Deep purification treatment method of environment-friendly phosphogypsum

Abstract

The invention discloses a deep purification treatment method of environment-friendly ardealite. The method comprises the following steps: (1) screening ardealite; (2) carrying out countercurrent washing on the phosphogypsum from which the slag is removed by using water to obtain washed phosphogypsum; (3) leaching the washed ardealite with olefine acid, and then filtering to obtain an ardealite filter cake; (4) adding water into the ardealite filter cake to prepare slurry, and then performing flotation treatment by adopting lauryl amine as a collecting agent and No.2 oil as a foaming agent to obtain ardealite ore pulp; and (5) adding quick lime and a chelating agent into the ardealite pulp, and carrying out reaction treatment. The content of CaSO4. 2H2O in the final purified product is greater than or equal to 97%, the soluble phosphorus content is less than or equal to 0.1%, and the soluble fluorine content is less than or equal to 0.06%, so that the final purified product completely meets the GB / T 23456-2018 standard, can be directly used for producing high-value products such as cement retarders and building gypsum boards, and breaks through the rigid bureau that phosphogypsum is mainly stockpiled.

Description

Technical Field

[0001] This invention relates to the field of phosphogypsum purification technology, and in particular to an environmentally friendly method for the deep purification and treatment of phosphogypsum. Background Technology

[0002] Phosphogypsum is an important byproduct of the wet-process phosphoric acid production process, and its main component is calcium sulfate dihydrate (CaSO4). The phosphogypsum contains 70%-90% H₂O, as well as soluble, eutectic, and insoluble phosphorus impurities, soluble (NaF), insoluble (CaF, Na₂SiF₆, Na₂AlF₆) fluorine impurities, and heavy metals. These impurities, such as soluble ones, not only significantly impact the resource utilization of calcium sulfate dihydrate, the main component of phosphogypsum, but also accelerate their release during long-term storage, causing serious pollution to the surrounding water and soil. Furthermore, the presence of eutectic phosphorus also damages the physical properties of the gypsum, thus affecting the quality of the final product.

[0003] Existing phosphogypsum treatment processes generally suffer from problems such as "poor targeting of single processes and imbalanced removal efficiency of multiple impurities." For example, traditional water washing processes can only remove soluble phosphorus and fluorine, but are ineffective against eutectic phosphorus encapsulated in the CaSO4·2H2O lattice; while single acid leaching processes can destroy the eutectic structure, the removal rate of insoluble phosphorus such as hydroxyapatite is less than 50%; fluorine impurity treatment mainly relies on simple precipitation, failing to achieve resource utilization, and insoluble fluorides such as Na2SiF6 and Na2AlF6 easily remain in the product. Meanwhile, heavy metal stabilization depends on high-temperature calcination, with energy consumption accounting for more than 50% of the treatment cost; some processes use highly polluting flotation agents, which can improve impurity removal efficiency, but the subsequent reagent degradation cost is high, creating a vicious cycle of "impurity removal-pollution," which contradicts the needs of phosphate chemical enterprises for "cost reduction and efficiency improvement, and green transformation." Summary of the Invention

[0004] The main objective of this invention is to provide an environmentally friendly method for the deep purification and treatment of phosphogypsum, aiming to solve at least one of the aforementioned technical problems.

[0005] To achieve the above objectives, the present invention provides an environmentally friendly method for the deep purification and treatment of phosphogypsum, comprising the following steps: (1) Screening The phosphogypsum is screened to remove slag from it. (2) Countercurrent washing The phosphogypsum after slag removal is washed countercurrently with water to obtain washed phosphogypsum. (3) Dilute acid leaching The phosphogypsum was leached with olefinic acid and then filtered to obtain a phosphogypsum filter cake. (4) Flotation for impurity removal The phosphogypsum filter cake was mixed with water to form a slurry, and then flotation was performed using dodecylamine as a collector and No. 2 oil as a frother to obtain the phosphogypsum slurry. (5) Composite stabilization Quicklime and chelating agent are added to the phosphogypsum slurry for reaction treatment.

[0006] Furthermore, in step (1), the vibrating screen used for screening has an aperture of 0.15 mm.

[0007] Furthermore, in step (2), the countercurrent washing adopts a three-stage countercurrent washing, with a solid-liquid ratio of 1:4, a water temperature of 25-30℃, and a stirring rate of 300r / min.

[0008] Further, in step (3), the olefinic acid is a sulfuric acid solution with a concentration of 5wt% and citric acid with a mass of 0.2% of the sulfuric acid solution is added. The liquid-solid ratio of the leaching treatment is 5:1, the temperature is 35℃, and the leaching time is 2h.

[0009] Furthermore, in step (4), the solid-liquid ratio of the prepared slurry is 1:3 to 5, and the pH is adjusted to 2.0.

[0010] Furthermore, in step (4), the dosage of dodecylamine is 200 g / t, the dosage of No. 2 oil is 20-50 g / t, and the flotation time is 15 min.

[0011] Furthermore, in step (5), the amount of quicklime added is 1 wt% of the phosphogypsum slurry, the amount of chelating agent added is 0.3 wt% of the phosphogypsum slurry, and the chelating agent is EDTA-2Na.

[0012] Furthermore, in step (5), before the reaction treatment, the pH is adjusted to 8-9, and the reaction treatment time is 30 min.

[0013] Furthermore, it also includes the following steps: (6) Fluorine recovery Add calcium chloride to the acid filtrate obtained in step (3) to react and generate calcium fluorosilicate precipitate. After filtration, the precipitate is reused in step (3).

[0014] Furthermore, the reaction temperature is 40℃ and the reaction time is 30–60 min.

[0015] The beneficial effects of this invention are reflected in: This invention removes large particles of slag through screening, reducing the burden on subsequent processes; countercurrent washing specifically removes soluble phosphorus (phosphate) and soluble fluorine (NaF), achieving removal rates of 85% and 90%, respectively; dilute acid leaching combined with citric acid as a leaching aid disrupts the eutectic structure, exposing and dissolving the eutectic phosphorus, achieving a removal rate of 92%, while simultaneously converting CaF2 into soluble fluoride ions; flotation purification uses dodecylamine as a collector, and under optimized conditions of pH=2.0, the removal rate of insoluble phosphorus (hydroxyapatite) reaches 90%, and the SiO2 content is reduced to below 1%; the composite stabilization stage, through the synergistic effect of quicklime and EDTA-2Na, achieves a heavy metal solidification rate ≥99%, and the leaching amount of radioactive nuclides uranium and thorium ≤0.02mg / L. The final purified product contains ≥97% CaSO4·2H2O, ≤0.1% soluble phosphorus, and ≤0.06% soluble fluorine, fully complying with GB / T 23456-2018 standard. It can be directly used to produce high-value products such as cement retarders and building gypsum boards, breaking the deadlock of "mainly stockpiling" phosphogypsum.

[0016] This invention achieves cost optimization through "resource recycling + low-energy consumption design". First, the reagents are recycled. The fluorine recovery step converts the fluorine in the acid leaching solution into calcium fluorosilicate for recovery, and the regenerated acid is directly recycled for the leaching step, significantly reducing sulfuric acid consumption. Second, energy consumption is significantly reduced. The "chelation + calcification" composite stabilization method replaces high-temperature calcination, reducing energy costs. Third, resource recovery benefits. This invention can recover calcium fluorosilicate, offsetting processing costs.

[0017] This invention is highly environmentally friendly and contributes to green and low-carbon transformation. The dodecylamine used in this invention has a biodegradability rate of ≥80%, and EDTA-2Na causes no secondary pollution, replacing traditional high-pollution flotation agents; the solid waste reduction effect is significant, and the flotation tailings (containing SiO2) can be used to prepare building material fillers, thus reducing the amount of solid waste generated. Detailed Implementation

[0018] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0019] Unless otherwise specified, the raw materials, reagents or devices used in the following embodiments can be obtained from conventional commercial sources or by existing known methods; unless otherwise specified, the methods used in the embodiments of the present invention are methods mastered by those skilled in the art.

[0020] Example 1 Deep purification treatment of environmentally friendly phosphogypsum (1) Screening The phosphogypsum was screened using a vibrating screen with an aperture of 0.15 mm at a screening rate of 10 t / h·screen and an amplitude of 5 mm. This step is used to remove slag larger than 0.15mm, which can reduce subsequent reagent consumption by about 15%. (2) Countercurrent washing The phosphogypsum after slag removal was subjected to a three-stage countercurrent washing with water. The solid-liquid ratio of the three-stage countercurrent washing was 1:4, the water temperature was 30℃, and the stirring speed was 300r / min, to obtain washed phosphogypsum. After testing, the removal rate of soluble phosphorus (H3PO4, Ca(H2PO4)2) in this step was 85%, and the removal rate of soluble fluorine (NaF) was 90%. (3) Dilute acid leaching Take a 5 wt% sulfuric acid solution, add 0.2% citric acid by mass, and then add washed phosphogypsum at a liquid-to-solid mass ratio of 5:1. Leach at 35℃ for 2 hours, and then filter to obtain phosphogypsum filter cake and acid filtrate. After testing, the removal rate of eutectic phosphorus (phosphorus compounds that form a eutectic structure with CaSO4·2H2O and are encapsulated within its crystal lattice, mainly calcium hydrogen phosphate (CaHPO4) and calcium phosphate (Ca3(PO4)2)) in this step was 92%. At the same time, CaF2 was converted into soluble fluoride ions in the acid filtrate, with a CaF2 conversion rate of 93.5%. (4) Flotation for impurity removal The phosphogypsum filter cake was mixed with water at a solid-liquid mass ratio of 1:4 to prepare a slurry. The pH was adjusted to 2.0 with 5wt% dilute sulfuric acid. Then, dodecylamine, a collector, was added at a dosage of 200g / t and stirred for 5 minutes to allow the reagent to be fully adsorbed on the surface of the impurity particles. Then, frother No. 2 oil was added at a dosage of 35g / t and stirred for 2 minutes. The flotation machine was then turned on and the flotation process was carried out for 15 minutes to obtain the phosphogypsum slurry. After testing, the removal rate of sparingly soluble phosphorus (hydroxyapatite) in this step was 90%, and the SiO2 content was reduced to below 1%. (5) Composite stabilization Quicklime and chelating agent EDTA-2Na were added to the phosphogypsum slurry. The amount of quicklime added was 1 wt% of the phosphogypsum slurry, and the amount of EDTA-2Na added was 0.3 wt% of the phosphogypsum slurry. At this time, the pH of the system was 8, and the reaction was carried out for 30 min. After testing, the heavy metal solidification rate in this step was ≥99%, and the leaching amount of radioactive nuclides uranium and thorium was ≤0.02mg / L. (6) Fluorine recovery Add calcium chloride to the acid filtrate obtained in step (3) (first test the fluorine content in the acid filtrate, and add calcium chloride in excess by 5% according to the fluorine-calcium molar ratio of calcium fluorosilicate), then react at 40°C for 45 min to generate calcium fluorosilicate precipitate, and finally filter it to obtain calcium fluorosilicate filter cake. The obtained filtrate is recycled to step (3).

[0021] After testing, the fluorine recovery rate in this step is ≥85%.

[0022] In the final purified product of this embodiment, the content of CaSO4·2H2O was ≥97%, the soluble phosphorus was ≤0.1%, and the soluble fluorine was ≤0.06%, which fully complies with the GB / T 23456-2018 standard.

[0023] Comparative Example 1 Comparison of purification treatment of phosphogypsum This comparative example is operated in the same way as in Example 1, except that the addition of citric acid is omitted in the dilute acid leaching process of step (3).

[0024] After verification, the removal rate of eutectic phosphorus in step (3) of this comparative example was 72%, and the conversion rate of CaF2 was 90%.

[0025] In this comparative example, the final purified product contained 94.5% CaSO4·2H2O, 0.3% soluble phosphorus, and the soluble fluorine was basically unaffected.

[0026] Comparative Example 2 Comparison of purification treatment of phosphogypsum This comparative example is operated in the same way as Example 1, except that the addition of No. 2 oil foaming agent is omitted in the flotation and impurity removal process of step (4).

[0027] After verification, the removal rate of sparingly soluble phosphorus (hydroxyapatite) in step (4) of this comparative example was 60%, and the SiO2 content was 3%.

[0028] The final purified product of the comparative example contained 95.5% CaSO4·2H2O, 0.15% soluble phosphorus, and the soluble fluorine was basically unaffected.

[0029] Comparative Example 3 Comparison of purification treatment of phosphogypsum This comparative example is operated in the same way as Example 1, except that the addition of quicklime is omitted in the composite stabilization process of step (5).

[0030] After verification, the heavy metal solidification rate in step (5) of this comparative example was 70%, and the leaching amount of radioactive nuclides uranium and thorium was 0.2 mg / L.

[0031] The final purified product of this comparative example contained 96% CaSO4·2H2O, 0.22% soluble phosphorus, and 0.1% soluble fluorine.

[0032] Comparative Example 4 Comparison of purification treatment of phosphogypsum This comparative example was operated in the same way as in Example 1, except that the addition of chelating agent EDTA-2Na was omitted in the composite stabilization process of step (5).

[0033] After verification, the heavy metal solidification rate in step (5) of this comparative example was 75%, and the leaching amount of radioactive nuclides uranium and thorium was 0.2 mg / L.

[0034] The final purified product of the comparative example contained 96.5% CaSO4·2H2O, 0.18% soluble phosphorus, and 0.08% soluble fluorine.

[0035] Comparative Example 5 Comparison of purification treatment of phosphogypsum This comparative example was operated in the same way as in Example 1, except that the citric acid used in step (3) dilute acid leaching was replaced with the following conventional leaching aid. The effects of eutectic phosphorus removal and CaF2 conversion after the replacement are shown in Table 1.

[0036] Table 1

[0037] It can be seen that the combination of sulfuric acid and citric acid in this invention has a better leaching effect.

[0038] Furthermore, it should be noted that this invention uses sulfuric acid, which is significantly cheaper than phosphoric acid and more effective than hydrochloric acid (hydrochloric acid introduces Cl into the system). - Impurities may affect the curing effect of heavy metals in subsequent stabilization steps.

[0039] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for the deep purification and treatment of environmentally friendly phosphogypsum, characterized in that, Includes the following steps: (1) Screening The phosphogypsum is screened to remove slag from it. (2) Countercurrent washing The phosphogypsum after slag removal is washed countercurrently with water to obtain washed phosphogypsum. (3) Dilute acid leaching The phosphogypsum was leached with olefinic acid and then filtered to obtain a phosphogypsum filter cake. (4) Flotation for impurity removal The phosphogypsum filter cake was mixed with water to form a slurry, and then flotation was performed using dodecylamine as a collector and No. 2 oil as a frother to obtain the phosphogypsum slurry. (5) Composite stabilization Quicklime and chelating agent are added to the phosphogypsum slurry for reaction treatment.

2. The method for deep purification and treatment of environmentally friendly phosphogypsum as described in claim 1, characterized in that, In step (1), the vibrating screen used for screening has an aperture of 0.15 mm.

3. The method for deep purification and treatment of environmentally friendly phosphogypsum as described in claim 1 or 2, characterized in that, In step (2), the countercurrent washing adopts a three-stage countercurrent washing with a solid-liquid ratio of 1:4, a water temperature of 25-30℃, and a stirring rate of 300r / min.

4. The method for deep purification and treatment of environmentally friendly phosphogypsum as described in claim 1 or 2, characterized in that, In step (3), the olefinic acid is a 5wt% sulfuric acid solution with 0.2% citric acid by mass of the sulfuric acid solution added. The liquid-solid ratio of the leaching treatment is 5:1, the temperature is 35℃, and the leaching time is 2h.

5. The method for deep purification and treatment of environmentally friendly phosphogypsum as described in claim 1 or 2, characterized in that, In step (4), the solid-liquid ratio of the prepared slurry is 1:3 to 5, and the pH is adjusted to 2.

0.

6. The method for deep purification and treatment of environmentally friendly phosphogypsum as described in claim 1 or 2, characterized in that, In step (4), the dosage of dodecylamine is 200 g / t, the dosage of No. 2 oil is 20-50 g / t, and the flotation time is 15 min.

7. The method for deep purification and treatment of environmentally friendly phosphogypsum as described in claim 1 or 2, characterized in that, In step (5), the amount of quicklime added is 1 wt% of the phosphogypsum slurry, the amount of chelating agent added is 0.3 wt% of the phosphogypsum slurry, and the chelating agent is EDTA-2Na.

8. The method for deep purification and treatment of environmentally friendly phosphogypsum as described in claim 1 or 2, characterized in that, In step (5), before the reaction treatment, the pH is adjusted to 8-9, and the reaction treatment time is 30 min.

9. The method for deep purification and treatment of environmentally friendly phosphogypsum as described in claim 1 or 2, characterized in that, It also includes the following steps: (6) Fluorine recovery Add calcium chloride to the acid filtrate obtained in step (3) to react and generate calcium fluorosilicate precipitate. After filtration, the precipitate is reused in step (3).

10. The method for deep purification and treatment of environmentally friendly phosphogypsum as described in claim 9, characterized in that, The reaction temperature is 40℃ and the reaction time is 30-60 min.

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