Phosphogypsum flotation impurity removal whitening process

Abstract

The present application relates to a phosphogypsum flotation impurity removal and whitening process, belonging to the technical field of solid waste treatment of phosphorus chemical industry, solves the problems of long process flow, complex operation, limited increase range of whiteness and purity of calcium sulfate dihydrate of the existing phosphogypsum impurity removal and whitening process. A phosphogypsum flotation impurity removal and whitening process, comprising the following steps: mixing phosphogypsum with water according to a certain mass percentage, and adding a certain amount of flotation reagent A; the ore pulp is stirred and scrubbed at high speed for a certain time; after scrubbing, the ore pulp is introduced into the flotation equipment for once reverse flotation; the underflow of reverse flotation is introduced into the stirring tank, and a certain amount of flotation reagent B is added; the ore pulp in the stirring tank is introduced into the flotation equipment for once again positive flotation, and the obtained foam product is obtained; the foam product is filtered and dewatered to obtain phosphogypsum concentrate. The process flow is short, the amount of flotation reagent is small, and the first-class product standard of GB / T23456-2018 "phosphogypsum" is met.

Description

Technical Field

[0001] This invention belongs to the field of phosphorus chemical solid waste treatment technology, specifically relating to a flotation process for removing impurities and whitening phosphogypsum. Background Technology

[0002] Phosphogypsum is mainly produced in the phosphorus chemical industry. It is a solid byproduct generated during the wet process of phosphoric acid production. The main component of phosphogypsum is calcium sulfate dihydrate (CaSO4·2H2O), making it a good resource for recycled gypsum. According to statistics, 5 to 6 tons of phosphogypsum (dry basis) are produced for every ton of phosphoric acid produced, with an actual quantity of about 7 tons.

[0003] In addition to its main component CaSO4·2H2O, phosphogypsum also contains various forms of phosphorus and fluorine compounds, organic matter, SiO2, alkali metal salts, and radioactive elements, among other impurities. These impurities have a significant impact on the environment and the performance of phosphogypsum. Therefore, purification and impurity removal are necessary steps for the resource utilization of phosphogypsum. Flotation has begun to be applied in the removal of impurities and whitening of phosphogypsum due to its low cost, simple operation, and ease of large-scale, industrial, and automated production. Zhang Lizhen et al. used dodecylamine as a collector and employed a "one roughing and two cleaning" positive flotation process to improve the quality and reduce impurities of phosphogypsum, obtaining a concentrate with a gypsum dihydrate (CaSO4·2H2O) mass fraction of 97.5% and a silica mass fraction of 1.17% (Inorganic Salt Industry, 2021, 53(06), 171-173+184). This process can remove most silicate impurities, but the organic matter removal rate is low, and the increase in whiteness is limited. Patent CN202111600207.9 discloses a method for flotation washing, decolorization, and purification of phosphogypsum, using ether diamine as a collector and employing three reverse flotation processes to obtain a concentrate with a calcium sulfate dihydrate purity of 95.81% and a whiteness of 56.57%. However, this method suffers from problems such as a long flotation process, large reagent dosage, and limited increase in whiteness and calcium sulfate dihydrate purity. Patent CN201510930935.4 discloses a method for preparing a phosphogypsum flotation collector, which is applied to phosphogypsum flotation. After one roughing and one cleaning process, a concentrate with a calcium sulfate dihydrate content of 95.28% and a silica content of 2.87% is obtained. However, this method suffers from complex collector preparation and a limited increase in phosphogypsum whiteness, affecting subsequent applications in high-end building materials. Therefore, developing a phosphogypsum impurity removal and whitening process with a short process flow, simple operation, and a significant increase in whiteness and calcium sulfate dihydrate purity is of great significance. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide a phosphogypsum flotation process for impurity removal and whitening, in order to solve the problems of existing phosphogypsum impurity removal and whitening processes being long, complex to operate, and having limited increases in whiteness and calcium sulfate dihydrate purity.

[0005] The main objective of this invention is achieved through the following technical solution:

[0006] A process for removing impurities and whitening phosphogypsum by flotation includes the following steps:

[0007] Step 1: Mix phosphogypsum and water according to a certain mass percentage, and add a certain amount of flotation reagent A. Stir and adjust the slurry to obtain the slurry. The raw material composition of flotation reagent A by weight is: 40-60 parts of vinyltrimethoxysilane, 30-45 parts of acetic acid solution, and 10-15 parts of alkanetrimethylammonium bromide.

[0008] Step 2: Stir and scrub the slurry at high speed for a certain period of time;

[0009] Step 3: After scrubbing, the slurry is introduced into the flotation equipment for a reverse flotation.

[0010] Step 4: Introduce the reverse flotation underflow into the stirred tank and add a certain amount of flotation reagent B. Flotation reagent B is one or more of the following: dodecylamine hydrochloride, hexadecylamine hydrochloride, octadecylamine hydrochloride, dodecylamine acetate, hexadecylamine acetate, and octadecylamine acetate.

[0011] Step 5: Pour the slurry in the mixing tank into the flotation equipment for another positive flotation to obtain the froth product;

[0012] Step 6: Filter and dehydrate the foam product to obtain phosphogypsum concentrate.

[0013] Furthermore, in step one, the mass fraction of the acetic acid solution is 0.5-5.0%.

[0014] Further, in step one, the alkanetrimethylammonium bromide includes one or more of dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide.

[0015] Furthermore, in step one, the amount of flotation reagent A is 90-250 g / t according to the mass ratio of phosphogypsum.

[0016] Furthermore, in step two, the phosphogypsum content in the slurry is 35-65% by mass.

[0017] Furthermore, in step two, the high-speed stirring speed is 4000-8000 rpm.

[0018] Furthermore, in step two, the high-speed stirring time is 10-60 minutes.

[0019] Furthermore, in step three, the reverse flotation pulp concentration is 18-35%, and the reverse flotation time is 3-8 minutes.

[0020] Furthermore, in step four, the amount of flotation reagent B is 80-300 g / t according to the mass ratio of phosphogypsum.

[0021] Furthermore, in step five, the positive flotation time is 4-9 minutes.

[0022] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0023] 1. The phosphogypsum flotation process for impurity removal and whitening provided by the present invention, by adding flotation reagent A and flotation reagent B, can not only remove organic matter, but also remove impurities such as pyrite and quartz, with strong collection ability and good impurity removal effect.

[0024] 2. The phosphogypsum flotation impurity removal and whitening process provided by this invention uses "one reverse and one forward" flotation to remove impurities and whiten phosphogypsum, which can increase the whiteness of phosphogypsum from 34% to over 70%. It can be directly used in building gypsum to produce α-hemihydrate high-strength gypsum, etc. It does not require subsequent whitening processes such as acid leaching and bleaching. The process is simple, the cost is low, and it reduces the pollution of the ecological environment caused by chemical whitening. It has a wide range of applications.

[0025] 3. The phosphogypsum flotation process for impurity removal and whitening provided by this invention does not require calcination for impurity removal and has low energy consumption.

[0026] 4. The phosphogypsum flotation process for impurity removal and whitening provided by this invention employs high-speed stirring and scrubbing to remove colored organic matter adhering to the surface of the phosphogypsum. During the scrubbing process, flotation reagent A is added to rapidly capture the colored organic matter, preventing it from re-adhering to the phosphogypsum surface after scrubbing. This significantly increases the removal efficiency of colored organic matter and substantially improves the whiteness of the phosphogypsum concentrate. Furthermore, the addition of flotation reagent A during the high-speed stirring and scrubbing process ensures that reagent A is evenly dispersed in the slurry, allowing it to interact more fully with impurities and enhancing the impurity removal effect.

[0027] 5. The phosphogypsum flotation impurity removal and whitening process provided by the present invention only uses scrubbing and two flotation processes of "one reverse and one forward". Compared with the commonly used phosphogypsum reverse flotation process of one roughing-forward flotation-five cleaning reverse-forward flotation in the prior art, the process is shorter, the amount of reagents used is less, the flotation process does not require adjustment of pulp pH, the operation is simple and the cost is low.

[0028] 6. The phosphogypsum flotation process for impurity removal and whitening provided by this invention results in phosphogypsum with a whiteness greater than 72% after flotation and drying, which meets the first-grade standard of GB / T23456-2018 "Phosphogypsum".

[0029] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0030] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0031] Figure 1 Process flow diagram of this invention;

[0032] Figure 2 X-ray diffraction pattern of the reverse flotation foam product in Example 2;

[0033] Figure 3 Scanning electron microscope image of phosphogypsum concentrate in Example 3. Detailed Implementation

[0034] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0035] This invention provides a flotation process for removing impurities and whitening phosphogypsum, comprising the following steps:

[0036] Step 1: Mix phosphogypsum and water according to a certain mass percentage, and add a certain amount of flotation reagent A. Stir and adjust the slurry to obtain the slurry. The raw material composition of flotation reagent A by weight is: 40-60 parts of vinyltrimethoxysilane, 30-45 parts of acetic acid solution, and 10-15 parts of alkanetrimethylammonium bromide.

[0037] Step 2: Stir and scrub the slurry at high speed for a certain period of time;

[0038] Step 3: After scrubbing, the slurry is introduced into the flotation equipment for a reverse flotation.

[0039] Step 4: Introduce the reverse flotation underflow into the stirred tank and add a certain amount of flotation reagent B. Flotation reagent B is one or more of the following: dodecylamine hydrochloride, hexadecylamine hydrochloride, octadecylamine hydrochloride, dodecylamine acetate, hexadecylamine acetate, and octadecylamine acetate.

[0040] Step 5: Pour the slurry in the mixing tank into the flotation equipment for another positive flotation to obtain the froth product;

[0041] Step 6: Filter and dehydrate the foam product to obtain phosphogypsum concentrate.

[0042] In existing technologies, the phosphogypsum impurity removal and whitening process suffers from long flotation processes, complex operation, and limited increase in whiteness and calcium sulfate dihydrate purity.

[0043] The colored organic matter adhering to the surface of phosphogypsum is the main factor affecting its whiteness. In addition, small amounts of impurities such as apatite, fritillary olivine, and biotite can also negatively impact whiteness. This invention first employs high-speed stirring and scrubbing, adding flotation reagent A during the scrubbing process. The high-speed stirring and scrubbing removes the colored organic matter adhering to the phosphogypsum surface, which then quickly combines with vinyltrimethoxysilane in flotation reagent A through dehydration condensation, changing its surface from hydrophilic to hydrophobic, thereby promoting flotation separation. Simultaneously, impurities such as pyrite and quartz in the phosphogypsum combine with vinyltrimethoxysilane through hydrogen bonding and dehydration condensation, further enhancing its surface hydrophobicity, thus achieving separation through reverse flotation. Furthermore, high-speed stirring and scrubbing also promotes the dispersion of flotation reagent A in the pulp, facilitating its full interaction with colored organic matter, pyrite, and quartz impurities, enhancing the impurity removal and whitening effect. During the flotation process, flotation reagent B is strongly adsorbed onto the gypsum surface under electrostatic action, altering its hydrophobicity and improving its floatability, thus achieving the separation of gypsum from other impurities. Compared with existing technologies, this invention features a shorter process flow, simpler operation, and lower cost; it can not only significantly remove colored organic impurities but also substantially remove impurities such as pyrite, silicate minerals, solid phosphorus and fluorine, and free phosphorus and fluorine; the flotation reagent dosage is low, and the phosphogypsum concentrate meets the first-grade standard of GB / T23456-2018 "Phosphogypsum".

[0044] Preferably, in step one, the raw material composition of flotation reagent A is 55 parts by weight of vinyltrimethoxysilane, 35 parts by weight of 2.5% acetic acid solution, and 10 parts by weight of hexadecyltrimethylammonium bromide. Under this weight ratio, after treatment with the phosphogypsum impurity removal and whitening process of the present invention, the whiteness of the phosphogypsum is 72.7%, and the calcium sulfate dihydrate content is 98.7%.

[0045] Specifically, the acetic acid solution has a mass fraction of 0.5-5.0%.

[0046] Specifically, alkyltrimethylammonium bromide includes one or more of dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide.

[0047] Existing technologies generally use flotation reagents such as methyl isobutyl methanol (MIBC) and pine oil (2# oil), which are ineffective in removing organic matter and do not significantly increase the whiteness of phosphogypsum concentrate. This invention employs flotation reagent A, prepared from vinyltrimethoxysilane, a 0.5-5.0% (w / w) acetic acid solution, and alkyltrimethylammonium bromide. Vinyltrimethoxysilane hydrolyzes in the pulp to produce Si-OH groups, which can bind together the surfaces of organic matter, pyrite, and silicate minerals in phosphogypsum through dehydration condensation, thus changing the surface of these impurities from hydrophilic to hydrophobic, thereby promoting their flotation separation. The acetic acid solution increases the solubility of vinyltrimethoxysilane in aqueous solution, facilitating better dispersion of vinyltrimethoxysilane in the pulp and its interaction with impurities such as organic matter, pyrite, and silicate minerals. Furthermore, the acetic acid solution can react with alkyltrimethylammonium bromide to form alkyltrimethylammonium acetate, increasing its collecting and foaming properties. Alkyltrimethylammonium bromide can react with silicate minerals to remove them; it also has foaming properties, promoting the adhesion of vinyltrioxysilane and impurity compounds to bubbles, which then rise and separate. Flotation reagent A can remove not only organic matter but also impurities such as pyrite and quartz, exhibiting strong collecting ability and good impurity removal effect.

[0048] When the acetic acid solution has a mass fraction below 0.5%, it cannot react completely with vinyltrimethoxysilane and alkyltrimethylammonium bromide in equal proportions, failing to achieve a synergistic effect. When the mass fraction is above 5.0%, even after complete reaction with vinyltrimethoxysilane and alkyltrimethylammonium bromide in equal proportions, there will still be residue. This will affect the pH value of the pulp, which is detrimental to flotation; furthermore, it will waste acetic acid, increase costs, and be uneconomical.

[0049] Specifically, in step one, the amount of flotation reagent A is 90-250 g / t according to the mass ratio of phosphogypsum.

[0050] When the dosage of flotation reagent A is below 90 g / t, the impurity removal effect is poor, and the increase in whiteness is minimal. When the dosage of flotation reagent A is above 250 g / t, the whiteness of the phosphogypsum flotation product remains almost unchanged, and further increasing the dosage of flotation reagent A leads to increased costs. In this invention, the dosage of flotation reagent A is 90-250 g / t based on the mass ratio of phosphogypsum.

[0051] Specifically, in step two, the phosphogypsum content in the slurry is 35-65% by mass.

[0052] If the concentration of phosphogypsum is too low, the collision and friction between phosphogypsum particles are insufficient to remove the organic matter adhering to their surfaces, resulting in ineffective removal of organic matter in subsequent flotation and a minimal increase in the whiteness of the flotation concentrate. Increasing the phosphogypsum content in the pulp increases the probability of particle collisions during scrubbing, leading to stronger frictional stripping and better removal of organic matter adhering to the particle surfaces. However, excessively high scrubbing concentrations significantly increase energy consumption and can cause equipment malfunctions. In this invention, the phosphogypsum mass percentage in the pulp is 35%-65%.

[0053] Specifically, in step two, the high-speed stirring speed is 4000-8000 rpm, and the time is 10-60 min.

[0054] During the scrubbing process, a higher rotation speed increases the frequency of collisions and friction between phosphogypsum particles, resulting in stronger collision and friction effects and making it easier for the colored organic matter adhering to the phosphogypsum surface to detach. Additionally, a higher rotation speed improves the dispersion of flotation reagent A in the pulp. A longer scrubbing time leads to more collisions and friction between phosphogypsum particles, further enhancing the removal of organic matter adhering to the phosphogypsum surface and thus increasing its flotation effect. When the high-speed stirring speed is below 4000 rpm and the time is below 10 minutes, the frequency and effect of collisions and friction between phosphogypsum particles are insufficient, resulting in uneven dispersion of flotation reagent A in the pulp. When the high-speed stirring speed is above 8000 rpm and the time is above 60 minutes, the colored organic matter adhering to the phosphogypsum surface has already largely detached during the process, and further increases in speed and time have no effect. In this invention, the high-speed stirring speed is 4000-8000 rpm, and the time is 10-60 minutes.

[0055] Specifically, in step three, the reverse flotation pulp concentration is 18-35%, and the reverse flotation time is 3-8 minutes.

[0056] When the pulp concentration in reverse flotation is below 18%, the throughput per unit time is low, making it uneconomical; above 35%, the improvement in whiteness is small, and the whitening effect is not significant. If the reverse flotation time is less than 3 minutes, the phosphogypsum recovery rate is insufficient. As the flotation time increases, the phosphogypsum recovery rate increases, but after the reverse flotation time exceeds 8 minutes, further extending the flotation time no longer improves the recovery rate and instead reduces the concentrate quality. In this invention, the reverse flotation time is 3-8 minutes.

[0057] Specifically, in step four, flotation reagent B is one or more of the following: dodecylamine hydrochloride, hexadecylamine hydrochloride, octadecylamine hydrochloride, dodecylamine acetate, hexadecylamine acetate, and octadecylamine acetate.

[0058] Flotation reagent B is selectively adsorbed onto the surface of phosphogypsum through strong electrostatic interaction, which changes the hydrophobicity of phosphogypsum and improves its floatability. This allows it to be separated from impurities such as apatite, fritillary olivine, biotite, and quartz through positive flotation.

[0059] Specifically, in step four, the amount of flotation reagent B is 80-300 g / t according to the mass ratio of phosphogypsum.

[0060] If the dosage of flotation reagent B is below 80 g / t, it cannot effectively capture and float all the phosphogypsum, resulting in a low final concentrate yield. If the dosage is above 300 g / t, the increase in phosphogypsum whiteness is not significant. Excessive flotation reagent B will capture quartz, fir olivine, etc., and carry them out along with the phosphogypsum through positive flotation, causing a decrease in the final concentrate whiteness and calcium sulfate dihydrate content. In addition, excessive flotation reagent B will also increase costs. In this invention, the dosage of flotation reagent B is 80-300 g / t based on the mass ratio of phosphogypsum.

[0061] Specifically, in step five, the positive flotation time is 4-9 minutes.

[0062] Experiments showed that when the direct flotation time was less than 4 minutes, the phosphogypsum recovery rate was insufficient. While the recovery rate increased with longer flotation time, further increases beyond 9 minutes did not improve the recovery rate and instead decreased the concentrate quality. In this invention, the direct flotation time is 4-9 minutes.

[0063] Specifically, neither reverse flotation nor direct flotation requires adjustment of the pulp pH.

[0064] According to experiments, reverse flotation achieves better impurity removal and whitening effects and higher concentrate yield when the pulp pH is between 1.5 and 3.5. Phosphogypsum is derived from the phosphoric acid preparation process, and the original pH of the phosphogypsum pulp is generally between 2.0 and 2.5, which falls within the optimal pH range for reverse flotation. Therefore, the reverse flotation process of this invention does not require adjustment of the pulp pH.

[0065] Specifically, the flotation equipment used for reverse flotation and forward flotation can be one or a combination of flotation machines and flotation columns.

[0066] Example 1-1

[0067] This embodiment provides a flotation process for removing impurities and whitening phosphogypsum, the process flow of which is as follows: Figure 1 As shown.

[0068] In this embodiment, a phosphogypsum from Guizhou Province was used, with a whiteness of 34.0%, a CaSO4·2H2O content of 88.7%, and soluble phosphorus and soluble fluorine contents of 0.24% and 0.28%, respectively. XRF analysis results showed that the main impurities were P2O5 (1.58 wt.%), Fe2O3 (0.255 wt.%), SiO2 (4.25 wt.%), Al2O3 (0.23 wt.%), and colored organic matter.

[0069] Step 1: Prepare a slurry with a phosphogypsum content of 55% by mass using phosphogypsum and water, and add 90 g / t of flotation reagent A. Stir at a high speed of 4000 rpm for 60 min. The composition of flotation reagent A is: 55 parts vinyltrimethoxysilane, 35 parts acetic acid solution with a mass fraction of 2.5%, and 10 parts hexadecyltrimethylammonium bromide.

[0070] Step 2: Pour the stirred slurry into the flotation machine, control the slurry concentration to 18%, and float for 3 minutes;

[0071] Step 3: Pour the underflow after flotation into a stirred tank and add 80 g / t of dodecylamine hydrochloride as flotation reagent B, and stir.

[0072] Step 4: Pour the slurry from the mixing tank into the flotation machine and float for 4 minutes;

[0073] Step 5: Filter and dehydrate the flotation foam product to obtain phosphogypsum concentrate.

[0074] Test results show that the yield of phosphogypsum concentrate is 67.2%, the whiteness is 72.7%, the calcium sulfate dihydrate content is 98.7%, and other main components are shown in Table 1.

[0075] Table 1. Analysis results of phosphogypsum concentrate in Example 1

[0076]

[0077]

[0078] Examples 1-2

[0079] Step 1: Prepare a phosphogypsum slurry with a phosphogypsum mass fraction of 55% using phosphogypsum and water, and add 90 g / t of flotation reagent A. Stir at a high speed of 4000 rpm for 60 min. The composition of flotation reagent A is: 40 parts vinyltrimethoxysilane, 45 parts acetic acid solution with a mass fraction of 2.5%, and 15 parts hexadecyltrimethylammonium bromide. Other process conditions are the same as in Example 1.

[0080] Test results showed that the yield of phosphogypsum concentrate was 65.9%, the whiteness was 70.9%, and the calcium sulfate dihydrate content was 98.3%.

[0081] Examples 1-3

[0082] In this embodiment, in step one, a slurry with a phosphogypsum mass fraction of 55% is prepared using phosphogypsum and water, and 90 g / t of flotation reagent A is added. The mixture is then stirred at a high speed of 8000 rpm for 10 minutes. Other process conditions and steps are the same as in Example 1.

[0083] Test results showed that the yield of phosphogypsum concentrate was 66.9%, the whiteness was 73.6%, and the content of calcium sulfate dihydrate was 98.9%.

[0084] Examples 1-4

[0085] In this embodiment, in step one, a slurry with a phosphogypsum mass fraction of 55% is prepared using phosphogypsum and water, and 90 g / t of flotation reagent A is added. The mixture is then stirred at a high speed of 4000 rpm for 30 minutes. Other process conditions and steps are the same as in Example 1.

[0086] Test results showed that the yield of phosphogypsum concentrate was 67.4%, the whiteness was 71.9%, and the calcium sulfate dihydrate content was 97.4%.

[0087] Comparative Example 1-1

[0088] In this comparative example, a phosphogypsum from Guizhou Province was used, with a whiteness of 34.0%, a CaSO4·2H2O content of 88.7%, and soluble phosphorus and soluble fluorine contents of 0.24% and 0.28%, respectively. XRF analysis showed that the main impurities were P2O5 (1.58 wt.%), Fe2O3 (0.255 wt.%), SiO2 (4.25 wt.%), Al2O3 (0.23 wt.%), and colored organic matter.

[0089] Step 1: Prepare a slurry with a phosphogypsum mass fraction of 18% using phosphogypsum and water, and add 90g / t flotation reagent A. After stirring and dispersing, introduce the mixture into a flotation machine for flotation. The flotation time is 3min. The composition of flotation reagent A is: 55 parts of vinyltrimethoxysilane, 35 parts of acetic acid solution with a mass fraction of 2.5%, and 10 parts of hexadecyltrimethylammonium bromide.

[0090] Step 2: The underflow after flotation is introduced into a stirred tank, and 80 g / t of dodecylamine hydrochloride is added as flotation reagent B, and the mixture is stirred and dispersed.

[0091] Step 3: Pour the slurry from the mixing tank into the flotation machine and float for 4 minutes;

[0092] Step 4: Filter and dehydrate the flotation foam product to obtain phosphogypsum concentrate.

[0093] Test results showed that the yield of phosphogypsum concentrate was 69.4%, the whiteness was 53.3%, and the calcium sulfate dihydrate content was 97.1%.

[0094] Comparative Examples 1-2

[0095] In this comparative example, in step one, a slurry with a phosphogypsum mass fraction of 55% was prepared using phosphogypsum and water, and 90 g / t of flotation reagent A was added. The mixture was stirred at a high speed of 3000 rpm for 10 min. Other process conditions and steps were the same as in Example 1. The composition of flotation reagent A was: 55 parts of vinyltrimethoxysilane, 35 parts of acetic acid solution with a mass fraction of 2.5%, and 10 parts of hexadecyltrimethylammonium bromide.

[0096] Test results showed that the yield of phosphogypsum concentrate was 69.1%, the whiteness was 61.7%, and the calcium sulfate dihydrate content was 97.8%.

[0097] By comparing Examples 1-1, 1-2, 1-3, 1-4 and Comparative Example 1-1, it can be seen that under the same conditions of one reverse flotation and one direct flotation, adding flotation reagent A during high-speed stirring and scrubbing can increase the whiteness of phosphogypsum concentrate from 53.3% to 73.6% and the calcium sulfate dihydrate content from 97.1% to 98.9%, with significant increases in both whiteness and calcium sulfate dihydrate content.

[0098] Comparing Examples 1-1, 1-3, 1-4, and Comparative Example 1-2, it is evident that under the same process conditions, the rotation speed and time of high-speed stirring and scrubbing affect the whiteness and calcium sulfate dihydrate content of phosphogypsum concentrate. In Comparative Example 1-2, the rotation speed and time of high-speed stirring and scrubbing were outside the data range of this invention, resulting in lower whiteness and calcium sulfate dihydrate content in the obtained phosphogypsum concentrate. When the rotation speed and time of high-speed stirring and scrubbing are within the data range of this invention, the whiteness of the phosphogypsum concentrate can be increased from 61.7% to 73.6%, and the calcium sulfate dihydrate content from 97.8% to 98.9%, demonstrating a significant increase in both.

[0099] Example 2-1

[0100] This embodiment provides a flotation process for removing impurities and whitening phosphogypsum, the process flow of which is as follows: Figure 1 As shown.

[0101] In this embodiment, a phosphogypsum from Guizhou Province was used, with a whiteness of 34.0%, a CaSO4·2H2O content of 88.7%, and soluble phosphorus and soluble fluorine contents of 0.24% and 0.28%, respectively. XRF analysis results showed that the main impurities were P2O5 (1.58 wt.%), Fe2O3 (0.255 wt.%), SiO2 (4.25 wt.%), Al2O3 (0.23 wt.%), and colored organic matter.

[0102] Step 1: Prepare a slurry with a phosphogypsum content of 45% by mass using phosphogypsum and water, and add 150 g / t of flotation reagent A. Stir at a high speed of 6000 rpm for 20 minutes. The composition of flotation reagent A is: 55 parts vinyltrimethoxysilane, 35 parts acetic acid solution with a mass fraction of 2.5%, and 10 parts hexadecyltrimethylammonium bromide.

[0103] Step 2: Pour the stirred slurry into the flotation machine, control the slurry concentration to 25%, and float for 5 minutes;

[0104] Step 3: Pour the underflow after flotation into a stirred tank and add 150 g / t of hexadecylamine hydrochloride as flotation reagent B, and stir.

[0105] Step 4: Pour the slurry from the mixing tank into the flotation machine and float for 6 minutes;

[0106] Step 5: Filter and dehydrate the flotation foam product to obtain phosphogypsum concentrate.

[0107] Test results showed that the yield of phosphogypsum concentrate was 75.2%, the whiteness was 74.7%, and the calcium sulfate dihydrate content was 97.9%. The X-ray diffraction pattern of the reverse flotation froth product was as follows: Figure 2 As shown.

[0108] Comparative Example 2-1

[0109] In this comparative example, a phosphogypsum from Guizhou Province was used, with a whiteness of 34.0%, a CaSO4·2H2O content of 88.7%, and soluble phosphorus and soluble fluorine contents of 0.24% and 0.28%, respectively. XRF analysis showed that the main impurities were P2O5 (1.58 wt.%), Fe2O3 (0.255 wt.%), SiO2 (4.25 wt.%), Al2O3 (0.23 wt.%), and colored organic matter.

[0110] Step 1: Prepare a slurry with a phosphogypsum mass fraction of 45% by mixing with water and stir at a high speed of 6000 rpm for 20 minutes.

[0111] Step 2: Pour the stirred and scrubbed slurry into the mixing tank, adjust the slurry concentration to 25%, and add 150g / t of hexadecylamine hydrochloride as flotation reagent B, and stir.

[0112] Step 3: Pour the slurry from the mixing tank into the flotation machine and float for 6 minutes;

[0113] Step 4: Filter and dehydrate the flotation foam product to obtain phosphogypsum concentrate.

[0114] Test results showed that the yield of phosphogypsum concentrate was 84.7%, the whiteness was 48.3%, and the calcium sulfate dihydrate content was 96.2%.

[0115] Comparative Example 2-2

[0116] In this comparative example, in step one, a slurry with a phosphogypsum mass fraction of 45% was prepared using phosphogypsum and water, and stirred at a high speed of 6000 rpm for 20 minutes; that is, no flotation reagent A was added, and other process conditions and steps were the same as in Example 2-1.

[0117] Test results showed that the yield of phosphogypsum concentrate was 78.9%, the whiteness was 51.7%, and the content of calcium sulfate dihydrate was 95.9%.

[0118] Comparing Example 2-1 and Comparative Example 2-1, it can be seen that when flotation reagent A is added during high-speed stirring and scrubbing, followed by one reverse flotation, the whiteness of the phosphogypsum concentrate is 74.7%, and the calcium sulfate dihydrate content is 97.9%. However, when only high-speed stirring and scrubbing is performed, followed by one direct flotation, the whiteness of the phosphogypsum concentrate is only 48.3%, and the calcium sulfate dihydrate content is 96.2%. Adding flotation reagent A during high-speed stirring and scrubbing, followed by one reverse flotation, can significantly improve the whiteness and calcium sulfate dihydrate content of the phosphogypsum concentrate.

[0119] By comparing Example 2-1 and Comparative Example 2-2, it can be seen that under the same process conditions, flotation reagent A plays an important role in improving the whiteness and calcium sulfate dihydrate content of phosphogypsum concentrate. It can increase the whiteness of phosphogypsum concentrate from 51.7% to 74.7% and the calcium sulfate dihydrate content from 95.9% to 97.9%.

[0120] Example 3-1

[0121] This embodiment provides a flotation process for removing impurities and whitening phosphogypsum, the process flow of which is as follows: Figure 1 As shown.

[0122] In this embodiment, a certain phosphogypsum from Yunnan Province was used, with a whiteness of 35.1%, a CaSO4·2H2O content of 85.23%, and a SiO2 content of 6.69%.

[0123] Step 1: Prepare a slurry with a phosphogypsum content of 55% by mass using phosphogypsum and water, and add 250 g / t of flotation reagent A. Stir at a high speed of 8000 rpm for 10 minutes. The composition of flotation reagent A is: 55 parts vinyltrimethoxysilane, 35 parts acetic acid solution with a mass fraction of 2.5%, and 10 parts hexadecyltrimethylammonium bromide.

[0124] Step 2: Pour the stirred slurry into the flotation machine, control the slurry concentration to 35%, and float for 8 minutes;

[0125] Step 3: Pour the underflow after flotation into a stirred tank and add 300 g / t of octadecylamine hydrochloride as flotation reagent B, and stir.

[0126] Step 4: Pour the slurry from the mixing tank into the flotation machine and float for 9 minutes;

[0127] Step 5: Filter and dehydrate the flotation foam product to obtain phosphogypsum concentrate.

[0128] Test results showed that the yield of phosphogypsum concentrate was 81.4%, the whiteness was 76.9%, and the calcium sulfate dihydrate content was 97.1%. The scanning electron microscope image of the phosphogypsum concentrate is shown below. Figure 3 As shown.

[0129] Comparative Example 3-1

[0130] In this comparative example, a certain phosphogypsum from Yunnan Province was used, with a whiteness of 35.1%, a CaSO4·2H2O content of 85.23%, and a SiO2 content of 6.69%.

[0131] Step 1: Prepare a slurry with a phosphogypsum mass fraction of 55% by mixing phosphogypsum and water, and add 250g / t flotation reagent A. Stir at a high speed of 8000rpm for 10min.

[0132] Step 2: Pour the stirred slurry into the flotation machine, control the slurry concentration to 35%, and float for 8 minutes;

[0133] Step 3: Filter and dewater the underflow after flotation to obtain phosphogypsum concentrate.

[0134] Test results showed that the yield of phosphogypsum concentrate was 93.7%, the whiteness was 68.6%, and the calcium sulfate dihydrate content was 94.8%.

[0135] By comparing Implementation Case 3-1 and Comparative Example 3-1, it can be seen that under the same high-speed stirring and scrubbing and reverse flotation conditions, a single direct flotation can increase the whiteness of phosphogypsum concentrate from 68.6% to 76.9% and the calcium sulfate dihydrate content from 94.8% to 97.1%. A single direct flotation can effectively remove impurities such as silicate minerals, biotite, and fir olivine from phosphogypsum, significantly improving the whiteness and calcium sulfate dihydrate content of the phosphogypsum concentrate.

[0136] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A process for removing impurities and whitening phosphogypsum by flotation, characterized in that, Includes the following steps: Step 1: Mix phosphogypsum and water according to a certain mass percentage, and add a certain amount of flotation reagent A. Stir and adjust the slurry to obtain the slurry. The raw material composition of flotation reagent A by weight is: 40-60 parts of vinyltrimethoxysilane, 30-45 parts of acetic acid solution, and 10-15 parts of alkanetrimethylammonium bromide. Step 2: Stir and scrub the slurry at high speed for a certain period of time; Step 3: After scrubbing, the slurry is introduced into the flotation equipment for a reverse flotation. Step 4: Introduce the reverse flotation underflow into the stirred tank and add a certain amount of flotation reagent B. Flotation reagent B is one or more of the following: dodecylamine hydrochloride, hexadecylamine hydrochloride, octadecylamine hydrochloride, dodecylamine acetate, hexadecylamine acetate, and octadecylamine acetate. Step 5: Pour the slurry in the mixing tank into the flotation equipment for another positive flotation to obtain the froth product; Step 6: Filter and dehydrate the foam product to obtain phosphogypsum concentrate.

2. The impurity removal and whitening process according to claim 1, characterized in that, In step one, the acetic acid solution has a mass fraction of 0.5-5.0%.

3. The impurity removal and whitening process according to claim 1, characterized in that, In step one, the alkane-trimethylammonium bromide includes one or more of dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide.

4. The impurity removal and whitening process according to claim 1, characterized in that, In step one, the amount of flotation reagent A is 90-250 g / t according to the mass ratio of phosphogypsum.

5. The impurity removal and whitening process according to claim 1, characterized in that, In step two, the phosphogypsum content in the slurry is 35-65% by mass.

6. The impurity removal and whitening process according to claim 1, characterized in that, In step two, the high-speed stirring speed is 4000-8000 rpm.

7. The impurity removal and whitening process according to claim 1, characterized in that, In step two, the high-speed stirring time is 10-60 minutes.

8. The impurity removal and whitening process according to claim 1, characterized in that, In step three, the reverse flotation pulp concentration is 18-35%, and the reverse flotation time is 3-8 minutes.

9. The impurity removal and whitening process according to claim 1, characterized in that, In step four, the amount of flotation reagent B is 80-300 g / t according to the mass ratio of phosphogypsum.

10. The impurity removal and whitening process according to claim 1, characterized in that, In step five, the positive flotation time is 4-9 minutes.

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