A wet-process phosphoric acid purification method based on multi-stage centrifugal extraction

Abstract

The application discloses a kind of wet-process phosphoric acid purification methods based on multistage centrifugal extraction, belong to the technical field of refined phosphoric acid.The method sequentially includes: sequential pretreatment, centrifugal extraction, centrifugal washing and centrifugal stripping.Said sequential pretreatment uses one-pot method, first add H2O2 decolorization, then add sodium carbonate, calcium carbonate, sodium sulfide with nine water for defluorination, desulfurization, arsenic removal.Said centrifugal extraction, centrifugal washing and centrifugal stripping all use 5-stage centrifugal extractor in series, and specific temperature and speed range are controlled respectively.The application is through the synergistic effect of "sequential pretreatment+multistage centrifugal+parameter adaptation", effectively solves the problems of emulsification, phase separation difficulty, large equipment and high energy consumption in traditional solvent extraction method, realizes the efficient, low-consumption purification of wet-process phosphoric acid, and the obtained purified phosphoric acid has very high purity, which can be directly used in high-value-added fields.

Description

Technical Field

[0001] This invention belongs to the field of refined phosphoric acid technology, specifically relating to a wet phosphoric acid purification method based on multi-stage centrifugal extraction. Background Technology

[0002] Wet-process phosphoric acid has lower costs, energy consumption, and pollution than thermal-process phosphoric acid, making it suitable for applications with lower-grade phosphate rock. However, wet-process phosphoric acid contains a complex variety and high concentration of impurity ions, limiting its use to low-value-added compound fertilizer production and hindering its high-end applications. Therefore, to achieve high-value-added utilization of wet-process phosphoric acid, purification is essential.

[0003] Currently, there are numerous methods for purifying wet-process phosphoric acid, mainly including chemical precipitation, solvent extraction, ion exchange, and double salt crystallization. Among these, solvent extraction is one of the most widely used mainstream purification methods. Tributyl phosphate is the most commonly used extractant due to its advantages such as high extraction efficiency, good selectivity, and strong stability. However, wet-process phosphoric acid has high impurity content, high viscosity, and is prone to sedimentation, leading to problems such as emulsification, difficulty in two-phase separation, and significant impurity entrainment during extraction, resulting in unsatisfactory purification effects. In particular, existing solvent extraction methods mainly use extraction towers and extraction tanks, which suffer from low efficiency, poor separation effect, large size, difficult scaling and cleaning, high energy consumption, and high investment costs. For example, in the crude phosphoric acid pretreatment process of patent CN100400414C, the order of adding decolorizing and arsenic removal agents is disordered, making it difficult for arsenic ions to react with sulfur ions to form precipitates, resulting in low arsenic removal efficiency. Patent CN202122558447.9 uses rotary disc towers and vibrating screen plate towers as extraction and purification equipment. To improve extraction efficiency and phase separation, the tower height must be increased, resulting in large equipment size and difficult operation. Furthermore, rotary disc towers and vibrating screen plate towers suffer from complex internal structures, high costs, and difficult scaling and cleaning, making them unsuitable for wet phosphoric acid purification. Patent CN201510479134.0 uses extraction tanks as extraction and purification equipment. While avoiding the maintenance difficulties and high costs of tower equipment, tank equipment still suffers from multiple extraction stages, long phase separation time, low purification efficiency, large footprint, and difficult scaling and cleaning at the bottom of the tank. Using tributyl phosphate as an extractant to purify wet phosphoric acid requires addressing emulsification, impurity entrainment, poor separation effect, and extraction equipment issues during the extraction process. Therefore, there is an urgent need to develop an efficient and energy-saving integrated wet phosphoric acid purification solution. Summary of the Invention

[0004] This invention addresses the problems existing in the prior art by proposing a wet phosphoric acid purification method based on multi-stage centrifugal extraction. Through sequential pretreatment + five-stage countercurrent centrifugation + thermal energy circulation triple optimization, it achieves efficient and low-consumption purification.

[0005] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0006] A wet phosphoric acid purification method based on multi-stage centrifugal extraction includes the following steps:

[0007] (1) Sequential pretreatment: Crude phosphoric acid is pretreated by one-pot method. The crude phosphoric acid to be treated is placed in a container and H2O2 is added first for decolorization. Then sodium carbonate, calcium carbonate and sodium sulfide nonahydrate are added for defluorination, desulfurization and dearsenic removal. After stirring at 60-70℃, the solution is filtered to obtain phosphoric acid clear solution.

[0008] (2) Centrifugal extraction: Phosphate solution and extractant are pumped into a 5-stage centrifugal extractor in series. After centrifugal extraction, the light and heavy phases are separated to obtain saturated extractant and residual acid. The residual acid is used to produce compound fertilizer, and the saturated extractant is pumped into the centrifugal washing section.

[0009] (3) Centrifugal washing: Deionized water and saturated extractant obtained from the centrifugal extraction section are sequentially pumped into a 5-stage series centrifugal extractor for washing to obtain residual acid and washing extractant. The residual acid is used to produce high-end fertilizers, and the washing extractant is pumped into the centrifugal back-extraction section.

[0010] (4) Centrifugal back-extraction: Deionized water and washing extractant are sequentially pumped into a 5-stage centrifugal extractor connected in series for back-extraction to obtain back-extracted acid and extractant. Depending on actual usage requirements, a portion of the back-extracted acid can be returned to the centrifugal washing process as washing phosphoric acid to replace deionized water, while the other portion is concentrated to obtain purified phosphoric acid. The extractant is returned to the centrifugal extraction section for recycling. After the centrifugal back-extraction is completed, the higher-temperature extractant enters a heat exchanger to heat the saturated extractant after extraction, achieving heat energy recycling.

[0011] Preferably, the amount of H2O2 used is 1-3% of the mass of crude phosphoric acid, and the decolorization reaction time is 0.5-1h; the amount of sodium carbonate added is 0.6-1.0 times the molar amount of fluorine in crude phosphoric acid, the amount of calcium carbonate added is 0.8-1.0 times the molar amount of sulfate in crude phosphoric acid, and the amount of sodium sulfide nonahydrate added is 1.0-1.2 times the molar amount of arsenic in crude phosphoric acid, and the defluorination, desulfurization and dearsenic removal reaction time is 2-4h.

[0012] Preferably, in the centrifugal extraction, the extractant is obtained by mixing tributyl phosphate and sulfonated kerosene in a volume ratio of 5:2.

[0013] Preferably, in centrifugal extraction, the centrifugal extraction temperature is ≤40℃ and the centrifugal speed is ≤1200 rpm.

[0014] Preferably, during centrifugal washing, the washing temperature is 50-80℃ and the centrifugal speed is 1000-2000 rpm.

[0015] Preferably, in the centrifugal back-extraction, the back-extraction temperature is ≥80℃ and the centrifugal speed is ≥1500 rpm. After back-extraction, the extractant can enter a heat exchanger to heat the saturated extractant after extraction, realizing heat energy circulation, and then be recycled back to the centrifugal extraction section.

[0016] Beneficial effects:

[0017] (1) The sequential pretreatment is carried out in a one-pot process, that is, decolorization, defluorination, desulfurization and dearsenic removal are carried out in the same reaction tank, which simplifies the pretreatment process, reduces the number of equipment and lowers equipment investment. The sequential pretreatment utilizes the strong oxidizing property of hydrogen peroxide to decompose the colored organic matter in crude phosphoric acid, reduce the viscosity of phosphoric acid, which is conducive to the full sedimentation of impurities and improves the removal efficiency of impurity ions; at the same time, the sequential pretreatment avoids the reaction between hydrogen peroxide and the sulfides in the subsequent dearsenic removal, thus improving the dearsenic removal efficiency.

[0018] (2) The centrifugal extraction, centrifugal washing and centrifugal back-extraction processes are carried out using a 5-stage series centrifugal extractor, which has the advantages of small equipment size, small footprint, short phase separation time, high purification efficiency and low energy consumption.

[0019] (3) Centrifugal extraction has the advantages of high phosphorus extraction efficiency, fast two-phase separation speed and low emulsification of extractant by controlling the extraction temperature and centrifuge speed.

[0020] (4) Centrifugal washing has the advantages of good elution effect of impurity ions, low amount of washing acid, fast two-phase separation speed and low entrainment of washing acid by controlling the washing temperature and centrifuge speed.

[0021] (5) Centrifugal back-extraction has the advantages of high phosphorus back-extraction efficiency, fast two-phase separation speed, low emulsification of extractant and low content of back-extraction acid impurities by controlling the back-extraction temperature and centrifuge speed.

[0022] (6) After centrifugal back-extraction is completed, the extractant with higher temperature enters the heat exchanger to heat the saturated extractant after extraction, thereby realizing heat energy circulation and reducing energy consumption. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the purification process of the present invention. Detailed Implementation

[0024] The technical solution of the present invention will be further described below with reference to specific embodiments, but it is not limited thereto.

[0025] Example 1

[0026] The main components of the raw material crude phosphoric acid are shown in Table 1:

[0027] Table 1 Composition of crude phosphoric acid in raw material

[0028]

[0029] Implement it according to the following methods:

[0030] A wet phosphoric acid purification method based on multi-stage centrifugal extraction includes the following steps:

[0031] (1) Sequential pretreatment: Crude phosphoric acid was pretreated using a one-pot method. 16 kg of crude phosphoric acid to be treated was placed in a container, and 0.32 kg of H2O2 was added for decolorization at 60-70℃ for 0.5 h. Then, 0.1 kg of sodium carbonate, 0.24 kg of calcium carbonate, and 0.05 kg of sodium sulfide nonahydrate were added for defluorination, desulfurization, and dearsenic removal. After stirring at 60-70℃ for 3 hours, the mixture was filtered to obtain a clear phosphoric acid solution. The specific gravity of the clear phosphoric acid solution was 1.62 g / ml, and the main components are shown in Table 2.

[0032] Table 2 Main components of phosphate solution

[0033]

[0034] (2) Centrifugal extraction: Phosphate solution is pumped into the heavy phase zone of a 5-stage centrifugal extractor connected in series at a flow rate of 75 ml / min, and extractant is pumped into the light phase zone of the same centrifugal extractor at a flow rate of 300 ml / min. After centrifugal extraction, the light and heavy phases are separated to obtain saturated extractant and residual acid. The residual acid is used to produce compound fertilizer, and the saturated extractant is pumped into the centrifugal washing section. The centrifugal extraction maintains a material temperature of 40℃ and a centrifugal extractor speed of 1200 r / min.

[0035] The residual acid discharge flow rate was 25 ml / min, the specific gravity was 1.37 g / ml, and the main components are shown in Table 3.

[0036] Table 3. Main components of residual acid

[0037]

[0038] (3) Centrifugal washing: The saturated extractant obtained from the centrifugal extraction section is pumped into the light phase zone of a 5-stage centrifugal extractor connected in series at a flow rate of 300 ml / min, and deionized water is pumped into the light and heavy phase zones of the 5-stage centrifugal extractor connected in series at a flow rate of 20 ml / min for washing, to obtain residual acid and washing extractant. The residual acid is used to produce high-end fertilizers, and the washing extractant is pumped into the centrifugal back-extraction section. The centrifugal washing temperature is maintained at 60℃, and the speed of the centrifugal extractor is adjusted to 1000 r / min.

[0039] The residual acid discharge flow rate was 25 ml / min, the specific gravity was 1.45 g / ml, and the main components are shown in Table 4.

[0040] Table 4 Main components of residual acid

[0041]

[0042] (4) Centrifugal back-extraction: The washing extractant is pumped into the light phase zone of a 5-stage centrifugal extractor connected in series at a flow rate of 300 ml / min, and deionized water is pumped into the heavy phase zone of the same centrifugal extractor at a flow rate of 50 ml / min for back-extraction, yielding back-extracted acid and extractant. Depending on actual usage requirements, a portion of the back-extracted acid can be returned to the centrifugal washing process as washing phosphoric acid to replace deionized water, while the remaining portion is concentrated to obtain purified phosphoric acid. The extractant is returned to the centrifugal extraction section for recycling. The back-extraction temperature is 80℃, and the centrifugal extractor speed is 1500 r / min. The back-extracted acid discharge flow rate is 55 ml / min, with a specific gravity of 1.25 g / ml. The main components are shown in Table 5.

[0043] Table 5. Main components of back-extracting acid

[0044]

[0045] Example 2

[0046] The composition of the crude phosphoric acid raw material is the same as in Example 1.

[0047] A wet phosphoric acid purification method based on multi-stage centrifugal extraction includes the following steps:

[0048] (1) Sequential preprocessing: Same as in Example 1.

[0049] (2) Centrifugal extraction: Phosphate solution is pumped into the heavy phase zone of a 5-stage centrifugal extractor connected in series at a flow rate of 75 ml / min, and extractant is pumped into the light phase zone of the same centrifugal extractor at a flow rate of 300 ml / min. After centrifugal extraction, the light and heavy phases are separated to obtain saturated extractant and residual acid. The residual acid is used to produce compound fertilizer, and the saturated extractant is pumped into the centrifugal washing section. The centrifugal extraction maintains a material temperature of 30℃ and a centrifugal extractor speed of 500 r / min.

[0050] The main components of residual acid are shown in Table 6:

[0051] Table 6. Main components of residual acid

[0052]

[0053] (3) Centrifugal washing: The saturated extractant obtained from the centrifugal extraction section is pumped into the light phase zone of a 5-stage centrifugal extractor connected in series at a flow rate of 300 ml / min, and deionized water is pumped into the light and heavy phase zones of the 5-stage centrifugal extractor connected in series at a flow rate of 20 ml / min for washing, to obtain residual acid and washing extractant. The residual acid is used to produce high-end fertilizers, and the washing extractant is pumped into the centrifugal back-extraction section. The centrifugal washing temperature is maintained at 50℃, and the speed of the centrifugal extractor is adjusted to 2000 r / min.

[0054] The main components of residual acid are shown in Table 7:

[0055] Table 7 Main components of residual acid

[0056]

[0057] (4) Centrifugal back-extraction: The washing extractant is pumped into the light phase zone of a 5-stage centrifugal extractor connected in series at a flow rate of 300 ml / min, and deionized water is pumped into the heavy phase zone of the same centrifugal extractor at a flow rate of 50 ml / min for back-extraction, yielding back-extractable acid and extractant. Depending on actual usage requirements, a portion of the back-extractable acid can be returned to the centrifugal washing process as washing phosphoric acid to replace deionized water, while the remaining portion is concentrated to obtain purified phosphoric acid. The extractant is returned to the centrifugal extraction section for recycling. The back-extraction temperature is 90℃, and the centrifugal extractor speed is 1800 r / min. The main components of the back-extractable acid are shown in Table 8.

[0058] Table 8. Main components of back-extracting acid

[0059]

[0060] Example 3

[0061] The composition of the crude phosphoric acid raw material is the same as in Example 1.

[0062] A wet phosphoric acid purification method based on multi-stage centrifugal extraction includes the following steps:

[0063] (1) Sequential preprocessing: Same as in Example 1.

[0064] (2) Centrifugal extraction: Phosphate solution is pumped into the heavy phase zone of a 5-stage centrifugal extractor connected in series at a flow rate of 75 ml / min, and extractant is pumped into the light phase zone of the same centrifugal extractor at a flow rate of 300 ml / min. After centrifugal extraction, the light and heavy phases are separated to obtain saturated extractant and residual acid. The residual acid is used to produce compound fertilizer, and the saturated extractant is pumped into the centrifugal washing section. The centrifugal extraction maintains a material temperature of 35℃ and a centrifugal extractor speed of 800 r / min.

[0065] The main components of the residual acid effluent are shown in Table 9:

[0066] Table 9. Main components of residual acid.

[0067]

[0068] (3) Centrifugal washing: The saturated extractant obtained from the centrifugal extraction section is pumped into the light phase zone of a 5-stage centrifugal extractor connected in series at a flow rate of 300 ml / min, and deionized water is pumped into the light and heavy phase zones of the 5-stage centrifugal extractor connected in series at a flow rate of 20 ml / min for washing, to obtain residual acid and washing extractant. The residual acid is used to produce high-end fertilizers, and the washing extractant is pumped into the centrifugal back-extraction section. The centrifugal washing temperature is maintained at 80℃, and the speed of the centrifugal extractor is adjusted to 1000 r / min.

[0069] The main components of residual acid are shown in Table 10:

[0070] Table 10 Main components of residual acid

[0071]

[0072] (4) Centrifugal back-extraction: The washing extractant is pumped into the light phase zone of a 5-stage centrifugal extractor connected in series at a flow rate of 300 ml / min, and deionized water is pumped into the heavy phase zone of the same centrifugal extractor at a flow rate of 50 ml / min for back-extraction, yielding back-extracted acid and extractant. Depending on actual usage requirements, a portion of the back-extracted acid can be returned to the centrifugal washing process as washing phosphoric acid to replace deionized water, while the remaining portion is concentrated to obtain purified phosphoric acid. The extractant is returned to the centrifugal extraction section for recycling. The back-extraction temperature is 90℃, and the centrifugal extractor speed is 2000 r / min. The main components of the back-extracted acid are shown in Table 11:

[0073] Table 11 Main components of stripping acid

[0074]

[0075] Comparative Example 1

[0076] Compared to Example 1, this comparative example differs from Example 1 in that, in the sequential pretreatment stage, 0.05 kg of sodium sulfide is added first to remove arsenic, followed by decolorization, defluorination, and desulfurization. All other process steps and parameters are the same. The main components of the obtained phosphoric acid solution are shown in Table 12.

[0077] Table 12 Main components of phosphate solution in Comparative Example 1

[0078]

[0079] Comparative Example 2

[0080] Compared to Example 1, this comparative example is identical to Example 1 in all process steps and parameters except for the change in the process parameters of the centrifugal extraction stage. That is:

[0081] A wet phosphoric acid purification method based on multi-stage centrifugal extraction includes the following steps:

[0082] (1) Sequential preprocessing: Same as in Example 1.

[0083] (2) Centrifugal extraction: Phosphate solution is pumped into the heavy phase zone of a 5-stage centrifugal extractor connected in series at a flow rate of 75 ml / min, and extractant is pumped into the light phase zone of the same centrifugal extractor at a flow rate of 300 ml / min. After centrifugal extraction, the light and heavy phases are separated to obtain saturated extractant and residual acid. The residual acid is used to produce compound fertilizer, and the saturated extractant is pumped into the centrifugal washing section. The centrifugal extraction maintains a material temperature of 50℃ and a centrifugal extractor speed of 1500 r / min.

[0084] (3) Centrifugal washing: Same as in Example 1.

[0085] (4) Centrifugal back-extraction: Same as in Example 1. The main components of the back-extraction acid are shown in Table 13. The centrifugal extraction process in this comparative example was carried out at a high temperature and at a high speed, which caused emulsification of the extraction system and a large number of impurities in the extractant, ultimately resulting in a high content of impurity ions in the back-extraction acid.

[0086] Table 13 Main components of stripping acid

[0087]

[0088] Comparative Example 3

[0089] Compared to Example 1, this comparative example is identical to Example 1 in all process steps and parameters except for the change in the process parameters of the centrifugal washing stage. That is:

[0090] A wet phosphoric acid purification method based on multi-stage centrifugal extraction includes the following steps:

[0091] (1) Sequential preprocessing: Same as in Example 1.

[0092] (2) Centrifugal extraction: Same as in Example 1.

[0093] (3) Centrifugal washing: The saturated extractant obtained from the centrifugal extraction section is pumped into the light phase zone of a 5-stage centrifugal extractor connected in series at a flow rate of 300 ml / min. Deionized water is pumped into the light and heavy phase zones of the 5-stage centrifugal extractor connected in series at a flow rate of 20 ml / min for washing to obtain residual acid and washing extractant. The residual acid is used to produce high-end fertilizers, and the washing extractant is pumped into the centrifugal back-extraction section. The centrifugal washing temperature is maintained at 40℃, and the speed of the centrifugal extractor is adjusted to 500 r / min.

[0094] (4) Centrifugal back-extraction: Same as in Example 1.

[0095] The main components of the back-extracting acid are shown in Table 14. In this comparative example, due to the low centrifugal washing temperature and low centrifuge speed during the centrifugal washing stage, the extractant emulsified and carried some washing impurities, which ultimately resulted in a high content of impurity ions in the back-extracting acid.

[0096] Table 14 Main Components of Re-extractable Acid

[0097]

[0098] Comparative Example 4

[0099] Compared to Example 1, this comparative example is identical to Example 1 in all process steps and parameters except for the change in the process parameters of the centrifugal washing stage. That is:

[0100] A wet phosphoric acid purification method based on multi-stage centrifugal extraction includes the following steps:

[0101] (1) Sequential preprocessing: Same as in Example 1.

[0102] (2) Centrifugal extraction: Same as in Example 1.

[0103] (3) Centrifugal washing: The saturated extractant obtained from the centrifugal extraction section is pumped into the light phase zone of a 5-stage centrifugal extractor connected in series at a flow rate of 300 ml / min. Deionized water is pumped into the light and heavy phase zones of the 5-stage centrifugal extractor connected in series at a flow rate of 20 ml / min for washing to obtain residual acid and washing extractant. The residual acid is used to produce high-end fertilizers, and the washing extractant is pumped into the centrifugal back-extraction section. The centrifugal washing temperature is maintained at 90℃, and the speed of the centrifugal extractor is adjusted to 2200 r / min.

[0104] (4) Centrifugal back-extraction: Same as in Example 1.

[0105] The main components of the back-extracting acid are shown in Table 15. In this comparative example, due to the high temperature and high speed of the centrifugation washing stage, the extractant emulsified and carried some washing impurities, which ultimately resulted in a high content of impurity ions in the back-extracting acid.

[0106] Table 15 Main Components of Re-extractable Acid

[0107]

[0108] Comparative Example 5

[0109] Compared to Example 1, this comparative example is identical to Example 1 in all process steps and parameters except for the change in the process parameters of the centrifugal back-extraction stage. That is:

[0110] A wet phosphoric acid purification method based on multi-stage centrifugal extraction includes the following steps:

[0111] (1) Sequential preprocessing: Same as in Example 1.

[0112] (2) Centrifugal extraction: Same as in Example 1.

[0113] (3) Centrifugal washing: Same as in Example 1.

[0114] (4) Centrifugal back-extraction: The washing extractant is pumped into the light phase zone of a 5-stage centrifugal extractor connected in series at a flow rate of 300 ml / min, and deionized water is pumped into the heavy phase zone of the same 5-stage centrifugal extractor at a flow rate of 50 ml / min for back-extraction, yielding back-extracted acid and extractant. Depending on actual usage requirements, a portion of the back-extracted acid can be returned to the centrifugal washing process as washing phosphoric acid to replace deionized water, while the other portion is concentrated to obtain purified phosphoric acid. The extractant is returned to the centrifugal extraction section for recycling. The back-extraction temperature is 60℃, and the centrifugal extractor speed is 1000 r / min. The main components of the back-extracted acid are shown in Table 16. The low centrifugal back-extraction temperature and low centrifugal speed result in insufficient back-extraction, with some P2O5 remaining in the extractant, ultimately leading to a low P2O5 concentration in the back-extracted acid.

[0115] Table 16 Main Components of Re-extractable Acid

[0116]

[0117] Comparative Example 6

[0118] Compared to Example 1, this comparative example is identical to Example 1 in all process steps and parameters except for changes to the process parameters in the centrifugal extraction and centrifugal washing stages. That is:

[0119] A wet phosphoric acid purification method based on multi-stage centrifugal extraction includes the following steps:

[0120] (1) Sequential preprocessing: Same as in Example 1.

[0121] (2) Centrifugal extraction: Phosphate solution is pumped into the heavy phase zone of a 5-stage centrifugal extractor connected in series at a flow rate of 75 ml / min, and extractant is pumped into the light phase zone of the same centrifugal extractor at a flow rate of 300 ml / min. After centrifugal extraction, the light and heavy phases are separated to obtain saturated extractant and residual acid. The residual acid is used to produce compound fertilizer, and the saturated extractant is pumped into the centrifugal washing section. The centrifugal extraction maintains a material temperature of 50℃ and a centrifugal extractor speed of 1500 r / min.

[0122] (3) Centrifugal washing: The saturated extractant obtained from the centrifugal extraction section is pumped into the light phase zone of a 5-stage centrifugal extractor connected in series at a flow rate of 300 ml / min, and deionized water is pumped into the light and heavy phase zones of the 5-stage centrifugal extractor connected in series at a flow rate of 20 ml / min for washing, to obtain residual acid and washing extractant. The residual acid is used to produce high-end fertilizers, and the washing extractant is pumped into the centrifugal back-extraction section. The centrifugal washing temperature is maintained at 40℃, and the speed of the centrifugal extractor is adjusted to 500 r / min.

[0123] (4) Centrifugal back-extraction: Same as in Example 1. The main components of the back-extracted acid are shown in Table 17. During the centrifugal extraction stage, the high temperature and high speed cause the phosphoric acid and the extractant to form an emulsion layer, making separation difficult. During the centrifugal washing stage, the low speed and low temperature result in insufficient washing, leading to a large number of residual impurity ions, which ultimately affects the quality of the purified phosphoric acid.

[0124] Table 17 Main Components of Reverse Acid

[0125]

[0126] Comparative Example 7

[0127] Compared to Example 1, this comparative example is identical to Example 1 in all process steps and parameters except for changes to the process parameters of the centrifugal extraction stage, the centrifugal washing stage, and the centrifugal back-extraction stage. That is:

[0128] A wet phosphoric acid purification method based on multi-stage centrifugal extraction includes the following steps:

[0129] (1) Sequential preprocessing: Same as in Example 1.

[0130] (2) Centrifugal extraction: Phosphate solution is pumped into the heavy phase zone of a 5-stage centrifugal extractor connected in series at a flow rate of 75 ml / min, and extractant is pumped into the light phase zone of the same centrifugal extractor at a flow rate of 300 ml / min. After centrifugal extraction, the light and heavy phases are separated to obtain saturated extractant and residual acid. The residual acid is used to produce compound fertilizer, and the saturated extractant is pumped into the centrifugal washing section. The centrifugal extraction maintains a material temperature of 50℃ and a centrifugal extractor speed of 1500 r / min.

[0131] (3) Centrifugal washing: The saturated extractant obtained from the centrifugal extraction section is pumped into the light phase zone of a 5-stage centrifugal extractor connected in series at a flow rate of 300 ml / min, and deionized water is pumped into the light and heavy phase zones of the 5-stage centrifugal extractor connected in series at a flow rate of 20 ml / min for washing, to obtain residual acid and washing extractant. The residual acid is used to produce high-end fertilizers, and the washing extractant is pumped into the centrifugal back-extraction section. The centrifugal washing temperature is maintained at 90℃, and the speed of the centrifugal extractor is adjusted to 2200 r / min.

[0132] (4) Centrifugal back-extraction: The washing extractant is pumped into the light phase zone of a 5-stage centrifugal extractor connected in series at a flow rate of 300 ml / min, and deionized water is pumped into the heavy phase zone of the same 5-stage centrifugal extractor at a flow rate of 50 ml / min for back-extraction, yielding back-extracted acid and extractant. Depending on actual usage requirements, a portion of the back-extracted acid can be returned to the centrifugal washing process as washing phosphoric acid to replace deionized water, while the other portion is concentrated to obtain purified phosphoric acid. The extractant is returned to the centrifugal extraction section for recycling. The back-extraction temperature is 60℃, and the centrifugal extractor speed is 1000 r / min. The main components of the back-extracted acid are shown in Table 18. This comparison altered the process parameters of centrifugal extraction, centrifugal washing, and centrifugal back-extraction, resulting in severe emulsification of the acid and extractant, incomplete phase separation, decreased washing efficiency, and reduced removal rate of impurity ions.

[0133] Table 18 Main Components of Re-extractable Acid

[0134]

[0135] As can be seen from the comparison of Comparative Examples 2-7, changing the process parameters of centrifugal extraction, centrifugal washing, and centrifugal back-extraction in this invention significantly affects the phase separation effect and purification efficiency, leading to increased emulsification, decreased impurity removal rate, and ultimately affecting the quality of purified phosphoric acid. Only by maintaining the centrifugal speed and temperature parameters specified in this invention can emulsification be effectively avoided, ensuring thorough phase separation, maintaining high washing efficiency and impurity ion removal rate, thereby guaranteeing the stable quality of purified phosphoric acid. Even slight deviations in process parameters can lead to system imbalance, affecting the continuity and efficiency of the entire extraction-washing-back-extraction process, and consequently affecting the purity of the final product.

[0136] Comparative Example 8

[0137] The existing phosphoric acid purification process references the process flow of application number CN201610517719.1 for the purification of crude phosphoric acid. The raw material crude phosphoric acid is the same as that used in Example 1. The purification effect is shown in Table 19:

[0138] Table 19 Main Components of Purifying Acid

[0139]

[0140] Compared to the process of this invention, this method lacks effective phase dispersion control in the extraction and washing stages, resulting in low mass transfer efficiency, severe emulsification, and failure to achieve sufficient separation during the back-extraction process, thus leading to high levels of impurity residue.

[0141] It should be noted that the above embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

Claims

1. A wet phosphoric acid purification method based on multi-stage centrifugal extraction, characterized in that, Includes the following steps: (1) Sequential pretreatment: Crude phosphoric acid is pretreated by one-pot method. The crude phosphoric acid to be treated is placed in a container and H2O2 is added first for decolorization. Then sodium carbonate, calcium carbonate and sodium sulfide nonahydrate are added for defluorination, desulfurization and dearsenic removal. After stirring at 60-70℃, the solution is filtered to obtain phosphoric acid clear solution. (2) Centrifugal extraction: Phosphate solution and extractant are pumped into a 5-stage centrifugal extractor in series. After centrifugal extraction, the light and heavy phases are separated to obtain saturated extractant and residual acid. The residual acid from the extraction process is used to produce compound fertilizer, and the saturated extractant is pumped into the centrifugal washing section. (3) Centrifugal washing: Deionized water and saturated extractant obtained from the centrifugal extraction section are sequentially pumped into a 5-stage series centrifugal extractor for washing to obtain residual acid and washing extractant. The residual acid is used to produce high-end fertilizers, and the washing extractant is pumped into the centrifugal back-extraction section. (4) Centrifugal back-extraction: Deionized water and washing extractant are pumped into a 5-stage centrifugal extractor in series for back-extraction to obtain back-extracted acid and extractant. The back-extracted acid is concentrated to obtain purified phosphoric acid. In centrifugal extraction, the extraction temperature should be ≤40℃ and the centrifugation speed should be ≤1200 rpm. During centrifugal washing, the washing temperature is 50-80℃ and the centrifugal speed is 1000-2000 rpm; during centrifugal back-extraction, the back-extraction temperature is ≥80℃ and the centrifugal speed is ≥1500 rpm.

2. The wet phosphoric acid purification method based on multi-stage centrifugal extraction according to claim 1, characterized in that, The amount of H2O2 used is 1-3% of the mass of crude phosphoric acid, the decolorization reaction time is 0.5-1h, and the decolorization reaction temperature is 60-70℃; the amount of sodium carbonate added is 0.6-1.0 times the molar amount of fluorine in crude phosphoric acid, the amount of calcium carbonate added is 0.8-1.0 times the molar amount of sulfate in crude phosphoric acid, and the amount of sodium sulfide nonahydrate added is 1.0-1.2 times the molar amount of arsenic in crude phosphoric acid; the defluorination, desulfurization and dearsenic removal reaction time is 2-4h.

3. The wet phosphoric acid purification method based on multi-stage centrifugal extraction according to claim 1, characterized in that, In the centrifugal extraction, the extractant is obtained by mixing tributyl phosphate and sulfonated kerosene in a volume ratio of 5:2.

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