%, SiO 2 The content was reduced to 2.53%, the whiteness was increased to 52.9%, and the desiliconization rate was 46.6%, achieving the desiliconization and whitening of phosphogypsum. However, the whiteness of the concentrate and CaSO 4 ·2H 2 O grade improvement is limited, SiO 2 The removal effect is poor, and only SiO 2 The removal of impurities has not been studied in the process of organic matter and fluoride impurities. CN 117861862A discloses a method for synchronous desiliconization and organic matter removal of phosphogypsum by co-reverse flotation of alkyl dimethyl tertiary amine and alcohol foaming agent, which achieves the removal of SiO2 in phosphogypsum. 2 The method can remove impurities and decolorize phosphogypsum effectively, greatly improving the whiteness and grade of phosphogypsum. However, the desiliconization effect and whiteness improvement effect are limited. CN 117181437A discloses a method for preparing high-white gypsum by extracting and flotating phosphogypsum. After deep purification by one extraction reverse flotation and three positive flotations, the whiteness of the obtained phosphogypsum is increased to 72.41%; the grade is increased to 96.69%; and the yield reaches 60.45%. Although the phosphogypsum can be effectively impurized and decolorized, the whiteness and grade of the phosphogypsum can be greatly improved. However, the components of the reverse flotation extractant used are complex, the purification process involves one extraction reverse flotation and three positive flotations, the flotation process is complex, the energy consumption is large, and the separation and reuse of the returned water are complex. In addition, the extractant composition is complex and easily causes secondary pollution.

[0005] In summary, a variety of patented technologies have been published for the purification pretreatment of phosphogypsum, but these methods still have problems such as complex processes, multiple process steps, high energy consumption, single agent selection performance and poor agent stability. At the same time, silicate impurities such as quartz, apatite and feldspar in phosphogypsum cannot be removed efficiently. CaSO 4 ·2H 2 The improvement of O grade is limited, and the improvement of concentrate whiteness is not significant. Therefore, it is urgent to find a simpler and more efficient method for purifying and removing impurities from phosphogypsum. Summary of the invention

[0006] Based on the above shortcomings of the prior art, the purpose of the present invention is to provide a combined process for reverse-forward flotation desiliconization and impurity removal of phosphogypsum. The combined process of reverse-forward flotation desiliconization and impurity removal of the present invention can achieve the simultaneous removal of various impurities such as silicon, organic matter, and fluorine in phosphogypsum, especially the desiliconization effect is significant, which can be reduced to less than 1.50wt%, and the desiliconization rate is more than 75%; and it can take into account the removal effect of silicon, organic matter and fluorine in the concentrate while ensuring the yield. The concentrate yield after flotation can reach 75%, CaSO 4 ·2H 2The O grade is above 97.7%. The process of the invention is simple, efficient and low in cost, and the obtained purified phosphogypsum product can be used as a high-quality raw material for α high-strength gypsum or environmental functional materials.

[0007] In order to achieve the above object, the present invention adopts the following technical scheme:

[0008] A combined process for reverse-forward flotation desiliconization and impurity removal of phosphogypsum, comprising the following steps:

[0009] (1) Add phosphogypsum and water into a flotation tank, start stirring, and stir evenly (3-5 minutes) to obtain slurry;

[0010] (2) Add an aqueous solution of a reverse flotation agent to the ore pulp, stir evenly (1-3 minutes), aerate and perform reverse flotation, scrape the foam until it turns completely white, stop aeration, and the product obtained in the tank is a purified slurry;

[0011] (3) The pH of the purified slurry in the tank is adjusted to 1.50±0.02, and then an aqueous solution of a positive flotation agent is added to the slurry. After stirring evenly (1-2 minutes), aeration is performed for positive flotation. The foam is scraped until no floating gypsum is present. The aeration is stopped, the stirring is turned off, and the foam product is filtered and dried to obtain a concentrate product.

[0012] Among them, the reverse flotation reagent is C12-18 alkyl dimethyl ethyl benzyl ammonium chloride, such as dodecyl dimethyl ethyl benzyl ammonium chloride, tetradecyl dimethyl ethyl benzyl ammonium chloride, hexadecyl dimethyl ethyl benzyl ammonium chloride and octadecyl dimethyl ethyl benzyl ammonium chloride; the positive flotation reagent is R-NH 2 or its hydrochloride and R-OSO 3 Na mixture, R in the positive flotation agent is an alkyl group, and its carbon number is the same as that of the alkyl group in the reverse flotation agent. Preferably, the reverse flotation agent is dodecyl dimethyl ethyl benzyl ammonium chloride, and the positive flotation agent is a mixture of dodecylamine or dodecylamine hydrochloride and sodium dodecyl sulfate.

[0013] Among them, R-NH 2 The mass of the positive flotation agent accounts for 80%-95%, preferably 80%-90%, more preferably 86%-90%, and most preferably 88.9%.

[0014] Among them, the mass ratio of the reverse flotation agent in the aqueous solution of the added reverse flotation agent to the pulp is 140g / ton-160g / ton, preferably 150g / ton; the mass ratio of the positive flotation agent in the aqueous solution of the added positive flotation agent to the pulp is 80g / ton-100g / ton, preferably 90g / ton.

[0015] Furthermore, the concentration of phosphogypsum in the slurry is 25wt%-35wt%, preferably 30wt%.

[0016] Furthermore, the method for preparing the aqueous solution of the reverse flotation agent is as follows: the reverse flotation agent is mixed with water and stirred evenly.

[0017] Further, the method for preparing the aqueous solution of the positive flotation reagent is: directly taking R-NH 2 The hydrochloride salt, or R-NH 2 Mix with hydrochloric acid until the amine is completely dissolved to obtain R-NH 2 The hydrochloride of R-OSO 3 Mix Na and water and stir well.

[0018] Further, the concentration of the reverse flotation reagent in the aqueous solution is 1wt%, and the concentration of R-NH 2 The concentration is 1wt%.

[0019] Furthermore, the stirring speed in steps (1)-(3) is 1500-2500 rpm, preferably 2000 rpm.

[0020] Furthermore, the aeration rate in steps (2)-(3) is 0.10-0.30m 3 / h, preferably 0.20m 3 / h.

[0021] Furthermore, the pH of the purified slurry in the tank was adjusted to 1.50±0.02 with 1 mol / L sulfuric acid.

[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0023] (1) The present invention realizes the simultaneous removal of various impurities such as silicon, organic matter, and fluorine in phosphogypsum through a one-reverse-one-forward flotation process, especially the desiliconization effect is remarkable, which can be reduced to below 1.50wt%, and the desiliconization rate can reach 76.5%.

[0024] (2) The combined process of reverse-forward flotation desiliconization and impurity removal of phosphogypsum of the present invention can take into account the removal of silicon, organic matter and fluorine in the concentrate while ensuring the yield. The concentrate yield after flotation can reach 75%, CaSO 4 ·2H 2 O grade is above 97.7%.

[0025] (3) The process of the present invention is simple, efficient and low-cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a simplified operation flow chart of the combined process of reverse-positive flotation desiliconization and impurity removal of phosphogypsum of the present invention;

[0027] Figure 2 The appearance pictures of the concentrate after flotation (left) and the original phosphogypsum (right) in Example 1 of the present invention are shown;

[0028] Figure 3 This is a picture of the appearance of tailings II after flotation in Example 1 of the present invention. DETAILED DESCRIPTION

[0029] The specific implementation modes of the present invention are described in detail below, which is a part of this specification. The principles of the present invention are explained through examples. Other aspects, features and advantages of the present invention will become clear through the detailed description.

[0030] In the following examples, phosphogypsum from a Hubei Yidu Chemical Co., Ltd. is used. Figure 2 (Right) The particle size of the mineral is mainly 75-150μm and less than 75μm, accounting for 40.29% and 40.65% of the mass respectively; pH ​​is 2.72 measured by HJ 557-2010 standard at a solid-liquid ratio of 1:10; whiteness is 31.28%, main chemical components and content: CaSO 4 ·2H 2 O content (grade) is 87.46%, SiO 2 The content is 6.34wt%, the organic matter content is 0.76wt%, and the fluoride ion content is 0.37wt%.

[0031] The test methods described in the following examples are conventional methods unless otherwise specified; the reverse flotation reagents, forward flotation reagents and materials are commercially available unless otherwise specified.

[0032] 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.

[0033] Example 1 A combined process for reverse-forward flotation desiliconization and impurity removal of phosphogypsum

[0034] See the process flow chart Figure 1 .

[0035] In this embodiment, the reverse flotation reagent is dodecyl dimethyl ethyl benzyl ammonium chloride, and the forward flotation reagent is a mixture of dodecylamine and sodium dodecyl sulfate, and the mass ratio of dodecylamine to sodium dodecyl sulfate is 8:1.

[0036] The flotation process for phosphogypsum is as follows:

[0037] (1) 300 g of phosphogypsum ore and 700 g of tap water were added to a flotation tank, stirring was started, the speed was set to 2000 rpm (stirring was not stopped until the flotation was completed), and stirring was performed for 5 min to prepare a 30 wt% ore pulp;

[0038] (2) During the slurry preparation, 0.15 g of dodecyl dimethyl ethyl benzyl ammonium chloride was added to 15 g of tap water, and stirred evenly to prepare a 1% aqueous solution of the reverse flotation agent for standby use. After the slurry preparation was completed, the aqueous solution of the reverse flotation agent was added to the slurry, stirred for 3 minutes, and then aerated for reverse flotation operation. The aeration volume was 0.20 m 3 / h, start scraping when foam is generated, stop aeration when the foam turns completely white, the product obtained in the tank is purified slurry I, the pH value of which is 2.57, and the floated foam is recovered as tailings I;

[0039] (3) During the reverse flotation operation, 0.08 g of dodecylamine was added to 0.08 g of 37 wt% hydrochloric acid based on 90 g of positive flotation reagent per ton of ore pulp, and the mixture was stirred thoroughly until all the solid matter was dissolved. Then, 0.01 g of sodium dodecyl sulfate and 9 g of tap water were added thereto, and the mixture was stirred evenly to prepare a 1% aqueous solution of the positive flotation reagent for standby use. After the reverse flotation operation was completed, the purified slurry I in the tank was first adjusted to a pH of 1.50 with 1 mol / L sulfuric acid, and then the aqueous solution of the positive flotation reagent was added thereto. After stirring for 2 minutes, aeration was then performed for positive flotation operation, and the aeration volume was 0.20 m 3 / h, start scraping when foam is generated, until there is no floating gypsum, stop aeration, turn off stirring, filter, dry and grind the upper foam product to obtain purified phosphogypsum, which is the final concentrate, and the product in the tank is recovered as tailings II.

[0040] The appearance picture of the purified phosphogypsum obtained in this example is shown in Figure 2 (Left), yield is 74.83%, CaSO 4 ·2H 2 O grade is 97.76%, silicon content is 1.49wt%, organic matter content is 0.26wt%, fluorine content is 0.025wt%, whiteness is 61.52%. Figure 3 .

[0041] Comparative Example 1-1

[0042] Compared with Example 1, the only difference is that the positive flotation reagent is dodecylamine, and the preparation steps of the aqueous solution of the positive flotation reagent are: take 0.09g of dodecylamine and add it to 0.09g of 37wt% hydrochloric acid, stir it thoroughly until the solid matter is completely dissolved, then add 9g of tap water and stir it evenly. The yield of the purified phosphogypsum is 77.36%, CaSO4 ·2H 2 The O grade is 96.58%, the silicon content is 1.75wt%, the organic matter content is 0.35wt%, the fluorine content is 0.027wt%, and the whiteness is 61.18%.

[0043] Comparative Example 1-2

[0044] Compared with Example 1, the only difference is that the positive flotation agent is sodium dodecyl sulfate, and the preparation steps of the aqueous solution of the positive flotation agent are: take 0.09g of sodium dodecyl sulfate and add 9g of tap water, and stir evenly. The yield of the purified phosphogypsum is 53.23%, CaSO 4 ·2H 2 The O grade is 97.98%, the silicon content is 1.41wt%, the organic matter content is 0.22wt%, the fluorine content is 0.027wt%, and the whiteness is 62.32%.

[0045] Comparative Examples 1-3

[0046] Compared with Example 1, the only difference is that no reagent is added in the reverse flotation step (2)-(3) and the forward flotation step, and the purified phosphogypsum yield is 95.88%, CaSO 4 ·2H 2 The O grade is 89.07%, the silicon content is 5.60wt%, the organic matter content is 0.70wt%, the fluorine content is 0.292wt%, and the whiteness is 38.79%.

[0047] Comparative Examples 1-4

[0048] Compared with Example 1, the only difference is that in this comparative example, only steps (1)-(2) are performed, that is, only reverse flotation is performed in the flotation process, and the forward flotation step is not performed. The purified slurry I is filtered, dried, and ground to obtain purified phosphogypsum. The yield of the purified phosphogypsum is 80.68%, and CaSO 4 ·2H 2 The O grade is 94.23%, the silicon content is 3.34wt%, the organic matter content is 0.38wt%, the fluorine content is 0.025wt%, and the whiteness is 55.68%.

[0049] Comparative Examples 1-5

[0050] Compared with Comparative Examples 1-4, the only difference is that the dosage of the reverse flotation agent is 300g per ton of slurry. The yield of purified phosphogypsum is 76.82%, CaSO 4 ·2H 2The O grade is 96.35%, the silicon content is 2.12wt%, the organic matter content is 0.30wt%, the fluorine content is 0.024wt%, and the whiteness is 61.86%.

[0051] Comparative Examples 1-6

[0052] Compared with Comparative Examples 1-4, the only difference is that the dosage of the reverse flotation agent is 450g per ton of slurry. The yield of purified phosphogypsum is 73.89%, CaSO 4 ·2H 2 The O grade is 96.67%, the silicon content is 2.05wt%, the organic matter content is 0.29wt%, the fluorine content is 0.022wt%, and the whiteness is 62.58%.

[0053] Comparative Examples 1-7

[0054] Compared with Example 1, the only difference is that the mass ratio of dodecylamine to sodium dodecyl sulfate in the positive flotation reagent is different. The mass ratio of dodecylamine to sodium dodecyl sulfate in this comparative example is 3:1. The preparation steps of the aqueous solution of the positive flotation reagent are: take 0.0675g of dodecylamine and add it to 0.0675g of 37wt% hydrochloric acid, stir it thoroughly until all the solid matter is dissolved, then add 0.0225g of sodium dodecyl sulfate and 9g of tap water, stir it evenly. The obtained purified phosphogypsum yield is 63.21%, CaSO 4 ·2H 2 The O grade is 97.99%, the silicon content is 1.46wt%, the organic matter content is 0.20wt%, the fluorine content is 0.019wt%, and the whiteness is 62.13%.

[0055] Comparative Examples 1-8

[0056] Compared with Example 1, the only difference is that the mass ratio of dodecylamine to sodium dodecyl sulfate in the positive flotation reagent is different. The mass ratio of dodecylamine to sodium dodecyl sulfate in this comparative example is 25:1. The preparation steps of the aqueous solution of the positive flotation reagent are: take 0.0865g of dodecylamine and add it to 0.0865g of 37wt% hydrochloric acid, stir it thoroughly until all the solid matter is dissolved, then add 0.0035g of sodium dodecyl sulfate and 9g of tap water, stir it evenly. The obtained purified phosphogypsum yield is 76.11%, CaSO 4 ·2H 2 The O grade is 97.69%, the silicon content is 1.66wt%, the organic matter content is 0.31wt%, the fluorine content is 0.025wt%, and the whiteness is 61.47%.

[0057] Comparative Examples 1-9

[0058] Compared with Example 1, the only difference is that in this comparative example, only steps (1) and (3) are performed, that is, the flotation process does not perform reverse flotation but only performs forward flotation (before flotation, the pulp is adjusted to a pH of 1.5 with 1 mol / L sulfuric acid). The yield of the purified phosphogypsum obtained is 79.78%, CaSO 4 ·2H 2 The O grade is 94.05%, the silicon content is 3.61wt%, the organic matter content is 0.58wt%, the fluorine content is 0.164wt%, and the whiteness is 44.32%.

[0059] Example 2 A combined process for reverse-forward flotation desiliconization and impurity removal of phosphogypsum

[0060] Compared with Example 1, the only difference between this embodiment and Example 1 is that the mass ratio of dodecylamine to sodium dodecyl sulfate in the positive flotation reagent is different. The mass ratio of dodecylamine to sodium dodecyl sulfate in this embodiment is 4:1. The preparation steps of the aqueous solution of the positive flotation reagent are: take 0.072g of dodecylamine and add it to 0.072g of 37wt% hydrochloric acid, stir it thoroughly until all the solid matter is dissolved, then add 0.018g of sodium dodecyl sulfate and 9g of tap water, stir it evenly. The obtained purified phosphogypsum yield is 68.48%, CaSO 4 ·2H 2 The O grade is 97.88%, the silicon content is 1.48wt%, the organic matter content is 0.21wt%, the fluorine content is 0.021wt%, and the whiteness is 61.69%.

[0061] Comparative Example 2-1

[0062] The difference between this comparative example and Example 2 is that after the completion of steps (1)-(2), the pH of the slurry is not adjusted during the positive flotation in step (3), that is, the pH of the slurry is kept at 2.57 and the positive flotation is directly carried out. The yield of the purified phosphogypsum is 53.78%, and the CaSO 4 ·2H 2 The O grade is 98.07%, the silicon content is 1.40wt%, the organic matter content is 0.20wt%, the fluorine content is 0.024wt%, and the whiteness is 62.43%.

[0063] Example 3 A combined process for reverse-forward flotation desiliconization and impurity removal of phosphogypsum

[0064] Compared with Example 1, the only difference between this embodiment and Example 1 is that the mass ratio of dodecylamine to sodium dodecyl sulfate in the positive flotation reagent is different. The mass ratio of dodecylamine to sodium dodecyl sulfate in this embodiment is 16:1. The preparation steps of the aqueous solution of the positive flotation reagent are as follows: add 0.0847g of dodecylamine to 0.0847g of 37wt% hydrochloric acid, stir thoroughly until all the solid matter is dissolved, then add 0.0053g of sodium dodecyl sulfate and 9g of tap water, stir evenly. The obtained purified phosphogypsum yield is 75.52%, CaSO 4 ·2H 2 The O grade is 97.53%, the silicon content is 1.56wt%, the organic matter content is 0.28wt%, the fluorine content is 0.024wt%, and the whiteness is 61.33%.

[0065] Comparative Example 3-1

[0066] The only difference between this comparative example and Example 3 is that after the completion of steps (1)-(2), the pH of the slurry is not adjusted during the positive flotation of step (3), that is, the pH of the slurry is kept at 2.57 and the positive flotation is directly carried out. The yield of the purified phosphogypsum is 54.64%, and the CaSO 4 ·2H 2 The O grade is 97.98%, the silicon content is 1.49wt%, the organic matter content is 0.23wt%, the fluorine content is 0.027wt%, and the whiteness is 62.17%.

[0067] The test results of the concentrates obtained in the above embodiments and comparative examples are shown in Table 1.

[0068] Table 1

[0069]

[0070] Note: The ratio is the mass ratio of dodecylamine to sodium dodecyl sulfate.

[0071] From the results in Table 1, we can see that:

[0072] Comparing Example 1 with Comparative Examples 1-3, compared with simple water washing, the CaSO 4 ·2H 2 The O grade can be increased to 97.76%, the silicon content can be reduced to 1.49%, the organic matter content can be reduced to 0.26%, the fluorine content can be reduced to 0.025%, the whiteness can be increased to 61.52%, the yield can reach 74.83%, the impurity content can be greatly reduced, the gypsum grade can be significantly improved, and the desiliconization rate can be 76.5%.

[0073] By comparing Example 1 with Comparative Examples 1-4 and 1-9, it can be seen that the silicon removal effect is poor only by the reverse flotation process or the forward flotation process. In addition, the removal effect of organic matter and fluorine impurities by the forward flotation process alone is also poor, and the whiteness improvement is not obvious.

[0074] By comparing Comparative Examples 1-4, 1-5, and 1-6, it can be seen that by using dodecyl dimethyl ethyl benzyl ammonium chloride as a reverse flotation agent, only one-step reverse flotation process is performed, and within a certain range (150g-450g of reverse flotation agent per ton of slurry), increasing the amount of reverse flotation agent can effectively reduce the silicon, organic matter and fluorine contents in the concentrate, and CaSO 4 ·2H 2 O grade and whiteness will be improved, but there is a bottleneck. The best removal effect of silicon by a single reverse flotation process is about 2wt%. It is difficult to further improve it, which may be a deficiency of the process itself. Among them, in Comparative Examples 1-4, only dodecyl dimethyl ethyl benzyl ammonium chloride is used as a reverse flotation agent, and 150g of reverse flotation agent is added per ton of pulp. The silicon content after flotation is 3.34wt%.

[0075] By comparing Example 1 with Comparative Example 1-1 and Comparative Example 1-2, it can be seen that by using dodecyl dimethyl ethyl benzyl ammonium chloride as a reverse flotation agent and dodecylamine as a forward flotation agent through a reverse-forward flotation process, the concentrate yield can be guaranteed, but the silicon and organic matter contents in the concentrate are relatively high; by using dodecyl dimethyl ethyl benzyl ammonium chloride as a reverse flotation agent and sodium dodecyl sulfate as a forward flotation agent through a reverse-forward flotation process, the silicon and organic matter contents in the concentrate can be effectively reduced, but the concentrate yield is relatively low.

[0076] By comparing Examples 1, 2, 3 and Comparative Examples 1-7 and Comparative Examples 1-8, it can be seen that by using dodecyl dimethyl ethyl benzyl ammonium chloride as a reverse flotation agent and using a mixture of dodecylamine and sodium dodecyl sulfate as a forward flotation agent, the yield can be guaranteed while taking into account the removal effect of silicon and organic matter in the concentrate. According to the characteristics of the two agents, although dodecylamine has good selectivity for gypsum, it has poor foaming property. The addition of sodium dodecyl sulfate can effectively improve the foaming property and reduce the content of silicon and organic matter in the concentrate. However, since sodium dodecyl sulfate is not as selective for gypsum as dodecylamine, when too much sodium sulfate is added, the yield will drop significantly. In addition, the price of sodium dodecyl sulfate is about half of that of dodecylamine. The ratio of the two agents in the forward flotation agent is adjusted so that the mass of dodecylamine accounts for 80%-95% of the mass of the forward flotation agent, preferably 80%-90%, more preferably 86%-90%, and most preferably 88.9%.

[0077] By comparing Example 2, Comparative Example 2-1 with Example 3, Comparative Example 3-1, it can be seen that adjusting the pH before forward flotation in the reverse-forward flotation process is beneficial to improving the yield, but the silicon content in the concentrate will increase slightly. Taking all factors into consideration, the pH should be adjusted to 1.5 in actual experiments.

[0078] The combined use of reverse flotation and forward flotation processes can synergize and significantly reduce the impurities in phosphogypsum and improve the purity of its calcium sulfate dihydrate. When the mass of dodecylamine accounts for 80%-95% of the mass of the forward flotation reagent, the yield of purified phosphogypsum is 68.48%-75.52%, and the whiteness of the final product can be increased from 31.28% to 61.33%-61.69%. CaSO 4 ·2H 2 O grade can be increased from 87.46% to 97.53%~97.88%, silicon content can be reduced from 6.34wt% to 1.48wt%~1.56wt% (desiliconization rate is 75.4%~76.5%), organic matter content can be reduced from 0.76wt% to 0.21wt%~0.28wt%, fluorine content can be reduced from 0.37wt% to 0.021wt%~0.025wt%. The product can be used as a high-quality raw material for α high-strength gypsum or environmental functional materials in JC / T 2038-2010 "α-type high-strength gypsum". When the mass of dodecylamine accounts for 80%-90% of the mass of the positive flotation reagent, the yield of purified phosphogypsum is about 70%, and CaSO 4 ·2H 2 O grade is above 97.7%, silicon content drops to below 1.50wt%, desiliconization rate is above 76%, and the organic matter and fluorine content decrease significantly; when the mass of dodecylamine accounts for 86%-90% of the mass of the positive flotation agent, the yield of purified phosphogypsum will be further improved to about 75%.

[0079] The present invention provides a combined process for reverse-forward flotation desiliconization and impurity removal for phosphogypsum, which is an improvement over the applicant's previous work (CN117861862A, a method for synchronous desiliconization and organic matter removal of phosphogypsum by co-reverse flotation). In the present invention, the dosage of the reverse flotation agent is halved, which greatly reduces the cost and makes the silicon content in the concentrate lower. The positive flotation agent added in the newly added positive flotation process is low in cost, which is 1 / 10-1 / 5 of the reverse flotation agent, and the dosage is small, and no additional frother is required. Its cost and function are equivalent to the alcohol frother in the original process. Overall, the combined process for reverse-forward flotation desiliconization and impurity removal for phosphogypsum provided by the present invention is superior to that of the alcohol frother in the original process in terms of CaSO 4 ·2H 2 It has obvious advantages in improving O grade, reducing silicon and removing impurities, and cost.

[0080] The raw materials listed in the present invention, as well as the upper and lower limits and interval values ​​of the raw materials of the present invention, and the upper and lower limits and interval values ​​of the process parameters (such as temperature, time, etc.) can realize the present invention, and the embodiments are not listed one by one here. The above is only the preferred embodiment of the present invention, and of course it cannot be used to limit the scope of the rights of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and changes can be made without departing from the principle of the present invention, and these improvements and changes are also regarded as the protection scope of the present invention.

Claims

1. A combined process for reverse-forward flotation desiliconization and impurity removal of phosphogypsum, characterized in that: The steps include: (1) adding phosphogypsum and water into a flotation tank, starting stirring, and stirring evenly to obtain slurry; (2) Add an aqueous solution of a reverse flotation agent to the ore pulp, stir evenly, aerate and perform reverse flotation, scrape the foam until it turns completely white, stop aeration, and the product obtained in the tank is a purified slurry; (3) adjusting the pH of the purified slurry in the tank to 1.50±0.02, adding an aqueous solution of a positive flotation agent to the slurry, stirring evenly, aerating and performing positive flotation operations, scraping bubbles until no floating gypsum is present, stopping aeration, turning off stirring, filtering and drying the foam product, and obtaining a concentrate product; Wherein, the reverse flotation reagent is C12-18 alkyl dimethyl ethyl benzyl ammonium chloride, the positive flotation reagent is a mixture of R-NH2 or its hydrochloride and R-OSO3Na, and R in the positive flotation reagent is an alkyl group, and the number of carbon atoms of the alkyl group is the same as that of the reverse flotation reagent; The mass of R-NH2 in the positive flotation reagent accounts for 80%-95% of the mass of the positive flotation reagent.

2. The combined process for reverse-forward flotation desiliconization and impurity removal of phosphogypsum according to claim 1, characterized in that: The reverse flotation reagent is dodecyl dimethyl ethyl benzyl ammonium chloride, and the positive flotation reagent is dodecylamine or a mixture of dodecylamine hydrochloride and sodium dodecyl sulfate.

3. The combined process for reverse-forward flotation desiliconization and impurity removal of phosphogypsum according to claim 1, characterized in that: The mass of R-NH2 in the positive flotation reagent accounts for 80%-90% of the mass of the positive flotation reagent, more preferably 86%-90%, and most preferably 88.9%.

4. The combined process for reverse-forward flotation desiliconization and impurity removal of phosphogypsum according to claim 1, characterized in that: The mass ratio of the reverse flotation agent in the aqueous solution of the added reverse flotation agent to the pulp is 140g / ton-160g / ton; the mass ratio of the positive flotation agent in the aqueous solution of the added positive flotation agent to the pulp is 80g / ton-100g / ton.

5. The combined process for reverse-forward flotation desiliconization and impurity removal of phosphogypsum according to claim 1, characterized in that: The mass ratio of the reverse flotation agent in the aqueous solution of the added reverse flotation agent to the pulp is 150 g / ton; the mass ratio of the positive flotation agent in the aqueous solution of the added positive flotation agent to the pulp is 90 g / ton.

6. The combined process for reverse-forward flotation desiliconization and impurity removal of phosphogypsum according to claim 1, characterized in that: The concentration of phosphogypsum in the slurry is 25wt%-35wt%, preferably 30wt%.

7. The combined process for reverse-forward flotation desiliconization and impurity removal of phosphogypsum according to claim 1, characterized in that: The concentration of the reverse flotation reagent in the aqueous solution is 1 wt %, and the concentration of R-NH2 in the forward flotation reagent in the aqueous solution is 1 wt %.

8. The combined process for reverse-forward flotation desiliconization and impurity removal of phosphogypsum according to claim 1, characterized in that: The stirring speed in steps (1) to (3) is 1500-2500 rpm, preferably 2000 rpm.

9. The combined process for reverse-forward flotation desiliconization and impurity removal of phosphogypsum according to claim 1, characterized in that: The aeration volume in steps (2)-(3) is 0.10-0.30m 3 / h, preferably 0.20m 3 / h.

10. The combined process for reverse-forward flotation desiliconization and impurity removal of phosphogypsum according to claim 1, characterized in that: The method for preparing the aqueous solution of the positive flotation reagent is: directly take the hydrochloride of R-NH2 or mix R-NH2 with hydrochloric acid until the amine is completely dissolved to obtain the hydrochloride of R-NH2, then mix it with R-OSO3Na and water, and stir evenly to obtain the result.

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