CN111661953A - Method for separating fluorine and phosphorus in mixed rare earth alkaline wastewater and application - Google Patents
Method for separating fluorine and phosphorus in mixed rare earth alkaline wastewater and application Download PDFInfo
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- CN111661953A CN111661953A CN202010550727.2A CN202010550727A CN111661953A CN 111661953 A CN111661953 A CN 111661953A CN 202010550727 A CN202010550727 A CN 202010550727A CN 111661953 A CN111661953 A CN 111661953A
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- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
- C02F1/442—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by nanofiltration
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
- C02F2101/10—Inorganic compounds
- C02F2101/105—Phosphorus compounds
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
- C02F2101/10—Inorganic compounds
- C02F2101/12—Halogens or halogen-containing compounds
- C02F2101/14—Fluorine or fluorine-containing compounds
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- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2209/00—Controlling or monitoring parameters in water treatment
- C02F2209/02—Temperature
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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- C02F2209/03—Pressure
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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Abstract
The invention discloses a method for separating fluorine and phosphorus in mixed rare earth alkaline wastewater, which comprises the following steps: performing membrane separation on the mixed rare earth alkaline wastewater containing fluoride ions and phosphate ions by using a nanofiltration membrane, wherein the operation temperature is 10-35 ℃, and the operation pressure is 1.0-3.5 MPa, so as to obtain permeate liquid enriched with fluoride ions and hydroxide ions and retentate enriched with phosphate ions; the mixed rare earth alkaline wastewater is alkaline wastewater containing sodium hydroxide, which is obtained by subjecting mixed rare earth concentrate to an alkaline decomposition process; in the mixed rare earth alkaline wastewater, the concentration of hydroxide ions is 0.001-1.2 mol/L, the concentration of fluoride ions is 0.001-1.6 g/L by weight of fluorine, and the concentration of phosphate ions is 0.001-1.65 g/L by weight of phosphorus. The method can separate the fluoride ions and the phosphate ions with lower concentration in the mixed rare earth alkaline wastewater. The invention also discloses the application of the nanofiltration membrane in separating fluorine and phosphorus from the mixed rare earth alkaline wastewater.
Description
Technical Field
The invention relates to a method for recovering mixed rare earth alkaline wastewater, in particular to a method for separating fluorine and phosphorus in mixed rare earth alkaline wastewater and application of a nanofiltration membrane.
Background
The Baiyunebo mixed rare earth ore is the largest mixed rare earth ore in China. The rare resources such as fluorine, phosphorus and the like which are abundant in the Baiyunebo mixed rare earth ore are associated, and the fluorine and phosphorus resources are recovered by a simple method as far as possible while the mixed rare earth ore is decomposed and the rare earth is recovered.
The alkali decomposition process is one of the decomposition processes of the Baiyunebo mixed rare earth ore. In the traditional alkali decomposition process, firstly, dilute hydrochloric acid is adopted to treat mixed rare earth ore, and impurity element calcium in the ore is removed to obtain calcium-removed ore; then, carrying out decomposition reaction on the concentrated sodium hydroxide solution and the calcium-removed ore at 140-160 ℃ to generate rare earth hydroxide, and decomposing the rare earth hydroxide by using concentrated hydrochloric acid to obtain a rare earth chloride solution. Fluorine and phosphorus enter an alkaline solution containing sodium hydroxide in the form of sodium fluoride and sodium phosphate respectively, and finally the alkaline solution is treated by lime, the fluorine and the phosphorus form secondary waste residues in the form of a mixture of calcium fluoride and calcium phosphate, and the fluorine and phosphorus resources cannot be recovered. In the process, alkaline wastewater is difficult to treat, and resources such as fluorine, phosphorus and the like are not effectively recycled.
With the continuous progress of science and technology, the application range of rare earth in high and new technologies is continuously expanded, the demand of rare earth is gradually increased year by year, the environmental protection awareness is stronger and stronger while the exploitation amount of rare earth is continuously increased, and the efficient utilization and the comprehensive utilization of resources are inevitable trends. CN102277484A discloses a method for separating and recovering sodium phosphate and sodium fluoride in an alkaline smelting process of mixed rare earth concentrate. (1) Firstly, roasting the mixed rare earth concentrate at high temperature; (2) leaching the roasted mine with hydrochloric acid to obtain acid leaching residue and acid leaching solution; (3) carrying out alkali decomposition on the acid leaching residue by using sodium hydroxide to obtain minerals subjected to alkali decomposition; (4) performing countercurrent washing on the minerals subjected to alkali decomposition by 4-6 levels; (5) heating the first-stage water washing liquid, evaporating, crystallizing and filtering to obtain sodium fluoride and filtrate after evaporating, crystallizing and filtering; (6) carrying out condensation crystallization on the filtrate obtained after evaporation crystallization filtration to obtain sodium phosphate and a liquid obtained after condensation crystallization filtration; (7) heating, evaporating and crystallizing the liquid after the condensation crystallization and filtration to obtain solid sodium hydroxide. In this patent document, only sodium fluoride and sodium phosphate in the first-stage water-washing liquid are separated. The water washing liquid in other stages is not separated due to the low concentration of fluorine ions and phosphate ions, so that resource waste is caused. CN106586992B discloses a method for comprehensively recovering fluorine and phosphorus by alkali decomposition of mixed rare earth ore liquid: (1) firstly, mixing rare earth ore and sodium hydroxide solution for alkali decomposition; (2) carrying out hot filtration at the temperature of more than 80 ℃ after the alkali decomposition to obtain an alkali cake and concentrated alkali liquor, cooling and crystallizing the concentrated alkali liquor, filtering to obtain sodium phosphate crystals, and reusing the filtrate in the alkali decomposition process; (3) the alkali cake is washed by water slurry mixing, the alkali liquor is washed for the first time for concentration and crystallization, and sodium fluoride crystals are obtained by filtration; (4) and washing the alkali cake to be neutral, and dissolving the alkali cake with hydrochloric acid to obtain a rare earth chloride solution. In this patent document, only one wash is separated. Valuable elements in the washing liquid of other grades can not be recovered.
Nanofiltration (NF) is used to separate small molecular weight substances, such as inorganic salts or small organic molecules like glucose, sucrose, etc., from the solvent. Nanofiltration, also known as low pressure reverse osmosis, is an emerging field of membrane separation technology, and has separation performance between reverse osmosis and ultrafiltration, allowing some inorganic salts and some solvents to permeate through the membrane, thereby achieving separation effect. CN105776661A discloses a method for treating rare earth industrial wastewater by using a membrane. Firstly, removing an extractant, calcium, rare earth and the like in the wastewater, and then carrying out precision filtration to remove suspended matters invisible to naked eyes; and concentrating the wastewater by adopting a nanofiltration membrane. The method is mainly used for treating the waste water containing magnesium sulfate, magnesium chloride and ammonium sulfate generated in the rare earth smelting process, and does not relate to the mixed rare earth alkaline waste water containing fluorine and phosphorus.
Disclosure of Invention
In view of the above, an object of the present invention is to provide a method for separating fluorine and phosphorus in mixed rare earth alkaline wastewater, which can separate fluorine ions and phosphate ions at lower concentrations in mixed rare earth alkaline wastewater by performing nanofiltration through a nanofiltration membrane, and has higher permeability of fluorine ions and higher rejection rate of phosphate ions. Further, the invention can respectively obtain sodium fluoride, sodium phosphate and concentrated sodium hydroxide solution. The invention also aims to provide the application of the nanofiltration membrane in separating fluorine and phosphorus from mixed rare earth alkaline wastewater. The invention adopts the following technical scheme to achieve the purpose.
In one aspect, the invention provides a method for separating fluorine and phosphorus in mixed rare earth alkaline wastewater, which comprises the following steps: performing membrane separation on the mixed rare earth alkaline wastewater containing fluoride ions and phosphate ions by using a nanofiltration membrane, wherein the operation temperature is 10-35 ℃, and the operation pressure is 1.0-3.5 MPa, so as to obtain permeate liquid enriched with fluoride ions and hydroxide ions and retentate enriched with phosphate ions;
the mixed rare earth alkaline wastewater is alkaline wastewater containing sodium hydroxide, which is obtained by subjecting mixed rare earth concentrate to an alkaline decomposition process; in the mixed rare earth alkaline wastewater, the concentration of hydroxide ions is 0.001-1.2 mol/L, the concentration of fluoride ions is 0.001-1.6 g/L by weight of fluorine, and the concentration of phosphate ions is 0.001-1.65 g/L by weight of phosphorus.
According to the method, preferably, in the mixed rare earth alkaline wastewater, the concentration of hydroxide ions is 0.01-1.2 mol/L, the concentration of fluoride ions by weight of fluorine is 0.01-1.6 g/L, and the concentration of phosphate ions by weight of phosphorus is 0.01-1.65 g/L.
According to the method, the operation temperature of the membrane separation process is preferably 15-30 ℃, and the operation pressure is preferably 1.0-3.0 MPa.
According to the method, the operation temperature of the membrane separation process is preferably 20-30 ℃, and the operation pressure is preferably 1.5-3.0 MPa.
According to the method, the nanofiltration membrane is preferably a polyamide nanofiltration membrane with a rolled structure or a polyamide nanofiltration membrane with a flat plate structure.
According to the method of the present invention, preferably, the method further comprises the steps of: and concentrating and filtering the permeate to obtain sodium fluoride crystals and a concentrated solution containing sodium hydroxide.
According to the method of the present invention, preferably, the method further comprises the steps of: concentrating the trapped solution, and then evaporating and crystallizing to obtain sodium phosphate.
In another aspect, the invention also provides the application of the nanofiltration membrane in separating fluorine and phosphorus from mixed rare earth alkaline wastewater.
The use according to the invention preferably comprises the following steps:
performing membrane separation on the mixed rare earth alkaline wastewater containing fluoride ions and phosphate ions by using a nanofiltration membrane, wherein the operation temperature is 10-35 ℃, and the operation pressure is 1.0-3.5 MPa, so as to obtain permeate liquid enriched with fluoride ions and hydroxide ions and retentate enriched with phosphate ions;
the mixed rare earth alkaline wastewater is alkaline wastewater containing sodium hydroxide, which is obtained by subjecting mixed rare earth concentrate to an alkaline decomposition process; in the mixed rare earth alkaline wastewater, the concentration of hydroxide ions is 0.001-1.2 mol/L, the concentration of fluoride ions is 0.001-1.6 g/L by weight of fluorine, and the concentration of phosphate ions is 0.001-1.65 g/L by weight of phosphorus.
According to the use of the invention, preferably, the nanofiltration membrane is a polyamide nanofiltration membrane with a rolled structure or a polyamide nanofiltration membrane with a flat plate structure.
The invention adopts a nanofiltration membrane to separate fluoride ions and phosphate ions with lower concentration in different types of mixed rare earth alkaline wastewater, and the permeability (F) of the fluoride ions-Permeability) and phosphate radical ionizationRetention rate of seed (PO)4 3-Retention rate) is high. The method can also respectively obtain sodium fluoride and sodium phosphate byproducts, realize the comprehensive utilization of resources and achieve the zero discharge of wastewater.
Detailed Description
The present invention will be further described with reference to specific embodiments, but the scope of the present invention is not limited thereto.
The mixed rare earth alkaline wastewater is alkaline wastewater containing sodium hydroxide, which is obtained by carrying out different types of alkaline decomposition processes on mixed rare earth concentrate. In certain embodiments, the mixed rare earth ore is directly decomposed by alkali, washed by water after decomposition and filtered to obtain water washing slag containing rare earth and alkaline wastewater containing sodium hydroxide; the mixed rare earth alkaline wastewater can be triple water washing liquid and quartic water washing liquid, and does not comprise primary water washing liquid and secondary water washing liquid. In other embodiments, the mixed rare earth ore is mixed with hydrochloric acid to perform acid soaking to remove calcium, then the mixed rare earth ore is filtered, and a filter cake is washed to be neutral to obtain calcium-removed ore after calcium removal; and decomposing the decalcified ore with alkali, washing for many times, and filtering to obtain washing slag containing rare earth and alkaline wastewater containing sodium hydroxide. In still other embodiments, the mixed rare earth ore is oxidized and roasted, and the roasted ore is subjected to acid leaching with concentrated hydrochloric acid, then filtered and leached to neutrality to obtain a filter cake; and carrying out alkaline decomposition reaction on the filter cake, then washing for many times and filtering to obtain washing slag containing rare earth and obtain alkaline wastewater containing sodium hydroxide.
The method comprises a nanofiltration separation step and a treatment step of permeate and retentate. The invention also provides the application of the nanofiltration membrane. As described in detail below.
< nanofiltration separation step >
Performing membrane separation on the mixed rare earth alkaline wastewater containing fluoride ions and phosphate ions by using a nanofiltration membrane, wherein the operation temperature is 10-35 ℃, and the operation pressure is 1.0-3.5 MPa, so as to obtain permeate liquid enriched with fluoride ions and hydroxide ions and retentate enriched with phosphate ions; the mixed rare earth alkaline wastewater is alkaline wastewater containing sodium hydroxide, which is obtained by subjecting mixed rare earth concentrate to an alkaline decomposition process; in the mixed rare earth alkaline wastewater, the concentration of hydroxide ions is 0.001-1.2 mol/L, the concentration of fluoride ions is 0.001-1.6 g/L by weight of fluorine, and the concentration of phosphate ions is 0.001-1.65 g/L by weight of phosphorus. Therefore, fluoride ions and phosphate ions with lower concentration in the mixed rare earth alkaline wastewater of different types can be better separated, and the separation selectivity is high, namely, higher fluoride ion transmittance and phosphate ion retention rate are realized; so as to realize comprehensive recycling of resources and achieve zero discharge of wastewater. In the prior art, only alkaline wastewater (namely primary water washing liquid) containing higher-concentration hydroxide ions, fluoride ions and phosphate ions is generally treated by concentration or evaporative crystallization to obtain sodium fluoride and sodium phosphate through separation; and for the tertiary water washing liquid, the quaternary water washing liquid and the like which contain lower-concentration fluoride ions and phosphate ions, sodium fluoride and sodium phosphate cannot be separated.
The nanofiltration membrane is adopted for membrane separation in the invention, which means that the membrane separation is carried out by a nanofiltration membrane filtering device.
In the mixed rare earth alkaline wastewater of the invention, hydroxyl ions (OH)-) The concentration of (B) may be 0.001 to 1.2mol/L, preferably 0.01 to 1.2mol/L, and more preferably 0.05 to 1.0 mol/L. The concentration of fluoride ion may be 0.001 to 1.6g/L, preferably 0.01 to 1.6g/L, and more preferably 0.05 to 1.5g/L, based on the weight of fluorine. The concentration of phosphate ions based on the weight of phosphorus can be 0.001-1.65 g/L, preferably 0.01-1.55 g/L, and more preferably 0.05-1.55 g/L. According to one embodiment of the invention, in the mixed rare earth alkaline wastewater, the concentration of hydroxide ions is 0.05-1.5 mol/L, the concentration of fluoride ions is 0.01-1.6 g/L by weight of fluorine, and the concentration of phosphate ions is 0.01-1.55 g/L by weight of phosphorus. Such mixed rare earth alkaline wastewater is suitable for the process of the present invention.
In the invention, the operation temperature in the membrane separation process can be 10-35 ℃, preferably 15-30 ℃ and more preferably 20-30 ℃. The operating pressure may be 1.0 to 3.5MPa, preferably 1.0 to 3.0MPa, and more preferably 1.5 to 3.0 MPa. According to one embodiment of the invention, the operation temperature of the membrane separation process is 15-35 ℃, and the operation pressure is 1.0-3.5 MPa. Operating temperatures and pressures outside the above ranges will result in poor separation of fluoride ions and phosphate ions at lower concentrations in the misch metal alkaline wastewater. The operating temperature and pressure are in the above ranges, and the separation selectivity of fluoride ions and phosphate ions at lower concentrations is high.
The nanofiltration membrane of the invention is preferably a polyamide membrane, more preferably an alkali-resistant polyamide membrane. Thus being beneficial to realizing the separation of fluoride ions and phosphate ions with lower concentration in the mixed rare earth alkaline wastewater. In certain embodiments, the nanofiltration membrane may be a wound-structure polyamide nanofiltration membrane. In other embodiments, the nanofiltration membrane may be a polyamide nanofiltration membrane of a flat panel construction. The type of the nanofiltration membrane is not particularly limited as long as the present invention is satisfied. For example, the nanofiltration membrane may be a nanofiltration membrane manufactured by Koch (Koch) filtration Membrane; israel AMS B-4022 series; the U.S. delaunay melr BR series; NF90 series from Filmtec corporation, usa; NTR-7400 series by Nissan electrician and TMN10H model by Dongli corporation.
After membrane separation, permeate and retentate are obtained. The permeation solution is enriched with fluorine ions and hydroxyl ions; the trapped liquid is rich in phosphate ions. Thus, the separation of the fluoride ions and the phosphate ions is realized, and the separation selectivity is high. By adopting the operating conditions of the invention, the permeability to fluorine ions is more than or equal to 93 percent, and the retention rate to phosphate ions is more than or equal to 92 percent. Permeability (F) of fluorine ion-Permeability) and rejection rate of phosphate ions (PO)4 3-Rejection) is as follows:
the permeability of fluoride ion (weight of fluorine in the permeated liquid/weight of fluorine in the basic wastewater as a raw liquid) x 100%.
The retention rate of phosphate ions (weight of phosphorus in the retention solution/weight of phosphorus in the raw solution alkaline wastewater) x 100%.
The higher the permeability of the fluorine ions is, the higher the rejection rate of the phosphate ions is, which indicates that the separation selectivity of the nanofiltration membrane on the fluorine ions and the phosphate ions is higher.
According to the needs, the method can also carry out membrane separation on the trapped fluid enriched with phosphate ions or the permeate enriched with fluoride ions again by adopting a nanofiltration membrane. For example, the retentate enriched in phosphate ions is subjected to membrane separation again by using a nanofiltration membrane, so that a secondary retentate with a higher phosphate ion concentration can be obtained. And (3) carrying out membrane separation on the permeation liquid enriched with the fluorine ions again by adopting a nanofiltration membrane to obtain secondary permeation liquid with higher fluorine ion concentration.
< step of treating permeate and retentate >
Treatment step of permeate
The method of the invention also comprises the following steps: and concentrating and filtering the permeate to obtain sodium fluoride crystals and a concentrated solution containing sodium hydroxide.
As the permeation solution is enriched with fluorine ions and hydroxide ions, the permeation solution mainly contains sodium fluoride and sodium hydroxide. Concentrating the permeate, and filtering to obtain sodium fluoride crystal and concentrated solution containing sodium hydroxide. The temperature of concentration and the extent of concentration are not particularly limited and reference may be made to CN106586992B, which is incorporated herein in its entirety. The concentrated solution containing sodium hydroxide can be used for alkaline decomposition of mixed rare earth ore. Thus being beneficial to realizing the reutilization of resources and realizing the zero discharge of waste water.
Treatment step of trapped liquid
The method of the present invention may further comprise the steps of: concentrating the trapped solution, and then evaporating and crystallizing to obtain sodium phosphate. The trapped fluid contains sodium phosphate, and the trapped fluid is concentrated and then evaporated for crystallization to obtain the sodium phosphate. The conditions for the concentration and the evaporative crystallization are not particularly limited and will not be described in detail.
< use of nanofiltration Membrane >
The invention also provides application of the nanofiltration membrane in separating fluorine and phosphorus from mixed rare earth alkaline wastewater, which comprises the following steps:
carrying out membrane separation on the mixed rare earth alkaline wastewater containing fluoride ions and phosphate ions by adopting a nanofiltration membrane, wherein the operation temperature is 10-35 ℃, and the operation pressure is 1.0-3.5 MPa, so as to obtain a permeation solution enriched with fluoride ions and an trapped solution enriched with phosphate ions;
the mixed rare earth alkaline wastewater is alkaline wastewater containing sodium hydroxide, which is obtained by subjecting mixed rare earth concentrate to an alkaline decomposition process; in the mixed rare earth alkaline wastewater, the concentration of hydroxide ions is 0.001-1.2 mol/L, the concentration of fluoride ions is 0.001-1.6 g/L by weight of fluorine, and the concentration of phosphate ions is 0.001-1.65 g/L by weight of phosphorus.
The operation temperature in the membrane separation process can be 10-35 ℃, preferably 15-30 ℃ and more preferably 20-30 ℃. The operating pressure may be 1.0 to 3.5MPa, preferably 1.0 to 3.0MPa, and more preferably 1.5 to 3.0 MPa. Operating temperatures and pressures outside the above ranges will result in poor separation of fluoride ions and phosphate ions at lower concentrations in the misch metal alkaline wastewater. The operating temperature and pressure are in the above ranges, and the separation selectivity of fluoride ions and phosphate ions at lower concentrations is high.
The nanofiltration membrane of the invention is preferably a polyamide membrane, more preferably an alkali-resistant polyamide membrane. Thus being beneficial to realizing the separation of fluoride ions and phosphate ions with lower concentration in the mixed rare earth alkaline wastewater. In certain embodiments, the nanofiltration membrane may be a wound-structure polyamide nanofiltration membrane. In other embodiments, the nanofiltration membrane may be a polyamide nanofiltration membrane of a flat panel construction. The type of the nanofiltration membrane is not particularly limited as long as the present invention is satisfied. For example, the nanofiltration membrane may be a nanofiltration membrane manufactured by Koch (Koch) filtration Membrane; israel AMS B-4022 series; the U.S. delaunay melr BR series; NF90 series from Filmtec corporation, usa; NTR-7400 series by Nissan electrician and TMN10H model by Dongli corporation.
In the mixed rare earth alkaline wastewater of the invention, hydroxyl ions (OH)-) The concentration of (B) may be 0.001 to 1.2mol/L, preferably 0.01 to 1.2mol/L, and more preferably 0.05 to 1.0 mol/L. With fluorineThe concentration of the fluoride ion may be 0.001 to 1.6g/L, preferably 0.01 to 1.6g/L, and more preferably 0.05 to 1.5 g/L. The concentration of phosphate ions based on the weight of phosphorus can be 0.001-1.65 g/L, preferably 0.01-1.55 g/L, and more preferably 0.05-1.55 g/L. According to one embodiment of the invention, in the mixed rare earth alkaline wastewater, the concentration of hydroxide ions is 0.05-1.5 mol/L, the concentration of fluoride ions is 0.01-1.6 g/L by weight of fluorine, and the concentration of phosphate ions is 0.01-1.55 g/L by weight of phosphorus. The invention finds that the method is beneficial to implement by controlling the concentration of various ions of the mixed rare earth alkaline wastewater within the range.
The application of the nanofiltration membrane in separating fluorine and phosphorus from mixed rare earth alkaline wastewater also comprises a treatment step of permeate and retentate. The process conditions in the application of the nanofiltration membrane are the same as those of the method for separating fluorine and phosphorus in the mixed rare earth alkaline wastewater, and are not repeated herein.
< measuring method >
Determination of the concentration of fluoride ions by weight of fluorine: EDTA titration method.
Determination of the concentration of phosphate ions by weight of phosphorus: spectrophotometry.
Determination of hydroxide ion concentration: acid-base titration.
The starting materials used in the following examples and comparative examples are illustrated below:
nanofiltration membrane: a nanofiltration membrane of type MPS34, manufactured by coriolis filter co.
Example 1
Mixing the mixed rare earth ore with the grade of 60% with 1.1mol/L hydrochloric acid according to the solid-to-liquid ratio of 1:4, carrying out acid soaking to remove calcium, preserving heat at 95 ℃ for 3 hours, then filtering, and washing a filter cake to be neutral to obtain the calcium-removed ore after calcium removal. And (3) carrying out alkali decomposition on the calcium-removed ore and 65 wt% of sodium hydroxide solution according to the ore-alkali ratio (weight ratio) of 1:0.9, and carrying out heat preservation reaction at 145 ℃ for 30 min. Then washing with water and filtering to obtain washing slag containing rare earth. The washing times are four times, the solid-liquid ratio is 1:3 (volume ratio), and a primary washing liquid, a secondary washing liquid, a tertiary washing liquid and a quartic washing liquid are respectively obtained. Wherein, in the quartic water washing liquid, the concentration of sodium hydroxide is 0.05mol/L, the concentration of fluoride ions by weight of fluorine is 0.97g/L, and the concentration of phosphate ions by weight of phosphorus is 0.78 g/L.
Carrying out membrane separation on the alkaline wastewater of the quartic water washing liquid by adopting a nanofiltration membrane, wherein the operation temperature is 25 ℃, and the operation pressure is 3.0MPa, so as to obtain enriched F-And OH-Permeate and enriched PO4 3-The trapped liquid of (2). F-Transmittance of 98%, PO4 3-The rejection was 97%.
Concentrating the permeate to 10% of the original volume, and filtering to obtain sodium fluoride with purity of 95.2% and concentrated solution containing sodium hydroxide; the concentrated solution containing sodium hydroxide is recycled into the alkali decomposition process.
Concentrating the trapped solution, evaporating and crystallizing to obtain the sodium phosphate with the purity of 94.7 percent.
Comparative examples 1 to 3
See table 1 for operating process parameters, otherwise the same as in example 1.
TABLE 1
The components of the mixed rare earth alkaline wastewater are very complex, and the influence factors of the nanofiltration effect are very many. As can be seen from the comparison between example 1 and comparative examples 1 to 3, the operation temperature and pressure of the nanofiltration membrane have an important influence on the separation effect in the mixed rare earth alkaline wastewater having low concentrations of fluoride ions and phosphate ions. When outside the operating temperature and pressure ranges of the present invention, result in F-Transmittance and PO4 3-The rejection rate is significantly reduced.
Example 2
Oxidizing and roasting the mixed rare earth ore with the grade of 56% at 500 ℃ for 90min, carrying out acid leaching on the roasted ore and concentrated hydrochloric acid according to the mineral acid ratio (volume ratio) of 1:4, then filtering, and leaching to be neutral to obtain a filter cake. And (3) carrying out alkali decomposition reaction on the filter cake and 65 wt% of sodium hydroxide solution at 170 ℃ for 60min, then washing with water and filtering to obtain washing slag containing rare earth. The washing times are four times, the solid-liquid ratio is 1:7 (volume ratio), and a primary washing liquid, a secondary washing liquid, a tertiary washing liquid and a quartic washing liquid are respectively obtained. Wherein, in the primary water washing liquid, the concentration of hydroxide ions is 0.56mol/L, the concentration of fluoride ions by weight of fluorine is 1.23g/L, and the concentration of phosphate ions by weight of phosphorus is 1.53 g/L.
Carrying out membrane separation on the alkaline wastewater of the primary washing liquid by adopting a nanofiltration membrane, wherein the operation temperature is 28 ℃, and the operation pressure is 1.5MPa, so as to obtain enriched F-And OH-Permeate and enriched PO4 3-The trapped liquid of (2). F-Transmittance of 96%, PO4 3-The rejection was 97.8%.
Concentrating the permeate to 10% of the original volume, and filtering to obtain sodium fluoride with the purity of 98.9% and concentrated solution containing sodium hydroxide; the concentrated solution containing sodium hydroxide is recycled into the alkali decomposition process.
Concentrating the trapped solution, evaporating and crystallizing to obtain the sodium phosphate with the purity of 97.8 percent.
Comparative example 4
See table 2 for operating process parameters, otherwise the same as in example 2.
TABLE 2
Example 3
The difference from example 2 is that the alkaline waste water used is a triple water wash. Wherein, in the tertiary water washing liquid, the concentration of hydroxide ions is 0.14mol/L, the concentration of fluoride ions by weight of fluorine is 0.10g/L, and the concentration of phosphate ions by weight of phosphorus is 0.31 g/L.
Carrying out membrane separation on the alkaline wastewater of the tertiary water washing liquid by adopting a nanofiltration membrane, wherein the operation temperature is 25 ℃, and the operation pressure is 1.0MPa, so as to obtain enriched F-And OH-Permeate and enriched PO4 3-The trapped liquid of (2). F-Transmittance of 93%, PO4 3-The rejection was 96%.
Concentrating the permeate to 5% of the original volume, and filtering to obtain sodium fluoride with the purity of 96.8% and concentrated solution containing sodium hydroxide; the concentrated solution containing sodium hydroxide is recycled into the alkali decomposition process.
Concentrating the trapped solution, evaporating and crystallizing to obtain the sodium phosphate with the purity of 95.3 percent.
Comparative example 5
See table 3 for operating process parameters, otherwise the same as in example 3.
TABLE 3
Example 4
The mixed rare earth ore with the grade of 65 percent and a sodium hydroxide solution with the concentration of 65 percent by weight are subjected to direct alkali decomposition reaction for 6 hours at 145 ℃ according to the ore-alkali ratio of 1:0.85 (weight ratio), and then are washed and filtered to obtain washing slag containing rare earth. The washing times are four times, the solid-liquid ratio is 1:2 (volume ratio), and a primary washing liquid, a secondary washing liquid, a tertiary washing liquid and a quartic washing liquid are respectively obtained. Wherein, in the quartic water washing liquid, the concentration of hydroxide ions is 0.16mol/L, the concentration of fluoride ions by weight of fluorine is 0.87g/L, and the concentration of phosphate ions by weight of phosphorus is 0.08 g/L.
Carrying out membrane separation on the alkaline wastewater of the quartic water washing liquid by adopting a nanofiltration membrane at the operating temperature of 25 ℃ and the operating pressure of 3.0MPa to obtain the F-rich wastewater-And OH-Permeate and PO-rich4 3-The trapped liquid of (2). F-Transmittance of 97%, PO4 3-The retention rate was 92%.
Concentrating the permeate to 18% of the original volume, and filtering to obtain sodium fluoride with the purity of 97.3% and concentrated solution containing sodium hydroxide; the concentrated solution containing sodium hydroxide is recycled into the alkali decomposition process.
Concentrating the trapped solution, evaporating and crystallizing to obtain a sodium phosphate product with the purity of 95.5 percent.
Comparative example 6
See table 4 for operating process parameters, otherwise the same as in example 4.
TABLE 4
As can be seen from the comparison between examples 2 to 4 and comparative examples 4 to 6, the above-mentioned operating temperature and pressure are suitable for different types of mixed rare earth alkaline wastewater having low concentrations of fluoride ions and phosphate ions. When outside the operating temperature and pressure ranges of the present invention, result in F-Transmittance and PO4 3-The rejection rate is significantly reduced.
The present invention is not limited to the above-described embodiments, and any variations, modifications, and substitutions which may occur to those skilled in the art may be made without departing from the spirit of the invention.
Claims (10)
1. A method for separating fluorine and phosphorus in mixed rare earth alkaline wastewater is characterized by comprising the following steps: performing membrane separation on the mixed rare earth alkaline wastewater containing fluoride ions and phosphate ions by using a nanofiltration membrane, wherein the operation temperature is 10-35 ℃, and the operation pressure is 1.0-3.5 MPa, so as to obtain permeate liquid enriched with fluoride ions and hydroxide ions and retentate enriched with phosphate ions;
the mixed rare earth alkaline wastewater is alkaline wastewater containing sodium hydroxide, which is obtained by subjecting mixed rare earth concentrate to an alkaline decomposition process; in the mixed rare earth alkaline wastewater, the concentration of hydroxide ions is 0.001-1.2 mol/L, the concentration of fluoride ions is 0.001-1.6 g/L by weight of fluorine, and the concentration of phosphate ions is 0.001-1.65 g/L by weight of phosphorus.
2. The method according to claim 1, wherein the concentration of hydroxide ions in the alkaline waste water of mixed rare earth is 0.01-1.2 mol/L, the concentration of fluoride ions is 0.01-1.6 g/L based on the weight of fluorine, and the concentration of phosphate ions is 0.01-1.65 g/L based on the weight of phosphorus.
3. The method of claim 2, wherein the membrane separation process is operated at a temperature of 15 to 30 ℃ and at a pressure of 1.0 to 3.0 MPa.
4. The method of claim 3, wherein the membrane separation process is operated at a temperature of 20 to 30 ℃ and an operating pressure of 1.5 to 3.0 MPa.
5. The method according to claim 1, wherein the nanofiltration membrane is a wound-structure polyamide nanofiltration membrane or a flat-plate structure polyamide nanofiltration membrane.
6. The method of claim 1, further comprising: and concentrating and filtering the permeate to obtain sodium fluoride crystals and a concentrated solution containing sodium hydroxide.
7. The method according to any one of claims 1 to 6, further comprising the steps of: concentrating the trapped solution, and then evaporating and crystallizing to obtain sodium phosphate.
8. An application of a nanofiltration membrane in separating fluorine and phosphorus from mixed rare earth alkaline wastewater.
9. Use according to claim 8, characterized in that it comprises the following steps: performing membrane separation on the mixed rare earth alkaline wastewater containing fluoride ions and phosphate ions by using a nanofiltration membrane, wherein the operation temperature is 10-35 ℃, and the operation pressure is 1.0-3.5 MPa, so as to obtain permeate liquid enriched with fluoride ions and hydroxide ions and retentate enriched with phosphate ions;
the mixed rare earth alkaline wastewater is alkaline wastewater containing sodium hydroxide, which is obtained by subjecting mixed rare earth concentrate to an alkaline decomposition process; in the mixed rare earth alkaline wastewater, the concentration of hydroxide ions is 0.001-1.5 mol/L, the concentration of fluoride ions is 0.001-1.6 g/L by weight of fluorine, and the concentration of phosphate ions is 0.001-1.65 g/L by weight of phosphorus.
10. Use according to claim 9, wherein the nanofiltration membrane is a wound-structure polyamide nanofiltration membrane or a flat-plate structure polyamide nanofiltration membrane.
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