A method for pretreatment and resource recovery of phosphogypsum leachate

Abstract

The application belongs to the technical field of phosphogypsum resource utilization, and particularly relates to a pretreatment and resource recovery method of phosphogypsum leaching solution. The pretreatment method comprises the following steps: the phosphogypsum leaching solution is subjected to coarse filtration and flocculation sedimentation treatment, then an alkaline precipitant is added to adjust the pH to 9.5-11.5, a stirring sedimentation reaction is performed, a reducing agent and / or a sulfidizing agent are added, a stirring reduction and / or sulfidization reaction is performed, and after the reaction is completed, the precipitated flocculation and colloid are removed by filtration; the obtained filtrate is subjected to adsorption fine removal to remove residual dissolved heavy metals, and the pretreated phosphogypsum leaching solution is obtained. The application organically integrates traditional precipitation, sulfidization, adsorption and other methods, and realizes efficient and selective removal of various metal impurities and easily co-precipitated interfering ions in the phosphogypsum leaching solution, which is convenient for coupling with subsequent resource utilization (F / P recovery).

Description

Technical Field

[0001] This invention belongs to the field of phosphogypsum resource utilization technology, specifically relating to a method for pretreatment and resource recovery of phosphogypsum leaching solution. Background Technology

[0002] Phosphogypsum is a solid industrial waste residue discharged by phosphate chemical companies during the wet process of phosphoric acid production. The leaching solution produced after washing phosphogypsum to remove impurities contains a large number of dissolved ions (such as calcium ions). 2+ SO4 2- PO4 3- F - It contains various metallic impurities (Fe, Al, Si, Mg, Cd, Pb, As, Cr, Hg, Zn, Cu, Ni, etc.), as well as organic colloids, suspended solids, and trace radioactive components. Existing treatment methods are often designed specifically for a particular type of pollutant (such as fluoride or phosphorus removal), and are insufficient for the synergistic removal of coexisting impurities such as heavy metals, making it difficult to balance economic efficiency with water reuse requirements. In addition, existing treatment methods struggle to achieve valuable recovery of fluoride / phosphorus resources, and the recovered products contain easily co-precipitating interfering ions (Fe, Al, Si, Mg), making it difficult to meet reuse requirements. Summary of the Invention

[0003] In view of the shortcomings and deficiencies of the existing technology, the primary objective of this invention is to provide a pretreatment method for phosphogypsum leaching solution.

[0004] Another objective of this invention is to provide a method for resource recovery of phosphogypsum leaching solution.

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

[0006] A pretreatment method for phosphogypsum leaching solution includes the following steps:

[0007] (1) The phosphogypsum leaching solution is coarsely filtered to remove large particles, and then the total suspended solids (TSS) are reduced by flocculation and sedimentation.

[0008] (2) Add an alkaline precipitant to the solution after treatment in step (1) to adjust the pH to 9.5~11.5, stir to carry out precipitation reaction, then add a reducing agent and / or a sulfurizing agent, stir to carry out reduction and / or sulfurization reaction, and filter to remove the precipitated flocs and colloids after the reaction is completed.

[0009] (3) Remove the residual dissolved heavy metals from the filtrate after step (2) by adsorption to obtain the pretreated phosphogypsum rinsing solution.

[0010] Furthermore, the coarse filtration mentioned in step (1) refers to coarse filtration using a sieve or sand filter with a pore size of 50~200μm.

[0011] Further, the flocculation and sedimentation mentioned in step (1) refers to adding polyacrylamide flocculant with a concentration of 1~30 mg / L for flocculation and sedimentation.

[0012] Furthermore, the alkaline precipitant mentioned in step (2) is selected from one or more of CaO, Ca(OH)2, CaCO3, K2CO3, KOH, NaOH, Na2CO3, and NaHCO3. The alkaline precipitation reaction causes easily co-precipitating interfering ions (Fe, Al, Si, Mg) and most heavy metal ions to precipitate as hydroxides, facilitating subsequent resource recovery (F / P recovery).

[0013] Furthermore, in step (2), the temperature for stirring to carry out the precipitation reaction and the temperature for stirring to carry out the reduction and / or sulfidation reaction are 20~60℃, the stirring speed is 200~800 rpm, and the reaction time is 10~60 min. The above conditions are used to optimize the formation of precipitated flocs and colloids.

[0014] Further, the reducing agent in step (2) is one or more of Na2S, FeSO4 or sulfite; the sulfiding agent is Na2S or H2S; and the concentration of the reducing agent and the sulfiding agent added is 0.5~2.0 mmol / L.

[0015] By adding a reducing agent, Cr(VI) that is difficult to precipitate can be reduced to Cr(III) and then removed by precipitation under alkaline conditions; by adding a sulfiding agent, Hg, Cd, Pb, As and other metals can be precipitated more selectively, generating insoluble metal sulfide precipitates for removal.

[0016] Furthermore, the filtration mentioned in step (2) refers to filtration using microfiltration (MF) or ultrafiltration (UF).

[0017] Furthermore, the adsorption and purification described in step (3) refers to the adsorption and purification using activated carbon, activated alumina, layered double hydroxide (LDH), functionalized biochar, bentonite-modified materials, or diatomaceous earth. These adsorbents exhibit good selective adsorption effects on specific heavy metal ions, while having minimal impact on subsequent resource recovery (F / P recovery) components. Adsorption and purification can reduce residual heavy metals to the ppb level.

[0018] A method for resource recovery of phosphogypsum leaching solution includes the following steps:

[0019] The pretreated phosphogypsum leaching solution was adjusted to a Ca:P:F molar ratio of (4.8~5.2):(2.8~3.2):(0.8~1.2) by adding a Ca source, or by adding both a Ca source and a P or F source. Then, the pH was adjusted to the favorable crystallization range of 7~9. Fluoroapatite seed crystals were added and stirred to crystallize. The crystals were then separated and dried to obtain high-purity fluoroapatite (Ca5(PO4)3F).

[0020] Furthermore, the concentration of the fluorapatite seed crystals added is 0.2~1.0 wt%.

[0021] Furthermore, the stirring crystallization can be carried out using equipment such as a stirred crystallizer, a continuous fluidized bed, or a circulating insulated crystallizer, with the stirring crystallization temperature being 20~90℃ and the time being 0.5~24 h.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] (1) This invention organically integrates traditional precipitation, sulfidation, adsorption and other methods to achieve efficient and selective removal of various metal impurities and easily co-precipitated interfering ions in phosphogypsum leaching solution, which is convenient for subsequent resource recovery (F / P recovery).

[0024] (2) The combined treatment of heavy metals (hydroxide precipitation + sulfide precipitation + adsorption / ion exchange) takes into account both the removal efficiency and reduces the chemical consumption caused by non-selective precipitation.

[0025] (3) The generated sludge can be further stabilized or recycled, reducing the risk of secondary pollution. Attached Figure Description

[0026] Figure 1 The image shows the XRD pattern of the fluorapatite product obtained in Example 4. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0028] Example 1

[0029] A pretreatment method for phosphogypsum leaching solution includes the following steps:

[0030] (1) The phosphogypsum leaching solution (pH=4.5, TSS=359 mg / L, Fe=100 mg / L, Al=140 mg / L, Cd=30 mg / L, Pb=70 mg / L, total Cr=70 mg / L, As=25 mg / L) was coarsely filtered at 100 μm to remove large particles. Then, 10 mg / L of polyacrylamide flocculant was added and the solution was allowed to stand for 20 min to reduce the total suspended solids (TSS) through flocculation and sedimentation.

[0031] (2) Add Ca(OH)2 to the solution after treatment in step (1) to adjust the pH to 10.5, stir at 500 rpm for 20 min at room temperature, and let stand for 30 min to precipitate and remove Fe / Al, etc., and the metal content of the filtrate will decrease significantly; then add 1 mmol / L Na2S for sulfide precipitation and reduction treatment, stir for 20 min and let stand for 30 min to form sulfide and hydroxide precipitates of Cd / Pb / As / Cr. Then remove the flocs by UF (0.05~0.1μm).

[0032] (3) The filtrate after step (2) is passed through a 5 L adsorption bed (1 kg of activated carbon or 0.5 kg of functional biochar, flow rate 1~5 BV / h) to remove residual dissolved heavy metals and obtain pretreated phosphogypsum leaching solution.

[0033] The parameters of the phosphogypsum leaching solution before and after pretreatment in this embodiment are shown in Table 1 below.

[0034] Table 1. Indicators of phosphogypsum leaching solution before and after pretreatment

[0035] 1 TSS 359 10 mg / L 2 Fe 100 2 mg / L 3 Al 140 1 mg / L 4 Cd 30 0 mg / L 5 Pb 70 0 mg / L 6 As 25 0 mg / L 7 Cr 70 0 mg / L

[0036] Example 2

[0037] A pretreatment method for phosphogypsum leaching solution includes the following steps:

[0038] (1) The phosphogypsum leaching solution (pH=4.5, TSS=359 mg / L, Fe=100 mg / L, Al=140 mg / L, Cd=30 mg / L, Pb=70 mg / L, total Cr=70 mg / L, As=25 mg / L) was coarsely filtered at 50 μm to remove large particles. Then, 5 mg / L of polyacrylamide flocculant was added and the solution was allowed to stand for 30 min to reduce the total suspended solids (TSS) through flocculation and sedimentation.

[0039] (2) Add NaHCO3 to the solution treated in step (1) to adjust the pH to 9.5, stir at 400 rpm for 30 min at room temperature, and let stand for 30 min to precipitate and remove Fe / Al, etc. The metal content of the filtrate decreases significantly; then add 0.5 mmol / L H2S for sulfide precipitation and reduction treatment, stir for 30 min and let stand for 30 min to form sulfide and hydroxide precipitates of Cd / Pb / As / Cr. Then remove the flocs by UF (0.05~0.1μm).

[0040] (3) The filtrate after step (2) is passed through a 5 L adsorption bed (1 kg of activated carbon or 0.5 kg of functional biochar, flow rate 1~5 BV / h) to remove residual dissolved heavy metals and obtain pretreated phosphogypsum leaching solution.

[0041] The effluent parameters of the phosphogypsum leaching solution after pretreatment in this embodiment are shown in Table 2 below.

[0042] Table 2. Indicators of phosphogypsum leaching solution before and after pretreatment

[0043] 1 TSS 359 12 mg / L 2 Fe 100 2 mg / L 3 Al 140 2 mg / L 4 Cd 30 0 mg / L 5 Pb 70 0 mg / L 6 As 25 0 mg / L 7 Cr 70 1 mg / L

[0044] Example 3

[0045] A pretreatment method for phosphogypsum leaching solution includes the following steps:

[0046] (1) The phosphogypsum leaching solution (pH=4.5, TSS=359 mg / L, Fe=100 mg / L, Al=140 mg / L, Cd=30 mg / L, Pb=70 mg / L, total Cr=70 mg / L, As=25 mg / L) was coarsely filtered at 200 μm to remove large particles. Then, 20 mg / L of polyacrylamide flocculant was added and the solution was allowed to stand for 15 min to reduce the total suspended solids (TSS) through flocculation and sedimentation.

[0047] (2) Add NaHCO3 to the solution treated in step (1) to adjust the pH to 11.5, stir at 300 rpm for 15 min at room temperature, and let stand for 30 min to precipitate and remove Fe / Al, etc. The metal content of the filtrate decreased significantly; then add 2 mmol / L sodium sulfite for sulfide precipitation and reduction treatment, stir for 15 min and let stand for 30 min to form sulfide and hydroxide precipitates of Cd / Pb / As / Cr. Then remove the flocs by UF (0.05~0.1μm).

[0048] (3) The filtrate after step (2) is passed through a 5 L adsorption bed (1 kg of activated carbon or 0.5 kg of functional biochar, flow rate 1~5 BV / h) to remove residual dissolved heavy metals and obtain pretreated phosphogypsum leaching solution.

[0049] The effluent parameters of the phosphogypsum leaching solution after pretreatment in this embodiment are shown in Table 3 below.

[0050] Table 3. Indicators of phosphogypsum leaching solution before and after pretreatment

[0051] 1 TSS 359 9 mg / L 2 Fe 100 1 mg / L 3 Al 140 1 mg / L 4 Cd 30 0 mg / L 5 Pb 70 0 mg / L 6 As 25 0 mg / L 7 Cr 70 0 mg / L

[0052] Example 4

[0053] A method for resource recovery of phosphogypsum leaching solution includes the following steps:

[0054] The phosphogypsum eluent pretreated in Example 1 was adjusted to a Ca:P:F molar ratio of 5:3:1 by adding Ca(OH)2 suspension and phosphoric acid. The pH was then adjusted to 7.8, and 0.5 wt% pre-prepared FA seed crystals were added and stirred for crystallization at 50°C for 5 hours. The solid phase was separated by plate and frame filtration, dried, and the product was obtained. The XRD pattern of the obtained product is shown below. Figure 1 As shown. ICP-OES characterization of the product showed that the P content was 18.36 wt%, the P2O5 content was 42.05 wt%, and the Ca / P molar ratio was 1.65. This indicates that the obtained product is high-purity fluorapatite (Ca5(PO4)3F).

[0055] Comparative Example 1

[0056] A method for resource recovery of phosphogypsum leaching solution includes the following steps:

[0057] (1) The phosphogypsum leaching solution (pH=4.5, TSS=359 mg / L, Fe=100 mg / L, Al=140 mg / L, Cd=30 mg / L, Pb=70 mg / L, total Cr=70 mg / L, As=25 mg / L) was coarsely filtered at 100 μm to remove large particles. Then, 10 mg / L of polyacrylamide flocculant was added and the solution was allowed to stand for 20 min to reduce the total suspended solids (TSS) through flocculation and sedimentation.

[0058] (2) The phosphogypsum leaching solution treated in step (1) was adjusted to a Ca:P:F molar ratio of 5:3:1 by adding Ca(OH)2 suspension and phosphoric acid. Then, the pH was adjusted to 7.8, and 0.5 wt% pre-prepared FA seed crystals were added and stirred for crystallization at 50℃ for 5 h. The solid phase was separated by plate and frame filtration, and the solid phase was dried to obtain the product. The ICP-OES characterization results of the obtained product showed that the P2O5 content was 23.56 wt% and the Ca / P molar ratio was 1.49, which was significantly lower than the typical fluorapatite index. This indicates that the pretreatment method of the present invention can significantly improve the product quality of the recovered fluorapatite (Ca5(PO4)3F).

[0059] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for resource recovery of phosphogypsum leaching solution, characterized in that: Includes the following steps: (1) The phosphogypsum leaching solution is coarsely filtered to remove large particles, and then the total suspended solids are reduced by flocculation and sedimentation. (2) Add an alkaline precipitant to the solution after treatment in step (1) to adjust the pH to 9.5~11.5, stir to carry out the precipitation reaction, then add a reducing agent and / or a sulfiding agent, stir to carry out the reduction and / or sulfidation reaction, and filter to remove the precipitated flocs and colloids after the reaction is completed; the reducing agent is one or more of Na2S, FeSO4 or sulfite; the sulfiding agent is Na2S or H2S; the concentration of the reducing agent and sulfiding agent added is 0.5~2.0 mmol / L; (3) Remove the residual dissolved heavy metals from the filtrate after step (2) by adsorption to obtain the pretreated phosphogypsum rinsing solution. (4) The phosphogypsum rinsing solution after the pretreatment in step (3) is adjusted to the Ca:P:F molar ratio of (4.8~5.2):(2.8~3.2):(0.8~1.2) by adding Ca source or simultaneously adding Ca source and P or F source. Then the pH is adjusted to the crystallization range of 7~9. Fluoroapatite seed crystals are added and stirred to crystallize. The crystals are separated and dried to obtain high-purity fluoroapatite.

2. The method for resource recovery of phosphogypsum leaching solution according to claim 1, characterized in that: The coarse filtration mentioned in step (1) refers to coarse filtration using a sieve or sand filter with a pore size of 50~200μm; the flocculation and sedimentation refers to flocculation and sedimentation by adding polyacrylamide flocculant with a concentration of 1~30 mg / L.

3. The method for resource recovery of phosphogypsum leaching solution according to claim 1, characterized in that: The alkaline precipitant mentioned in step (2) is selected from one or more of CaO, Ca(OH)2, CaCO3, K2CO3, KOH, NaOH, Na2CO3, and NaHCO3.

4. The method for resource recovery of phosphogypsum leaching solution according to claim 1, characterized in that: The temperature for the precipitation reaction and the reduction and / or sulfidation reaction described in step (2) is 20~60℃, the stirring speed is 200~800 rpm, and the reaction time is 10~60 min.

5. The method for resource recovery of phosphogypsum leaching solution according to claim 1, characterized in that: The filtration mentioned in step (2) refers to filtration using microfiltration or ultrafiltration.

6. The method for resource recovery of phosphogypsum leaching solution according to claim 1, characterized in that: The adsorption and purification process mentioned in step (3) refers to the adsorption and purification process using activated carbon, activated alumina, layered double hydroxides, functionalized biochar, bentonite-modified materials, or diatomaceous earth.

7. The method for resource recovery of phosphogypsum leaching solution according to claim 1, characterized in that: The concentration of the fluorapatite seed crystals added is 0.2~1.0 wt%.

8. The method for resource recovery of phosphogypsum leaching solution according to claim 1, characterized in that: The stirring crystallization can be carried out using equipment such as a stirred crystallizer, a continuous fluidized bed, or a circulating insulated crystallizer. The stirring crystallization temperature is 20~90℃, and the time is 0.5~24 h.

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