Method and device for purifying and recovering phosphoric acid from phosphoric acid waste liquid by whole membrane process

Abstract

The invention discloses a method for purifying and recovering phosphoric acid from phosphoric acid waste liquid by a whole membrane method, which mainly comprises a pretreatment device for removing suspended matters and solid particle impurities in the phosphoric acid waste liquid; the waste phosphoric acid separation and purification device is used for removing metal salt impurities in the phosphoric acid waste liquid through a three-stage separation membrane; the waste phosphoric acid dialysis and purification device is used for recovering phosphoric acid from concentrated acid generated by the separation and purification device through a two-stage dialysis membrane; the acid concentration device is used for concentrating and reducing dilute phosphoric acid generated by the separation and purification device and the dialysis and purification device through a concentration membrane; the waste acid storage tank and the dilution tank are used for homogenizing and diluting the phosphoric acid waste liquid; through the method, the final phosphoric acid recovery rate is greater than 90%, and the removal rate of metal salt impurities in the recovered phosphoric acid is greater than 95%.

Description

Technical Field

[0001] The invention relates to a method for purifying phosphoric acid waste liquid and recovering phosphoric acid, and belongs to the field of water treatment. Background Art

[0002] In recent years, the phosphorus chemical industry, lithium iron phosphate battery, and corrosion foil industries have developed rapidly. At present, the phosphoric acid recovery process faces the problems of low acid recovery rate, low quality of recovered phosphoric acid, and high energy consumption of the recovery process. Patent CN 103030123 A uses a process combining pressure separation membrane and resin to purify and recover waste phosphoric acid, but the recovered phosphoric acid concentration is low, only about 5%, and the resin is used to remove high-concentration Al in the waste acid. 3+ The resin needs to be regenerated frequently, and there is still about 10% Al in the recovered acid. 3+ If the waste acid contains multiple heavy metal ions, multiple resins need to be used in combination. Patent CN 111268848 A uses anion exchange membrane and low-temperature evaporation to recover phosphoric acid. Although the removal rate of metal salts is ≥99.6%, the phosphoric acid recovery rate is only 70%, which is a low recovery rate. Patent CN 116621136 A uses anion and cation resins and negative pressure evaporation to recover waste phosphoric acid. Although the phosphoric acid yield is ≥90% and the removal rate of metal ions and other impurities is ≥85%, sulfuric acid is required to regenerate the resin during the recovery process, and the recovery of phosphoric acid produces waste sulfuric acid.

[0003] The waste phosphoric acid recovery processes introduced in the above three patents all have their own shortcomings, and there is an urgent need for a clean and efficient phosphoric acid recovery method with high phosphoric acid recovery rate, high metal salt impurity removal rate and low energy consumption. Summary of the invention

[0004] The invention aims to solve the problems of low phosphoric acid recovery rate, low metal salt impurity removal rate and high energy consumption in the existing waste phosphoric acid recovery process, and realizes efficient removal of metal salt impurities in waste phosphoric acid and efficient recovery of phosphoric acid through the integration of a pretreatment device, a separation and purification device, an acid dialysis device and an acid concentration device.

[0005] A method for purifying and recovering phosphoric acid from phosphoric acid waste liquid by a full membrane method comprises the following steps:

[0006] Step 1, pre-filtering the phosphoric acid waste liquid to remove suspended matter and solid particle impurities in the phosphoric acid waste liquid;

[0007] Step 2, after diluting the obtained waste liquid, filtering it with a nanofiltration membrane to allow phosphoric acid to pass through and to retain divalent or polyvalent metal cations;

[0008] Step 3, concentrating the permeate of the nanofiltration membrane to obtain recovered phosphoric acid.

[0009] In the step 2, the dilution end point is 10wt% to 20wt%.

[0010] In the step 2, when the nanofiltration membrane is used for filtration treatment, one-stage, two-stage or multi-stage filtration is adopted.

[0011] When two-stage or multi-stage filtration is used, the concentrated liquid from the next stage of nanofiltration membrane is returned to the previous stage for further filtration.

[0012] The concentrate from the first-stage nanofiltration membrane is diluted and then dialyzed using a nanofiltration membrane.

[0013] The diluent used in the dialysis process is the fresh water produced in the acid concentration process, and the end point of the dilution is 10wt% to 20wt%.

[0014] The dialysis process adopts a two-stage dialysis, and the concentrated solution of the previous stage is diluted before the next stage of dialysis.

[0015] A precipitant is added to the concentrated solution obtained during the dialysis process to precipitate the metal ions; the precipitant is an alkali.

[0016] The ratio of dilute acid to concentrated acid produced by the nanofiltration membrane is greater than 4:1, and the retention rate of divalent and above metal ions in phosphoric acid waste liquid is ≥95%.

[0017] In step 3, the concentration membrane used in the concentration process is an acid-resistant reverse osmosis membrane, which can increase the concentration of phosphoric acid to 25wt% to 35wt%.

[0018] A device for purifying phosphoric acid waste liquid by full membrane method and recovering phosphoric acid, comprising:

[0019] A pre-filter is used for pre-filtering the phosphoric acid waste liquid to remove suspended matter and solid particle impurities in the phosphoric acid waste liquid;

[0020] A first dilution tank, connected to the pre-filter, for diluting the filtrate obtained in the pre-filter;

[0021] A nanofiltration membrane device, connected to the first dilution tank, is used to perform nanofiltration treatment on the diluted wastewater, so that phosphoric acid can pass through and divalent or multivalent metal cations can be retained;

[0022] A concentration device, connected to the nanofiltration membrane device, used for concentrating the permeate in the nanofiltration membrane device;

[0023] The dialysis device is connected to the interception side of the nanofiltration membrane device and is used to perform dialysis treatment on the nanofiltration concentrate to obtain phosphoric acid.

[0024] The osmotic side of the dialysis device is connected to a concentrating device.

[0025] The nanofiltration membrane in the nanofiltration membrane device is single-stage, double-stage or multi-stage.

[0026] The dialysis device is equipped with a nanofiltration membrane.

[0027] The dialysis device also includes a second dilution tank connected to the retentate side of the nanofiltration membrane device and used for diluting the concentrated solution entering the dialysis device.

[0028] One or two stages are used in the dialysis device.

[0029] The permeate side of the concentration device is connected to the feed side of the dialysis device for dialyzing the dilute liquid obtained from the permeate side.

[0030] Beneficial Effects

[0031] 1. Use three-stage separation and purification membrane to remove impurities from phosphoric acid waste liquid, and the removal rate of divalent and above impurity metal ions is greater than 95%;

[0032] 2. Use a two-stage acid dialysis membrane to dialysis-purify the concentrated acid produced by the separation and purification membrane, so that the overall recovery rate of phosphoric acid is greater than 90%; 3. Concentrate the dilute acid after separation and purification and the dilute acid after dialysis purification through acid-resistant reverse osmosis, and the concentration of the recovered phosphoric acid can reach 25% to 35%;

[0033] 4. The full membrane method is used to recover phosphoric acid. Only pure water is used in the process, and no new impurities are introduced. The recovery process is clean and efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is the flow chart of this patent;

[0035] Figure 2 It is the device diagram of this patent.

[0036] 1. Pre-filter; 2. First dilution tank; 3. Nanofiltration membrane device; 4. Concentration device; 5. Dialysis device; 6. Second dilution tank; 7. Nanofiltration membrane. DETAILED DESCRIPTION

[0037] This patent discloses a method for purifying and recovering phosphoric acid from phosphoric acid waste liquid by full membrane method, which mainly includes 1. pretreatment system, 2. phosphoric acid separation and purification system, 3. phosphoric acid dialysis purification system, and 4. dilute phosphoric acid concentration system. First, the phosphoric acid waste liquid is pretreated with an ultrafiltration membrane to remove suspended matter and solid particle impurities in the waste liquid, the pretreated phosphoric acid waste liquid is diluted with pure water, the diluted phosphoric acid waste liquid enters the separation and purification system, and is filtered and purified with a three-stage separation and purification membrane to remove divalent and above metal impurities in the phosphoric acid waste liquid; the concentrated acid produced by the secondary separation and purification membrane is returned to the front end of the primary separation and purification membrane, the concentrated acid produced by the tertiary separation and purification membrane is returned to the front end of the secondary separation and purification membrane, and the dilute acid produced by the tertiary separation and purification membrane enters the dilute acid concentration system for concentration; the fresh water produced by the dilute phosphoric acid concentration system is used to dilute the concentrated acid produced by the primary separation and purification membrane, the dilute liquid enters the primary phosphoric acid dialysis purification membrane, the concentrated acid produced by the primary dialysis purification membrane is diluted by the fresh water produced by the dilute phosphoric acid concentration system and then enters the secondary dialysis purification membrane, and the dilute acid produced by the primary and secondary dialysis purification membranes enters the dilute phosphoric acid concentration system for concentration.

[0038] In one embodiment, the water quality of the phosphoric acid waste liquid is:

[0039] Table 1

[0040] Serial number project unit Washing water 1 Phosphoric acid wt% 30.7 2 <![CDATA[Fe 2+ / 3+ ]]> mg / L 320 3 <![CDATA[Al 3+ ]]> mg / L 200 4 <![CDATA[Ca 2+ ]]> mg / L 260 5 <![CDATA[Mg 2+ ]]> mg / L 1640 6 <![CDATA[Na + ]]> mg / L 30 7 <![CDATA[Si (calculated as SiO2)]]> mg / L 170 8 <![CDATA[K + ]]> mg / L 8 9 <![CDATA[F - ]]> mg / L 10 10 <![CDATA[SO4 2- ]]> mg / L 3700 11 <![CDATA[Cl - ]]> mg / L 20 12 As mg / L 20

[0041] The phosphoric acid concentration in phosphoric acid waste liquid is about 30wt%, and the main impurities are metal ions such as iron, aluminum, calcium, magnesium, etc. It also contains a large amount of sulfate ions and a small amount of sodium, potassium, fluorine, chlorine, and arsenic.

[0042] The method for purifying phosphoric acid waste liquid by full membrane method and recovering phosphoric acid comprises the following steps:

[0043] First, the phosphoric acid waste liquid passes through a pretreatment system to remove suspended matter and solid particle impurities. The pretreatment system uses a microfiltration or ultrafiltration membrane with an average pore size range of 50-200nm. This step of filtration uses a cross-flow filtration method, and the membrane surface flow rate can be 1-10m / s. The microfiltration or ultrafiltration membrane can be made of inorganic ceramic membrane materials and high molecular polymer materials.

[0044] Next, the phosphoric acid waste liquid after pretreatment and filtration enters the 1# dilution tank, which also includes a pump, a mechanical agitator, and a liquid level meter, and uses pure water to dilute the phosphoric acid waste liquid to 10wt%-20wt%.

[0045] The diluted phosphoric acid waste liquid enters the primary separation and purification device, which includes a pump, a safety filter and a separation and purification membrane. The function of the primary separation and purification device is to separate free phosphoric acid and divalent or higher impurity metal ions in the phosphoric acid waste liquid, and the removal rate of impurity metal ions is above 95%.

[0046] The dilute phosphoric acid produced by the primary separation and purification device enters the secondary separation and purification device, which includes a pump, a safety filter and a separation and purification membrane. The function of the secondary separation and purification device is to further remove the impurity metal ions that the primary separation and purification device has not been able to remove. The concentrated acid produced by the secondary separation and purification device is returned to the primary separation and purification device.

[0047] The dilute phosphoric acid produced by the secondary separation and purification device enters the tertiary separation and purification device, which includes a pump, a safety filter and a separation and purification membrane. The function of the tertiary separation and purification device is to further remove the impurity metal ions that the secondary separation and purification device has not been able to remove. 95% of divalent and above metal ions can be removed through the primary, secondary and tertiary separation and purification devices. The concentrated acid produced by the tertiary separation and purification device is returned to the secondary separation and purification device.

[0048] The primary, secondary and tertiary separation and purification devices use nanofiltration membranes that can withstand phosphoric acid corrosion. The membrane types include but are not limited to roll type and hollow fiber type. The membrane element desalination rate is not less than 97%, the operating temperature does not exceed 45°C, and the operating pressure is 0.1-6MPa.

[0049] The dilute phosphoric acid produced by the three-stage separation and purification device enters the acid concentration device, which includes a pump, a safety filter and an acid concentration membrane. The function of the acid concentration device is to increase the concentration of phosphoric acid. After concentration by the acid concentration device, phosphoric acid with a concentration of 25wt%-35wt% can be obtained.

[0050] The acid concentration device adopts a reverse osmosis membrane that can withstand phosphoric acid corrosion. The membrane type includes but is not limited to roll type and disc type. The desalination rate of the membrane element is not less than 97%, the operating temperature does not exceed 45°C, and the operating pressure is 0.1-6MPa.

[0051] The concentrated acid produced by the primary separation and purification device enters the 2# dilution tank, which also includes a pump, a mechanical agitator, and a liquid level meter. The concentrated acid is diluted with fresh water produced by the acid concentration device to 10wt%-20wt%.

[0052] The phosphoric acid waste liquid diluted by the 2# dilution tank enters the primary acid dialysis device, which includes a pump, a safety filter, and an acid dialysis membrane. The function of the primary acid dialysis device is to dialysis and purify the phosphoric acid in the concentrated acid produced by the primary separation and purification device, recover the phosphoric acid and remove the divalent and above impurity metal ions therein. The dilute acid produced by the primary acid dialysis device enters the acid concentration device for concentration and recovery of phosphoric acid.

[0053] The concentrated acid produced by the primary acid dialysis device enters the 3# dilution tank, which also includes a pump, a mechanical agitator, and a liquid level meter. The concentrated acid produced by the primary acid dialysis device is diluted with fresh water produced by the acid concentration device to 10wt%-20wt%.

[0054] The phosphoric acid waste liquid diluted by the 3# dilution tank enters the secondary acid dialysis device, which includes a pump, a safety filter, and an acid dialysis membrane. The function of the secondary acid dialysis device is to dialysis and purify the phosphoric acid in the concentrated acid produced by the primary acid dialysis device, recover the phosphoric acid and remove the divalent and above impurity metal ions therein. The dilute acid produced by the secondary acid dialysis device enters the acid concentrator for concentration and recovers the phosphoric acid.

[0055] The primary and secondary acid dialysis devices use a special nanofiltration membrane that can withstand phosphoric acid corrosion. The membrane types include but are not limited to roll type and hollow fiber type. The membrane element has a desalination rate of not less than 97%, an operating temperature of not more than 45°C, and an operating pressure of 0.1-6MPa.

[0056] The method of the present invention can not only recover more than 90% of phosphoric acid, but also the removal rate of divalent and above impurity metal ions in the recovered phosphoric acid reaches more than 95%, and the recovered high-quality phosphoric acid can be directly used for production.

[0057] Example 1

[0058] Phosphoric acid treatment process of full membrane phosphoric acid waste liquid purification and recovery:

[0059] The water quality is shown in Table 1.

[0060] (1) First, a 50 nm ceramic ultrafiltration membrane is used to filter the phosphoric acid waste liquid to remove suspended matter and solid particle impurities in the phosphoric acid waste liquid, with a cross-flow velocity of 2.5 m / s and a filtration pressure of 3 bar; pure water is added to the filtrate to dilute the phosphoric acid waste liquid to 14 wt %; the diluted phosphoric acid waste liquid is separated and purified by an acid-resistant nanofiltration membrane, and the first-stage control of dilute acid: concentrated acid = 4:1, the dilute acid generated by the first-stage acid-resistant nanofiltration membrane enters the second-stage acid-resistant nanofiltration membrane, and the dilute acid: concentrated acid = 4:1, and the dilute acid generated by the second-stage acid-resistant nanofiltration membrane enters the third-stage acid-resistant nanofiltration membrane, and the dilute acid: concentrated acid = 6:1.

[0061] (2) The dilute acid produced by the tertiary acid-resistant nanofiltration membrane in (1) is concentrated by an acid-resistant reverse osmosis membrane with a concentration factor of 2.2, thereby increasing the phosphoric acid concentration to 25 wt %.

[0062] (3) The concentrated acid produced by the primary acid-resistant nanofiltration membrane in (1) is diluted with fresh water produced by the acid-resistant reverse osmosis in (2) to dilute the phosphoric acid concentration to 14wt%, and the diluted solution is dialyzed and purified by the acid-resistant nanofiltration membrane to control the ratio of dilute acid to concentrated acid to 4:1. The concentrated acid produced by the primary dialysis nanofiltration membrane is diluted with fresh water produced by the acid-resistant reverse osmosis membrane in (2) to dilute the phosphoric acid concentration to 16wt%, and the dilute acid produced by the primary and secondary dialysis nanofiltration membranes enters the acid-resistant reverse osmosis membrane in (2) for concentration.

[0063] The quality of the final recovered phosphoric acid water is as follows:

[0064] Table 2 Recovered phosphoric acid water quality

[0065] project Phosphoric acid / wt% <![CDATA[Fe 2+ / 3+ / mg / L]]> <![CDATA[Al 3+ / mg / L]]> <![CDATA[Ca 2+ / mg / L]]> <![CDATA[Mg 2+ / mg / L]]> <![CDATA[Si (calculated as SiO2) / mg / L]]> <![CDATA[SO4 2- / mg / L]]> Numeric 25.4 7.3 5.4 6.2 22.1 3.7 53.3

[0066] Example 2

[0067] Phosphoric acid treatment process of full membrane phosphoric acid waste liquid purification and recovery:

[0068] The water quality is shown in Table 1.

[0069] (1) First, a 100 nm ceramic ultrafiltration membrane is used to filter the phosphoric acid waste liquid to remove suspended matter and solid particle impurities in the phosphoric acid waste liquid, with a cross-flow velocity of 3 m / s and a filtration pressure of 3 bar; pure water is added to the filtrate to dilute the phosphoric acid waste liquid to 20 wt %; the diluted phosphoric acid waste liquid is separated and purified by an acid-resistant nanofiltration membrane, and the first-stage control of dilute acid: concentrated acid = 4:1, the dilute acid generated by the first-stage acid-resistant nanofiltration membrane enters the second-stage acid-resistant nanofiltration membrane, and the dilute acid: concentrated acid = 4:1, and the dilute acid generated by the second-stage acid-resistant nanofiltration membrane enters the third-stage acid-resistant nanofiltration membrane, and the dilute acid: concentrated acid = 5:1.

[0070] (2) The dilute acid produced by the tertiary acid-resistant nanofiltration membrane in (1) is concentrated by an acid-resistant reverse osmosis membrane, with the concentration factor being 2 times, thereby increasing the phosphoric acid concentration to 30 wt%.

[0071] (3) The concentrated acid produced by the primary acid-resistant nanofiltration membrane in (1) is diluted with fresh water produced by the acid-resistant reverse osmosis in (2) to dilute the phosphoric acid concentration to 20wt%, and the diluted solution is dialyzed and purified using the acid-resistant nanofiltration membrane to control the ratio of dilute acid to concentrated acid to 4:1. The concentrated acid produced by the primary dialysis nanofiltration membrane is diluted with fresh water produced by the acid-resistant reverse osmosis membrane in (2) to dilute the phosphoric acid concentration to 18wt%, and the dilute acid produced by the primary and secondary dialysis nanofiltration membranes enters the acid-resistant reverse osmosis membrane in (2) for concentration.

[0072] The quality of the final recovered phosphoric acid water is as follows:

[0073] Table 3 Recovered phosphoric acid water quality

[0074] project Phosphoric acid / wt% <![CDATA[Fe 2+ / 3+ / mg / L]]> <![CDATA[Al 3+ / mg / L]]> <![CDATA[Ca 2+ / mg / L]]> <![CDATA[Mg 2+ / mg / L]]> <![CDATA[Si (calculated as SiO2) / mg / L]]> <![CDATA[SO4 2- / mg / L]]> Numeric 30.2 8.6 6.6 8.7 27.1 5.2 64.7

Claims

1. A method for purifying and recovering phosphoric acid from phosphoric acid waste liquid by a full membrane method, characterized in that: The steps include: Step 1, pre-filtering the phosphoric acid waste liquid to remove suspended matter and solid particle impurities in the phosphoric acid waste liquid; Step 2, after diluting the obtained waste liquid, filtering it with a nanofiltration membrane to allow phosphoric acid to pass through and to retain divalent or polyvalent metal cations; Step 3, concentrating the permeate of the nanofiltration membrane to obtain recovered phosphoric acid.

2. The method for purifying and recovering phosphoric acid from phosphoric acid waste liquid by full membrane method according to claim 1, characterized in that: In the step 2, the dilution end point is 10wt% to 20wt%; when the nanofiltration membrane is used for filtration, one-stage, two-stage or multi-stage filtration is adopted.

3. The method for purifying and recovering phosphoric acid from phosphoric acid waste liquid by full membrane method according to claim 2, characterized in that: When two-stage or multi-stage filtration is used, the concentrated liquid from the next stage of nanofiltration membrane is returned to the previous stage for further filtration.

4. The method for purifying and recovering phosphoric acid from phosphoric acid waste liquid by full membrane method according to claim 1, characterized in that: The concentrate from the first-stage nanofiltration membrane is diluted and then dialyzed using a nanofiltration membrane.

5. The method for purifying and recovering phosphoric acid from phosphoric acid waste liquid by full membrane method according to claim 4, characterized in that: The diluent used in the dialysis process is the fresh water produced in the acid concentration process, and the end point of the dilution is 10wt% to 20wt%.

6. The method for purifying and recovering phosphoric acid from phosphoric acid waste liquid by full membrane method according to claim 1, characterized in that: The dialysis process adopts two-stage dialysis, and the concentrated solution of the previous stage is diluted before the next stage of dialysis. The concentrated solution obtained in the dialysis process is added with a precipitant to precipitate the metal ions; the precipitant is an alkali.

7. The method for purifying and recovering phosphoric acid from phosphoric acid waste liquid by full membrane method according to claim 1, characterized in that: The ratio of dilute acid to concentrated acid produced by the nanofiltration membrane is greater than 4:1, and the retention rate of divalent and above metal ions in the phosphoric acid waste liquid is ≥95%; in step 3, the concentration membrane used in the concentration process is an acid-resistant reverse osmosis membrane, which can increase the phosphoric acid concentration to 25wt% to 35wt%.

8. A device for purifying and recovering phosphoric acid from phosphoric acid waste liquid by full membrane method, characterized in that: include: A pre-filter (1) is used for pre-filtering the phosphoric acid waste liquid to remove suspended matter and solid particle impurities in the phosphoric acid waste liquid; A first dilution tank (2) is connected to the pre-filter (1) and is used to dilute the filtrate obtained in the pre-filter 1; a nanofiltration membrane device (3) is connected to the first dilution tank (2) and is used to perform nanofiltration on the diluted wastewater to allow phosphoric acid to pass through and to retain divalent or polyvalent metal cations; A concentrating device (4) is connected to the nanofiltration membrane device (3) and is used to concentrate the permeate in the nanofiltration membrane device (3); The dialysis device (5) is connected to the interception side of the nanofiltration membrane device (3) and is used to perform dialysis treatment on the concentrated liquid of the nanofiltration to obtain phosphoric acid.

9. The device according to claim 8, characterized in that The permeation side of the dialysis device (5) is connected to the concentration device (4); the nanofiltration membrane in the nanofiltration membrane device (3) is single-stage, double-stage or multi-stage; and the dialysis device (5) is installed with a nanofiltration membrane (7).

10. The device according to claim 8, characterized in that The dialysis device (5) also includes a second dilution tank (6) connected to the interception side of the nanofiltration membrane device (3) for diluting the concentrated liquid entering the dialysis device (5); the dialysis device (5) adopts one or two stages; the permeation side of the concentration device (4) is connected to the feed side of the dialysis device (5) for dialyzing the dilute liquid obtained from the permeation side.

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