Method for purifying phosphogypsum by reverse flotation desilication using dodecylpyridinium chloride

Abstract

The application discloses a method for desilication and purification of phosphogypsum by reverse flotation with dodecyl pyridine chloride, and relates to the technical fields of inorganic non-metallic materials, mineral flotation separation technology and the like. The steps are as follows: the phosphogypsum raw ore is subjected to grinding treatment to dissociate quartz particles in the phosphogypsum; the phosphogypsum ore slurry after the grinding treatment is transferred to a flotation tank, is stirred by a flotation machine, dodecyl pyridine chloride is added into the flotation tank as a collecting agent, and the collecting agent is fully mixed with the ore slurry by stirring; air is filled into the flotation tank, and a foam product generated by flotation is scraped and discharged as tailings; and the ore slurry in the flotation tank is filtered and dried to obtain phosphogypsum concentrate. In the application, the dodecyl pyridine chloride is preferentially adsorbed on the surface of quartz by electrostatic attraction and weak hydrogen bond effect, so that the quartz is hydrophobic and floats up, and separation of the quartz and the gypsum is realized.

Description

Technical Field

[0001] This invention relates to the technical fields of inorganic non-metallic materials and mineral flotation separation technology, and in particular to a method for desilication and purification of phosphogypsum by reverse flotation using dodecyl pyridine chloride. Background Technology

[0002] Phosphogypsum is a solid byproduct of the wet-process phosphoric acid production process, generating approximately 4.5 to 5.5 tons of phosphogypsum for every ton of phosphoric acid produced. The main component of phosphogypsum is calcium sulfate dihydrate, but it also contains impurities such as phosphorus, fluorine, silicon, and iron, with silicon dioxide primarily existing in the form of quartz. The presence of quartz impurities affects the thermal decomposition process performance of phosphogypsum and limits its application in cement production. Furthermore, according to GB / T23456—2025, a calcium sulfate dihydrate content ≥90% is required to meet the requirements for Grade I phosphogypsum. Therefore, desiliconization and purification treatment of phosphogypsum is a crucial prerequisite for achieving high-value utilization of phosphogypsum.

[0003] Currently, desilication methods for phosphogypsum mainly include sieving, extraction, and flotation. Compared to other methods, flotation offers a wider range of impurities removed, is more targeted, and has higher efficiency. Reverse flotation desilication, in particular, has attracted significant attention from researchers due to its high desilication efficiency and low reagent consumption. Reverse flotation desilication primarily uses cationic collectors, among which amine collectors such as primary amines, tertiary amines, and quaternary ammonium salts have been extensively studied in quartz flotation. Studies have shown that amine collectors with carbon chain lengths of 12–14 exhibit the best flotation performance, while quaternary ammonium salt collectors have a wider pH range and stronger quartz collection ability. In existing technologies, quaternary ammonium salts with different carbon chain lengths, such as dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, and octadecyltrimethylammonium chloride, have been used for reverse flotation desilication. However, most existing amine collectors have a narrow effective flotation range, and some collectors have limited selective adsorption capacity for quartz, which will simultaneously collect some gypsum during the flotation process, resulting in a decrease in the recovery rate of gypsum concentrate. Therefore, developing and selecting a new collector is of great significance for the flotation desilication process of phosphogypsum and for improving the quality of phosphogypsum concentrate.

[0004] To address the above limitations, this invention proposes a method for desilication and purification of phosphogypsum using dodecyl pyridine chloride via reverse flotation. Summary of the Invention

[0005] The main objective of this invention is to provide a method for desilication and purification of phosphogypsum by reverse flotation using dodecyl pyridine chloride. This method utilizes the properties of dodecyl pyridine chloride to achieve highly selective separation of quartz impurities in phosphogypsum, thereby obtaining high-grade and high-recovery phosphogypsum concentrate.

[0006] Based on the first main aspect of the present invention, a method for desilication purification of phosphogypsum using dodecyl pyridine chloride by reverse flotation is provided, comprising the following steps:

[0007] Mechanical grinding is applied to the phosphogypsum ore to dissociate the quartz impurity particles in the phosphogypsum from the gypsum matrix.

[0008] The phosphogypsum slurry after grinding is transferred to a flotation machine, and the particles in the slurry are kept in suspension by agitation.

[0009] Dodecyl pyridine chloride is added to the slurry as a collector. The molecule of dodecyl pyridine chloride consists of a pyridine ring cationic head group and a dodecyl straight-chain hydrophobic tail chain attached to the nitrogen atom of the pyridine ring.

[0010] Under stirring, the dodecyl pyridine chloride molecule dissolves in the slurry liquid phase. The positively charged nitrogen atom on its pyridine ring is electrostatically attracted to the negatively charged quartz surface. At the same time, the hydrogen atom attached to the carbon atom adjacent to the nitrogen atom on the pyridine ring forms a weak hydrogen bond with the oxygen atom exposed on the quartz surface.

[0011] After the slurry has been treated with the addition of a collector and agitation, air bubbles are introduced from the bottom of the flotation equipment. The air bubbles rise in the slurry, causing hydrophobic quartz particles with dodecyl pyridine chloride to collide with and adhere to the air bubbles. As the air bubbles rise to the surface of the slurry, a foam layer is formed. The foam layer is scraped off by a scraper device as quartz tailings. At the same time, the solid phase of the slurry in the flotation cell is collected, filtered, and dried to obtain desiliconized and purified phosphogypsum concentrate.

[0012] The core process of this invention first involves grinding to dissociate quartz particles, and secondly, the dodecylpyridine chloride molecule used has special properties. The structure consists of a conjugated aromatic cationic head group and a long-chain alkyl group. The nitrogen atom on the pyridine ring carries a fixed positive charge, which generates a strong electrostatic attraction with the negatively charged quartz surface. At the same time, the hydrogen atom attached to the carbon atom adjacent to the nitrogen atom on the pyridine ring can form a weak hydrogen bond with the oxygen atom on the quartz surface.

[0013] The collector selectively adsorbs onto the quartz surface through the combined effect of electrostatic attraction and hydrogen bonding. After adsorption, the dodecyl linear hydrophobic tail extends outward into the liquid phase, imparting strong hydrophobicity to the quartz surface. This invention abandons the traditional formulation of amine collectors that require strict pH control or multiple reagents, achieving desilication solely through the synergistic recognition of dual active genes on a single molecule.

[0014] As a further preferred embodiment, in the aforementioned method, the mechanical grinding action applied to the phosphogypsum during the grinding process is limited to the time required to achieve the individual dissociation of quartz particles and gypsum particles, and the grinding equipment is a ball mill.

[0015] In the above technical solution, the shearing and impact forces generated by ball milling cause the quartz particles to be fully separated from the gypsum matrix.

[0016] As a further preferred embodiment, in the aforementioned method, the pH value of the slurry is the natural pH value spontaneously formed after the phosphogypsum ore is mixed with tap water.

[0017] Alternatively, acid or alkali can be added to the pulp before flotation to adjust the pH value of the pulp to a set value that is weakly acidic to neutral.

[0018] By defining a specific pH adaptation window that precisely covers the natural pH fluctuation range after mixing phosphogypsum ore with water, it is possible to reduce reagent costs and the risk of equipment corrosion, while also avoiding interference from the introduction of additional ions into the slurry system.

[0019] As a further preferred option, in the aforementioned method, when preparing the slurry, the mixing ratio of phosphogypsum material and water medium is determined to achieve a solid content that allows the slurry to be floated.

[0020] The flotation process is carried out at room temperature without heating or cooling devices, and no flotation reagents other than dodecylpyridine chloride are added to the pulp during the flotation process.

[0021] The flotation equipment is a mechanical stirring device, in which the impeller rotates to form a slurry circulation flow within the flotation cell.

[0022] An appropriate pulp concentration ensures a balance between turbulence intensity and bubble collision probability within the flotation cell, providing particles with sufficient kinetic energy to adhere to bubbles without hindering bubble rise due to excessive pulp viscosity. Operation at room temperature avoids excessively high temperatures that could intensify molecular thermal motion, thus preventing the collector already adsorbed on the quartz surface from losing selectivity due to thermal desorption.

[0023] Most importantly, without adding any other agents such as foaming agents, inhibitors, or modifiers, the competitive or synergistic disordered adsorption interference of dissimilar surfactants at the solid-liquid interface is eliminated. This allows the adsorption behavior of dodecyl pyridine chloride in the quartz and gypsum mixture to be determined purely by its own molecular recognition ability. This creates a flotation system with a simple reagent regime, eliminating the antagonistic effects and cumulative environmental risks of multi-reagent combinations, and simplifying industrial operation control parameters.

[0024] As a further preferred embodiment, in the aforementioned method, when dodecyl pyridine chloride is added to the slurry, the amount added to the slurry is set to the amount of reagent added to form a selective adsorption layer on the quartz surface.

[0025] During adsorption, the dodecyl pyridine chloride molecules are arranged longitudinally on the quartz surface, and the dodecyl straight-chain hydrophobic tail of the dodecyl pyridine chloride molecules points towards the slurry solution; the adhesion mode during adsorption is a combination of electrostatic attraction and hydrogen bonding.

[0026] The bonding strength of the composite adhesion differs between the quartz surface and the gypsum surface, wherein the bonding strength on the quartz surface is greater than that on the gypsum surface.

[0027] After dodecylpyridine chloride is added to the slurry, it dissolves and dissociates into dodecylpyridine onium cationic active product under stirring. Driven by thermodynamics, its molecules tend to arrange themselves in the lowest energy configuration. The polar pyridine ring head group is firmly fixed to the quartz surface through electrostatic and hydrogen bonding, while the nonpolar dodecyl straight-chain hydrophobic tail chain extends into the aqueous phase as far away from the solid phase interface as possible due to the hydrophobic effect, forming a dense hydrophobic monolayer with directional arrangement.

[0028] As a further preferred option, in the aforementioned method, the flotation process is a single flotation operation, without a fine cleaning operation after roughing or a scavenging operation. The solid phase of the slurry in the flotation cell after flotation is directly collected as the final desilication phosphogypsum concentrate product without further flotation separation treatment.

[0029] After the foam layer is scraped off, it is discharged as tailings. The slurry entrained in the foam layer is separated into solid and liquid phases by filtration. The separated liquid phase is returned to the flotation equipment or reused as slurry conditioning water.

[0030] By compressing the reverse flotation process, the amount of flotation equipment and floor space required is reduced, thereby lowering the energy consumption and investment cost per unit product. At the same time, the internal recycling of the liquid phase reduces wastewater discharge.

[0031] Based on a second key aspect of the present invention, a phosphogypsum concentrate product is provided, which is obtained by the aforementioned method; the phosphogypsum concentrate product comprises calcium sulfate dihydrate particles and a small amount of residual quartz particles.

[0032] The mixing ratio of quartz particles and calcium sulfate dihydrate particles in the product changes compared to the ratio of the two in the raw phosphogypsum ore, with the proportion of quartz particles in the solid phase decreasing and the proportion of calcium sulfate dihydrate in the solid phase increasing.

[0033] Based on the third main aspect of the present invention, a flotation reagent system for reverse flotation desilication purification of phosphogypsum is provided, wherein the flotation reagent system uses dodecylpyridine chloride as a single collector and also has foaming properties.

[0034] The dodecyl pyridine chloride exists as a solid crystalline powder with a specific morphology. The solid crystalline powder maintains chemical stability under normal temperature conditions, and its conjugated pyridine ring structure does not undergo oxidative degradation during storage.

[0035] Alternatively, the dodecyl pyridine chloride may exist in the form of an aqueous solution, wherein the mass concentration of dodecyl pyridine chloride in the aqueous solution is within the range that, when added to the slurry, would allow for the formation of a monolayer adsorption coating on the quartz surface.

[0036] As a further preferred embodiment, the flotation reagent system exhibits better collection performance under weakly acidic and neutral conditions than under alkaline conditions.

[0037] The flotation reagent system does not contain inhibitors, activators, or other types of collectors and frothers.

[0038] Based on the fourth main aspect of the present invention, the application of dodecyl pyridine chloride as a collector in the reverse flotation desilication purification of phosphogypsum is provided, wherein the molecule of dodecyl pyridine chloride contains a pyridine ring and a dodecyl straight-chain hydrophobic tail chain attached to the nitrogen atom of the pyridine ring.

[0039] The dodecyl pyridine chloride selectively adsorbs onto the quartz surface in the phosphogypsum in a slurry with a pH value that is spontaneously formed after mixing phosphogypsum ore with tap water, or by adding acid or alkali to the slurry before flotation to adjust the pH value of the slurry to a set value that is weakly acidic to neutral. This causes the hydrophobic quartz to float to the surface, while the calcium sulfate dihydrate remains in the slurry, thus achieving desilication and purification.

[0040] Compared with existing technologies, this invention provides a method for desilication and purification of phosphogypsum using dodecylpyridine chloride via reverse flotation. First, this invention uses dodecylpyridine chloride as a collector, and the reverse flotation process can efficiently separate quartz impurities from phosphogypsum, improving the purity of the phosphogypsum. Dodecylpyridine chloride enables selective adsorption, and its long alkyl chain enhances the hydrophobicity of the quartz surface, causing quartz particles to preferentially adhere to bubbles and float during flotation, while the phosphogypsum concentrate remains in the tank. This effectively improves the concentrate grade while ensuring a high recovery rate of phosphogypsum.

[0041] Secondly, this invention eliminates the need for additional pH adjusters, achieving desilication and purification under the original pH conditions of the slurry. Furthermore, it requires fewer reagents and simplifies the process. The collector maintains stable flotation performance over a wide dosage range, offering significant process tolerance and ease of industrial control.

[0042] Finally, this invention achieves stable adsorption of the collector on the quartz surface through electrostatic attraction and hydrogen bonding. The adsorption force is stronger than that of traditional quaternary ammonium salt collectors, which rely solely on electrostatic attraction. This improves both the separation selectivity and the separation effect, providing an economical and efficient purification technology solution for the high-value utilization of phosphogypsum. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0044] Figure 1 A flowchart of a method for desilication and purification of phosphogypsum using dodecyl pyridine chloride in reverse flotation is shown in one embodiment of the present invention.

[0045] Figure 2 This diagram illustrates the effect of collector dosage on the flotation desilication and purification effect of phosphogypsum in one embodiment of the present invention.

[0046] Figure 3 This diagram illustrates the effect of pH value on the flotation desilication and purification of phosphogypsum in one embodiment of the present invention.

[0047] Figure 4 This diagram illustrates the effect of collector concentration on the flotation effect of artificially mixed ores in one embodiment of the present invention.

[0048] Figure 5 This diagram illustrates the effect of pH value on the flotation effect of artificially mixed ores in one embodiment of the present invention.

[0049] Figure 6 This diagram illustrates the variation of the zeta potential of quartz and gypsum with collector concentration in one embodiment of the present invention.

[0050] Figure 7 The diagram shows the changes in contact angles of quartz and gypsum after treatment with a collector in one embodiment of the present invention. In Figure (a), the contact angle of untreated quartz is shown; in Figure (b), the contact angle of quartz after treatment with a collector is shown; in Figure (c), the contact angle of untreated gypsum is shown; and in Figure (d), the contact angle of gypsum after treatment with a collector is shown. Detailed Implementation

[0051] The preferred embodiments of the present invention will be described in detail below to provide a clearer understanding of the purpose, features, and advantages of the invention. It should be understood that the following embodiments are not intended to limit the scope of the invention, but are merely illustrative of the essential spirit of the technical solution of the invention.

[0052] In the following description, certain specific details are set forth for the purpose of illustrating various disclosed embodiments in order to provide a thorough understanding of the various disclosed embodiments. However, those skilled in the art will recognize that the embodiments may be practiced without one or more of these specific details. In other instances, well-known techniques associated with the invention may not have been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments.

[0053] Throughout this specification, references to "an embodiment" or "an embodiment" indicate that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Therefore, the appearance of "in an embodiment" or "an embodiment" in various places throughout the specification does not necessarily refer to the same embodiment. Furthermore, a particular feature, structure, or characteristic may be combined in any manner in one or more embodiments.

[0054] Combination Figure 1 As shown, this invention provides a method for desilication and purification of phosphogypsum using dodecylpyridine chloride via reverse flotation, comprising the following steps:

[0055] The raw phosphogypsum ore and tap water are added to the ball mill. The ball mill is started, and the rotating cylinder drives the internal grinding media to exert impact and grinding action on the phosphogypsum material. The grinding time is limited to the point that the quartz particles in the phosphogypsum are dissociated from the gypsum matrix. In this embodiment, a grinding time of 2 minutes is used.

[0056] After grinding, the ground phosphogypsum slurry is added to the flotation tank. A stirring mechanism thoroughly mixes the solid and liquid phases to produce a slurry with uniform solid dispersion. The slurry concentration is adjusted to achieve a level suitable for flotation operations.

[0057] Under the stirring conditions of the flotation equipment, the solid particles in the slurry remain suspended and do not undergo significant sedimentation or stratification.

[0058] The pH of the pulp can be the natural pH value formed by the phosphogypsum ore and tap water, or the pH value of the pulp can be adjusted to weakly acidic or neutral by adding acid or alkali before the flotation operation as needed.

[0059] Dodecyl pyridine chloride is added as a collector to the stirred slurry. The dodecyl pyridine chloride is added directly to the slurry in the form of solid powder. The amount added to the slurry is set to the amount of reagent added to form a selective adsorption layer on the quartz surface. The liquid medium of the slurry and the stirring action are used to dissolve and disperse it.

[0060] Dodecyl pyridine chloride As a collector, it is a white to off-white solid crystalline powder at room temperature, soluble in water. The molecule of dodecylpyridine chloride consists of a pyridine ring cationic head group and a straight-chain hydrophobic tail chain of dodecyl attached to the nitrogen atom of the pyridine ring, wherein the pyridine ring is a... -Aromatic heterocycles in conjugated systems.

[0061] During adsorption, dodecylpyridine chloride molecules are arranged longitudinally on the quartz surface, with the pyridine ring acting as a polar head group adsorbed towards the quartz surface, and the straight-chain hydrophobic tail of the dodecyl group pointing towards the slurry solution after adsorption.

[0062] The adsorption method is a composite adhesion method of electrostatic attraction and hydrogen bonding. The bonding strength of the two methods differs between the quartz and gypsum surfaces, with the bonding strength on the quartz surface being greater than that on the gypsum surface.

[0063] The slurry, after being treated with the addition of dodecyl pyridine chloride and stirred, is kept in the flotation tank. The aeration mechanism is started, and air bubbles are introduced into the slurry from the bottom of the flotation tank. As the air bubbles rise, the hydrophobic quartz particles with dodecyl pyridine chloride on their surface collide with the air bubbles and adhere to them, rising with the air bubbles to the surface of the slurry.

[0064] After quartz particles adhere to the bubbles, the bubbles carry the particles to the surface, where they accumulate to form a foam layer. Calcium sulfate dihydrate particles that have not adsorbed dodecylpyridine chloride remain hydrophilic and do not adhere to the bubbles, remaining in the slurry phase.

[0065] Start the scraper device. The scraper moves horizontally along the upper edge of the flotation tank, continuously scraping the foam layer that accumulates on the surface of the slurry out of the flotation tank. The foam layer is discharged as quartz-containing tailings after being scraped out.

[0066] This flotation process is a single-stage flotation operation, without a fine-selection operation after roughing or a scavenging operation.

[0067] After flotation, the collected foam is separated into solid and liquid phases by filtration. The separated liquid phase is returned to the flotation equipment or reused as slurry water.

[0068] The solid phase of the slurry in the flotation cell is collected, filtered, and dried. This solid phase is used directly as the final desilication phosphogypsum concentrate product without further flotation separation. The liquid phase is returned to the flotation equipment or reused as slurry preparation water.

[0069] The desilication phosphogypsum concentrate product obtained by the above method contains calcium sulfate dihydrate particles and a small amount of residual quartz particles;

[0070] In this product, the mixing ratio of quartz particles and calcium sulfate dihydrate particles changes relative to the ratio of the two in the raw materials. Specifically, the proportion of quartz particles in the solid phase decreases, while the proportion of calcium sulfate dihydrate in the solid phase increases.

[0071] The gypsum grade in the obtained desilication phosphogypsum concentrate product is as follows: The mass percentage is recorded as 89% to 90%, and the gypsum recovery rate is 96% to 98%.

[0072] The flotation reagent system used in the above method is a flotation reagent system with dodecyl pyridine chloride as the single collector.

[0073] Dodecylpyridine chloride exists in the form of a solid crystalline powder, is readily soluble in water, and maintains chemical stability under normal temperature conditions. Its conjugated pyridine ring structure does not undergo oxidative degradation during storage.

[0074] The flotation reagent system exhibits better collection performance under weakly acidic to neutral conditions than under alkaline conditions.

[0075] Dodecyl pyridine chloride can also exist in the reagent system in the form of an aqueous solution. The mass concentration of dodecyl pyridine chloride in the aqueous solution is the concentration range that can form a monolayer adsorption coverage on the quartz surface after being added to the slurry.

[0076] The flotation reagent system does not contain inhibitors, activators, or other types of collectors and frothers.

[0077] In the following embodiments, the method and principle of the present invention are demonstrated and analyzed through experiments:

[0078] The phosphogypsum used in the following examples is a byproduct of the wet-process phosphoric acid production process, and its main components are... It also contains quartz in the form of Impurities.

[0079] X-ray diffraction was used to analyze the phase composition of the raw phosphogypsum ore, and the main phases were identified as follows: And quartz. The chemical composition of the raw phosphogypsum ore was determined using X-ray fluorescence spectrometry. The phosphogypsum mainly contained 31.726% CaO and 34.284% quartz. In addition, it also contains , , Impurities, among which The proportion was relatively large, reaching 6.621%.

[0080] During implementation, the above testing steps can be selectively used depending on the source of the raw materials in order to determine the basic grade and impurity content of the raw ore.

[0081] Dodecylpyridine chloride DPC, abbreviated as DPC, is a white to off-white solid crystalline powder at room temperature, and is soluble in water.

[0082] The grinding method is as follows: add tap water and grind the phosphogypsum ore at a mass concentration of 50% for 2 minutes to separate the quartz particles from the gypsum particles.

[0083] After grinding, the slurry is transferred to a 1000 mL RK / FD single-cell flotation machine, water is added to adjust the slurry concentration to 30%, and the stirring mechanism is started to fully mix the solid material with the water.

[0084] The stirring mechanism drives the impeller to rotate at a speed of 1992 r / min for 2 min, and under the stirring action, the components are uniformly dispersed in the slurry. Then, a weighed dodecylpyridine chloride collector is added to the slurry at a dosage of 100 g / t to 250 g / t.

[0085] After the collector is added, the stirring mechanism continues to run for 2 minutes to allow the collector to fully dissolve in the slurry and adsorb onto the surface of each mineral particle, causing the surface of the quartz particles to change from hydrophilic to hydrophobic.

[0086] The aeration mechanism of the flotation machine is activated, continuously introducing air into the slurry to create an upward flow of bubbles. As the bubbles rise in the slurry, hydrophobic quartz particles with pre-adsorbed collectors attach to them and rise with the bubbles to the slurry surface, aggregating to form a foam layer. Those without attached bubbles... Particles, including those that are not hydrophobic, remain in the flotation cell.

[0087] Start the scraper mechanism, and the scraper moves horizontally along the upper edge of the flotation tank, continuously scraping the foam layer out of the tank. The foam product, which is the tailings rich in quartz, is then discharged.

[0088] After flotation, the solid particles in the flotation cell are filtered, dehydrated, and dried to obtain phosphogypsum concentrate.

[0089] Example 1

[0090] This embodiment is used to determine the optimal dosage of dodecyl pyridine chloride collector in the actual desilication and purification of phosphogypsum.

[0091] Weigh out the raw phosphogypsum ore and grind it for 2 minutes at a grinding concentration of 50% to dissociate the quartz particles in the phosphogypsum.

[0092] After grinding, the slurry is transferred to a 1000 mL RK / FD single-cell flotation machine, and water is added to adjust the slurry concentration to 30%.

[0093] Start the stirring mechanism and stir at a speed of 1992 r / min for 2 minutes.

[0094] Weigh out dodecylpyridine chloride as a collector and add it in amounts of 50g, 100g, 150g, 200g, 250g, and 300g per ton of phosphogypsum raw material. Add it to the slurry and continue stirring at a speed of 1992 r / min for 2 minutes.

[0095] The pulp pH is the original pH condition, i.e., pH=6.11, without the addition of any pH adjuster.

[0096] The air-injection mechanism is activated to introduce air, forming bubbles for flotation.

[0097] The scraper removes the foam layer as tailings, collects the solid products in the flotation cell, filters and dries them, and measures their composition. content.

[0098] In this embodiment, combined with Figure 2 As shown, within the range of 100 g / t to 250 g / t of dodecyl pyridine chloride collector, the recovery rate is stable at 96% to 98%, and the gypsum grade is stable at 89% to 90%.

[0099] When the amount of dodecylpyridine chloride collector added is 250 g / t, the grade of gypsum concentrate is increased to 90.32% and the gypsum recovery rate reaches 96.64%.

[0100] When the amount of dodecyl pyridine chloride collector added is 300 g / t, excessive froth is generated during flotation, which carries the slurry into the tailings, resulting in a decrease in the gypsum recovery rate.

[0101] Example 2

[0102] This example is used to verify the influence range of pH on the desilication of phosphogypsum by the dodecyl chloride collector.

[0103] Weigh out the raw phosphogypsum ore and grind it for 2 minutes at a grinding concentration of 50% to dissociate the quartz particles in the phosphogypsum.

[0104] After grinding, the slurry is transferred to a 1000 mL RK / FD single-cell flotation machine, and water is added to adjust the slurry concentration to 30%.

[0105] Start the stirring mechanism and stir at a speed of 1992 r / min for 2 minutes.

[0106] Use acid or alkali to adjust the pH of the pulp to 2, 4, 6, 9, or 11.

[0107] Dodecyl pyridine chloride was used as a collector, with a fixed addition amount of 100g per ton of phosphogypsum raw material. The mixture was added to the slurry and stirred at 1992 r / min for 2 min.

[0108] The air-injection mechanism is activated to introduce air, forming bubbles for flotation.

[0109] The foam layer is scraped off by a scraper as tailings. The solid products in the tank are collected, filtered, dried, and the properties of the solid products in the tank are measured under different pH conditions. content.

[0110] In this embodiment, combined with Figure 3 As the pH of the slurry changes from acidic to alkaline, the purity of phosphogypsum first increases and then decreases. Within the pH range of 5 to 7, the gypsum grade is higher than that of the original ore. Dodecyl pyridine chloride can effectively separate quartz and gypsum. When the pH is 6.11, i.e., under the original slurry pH conditions, the purity of phosphogypsum is the highest at 89.06%. This shows that the separation ability of dodecyl pyridine chloride is stronger under weakly acidic and neutral conditions than under alkaline conditions, especially under alkaline conditions, the recovery rate of gypsum decreases.

[0111] In conclusion, flotation at the natural pulp pH without the addition of pH adjusters can effectively improve the purity and recovery rate of phosphogypsum.

[0112] Example 3

[0113] This embodiment investigates the selectivity of dodecyl chloride pyridine collector in separating quartz and gypsum by flotation of artificially mixed minerals.

[0114] The mass ratio of the quartz and gypsum mixed ore is 1:4. The mixed ore is placed in an XFGCII type flotation machine and 40ml of deionized water is added.

[0115] Stir for 2 minutes at a stirring speed of 1992 r / min to ensure that the minerals are fully mixed and dispersed.

[0116] Different concentrations of dodecyl pyridine chloride solution were added to the mixed ore slurry, and stirring was continued for 2 minutes under the same stirring conditions.

[0117] After stirring, air is introduced into the flotation cell, and the foam product is scraped off until the foam no longer carries minerals. The foam product and the product at the bottom of the cell are collected separately, and then filtered, dried, weighed and analyzed.

[0118] Combination Figure 4 In this embodiment, as the drug concentration increases from 1×10 -5 Increase mol / L to 5×10 -5 At a concentration of 4 × 10⁻⁶ mol / L, the purity of gypsum increased from 82.45% to 97.05%. -5 At a concentration of mol / L, the purity of the mixed minerals reaches its maximum value. Further increasing the reagent concentration will cause some gypsum to be carried into the foam product, resulting in a decrease in the grade and recovery rate of gypsum.

[0119] Example 4

[0120] Based on the investigation in Example 3, this embodiment further investigates the separation behavior of mixed quartz and gypsum ore under different pH conditions, thereby obtaining the suitable pH range for the collector.

[0121] The mass ratio of the quartz and gypsum mixed ore is 1:4. The mixed ore is placed in an XFGCII type flotation machine and 40ml of deionized water is added.

[0122] Stir for 2 minutes at a stirring speed of 1992 r / min to ensure that the minerals are fully mixed and dispersed.

[0123] Add 4×10 to the mixed ore slurry with different pH values ​​respectively -5 A mol / L solution of dodecyl pyridine chloride was stirred for another 2 minutes under the same stirring conditions.

[0124] After stirring, air is introduced into the flotation cell, and the foam product is scraped off until the foam no longer carries minerals. The foam product and the product at the bottom of the cell are collected separately, and then filtered, dried, weighed and analyzed.

[0125] Combination Figure 5 In this embodiment, the gypsum grade curve first rises and then falls. Under neutral conditions, the grade reaches a maximum of 97.05%, while the corresponding recovery rate is 81.64%. Therefore, the dodecyl pyridine chloride collector is beneficial for achieving flotation separation of quartz and gypsum under weakly acidic to neutral conditions.

[0126] Example 5

[0127] This embodiment is used to verify the adsorption difference of dodecyl pyridine chloride collector on the surface of quartz and gypsum, and the zeta potential of the mineral surface before and after flotation is tested.

[0128] Different concentrations of dodecyl pyridine chloride were added to quartz and gypsum suspensions to adjust the reagents to the target values, and the changes in particle surface potential were measured using a Zeta potential analyzer.

[0129] In this embodiment, combined with Figure 6The negative charge on the quartz surface is significantly stronger than that on the gypsum surface, which facilitates the electrostatic attraction of the dodecylpyridine chloride cationic collector on the negatively charged quartz surface. As the concentration of dodecylpyridine chloride increases, the surface potential of the quartz surface increases rapidly, while the surface potential of the gypsum surface increases slowly.

[0130] The variation range of the Zeta potential on the quartz surface is significantly greater than that on the gypsum surface, indicating that the adsorption amount of dodecyl pyridine chloride cations on the quartz surface is greater than that on the gypsum surface, thus verifying the selective adsorption of dodecyl pyridine chloride on quartz.

[0131] Example 6

[0132] This embodiment is used to characterize the changes in hydrophilicity and hydrophobicity of quartz and gypsum surfaces before and after the treatment with dodecyl pyridine chloride.

[0133] Quartz and gypsum block samples were cut and polished to obtain specimens with smooth surfaces. The polished quartz and gypsum specimens were then immersed in an aqueous solution of dodecylpyridine chloride, left to stand at room temperature for a certain period of time, and then removed and air-dried naturally.

[0134] The contact angle of the untreated and treated sample surfaces was measured using a contact angle meter and the droplet method.

[0135] In this embodiment, combined with Figure 7 The contact angle of the untreated quartz surface was 8.4°, and the contact angle of the untreated gypsum surface was 25.2°. After treatment with dodecyl pyridine chloride solution, the contact angle of the quartz surface increased to 57.5°, while that of the gypsum surface increased to 31.3°.

[0136] The change in contact angle on the quartz surface is greater than that on the gypsum surface, proving that the dodecyl pyridine chloride solution can selectively adsorb onto the quartz surface, making it more hydrophobic, and can effectively separate quartz and gypsum during flotation.

[0137] The technical terms, principles, or means related to the technical solutions of the present invention mentioned in the above embodiments, which are not described in detail above, are all well-known technologies or common practices that are known to those skilled in the art.

[0138] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for purifying phosphogypsum by reverse flotation desilication using dodecylpyridine chloride, characterized in that, Includes the following steps: Mechanical grinding is applied to the phosphogypsum ore to dissociate the quartz impurity particles in the phosphogypsum from the gypsum matrix. The phosphogypsum slurry after grinding is transferred to a flotation machine, and the particles in the slurry are kept in suspension by agitation. Dodecyl pyridine chloride is added to the slurry as a collector. The molecule of dodecyl pyridine chloride consists of a pyridine ring cationic head group and a dodecyl straight-chain hydrophobic tail chain attached to the nitrogen atom of the pyridine ring. Under stirring, the dodecyl pyridine chloride molecule dissolves in the slurry liquid phase. The positively charged nitrogen atom on its pyridine ring is electrostatically attracted to the negatively charged quartz surface. At the same time, the hydrogen atom attached to the carbon atom adjacent to the nitrogen atom on the pyridine ring acts as a hydrogen bond donor and forms a hydrogen bond with the oxygen atom exposed on the quartz surface. After the slurry has been treated with the addition of a collector and agitation, air bubbles are introduced from the bottom of the flotation equipment. The air bubbles rise in the slurry, causing hydrophobic quartz particles with dodecyl pyridine chloride to collide with and adhere to the air bubbles. As the air bubbles rise to the surface of the slurry, a foam layer is formed. The foam layer is scraped off by a scraper device as quartz tailings. At the same time, the solid phase of the slurry in the flotation cell is collected, filtered, and dried to obtain desiliconized and purified phosphogypsum concentrate.

2. The method for purifying phosphogypsum by reverse flotation desilication using dodecylpyridine chloride according to claim 1, characterized in that, During the grinding process, the mechanical grinding action applied to phosphogypsum is limited to the time required to achieve the individual separation of quartz particles and gypsum particles, and the grinding equipment is a ball mill.

3. The method for purifying phosphogypsum by reverse flotation desilication using dodecylpyridine chloride according to claim 1, characterized in that, The pH value of the slurry is the natural pH value that is spontaneously formed after the raw phosphogypsum ore is mixed with tap water. Alternatively, acid or alkali can be added to the pulp before flotation to adjust the pH value of the pulp to a set value that is weakly acidic to neutral.

4. The method for desilication and purification of phosphogypsum using dodecylpyridine chloride by reverse flotation according to claim 1, characterized in that, When preparing flotation slurry, the mixing ratio of phosphogypsum material and water medium should be based on the solid content of the slurry to enable flotation operation. The flotation process is carried out at room temperature without heating or cooling devices, and no flotation reagents other than dodecylpyridine chloride are added to the pulp during the flotation process. The flotation equipment is a mechanical stirring device, in which the impeller rotates to form a slurry circulation flow within the flotation cell.

5. The method for purifying phosphogypsum by reverse flotation desilication using dodecylpyridine chloride according to claim 1, characterized in that, When dodecyl pyridine chloride is added to the slurry, the amount added to the slurry is set to the amount of reagent added to form a selective adsorption layer on the quartz surface; The dodecyl pyridine chloride molecules are longitudinally aligned on the quartz surface during adsorption, and the dodecyl straight-chain hydrophobic tail of the dodecyl pyridine chloride molecules points towards the slurry solution after adsorption; the adhesion mode during adsorption is a combination of electrostatic attraction and hydrogen bonding. The bonding strength of the composite adhesion differs between the quartz surface and the gypsum surface, wherein the bonding strength on the quartz surface is greater than that on the gypsum surface.

6. The method for purifying phosphogypsum by reverse flotation desilication using dodecylpyridine chloride according to claim 1, characterized in that, The flotation process is a single-stage flotation operation, without a fine-grained operation after roughing or a scavenging operation. After flotation, the solid phase of the slurry in the flotation cell is directly collected as the final desilication phosphogypsum concentrate product without further flotation separation. After the foam layer is scraped off, it is discharged as tailings. Solid-liquid separation is achieved through filtration, and the separated liquid phase is returned to the flotation equipment or reused as slurry water.

7. A phosphogypsum concentrate product, prepared by the method according to any one of claims 1 to 6, characterized in that, The phosphogypsum concentrate product contains calcium sulfate dihydrate particles and a small amount of residual quartz particles. The mixing ratio of quartz particles and calcium sulfate dihydrate particles in the product changes compared to the ratio of the two in the raw phosphogypsum ore, with the proportion of quartz particles in the solid phase decreasing and the proportion of calcium sulfate dihydrate in the solid phase increasing.

8. A flotation reagent system for desilication and purification of phosphogypsum by reverse flotation, characterized in that, The flotation reagent system uses dodecyl pyridine chloride as the single collector and also has foaming properties; The dodecyl pyridine chloride exists in the flotation reagent system as a solid crystalline powder with a specific crystalline morphology. The solid crystalline powder maintains chemical stability under normal temperature conditions, and its conjugated pyridine ring structure does not undergo oxidative degradation during storage. Alternatively, the dodecyl pyridine chloride may exist in the form of an aqueous solution, wherein the mass concentration of dodecyl pyridine chloride in the aqueous solution is within the range that, when added to the slurry, would allow for the formation of a monolayer adsorption coating on the quartz surface.

9. The flotation reagent system for desilication and purification of phosphogypsum by reverse flotation according to claim 8, characterized in that, The flotation reagent system exhibits better collection performance under weakly acidic and neutral conditions than under alkaline conditions. The flotation reagent system does not contain inhibitors, activators, or other types of collectors and frothers.

10. The application of dodecylpyridine chloride as a collector in the reverse flotation desilication purification of phosphogypsum, characterized in that, The molecule of the dodecyl pyridine chloride contains a pyridine ring and a straight-chain hydrophobic tail of dodecyl attached to the nitrogen atom of the pyridine ring; The dodecyl pyridine chloride selectively adsorbs onto the quartz surface in the phosphogypsum in a slurry with a pH value that is spontaneously formed after mixing phosphogypsum ore with tap water, or by adding acid or alkali to the slurry before flotation to adjust the pH value of the slurry to a set value that is weakly acidic to neutral. This causes the hydrophobic quartz to float to the surface, while the calcium sulfate dihydrate remains in the slurry, thus achieving desilication and purification.

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