A method for purifying and removing impurities from wet-process phosphoric acid raffinate

Abstract

The present invention discloses a method for purifying and removing impurities from wet-process phosphoric acid raffinate, comprising the following steps: S1: taking wet-process phosphoric acid raffinate, preheating it to 55°C to 75°C, and setting it aside; S2: uniformly mixing dimethyl sulfoxide and tributyl phosphate to obtain an extractant; S3: adding a precipitation solvent and the extractant from step S2 to the raffinate from step S1, stirring and mixing; S4: cooling it to 35°C to 45°C and performing ultrasonic treatment; S5: washing and stripping the extract to obtain purified acid. The present invention addresses the problems of the solvent precipitation method, such as slow reaction, long time consumption, small generated crystal particles, and difficulty in separation. The method is modified to accelerate the reaction process, generate large precipitate particles, and achieve strong cohesion, making separation and removal easier.

Description

Technical Field

[0001] The invention relates to the technical field of calcium carbonate preparation, and in particular to a method for purifying and removing impurities from wet-process phosphoric acid raffinate. Background Art

[0002] Phosphoric acid is a commonly used chemical material in the chemical industry and is widely used in industries such as fertilizers, pharmaceuticals, and new energy materials (referring to lithium iron phosphate). In industrial production, the production process of phosphoric acid is divided into thermal process and wet process. The commonly used method of thermal phosphoric acid production is to use high-purity yellow phosphorus to burn in air to produce binary phosphorus pentoxide (P4O 10 ), bimolecular phosphorus pentoxide (P4O 10 ) is further hydrated to form phosphoric acid (H3PO4). This production process has high raw material requirements and is very energy-intensive. Currently, the industry's wet-process phosphoric acid production typically uses the hemihydrate-dihydrate method, a proven method that is both cost-effective (approximately 25% lower than the thermal method) and energy-efficient. Purification of wet-process phosphoric acid is imperative to replace thermal phosphoric acid. The main raw materials for wet-process phosphoric acid production are phosphate rock and sulfuric acid. During the acidification of phosphate rock with sulfuric acid, metallic impurities present in the phosphate rock dissolve into the phosphoric acid solution. The resulting phosphoric acid solution, in addition to P2O5 as its primary component, also contains numerous impurities such as Fe, Mg, Al, Ca, F, and As. Therefore, the phosphoric acid produced by the wet-process phosphoric acid process is of low purity and has limited applications. It is generally used as a phosphate fertilizer and rarely in high-value-added industries such as new energy battery materials. To obtain higher-purity, lower-impurity phosphoric acid from the wet-process phosphoric acid process, solvent extraction purification is required. Purifying wet-process phosphoric acid using solvent extraction, in addition to producing high-purity industrial phosphoric acid (or food-grade phosphoric acid), also produces a large amount of raffinate acid with a high impurity content. This high impurity content in the raffinate acid results in low utilization, leading to a large accumulation of raffinate acid that cannot be consumed, thus impacting production efficiency and economic benefits. Therefore, in this context, it is necessary to explore and invent a method for removing the raffinate acid impurities generated during the wet-process phosphoric acid purification process and subsequently utilizing it. This method would improve the quality of phosphoric acid, remove impurities, reduce phosphorus loss, and increase the economic benefits of the enterprise.

[0003] Chinese patent CN101708830B discloses a method for purifying raffinate acid, comprising the following steps: preheating raffinate acid containing 40.0% to 47.0% P2O5 by weight and 1.6% to 2.8% magnesium by weight to 50-75°C, then adding a mixed solvent 3-5 times the volume of the raffinate acid under stirring; adding the solvent for 0-40 minutes, and continuing the reaction for 30-90 minutes after the addition is complete; allowing the mixture to stand and cool to room temperature to 35°C, then filtering or decanting to obtain a clear solution. The clear solution is then distilled under a vacuum of 0.08 MPa and a temperature of 60-80°C to recover alcohol, yielding purified acid. This patent utilizes a solvent precipitation method, which is characterized by excellent magnesium removal, low energy consumption, and minimal solvent loss. However, the reaction is slow and time-consuming, and the resulting crystals are small, making separation difficult.

[0004] Chinese patent CN115872377A discloses a method for removing impurities from high-magnesium phosphoric acid, which relates to the field of wet-process phosphoric acid removal and industrial-grade phosphoric acid processing. The method for removing impurities from high-magnesium phosphoric acid comprises the following steps: a) reacting phosphoric acid with sufficient precipitant solution to make SiF6 2- The anions react with the metal cations in the acid to form a precipitate to obtain a reaction solution. The method for removing impurities from high-magnesium phosphoric acid is carried out by adding different concentrations of precipitant fluorosilicic acid to wet-process phosphoric acid with a high magnesium content. Fluorosilicic acid is a by-product of phosphoric acid production and is reused to reduce the introduction of external elements. After a series of filtration, evaporation, crystallization and centrifugation steps, the final magnesium removal rate reaches 60%-88%, the phosphorus yield reaches more than 90-95%, the P2O5 concentration reaches at least 52% and the residual fluorine content in the acid is less than 1%. The acid has good fluidity and a bright color. This patent adopts a chemical precipitation method, which has the advantages of high magnesium removal rate in wet-process phosphoric acid, simple process control, and industrialization. However, if you want to completely remove impurities, the precipitant will generally be excessive, and this process will introduce new impurities SiF6 2- , which increases the difficulty of removing impurities.

[0005] Chinese patent CN116022752A discloses a process for purifying acid using a composite extractant. The process involves diluting raffinate acid, originally at a 40% mass concentration, to a concentration of 20-25% by mass, followed by filtration to remove visible particulate matter. The diluted and filtered raffinate acid is then mixed with an extractant, extracting to produce an organic phase 1 and an aqueous phase 1. The extractant is a mixture of an acidic extractant and a diluent. The organic phase 1 is then stripped at least three times with a stripping solution. After stripping, the stripping solution is allowed to stand and separate to produce an organic phase 2 and an aqueous phase 2. The resulting organic phase 2 is the purified, regenerated extractant. The stripping solution is a strong or medium-strong acid. This patent utilizes an extraction method to remove iron, aluminum, magnesium, and manganese ions from the raffinate acid, but this inevitably removes some phosphoric acid, resulting in phosphoric acid loss. Summary of the Invention

[0006] The present invention addresses the problems of the solvent precipitation method, such as slow reaction, long time consumption, small generated crystal particles, and great difficulty in separation. The method is modified to accelerate the reaction process, and the generated precipitate particles are large, highly cohesive, and easy to separate and remove.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for purifying and removing impurities from wet-process phosphoric acid raffinate comprises the following steps:

[0009] S1: Take the residual acid from wet-process phosphoric acid and preheat it to 55°C to 75°C for later use;

[0010] S2: Evenly mix dimethyl sulfoxide and tributyl phosphate to obtain an extractant;

[0011] S3: adding the precipitation solvent and the extractant of step S2 to the raffinate of step S1, stirring and mixing;

[0012] S4: Cooling to 35-45°C and ultrasonic treatment;

[0013] S5: taking the extract and performing washing and back-extraction to obtain purified acid.

[0014] Preferably, in step S2, the amount of dimethyl sulfoxide added is 5-15% by weight of the extractant.

[0015] Preferably, in step S2, the precipitation solvent is a mixture of ethanol and isopropanol.

[0016] Preferably, the volume ratio of ethanol to isopropanol is 1 to 4:1.

[0017] Preferably, in step S2, the amount of the precipitation solvent added is 2 to 2.5 times the volume of the raffinate.

[0018] Preferably, in step S3, the stirring speed is 100-300 r / min.

[0019] Preferably, in step S3, the volume concentration of ethanol is 90-98%.

[0020] Preferably, in step S3, the amount of the extractant added is such that the ratio is 3 to 5.

[0021] Preferably, in step S2, the stirring time is 10 to 30 minutes.

[0022] Preferably, in step S2, the ultrasonic power is 30 to 80 W, the frequency is 10 to 30 kHz, and the ultrasonic treatment time is 15 to 30 min.

[0023] Compared with the prior art, the advantages and beneficial effects of the present invention include:

[0024] 1. The present invention addresses the problems of slow reaction, long time consumption, small crystal particles generated by solvent precipitation method and great difficulty in separation. The solvent precipitation method and the extraction method are combined to modify the extractant and specific process steps respectively. A mixture of dimethyl sulfoxide and tributyl phosphate is used as the extractant. Combined with ultrasonic treatment, the reaction process can be accelerated, and the generated precipitate particles are large and highly cohesive, which is convenient for separation and removal. The extraction stratification and directional extraction of the extractant are promoted, thereby greatly improving the impurity removal rate.

[0025] 2, among the present invention, adopt tributyl phosphate as extraction agent, because its viscosity is larger, the dimethyl sulfoxide (DMSO) of adding has the characteristics of high polarity, tributyl phosphate can be diluted, and can form hydrogen bond with-OH group of tributyl phosphate, thereby reduce the effect of tributyl phosphate to metal ion, increased the selectivity to metal ion, reduced the distribution ratio of metal ion in organic phase and aqueous phase, and dimethyl sulfoxide (DMSO) itself can be miscible with water, be present in the boundary of aqueous phase and oil phase, can effectively shorten the phase separation time, improve phase separation clarity.Ethanol and isopropyl alcohol react with water as precipitation solvent, and metal salt crystallization is separated out, and dimethyl sulfoxide (DMSO) has very strong water absorbency, can greatly accelerate crystallization, and impels crystallization more thoroughly.Ultrasound action not only can promote stratification, and to promoting crystallization there is remarkable effect, and ultrasonic oscillation effect can make metal ion effectively peel off, fast nucleation, and form the crystal of larger particle under low frequency condition, each crystal gathers together again, forms larger particle, is convenient to removing. Dimethyl sulfoxide and ultrasound have a synergistic effect in promoting crystallization and extraction, and ultimately synergistically purify and remove impurities, thereby improving the yield of phosphoric acid. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] The wet-process phosphoric acid raffinate used was brown-yellow and viscous. A small amount of sediment would be found at the bottom of the container after long-term standing. The amount used was 300 g. Its composition is shown in Table 1.

[0028] Table 1

[0029] <![CDATA[ω(P2O5) / %]]> <![CDATA[ω(Al 3+ ) / %]]> <![CDATA[ω(Fe 3+ ) / %]]> <![CDATA[ω(Mg 2+ ) / %]]> <![CDATA[ω(SO4 2－ ) / %]]> 45.66 0.47 0.79 2.56 1.77

[0030] Example 1

[0031] A method for purifying and removing impurities from wet-process phosphoric acid raffinate comprises the following steps:

[0032] S1: Take the raffinate from wet-process phosphoric acid and preheat it to 55°C for later use;

[0033] S2: Evenly mix dimethyl sulfoxide and tributyl phosphate to obtain an extractant; wherein the amount of dimethyl sulfoxide added is 5% by weight of the extractant;

[0034] S3: adding a precipitation solvent obtained by mixing 90% by volume ethanol and isopropanol in a volume ratio of 1:1 and the extractant of step S2 to the raffinate acid of step S1, and stirring and mixing; the stirring speed is 300 r / min; the amount of precipitation solvent added is 2 times the volume of the raffinate acid, and the amount of extractant added is such that the phase ratio is 3;

[0035] S4: Cool to 35°C and ultrasonicate at a power of 30 W and a frequency of 10 kHz for 10 min;

[0036] S5: taking the extract and performing washing and back-extraction to obtain purified acid.

[0037] Example 2

[0038] A method for purifying and removing impurities from wet-process phosphoric acid raffinate comprises the following steps:

[0039] S1: Take the raffinate from wet-process phosphoric acid and preheat it to 60°C for later use;

[0040] S2: Evenly mix dimethyl sulfoxide and tributyl phosphate to obtain an extractant; wherein the amount of dimethyl sulfoxide added is 10% by weight of the extractant;

[0041] S3: adding a precipitation solvent obtained by mixing 95% by volume ethanol and isopropanol in a volume ratio of 2:1 and the extractant of step S2 to the raffinate acid of step S1, and stirring and mixing; the stirring speed is 100 r / min; the amount of precipitation solvent added is 2.2 times the volume of the raffinate acid, and the amount of extractant added is such that the phase ratio is 4;

[0042] S4: Cool to 40°C and ultrasonicate for 30 min at a power of 40 W and a frequency of 20 kHz;

[0043] S5: taking the extract and performing washing and back-extraction to obtain purified acid.

[0044] Example 3

[0045] A method for purifying and removing impurities from wet-process phosphoric acid raffinate comprises the following steps:

[0046] S1: Take the raffinate from wet-process phosphoric acid and preheat it to 65°C for later use;

[0047] S2: Evenly mix dimethyl sulfoxide and tributyl phosphate to obtain an extractant; wherein the amount of dimethyl sulfoxide added is 15% by weight of the extractant;

[0048] S3: adding a precipitation solvent obtained by mixing 98% by volume ethanol and isopropanol in a volume ratio of 3:1 and the extractant of step S2 to the raffinate acid of step S1, and stirring and mixing; the stirring speed is 300 r / min; the amount of precipitation solvent added is 2.4 times the volume of the raffinate acid, and the amount of extractant added is such that the phase ratio is 4;

[0049] S4: Cool to 40°C and ultrasonicate for 20 min at a power of 50 W and a frequency of 30 kHz;

[0050] S5: taking the extract and performing washing and back-extraction to obtain purified acid.

[0051] Example 4

[0052] A method for purifying and removing impurities from wet-process phosphoric acid raffinate comprises the following steps:

[0053] S1: Take the raffinate from wet-process phosphoric acid and preheat it to 70°C for later use;

[0054] S2: Evenly mix dimethyl sulfoxide and tributyl phosphate to obtain an extractant; wherein the amount of dimethyl sulfoxide added is 10% by weight of the extractant;

[0055] S3: adding a precipitation solvent obtained by mixing 95% by volume ethanol and isopropanol in a volume ratio of 4:1 and the extractant of step S2 to the raffinate acid of step S1, and stirring and mixing; the stirring speed is 200 r / min; the amount of precipitation solvent added is 2.5 times the volume of the raffinate acid, and the amount of extractant added is such that the phase ratio is 4;

[0056] S4: Cool to 40°C and ultrasonicate for 15 min at a power of 40 W and a frequency of 20 kHz;

[0057] S5: taking the extract and performing washing and back-extraction to obtain purified acid.

[0058] Example 5

[0059] A method for purifying and removing impurities from wet-process phosphoric acid raffinate comprises the following steps:

[0060] S1: Take the raffinate from wet-process phosphoric acid and preheat it to 60°C for later use;

[0061] S2: Evenly mix dimethyl sulfoxide and tributyl phosphate to obtain an extractant; wherein the amount of dimethyl sulfoxide added is 12% by weight of the extractant;

[0062] S3: adding a precipitation solvent obtained by mixing 98% by volume ethanol and isopropanol in a volume ratio of 2:1 and the extractant of step S2 to the raffinate acid of step S1, and stirring and mixing; the stirring speed is 200 r / min; the amount of precipitation solvent added is 2.1 times the volume of the raffinate acid, and the amount of extractant added is such that the phase ratio is 5;

[0063] S4: Cool to 35°C and ultrasonicate at a power of 60 W and a frequency of 10 kHz for 10 min;

[0064] S5: taking the extract and performing washing and back-extraction to obtain purified acid.

[0065] Example 6

[0066] A method for purifying and removing impurities from wet-process phosphoric acid raffinate comprises the following steps:

[0067] S1: Take the raffinate from wet-process phosphoric acid and preheat it to 55°C for later use;

[0068] S2: Evenly mix dimethyl sulfoxide and tributyl phosphate to obtain an extractant; wherein the amount of dimethyl sulfoxide added is 15% by weight of the extractant;

[0069] S3: adding a precipitation solvent obtained by mixing 90% by volume ethanol and isopropanol in a volume ratio of 1:1 and the extractant of step S2 to the raffinate acid of step S1, and stirring and mixing; the stirring speed is 100 r / min; the amount of precipitation solvent added is 2.5 times the volume of the raffinate acid, and the amount of extractant added is such that the phase ratio is 3 to 5;

[0070] S4: Cool to 45°C and ultrasonicate for 30 min at a power of 80 W and a frequency of 30 kHz;

[0071] S5: taking the extract and performing washing and back-extraction to obtain purified acid.

[0072] Comparative Example 1

[0073] S1: Take the raffinate from wet-process phosphoric acid and preheat it to 70°C for later use;

[0074] S2: Tributyl phosphate as the extractant;

[0075] S3: adding a precipitation solvent obtained by mixing 95% by volume ethanol and isopropanol in a volume ratio of 4:1 and the extractant of step S2 to the raffinate acid of step S1, and stirring and mixing; the stirring speed is 200 r / min; the amount of precipitation solvent added is 2.5 times the volume of the raffinate acid, and the amount of extractant added is such that the phase ratio is 4;

[0076] S4: Cool to 40°C and let stand for 15 minutes;

[0077] S5: taking the extract and performing washing and back-extraction to obtain purified acid.

[0078] Comparative Example 2

[0079] S1: Take the raffinate from wet-process phosphoric acid and preheat it to 70°C for later use;

[0080] S2: Tributyl phosphate as the extractant;

[0081] S3: adding a precipitation solvent obtained by mixing 95% by volume ethanol and isopropanol in a volume ratio of 4:1 and the extractant of step S2 to the raffinate acid of step S1, and stirring and mixing; the stirring speed is 200 r / min; the amount of precipitation solvent added is 2.5 times the volume of the raffinate acid, and the amount of extractant added is such that the phase ratio is 4;

[0082] S4: Cool to 40°C and ultrasonicate for 15 min at a power of 40 W and a frequency of 20 kHz;

[0083] S5: taking the extractant for washing and back-extraction to obtain purified acid.

[0084] Comparative Example 3

[0085] S1: Take the raffinate from wet-process phosphoric acid and preheat it to 70°C for later use;

[0086] S2: Evenly mix dimethyl sulfoxide and tributyl phosphate to obtain an extract; wherein the amount of dimethyl sulfoxide added is 10% by weight of the extract;

[0087] S3: adding a precipitation solvent obtained by mixing 95% by volume ethanol and isopropanol in a volume ratio of 4:1 and the extract from step S2 to the raffinate acid from step S1, and stirring and mixing; the stirring speed is 200 r / min; the amount of precipitation solvent added is 2.5 times the volume of the raffinate acid, and the amount of extract added is such that the phase ratio is 4;

[0088] S4: Cool to 40°C and let stand for 15 minutes;

[0089] S5: taking the extract and performing washing and back-extraction to obtain purified acid.

[0090] Comparative experiment

[0091] The methods of Examples 1 to 6 and Comparative Examples 1 to 3 were used to treat wet-process phosphoric acid raffinate, respectively. The crystallization and stratification after treatment were observed, the precipitate was weighed, and the P2O5 yield and impurity ion removal rate were calculated.

[0092] Wherein, P2O5 yield (%) = P2O5 net yield / raffinate raw material weight * 100;

[0093] Impurity ion removal rate (%) = (raffinate acid raw material weight * impurity ion content - purified acid weight * purified acid impurity ion content) / (raffinate acid raw material weight * impurity ion content) * 100.

[0094] The results are shown in Table 2.

[0095] Table 2

[0096] Group Precipitation weight / g <![CDATA[P2O5 yield / %]]> <![CDATA[Al 3+ Removal rate / %]]> <![CDATA[Fe 3+ Removal rate / %]]> <![CDATA[Mg 2+ Removal rate / %]]> Example 1 180 42.08 80.4 90.6 73.4 Example 2 182 42.13 81.3 91.2 74.3 Example 3 183 43.25 82.9 92.0 76.2 Example 4 185 44.78 85.5 92.5 78.8 Example 5 184 43.44 83.1 91.5 77.0 Example 6 182 42.59 82.7 91.4 75.9 Comparative Example 1 170 38.43 78.4 88.9 65.2 Comparative Example 2 175 40.12 80.2 90.2 70.6 Comparative Example 3 178 41.24 82.7 90.8 71.9

[0097] As can be seen from the above table, when the methods of Examples 1 to 6 of the present invention are used to treat the raffinate, stratification and precipitate formation can be clearly observed, and the particles are relatively large and aggregated. The precipitate weight is above 180 g, the P2O5 yield is high, and the impurity removal rate is high, which can meet the requirements for qualified products of thermal phosphoric acid.

[0098] Comparative Example 1 is based on Example 4, but no dimethyl sulfoxide is added and no ultrasonic treatment is performed. The amount of precipitate generated is small and relatively dispersed, the boundary between the layers is not as clear as that in Example 4, and the impurity removal rate is also low, especially the removal rate of magnesium ions, which decreases significantly.

[0099] Comparative Examples 2 and 3, based on Comparative Example 1, respectively added dimethyl sulfoxide and performed ultrasonic treatment. The amount of precipitate generated increased compared with Comparative Example 1, the particles were relatively large and aggregated, and the impurity removal rate was also improved accordingly. However, there was still a large gap compared with Example 4.

[0100] The above description is a further detailed description of the present invention in conjunction with specific / preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. Those skilled in the art of the present invention may make various substitutions or modifications to the described embodiments without departing from the scope of the present invention, and such substitutions or modifications should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for purifying and removing impurities from wet-process phosphoric acid raffinate, characterized in that: The following steps are involved: S1: Take the residual acid from wet-process phosphoric acid and preheat it to 55°C to 75°C for later use; S2: Evenly mix dimethyl sulfoxide and tributyl phosphate to obtain an extractant; S3: adding a precipitation solvent and the extractant of step S2 to the raffinate of step S1, stirring and mixing; the precipitation solvent is a mixture of ethanol and isopropanol; S4: Cooling to 35-45°C and ultrasonic treatment; S5: taking the extract and performing washing and back-extraction to obtain purified acid.

2. The method for purifying and removing impurities from wet-process phosphoric acid raffinate according to claim 1, wherein: In step S2, the amount of dimethyl sulfoxide added is 5-15% of the weight of the extractant.

3. The method for purifying and removing impurities from wet-process phosphoric acid raffinate according to claim 1, wherein: The volume ratio of ethanol to isopropanol is 1 to 4:

1.

4. The method for purifying and removing impurities from wet-process phosphoric acid raffinate according to claim 1, wherein: In step S3, the amount of the precipitation solvent added is 2 to 2.5 times the volume of the raffinate.

5. The method for purifying and removing impurities from wet-process phosphoric acid raffinate according to claim 1, wherein: In step S3, the stirring speed is 100 to 300 r / min.

6. The method for purifying and removing impurities from wet-process phosphoric acid raffinate according to claim 1, wherein: In step S3, the volume concentration of ethanol is 90-98%.

7. The method for purifying and removing impurities from wet-process phosphoric acid raffinate according to claim 1, wherein: In step S3, the amount of the extractant added is such that the ratio is 3 to 5.

8. The method for purifying and removing impurities from wet-process phosphoric acid raffinate according to claim 1, characterized in that: In step S3, the stirring time is 10 to 30 minutes.

9. The method for purifying and removing impurities from wet-process phosphoric acid raffinate according to claim 1, characterized in that: In step S4, the ultrasonic power is 30 to 80 W, the frequency is 10 to 30 kHz, and the ultrasonic treatment time is 15 to 30 minutes.