Treatment method of wastewater containing fluorine, chlorine, sulfur and phosphorus

Abstract

The invention discloses a method for treating wastewater containing fluorine, chlorine, sulfur and phosphorus, and belongs to the technical field of wastewater treatment and resource utilization. The method comprises the following steps: adjusting the pH value of the fluorine-containing, chlorine-containing, sulfur-phosphorus wastewater to 4.5-9.0, and separating through a nanofiltration membrane to obtain sulfur-phosphorus-containing concentrated water and fluorine-chlorine-containing saline water; the concentrated water containing sulfur and phosphorus and calcium chloride are subjected to phosphate induced crystallization, and calcium superphosphate and phosphate crystallization mother liquor are obtained; the fluorine-containing chlorine salt water and calcium chloride are subjected to calcium fluoride induced crystallization, and calcium fluoride crystals and calcium fluoride crystal mother liquor are obtained; the calcium fluoride crystallization mother liquor and the phosphate crystallization mother liquor are concentrated through a reverse osmosis membrane, fresh water and sodium chloride-containing concentrated water are obtained, the sodium chloride-containing concentrated water is subjected to evaporative crystallization, and sodium chloride crystals and carnallite are obtained. According to the method, thiophosphofluorochloride in the wastewater is recycled step by step, calcium fluoride, sodium chloride and calcium superphosphate products are finally obtained, and the problems that in the prior art, the resource utilization rate is low, and the purity of resource pure products is low are solved.

Description

Technical Field

[0001] The invention relates to a method for treating wastewater containing fluorine, chlorine, sulfur and phosphorus, and belongs to the technical field of wastewater treatment and resource utilization. Background Art

[0002] Fluorine-containing chlorine, sulfur and phosphorus wastewater mainly comes from smelting and chemical industries. For example, rare earth smelting process will produce typical fluorine-containing chlorine, sulfur and phosphorus wastewater. After the rare earth ores (such as fluorocarbon cerium ore and monazite) undergo acid leaching and roasting processes, a large amount of fluorine, chlorine, sulfur and phosphorus are released in the form of ions (such as F - 、Cl - 、SO4 2- PO4 3- ) enters the wastewater, accompanied by the accumulation of sodium salts (such as NaCl and Na2SO4). This type of wastewater poses high environmental risks and is difficult to recycle. Traditional methods are difficult to achieve fluorine and phosphorus recovery and salt purification, and the salts can only be disposed of as hazardous waste, which is costly.

[0003] Current mainstream treatment technologies all have significant drawbacks. For example, when calcium salts are added to chemical precipitation for simultaneous fluoride and phosphorus removal, complex salts such as Ca5(PO4)3F are generated. Fluoride and phosphorus removal rates are mutually restricted, resulting in impure sludge. The purity of calcium fluoride is less than 60%, making it unusable as a resource. Step-by-step treatment processes consider removing fluoride first and then phosphorus, but excessive calcium ions interfere with subsequent phosphorus recovery. Direct evaporation of high-fluoride, chlorine, sulfur, and phosphorus wastewater produces complex salts such as Na3AlF6 and CaSO4·2H2O, with sodium chloride purity less than 70%, making it unrecoverable.

[0004] In order to solve the problems of difficulty in separating chlorofluorophosphine and low purity of crystalline products, and effectively improve the resource utilization of chlorofluorophosphine wastewater, it is necessary to develop an economical and efficient step-by-step separation and resource utilization technology for chlorofluorophosphine in chlorofluorophosphine wastewater. Summary of the Invention

[0005] In response to the problems existing in the above-mentioned prior art, the object of the present invention is to provide a method for treating fluorine-containing chlorosulfate and phosphorus-containing wastewater, which recovers and recycles the fluorine-containing chlorosulfate and phosphorus-containing wastewater in steps, and finally obtains calcium fluoride, sodium chloride, and superphosphate products, thereby solving the problems of low resource utilization rate and low purity of resource-recycled pure products in the prior art.

[0006] In order to achieve the above object, the first aspect of the present invention is to provide a method for treating wastewater containing fluorine, chlorine, sulfur and phosphorus, comprising the following steps:

[0007] (1) After adjusting the pH of the fluorine-containing, chlorine-containing, sulfur-containing and phosphorus-containing wastewater to 4.5-9.0, the wastewater is separated by a nanofiltration membrane to obtain sulfur-containing and phosphorus-containing concentrated water and fluorine-containing and chlorine-containing brine;

[0008] (2) subjecting the sulfur-phosphorus concentrated water and calcium chloride to phosphate-induced crystallization and solid-liquid separation to obtain superphosphate and phosphate crystallization mother liquor; the total molar ratio of calcium ions in the calcium chloride to sulfate and phosphate in the sulfur-phosphorus concentrated water is 1 to 1.5:1;

[0009] and subjecting the fluorine-containing chlorinated salt water and calcium chloride to calcium fluoride-induced crystallization, and solid-liquid separation to obtain calcium fluoride crystals and calcium fluoride crystal mother liquor; wherein the molar ratio of calcium ions in the calcium chloride to fluoride ions in the fluorine-containing chlorinated salt water is 0.5-0.8:1;

[0010] (3) The calcium fluoride crystallization mother liquor and the phosphate crystallization mother liquor are concentrated through a reverse osmosis membrane to obtain fresh water and concentrated water containing sodium chloride, and the concentrated water containing sodium chloride is crystallized by evaporation to obtain sodium chloride crystals and miscellaneous salts.

[0011] The method for treating wastewater containing fluorine, chlorine, sulfur and phosphorus of the present invention:

[0012] In step 1), a fluorine-chlorine separation system containing a nanofiltration membrane is mainly used to separate sulfur and phosphorus from fluorine and chlorine in the fluorine-chlorine-sulfur-phosphorus wastewater to obtain concentrated water containing sulfur and phosphorus and brine containing fluorine and chlorine. The main separation mechanism is the electrostatic repulsion of the nanofiltration membrane (Donnan effect). The surface of the polyamide nanofiltration membrane used has a negative charge (carboxyl group ionization degree > amino group protonation degree), which produces electrostatic repulsion to anions and high-valent ions (such as SO4 2- PO4 3- ) are subject to stronger repulsive force and higher interception rate, and mainly enter concentrated water, namely concentrated water containing sulfur and phosphorus. - 、F - ) have weak repulsive forces and primarily enter fresh water, i.e., salt water containing fluorine and chlorine. Controlling the pH between 4.5 and 9.0 helps control the forms of fluorine and chlorine, ensuring effective fluorine and chlorine separation.

[0013] In step 2), calcium chloride is mainly used to react with sulfur-phosphorus concentrated water to obtain sulfur-phosphorus crystals (superphosphate) containing calcium sulfate and calcium hydrogen phosphate and phosphate crystal mother liquor. The reaction is shown in formula (1) to (2):

[0014] Ca 2+ +SO4 2- =CaSO4↓ (1)

[0015] Ca 2+ +PO4 3- +H + =CaHPO4↓ (2)

[0016] In step 2), calcium chloride is mainly used to react with fluoride ions in fluorine-containing chlorine brine to obtain calcium fluoride crystals and calcium fluoride crystal mother liquor. The reaction is shown in formula (3):

[0017] Ca2+ +F - =CaF2↓ (3)

[0018] In step 3), the sodium chloride concentration in the calcium fluoride crystallization mother liquor and the phosphate crystallization mother liquor is mainly increased by reverse osmosis membrane concentration, and then sodium chloride crystals and miscellaneous salts are recovered by evaporation crystallization.

[0019] As a preferred embodiment, the nanofiltration membrane is a polypiperazineamide nanofiltration membrane. During the separation process using the nanofiltration membrane, the pressure is 3.0-5.0 MPa and the separation time is 0.5-4 hours. The polypiperazineamide nanofiltration membrane is formed by the polymerization of piperazine and an amide (such as terephthaloyl chloride).

[0020] As a preferred solution, the volume ratio of the sulfur-phosphorus concentrated water to the fluorine-chloride-containing brine is 1:1.5-4.

[0021] As a preferred solution, the fluoride ion concentration in the sulfur-phosphorus concentrated water is 5-15 g / L, the chloride ion concentration is 1-5 g / L, the phosphate concentration is 3-25 g / L, and the sulfate concentration is 6-40 g / L.

[0022] As a preferred solution, the fluorine ion concentration in the fluorine-containing chlorosulfuric acid wastewater is 5~15g / L, the phosphate concentration is 1~5g / L, the sulfate concentration is 2~8g / L, the sodium ion concentration is 12~25g / L, and the chloride ion concentration is 1~5g / L.

[0023] As a preferred embodiment, during the phosphate-induced crystallization process, the total molar ratio of calcium ions in the calcium chloride to sulfate and phosphate in the sulfur-phosphorus concentrated water is 1.1 to 1.3:1. In this preferred embodiment, reactions (1) to (2) can be fully carried out. If the total molar ratio of calcium ions to sulfate and phosphate in the sulfur-phosphorus concentrated water is less than 1.1:1, reactions (1) to (2) will not be fully carried out, and the superphosphate recovery rate will be reduced. If the total molar ratio of calcium ions to sulfate and phosphate in the sulfur-phosphorus concentrated water is greater than 1.3:1, there will be too much calcium ion, resulting in reagent waste and scaling of the subsequent sodium chloride concentration system.

[0024] As a preferred solution, during the phosphate-induced crystallization process and during the calcium fluoride-induced crystallization process, the calcium chloride is added in the form of an aqueous solution, and the concentration of the calcium chloride solution is independently 50-250 g / L.

[0025] As a preferred embodiment, during the calcium fluoride-induced crystallization process, the molar ratio of calcium ions in the calcium chloride to fluoride ions in the fluorine-containing chlorinated brine is 0.55 to 0.65:1. In this preferred embodiment, fluoride ions in the fluorine-containing chlorinated brine can be effectively removed. If the molar ratio of calcium ions to fluoride ions in the fluorine-containing chlorinated brine is less than 0.55:1, fluoride ion removal is incomplete, affecting the purity of sodium chloride crystals in subsequent steps. If the molar ratio of calcium ions to fluoride ions in the fluorine-containing chlorinated brine is greater than 0.65:1, excess calcium ions are present, resulting in reagent waste and affecting the purity of sodium chloride crystals.

[0026] As a preferred solution, the time for phosphate-induced crystallization is 0.5 to 3 hours.

[0027] As a preferred solution, the time for calcium fluoride to induce crystallization is 0.5 to 4 hours.

[0028] As a preferred solution, during the reverse osmosis membrane concentration process, the operating pressure is 3.0-6.0 MPa, the operating pH is 4.5-9.0, the concentration factor is 30-80 times, and the sodium chloride concentration in the concentrated water is 90 g / L-120 g / L. Controlling the appropriate sodium chloride concentration in the concentrated water can save energy for subsequent evaporation and crystallization.

[0029] As a preferred solution, the temperature of the evaporation crystallization is 95-105° C. and the pressure is -20--90 kPa. Controlling appropriate evaporation crystallization conditions is beneficial to improving the purity of sodium chloride crystals.

[0030] Compared with the prior art, the present invention has at least the following advantages:

[0031] The present invention realizes the cascade treatment and resource utilization of fluorine-containing chlorinated phosphorus wastewater. The comprehensive recovery rate of fluorine-containing chlorinated phosphorus in the wastewater is higher than 95%, and the degree of resource utilization is high. The recovered products such as calcium fluoride, sodium chloride, and superphosphate all meet the requirements of relevant national quality standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0033] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0034] The present invention is further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments. Obviously, the embodiments described below are only a part of the embodiments, and all other embodiments obtained by professionals in this field without making creative efforts are still within the scope of protection of the present invention.

[0035] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0036] In the following embodiments and comparative examples provided by the present invention, the fluorine-containing chlorosulfate and phosphorus wastewater used was taken from a rare earth smelter in Sichuan, wherein the fluorine concentration was 8 g / L, the phosphate concentration was 4 g / L, the sulfate concentration was 5 g / L, the sodium concentration was 13 g / L, the chlorine concentration was 2 g / L, and the pH was 6.2.

[0037] The nanofiltration membrane of the fluorine and chlorine separation system is a polypiperazineamide nanofiltration membrane.

[0038] Example 1

[0039] (1) Adjust the pH of the fluorine, chlorine, sulfur and phosphorus wastewater to 5.5, and pass 50L of the fluorine, chlorine, sulfur and phosphorus wastewater into the fluorine-chlorine (nanofiltration) separation system for nanofiltration membrane separation. The operating pressure is controlled at 3.0MPa and the time is 1.5h to obtain 10L of sulfur-phosphorus concentrated water and 40L of fluorine-chlorine brine. The concentrations of fluoride ion, chloride ion, sulfate ion and phosphate ion in the sulfur-phosphorus concentrated water are 0.6, 0.3, 24.5 and 19.6g / L respectively. The concentrations of fluoride ion, chloride ion, sulfate ion and phosphate ion in the fluorine-chlorine brine are 9.85, 2.43, 0.13 and 0.10g / L respectively.

[0040] (2) 10 L of sulfur-phosphorus concentrated water and 100 g / L, 5.63 L of calcium chloride solution were subjected to phosphate-induced crystallization, and the ratio of calcium ions in the calcium chloride solution to the total molar ratio of sulfate and phosphate in the sulfur-phosphorus concentrated water was controlled to be 1.1. The reaction was carried out for 2 h. After solid-liquid separation, 625 g of superphosphate (dry weight) and 14 L of phosphate crystallization mother liquor were obtained;

[0041] (3) 40 L of fluorine-containing chlorinated brine and 50 g / L and 13.8 L of calcium chloride solution were subjected to calcium fluoride-induced crystallization, and the molar ratio of calcium ions in the calcium chloride solution to fluoride ions in the fluorine-containing chlorinated brine was controlled to be 0.6. The reaction was carried out for 1.5 h. After solid-liquid separation, 792 g of calcium fluoride crystals (dry weight) and 52 L of calcium fluoride crystal mother liquor were obtained;

[0042] (4) 52 L of calcium fluoride crystallization mother liquor and 14 L of phosphate crystallization mother liquor were concentrated by reverse osmosis membrane at an operating pressure of 3.0 MPa, an operating pH of 6.0, and a concentration factor of 62 to obtain fresh water and concentrated water. The sodium chloride concentration in the concentrated water was 90 g / L. The concentrated water was evaporated and crystallized at a controlled evaporation temperature of 95°C and a pressure of -20 kPa to obtain 151 g of sodium chloride crystals and 40 g of miscellaneous salts.

[0043] Calculations show a comprehensive recovery rate of fluorinated chlorinated phosphorus in wastewater of 97.7%. Testing has confirmed that the quality of superphosphate meets the first-grade requirements of GB / T20413-2017 "Superphosphate," the quality of calcium fluoride crystals meets the qualified product requirements of GB / T27804-2011 "Calcium Fluoride," and the quality of sodium chloride crystals meets the first-grade industrial dry salt requirements of GB / T 5462-2015 "Industrial Salt."

[0044] Example 2

[0045] (1) Adjust the pH of the fluorine, chlorine, sulfur and phosphorus wastewater to 7.0, and pass 50L of the fluorine, chlorine, sulfur and phosphorus wastewater into the fluorine-chlorine (nanofiltration) separation system for nanofiltration membrane separation. The operating pressure is controlled at 4.0MPa and the time is 1h to obtain 15L of sulfur-phosphorus concentrated water and 35L of fluorine-chlorine brine. The concentrations of fluoride ion, chloride ion, sulfate ion and phosphate ion in the sulfur-phosphorus concentrated water are 0.5, 0.3, 16.3 and 13.1g / L respectively. The concentrations of fluoride ion, chloride ion, sulfate ion and phosphate ion in the fluorine-chlorine brine are 11.2, 2.73, 0.14 and 0.11g / L respectively.

[0046] (2) 15 L of sulfur-phosphorus concentrated water and 50 g / L, 13.3 L of calcium chloride solution were subjected to phosphate-induced crystallization, and the ratio of calcium ions in the calcium chloride solution to the total molar ratio of sulfate and phosphate in the sulfur-phosphorus concentrated water was controlled to be 1.3. The reaction was carried out for 1 h. After solid-liquid separation, 626 g of superphosphate (dry weight) and 27 L of phosphate crystallization mother liquor were obtained;

[0047] (3) 35 L of fluorine-containing chlorinated brine and 50 g / L and 6.3 L of calcium chloride solution were subjected to calcium fluoride-induced crystallization, and the molar ratio of calcium ions in the calcium chloride solution to fluoride ions in the fluorine-containing chlorinated brine was controlled to be 0.55. The reaction was carried out for 3 h. After solid-liquid separation, 781 g of calcium fluoride crystals (dry weight) and 40 L of calcium fluoride crystal mother liquor were obtained;

[0048] (4) 40 L of calcium fluoride crystallization mother liquor and 27 L of phosphate crystallization mother liquor were concentrated through a reverse osmosis membrane at an operating pressure of 4.0 MPa, an operating pH of 6.5, and a concentration factor of 62 to obtain fresh water and concentrated water. The sodium chloride concentration in the concentrated water was 100 g / L. The concentrated water was evaporated and crystallized at a controlled evaporation temperature of 100°C and a pressure of -40 kPa to obtain 149 g of sodium chloride crystals and 45 g of miscellaneous salts.

[0049] Calculations show a comprehensive recovery rate of fluorinated chlorinated phosphorus in wastewater of 97.2%. Testing has confirmed that the quality of superphosphate meets the first-grade requirements of GB / T20413-2017 "Superphosphate," the quality of calcium fluoride crystals meets the qualified product requirements of GB / T27804-2011 "Calcium Fluoride," and the quality of sodium chloride crystals meets the first-grade industrial dry salt requirements of GB / T 5462-2015 "Industrial Salt."

[0050] Example 3

[0051] (1) The pH of the fluorine, chlorine, sulfur, and phosphorus wastewater was adjusted to 9.0. 50 L of the fluorine, chlorine, sulfur, and phosphorus wastewater was fed into the fluorine-chlorine (nanofiltration) separation system for nanofiltration membrane separation. The operating pressure was controlled at 4.0 MPa for 2 h, resulting in 20 L of sulfur-phosphorus concentrated water and 30 L of fluorine-chlorine brine. The concentrations of fluoride ions, chloride ions, sulfate ions, and phosphate ions in the sulfur-phosphorus concentrated water were 0.4, 0.2, 12.2, and 9.8 g / L, respectively. The concentrations of fluoride ions, chloride ions, sulfate ions, and phosphate ions in the fluorine-chlorine brine were 13, 3.2, 0.17, and 0.13 g / L, respectively.

[0052] (2) 20 L of sulfur-phosphorus concentrated water and 250 g / L and 3.1 L of calcium chloride solution were subjected to phosphate-induced crystallization, and the ratio of calcium ions in the calcium chloride solution to the total molar ratio of sulfate and phosphate in the sulfur-phosphorus concentrated water was controlled to be 1.5. The reaction was carried out for 1 h. After solid-liquid separation, 627 g of superphosphate (dry weight) and 22 L of phosphate crystallization mother liquor were obtained;

[0053] (3) 30 L of fluorine-containing chlorinated brine and 150 g / L and 4.6 L of calcium chloride solution were subjected to calcium fluoride-induced crystallization, and the molar ratio of calcium ions in the calcium chloride solution to fluoride ions in the fluorine-containing chlorinated brine was controlled to be 0.6. The reaction was carried out for 1 h. After solid-liquid separation, 776 g of calcium fluoride crystals (dry weight) and 33 L of calcium fluoride crystal mother liquor were obtained;

[0054] (4) 33 L of calcium fluoride crystallization mother liquor and 22 L of phosphate crystallization mother liquor were concentrated through a reverse osmosis membrane at an operating pressure of 4.0 MPa, an operating pH of 8.5, and a concentration factor of 62 to obtain fresh water and concentrated water. The sodium chloride concentration in the concentrated water was 120 g / L. The concentrated water was evaporated and crystallized at a controlled evaporation temperature of 100°C and a pressure of -70 kPa to obtain 151 g of sodium chloride crystals and 50 g of miscellaneous salts.

[0055] Calculations show a comprehensive recovery rate of fluorinated chlorinated phosphorus in wastewater of 96.9%. Testing has confirmed that the quality of superphosphate meets the first-grade requirements of GB / T20413-2017 "Superphosphate," the quality of calcium fluoride crystals meets the qualified product requirements of GB / T27804-2011 "Calcium Fluoride," and the quality of sodium chloride crystals meets the first-grade industrial dry salt requirements of GB / T 5462-2015 "Industrial Salt."

[0056] Example 4

[0057] (1) The pH of the fluorine, chlorine, sulfur, and phosphorus wastewater was adjusted to 5.0. 50 L of the fluorine, chlorine, sulfur, and phosphorus wastewater was fed into the fluorine-chlorine (nanofiltration) separation system for nanofiltration membrane separation. The operating pressure was controlled at 5.0 MPa for 0.5 h, resulting in 10 L of sulfur-phosphorus concentrated water and 40 L of fluorine-chlorine brine. The concentrations of fluoride ions, chloride ions, sulfate ions, and phosphate ions in the sulfur-phosphorus concentrated water were 0.3, 0.3, 24.3, and 19.4 g / L, respectively. The concentrations of fluoride ions, chloride ions, sulfate ions, and phosphate ions in the fluorine-chlorine brine were 9.9, 2.4, 0.19, and 0.15 g / L, respectively.

[0058] (2) 10 L of sulfur-phosphorus concentrated water and 200 g / L and 2.6 L of calcium chloride solution were subjected to phosphate-induced crystallization, and the ratio of calcium ions in the calcium chloride solution to the total molar ratio of sulfate and phosphate in the sulfur-phosphorus concentrated water was controlled to be 1.0. The reaction was carried out for 3 h. After solid-liquid separation, 621 g of superphosphate (dry weight) and 11 L of phosphate crystallization mother liquor were obtained;

[0059] (3) 40 L of fluorine-containing chlorinated brine and 250 g / L and 3.0 L of calcium chloride solution were subjected to calcium fluoride-induced crystallization, and the molar ratio of calcium ions in the calcium chloride solution to fluoride ions in the fluorine-containing chlorinated brine was controlled to be 0.65. The reaction was carried out for 0.5 h. After solid-liquid separation, 786 g of calcium fluoride crystals (dry weight) and 42 L of calcium fluoride crystal mother liquor were obtained;

[0060] (4) 42 L of calcium fluoride crystallization mother liquor and 11 L of phosphate crystallization mother liquor were concentrated by reverse osmosis membrane at an operating pressure of 5.0 MPa, an operating pH of 5.5, and a concentration factor of 58 to obtain fresh water and concentrated water. The sodium chloride concentration in the concentrated water was 110 g / L. The concentrated water was evaporated and crystallized at a controlled evaporation temperature of 105°C and a pressure of -90 kPa to obtain 153 g of sodium chloride crystals and 56 g of miscellaneous salts.

[0061] Calculations show that the comprehensive recovery rate of fluorinated chlorinated phosphorus in wastewater is 96.5%. Testing has confirmed that the quality of superphosphate meets the first-grade requirements of GB / T20413-2017 "Superphosphate," the quality of calcium fluoride crystals meets the qualified product requirements of GB / T27804-2011 "Calcium Fluoride," and the quality of sodium chloride crystals meets the first-grade industrial dry salt requirements of GB / T 5462-2015 "Industrial Salt."

[0062] Example 5

[0063] Step (1) is the same as in Example 1;

[0064] Step (2): 10 L of sulfur-phosphorus concentrated water and 100 g / L of calcium chloride solution were subjected to phosphate-induced crystallization, and the ratio of calcium ions in the calcium chloride solution to the total molar ratio of sulfate and phosphate in the sulfur-phosphorus concentrated water was controlled to be 1.0, and the reaction was carried out for 2 h. After solid-liquid separation, 618 g of superphosphate (dry weight) and 11 L of phosphate crystallization mother liquor were obtained;

[0065] Step (3) is the same as in Example 1;

[0066] Step (4): 52 L of calcium fluoride crystallization mother liquor and 11 L of phosphate crystallization mother liquor were concentrated through a reverse osmosis membrane at an operating pressure of 3.0 MPa, an operating pH of 6, and a concentration factor of 66 to obtain fresh water and concentrated water. The sodium chloride concentration in the concentrated water was 100 g / L. The concentrated water was evaporated and crystallized at a controlled evaporation temperature of 95°C and a pressure of -20 kPa to obtain 154 g of sodium chloride crystals and 59 g of miscellaneous salts.

[0067] Calculations show that the comprehensive recovery rate of fluorinated chlorinated phosphorus in wastewater is 96.3%. Testing has confirmed that the quality of superphosphate meets the first-grade requirements of GB / T20413-2017 "Superphosphate," the quality of calcium fluoride crystals meets the qualified product requirements of GB / T27804-2011 "Calcium Fluoride," and the quality of sodium chloride crystals meets the first-grade industrial dry salt requirements of GB / T 5462-2015 "Industrial Salt."

[0068] Comparative Example 1

[0069] (1) Adjust the pH of the fluorine, chlorine, sulfur and phosphorus wastewater to 2, and pass 50L of fluorine, chlorine, sulfur and phosphorus wastewater into the fluorine-chlorine (nanofiltration) separation system for nanofiltration membrane separation. Control the operating pressure to 3.0MPa and the time to 1.5h to obtain 10L of sulfur-phosphorus concentrated water and 40L of fluorine-chlorine brine. The concentrations of fluoride ion, chloride ion, sulfate ion and phosphate ion in the sulfur-phosphorus concentrated water are 6.1, 5.3, 21.3 and 17.0g / L respectively. The concentrations of fluoride ion, chloride ion, sulfate ion and phosphate ion in the fluorine-chlorine brine are 8.5, 1.2, 0.94 and 0.75g / L respectively.

[0070] (2) 10 L of sulfur-phosphorus concentrated water and 100 g / L of calcium chloride solution were subjected to phosphate-induced crystallization, and the ratio of calcium ions in the calcium chloride solution to the total molar ratio of sulfate and phosphate in the sulfur-phosphorus concentrated water was controlled to be 1.1. The reaction was carried out for 2 h. After solid-liquid separation, 544 g of superphosphate (dry weight) and 14 L of phosphate crystallization mother liquor were obtained;

[0071] (3) 40 L of fluorine-containing chlorinated brine and 50 g / L calcium chloride solution were subjected to calcium fluoride-induced crystallization, and the molar ratio of calcium ions in the calcium chloride solution to fluoride ions in the fluorine-containing chlorinated brine was controlled to be 0.6. The reaction was carried out for 1.5 h. After solid-liquid separation, 681 g of calcium fluoride crystals (dry weight) and 52 L of calcium fluoride crystal mother liquor were obtained;

[0072] (4) 52 L of calcium fluoride crystallization mother liquor and 14 L of phosphate crystallization mother liquor were concentrated by reverse osmosis membrane at an operating pressure of 3.0 MPa, an operating pH of 6.0, and a concentration factor of 135 to obtain fresh water and concentrated water. The sodium chloride concentration in the concentrated water was 90 g / L. The concentrated water was evaporated and crystallized at a controlled evaporation temperature of 95°C and a pressure of -20 kPa to obtain 74 g of sodium chloride crystals and 113 g of miscellaneous salts.

[0073] Calculations show a comprehensive recovery rate of fluorinated chlorinated phosphorus in wastewater of 91.9%. Testing has confirmed that the quality of superphosphate meets the first-grade requirements of GB / T20413-2017 "Superphosphate," the quality of calcium fluoride crystals meets the qualified product requirements of GB / T27804-2011 "Calcium Fluoride," and the quality of sodium chloride crystals meets the first-grade industrial dry salt requirements of GB / T 5462-2015 "Industrial Salt."

[0074] Comparative Example 2

[0075] Step (1) is the same as in Example 1;

[0076] Step (2): 10 L of sulfur-phosphorus concentrated water and 100 g / L of calcium chloride solution were subjected to phosphate-induced crystallization, and the ratio of calcium ions in the calcium chloride solution to the total molar ratio of sulfate and phosphate in the sulfur-phosphorus concentrated water was controlled to be 0.8, and the reaction was carried out for 2 h. After solid-liquid separation, 432 g of superphosphate (dry weight) and 13 L of phosphate crystallization mother liquor were obtained;

[0077] Step (3) is the same as in Example 1;

[0078] Step (4): 52 L of calcium fluoride crystallization mother liquor and 13 L of phosphate crystallization mother liquor were concentrated through a reverse osmosis membrane at an operating pressure of 3.0 MPa, an operating pH of 6, and a concentration factor of 62 to obtain fresh water and concentrated water. The sodium chloride concentration in the concentrated water was 90 g / L. The concentrated water was evaporated and crystallized at a controlled evaporation temperature of 95°C and a pressure of -20 kPa to obtain 151 g of sodium chloride crystals and 87 g of miscellaneous salts.

[0079] Calculations show that the comprehensive recovery rate of fluorinated chlorinated phosphorus in wastewater is 93.3%. Testing has confirmed that the quality of superphosphate meets the first-grade requirements of GB / T20413-2017 "Superphosphate," the quality of calcium fluoride crystals meets the qualified product requirements of GB / T27804-2011 "Calcium Fluoride," and the quality of sodium chloride crystals meets the first-grade industrial dry salt requirements of GB / T 5462-2015 "Industrial Salt."

[0080] In this comparative example, the residual phosphate concentration in the phosphate crystallization mother liquor was 10.7 g / L, the amount of sulfur phosphorus crystals was reduced to 432 g, and the amount of impurities in the evaporation crystallization system increased to 87 g (due to the excess PO4 in the mother liquor). 3- With Ca 2+Ca3(PO4)2 precipitation is generated), which reduces the comprehensive recovery rate of chlorothion.

[0081] Comparative Example 3

[0082] Step (1) and step (2) are the same as in Example 1;

[0083] Step (3): 40 L of fluorine-containing chlorinated brine and 50 g / L of calcium chloride solution were subjected to calcium fluoride-induced crystallization, the molar ratio of calcium ions in the calcium chloride solution to fluoride ions in the fluorine-containing chlorinated brine was controlled to be 1.1, the reaction was carried out for 1.5 h, and after solid-liquid separation, 626 g of calcium fluoride crystals (dry weight) and 65 L of calcium fluoride crystal mother liquor were obtained;

[0084] Step (4): 65 L of calcium fluoride crystallization mother liquor and 14 L of phosphate crystallization mother liquor were concentrated through a reverse osmosis membrane at an operating pressure of 3.0 MPa, an operating pH of 6.0, and a concentration factor of 175 to obtain fresh water and concentrated water. The sodium chloride concentration in the concentrated water was 100 g / L. The concentrated water was evaporated and crystallized at a controlled evaporation temperature of 95°C and a pressure of -20 kPa to obtain 150 g of sodium chloride crystals and 38 g of miscellaneous salts.

[0085] Calculations show that the comprehensive recovery rate of fluorinated chlorinated phosphorus in the wastewater is 91.5%. Testing shows that the quality of superphosphate meets the first-class requirements of GB / T20413-2017 "Calcium Superphosphate." The resulting calcium fluoride crystals are colloidal aggregates, and XRF analysis shows they contain 6.7wt% CaSO4. However, the quality of the calcium fluoride crystals does not meet the requirements of GB / T27804-2011 "Calcium Fluoride." The residual Ca²⁺ concentration in the calcium fluoride crystallization mother liquor is 15.6g / L, resulting in subsequent evaporation and crystallization with SO4. 2- Combined with calcium chloride to form mixed salts, the purity of sodium chloride does not meet the requirements of first-class industrial dry salt in GB / T 5462-2015 "Industrial Salt".

[0086] Combined with the examples provided by the present invention, it can be seen that if the method of the present invention is not adopted, the comprehensive recovery rate of chlorofluorophosphine cannot be guaranteed to be higher than 95%, or the product quality of calcium fluoride, sodium chloride, and chlorophosphine crystals does not meet the requirements of relevant national standards.

[0087] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for treating wastewater containing fluorine, chlorine, sulfur and phosphorus, characterized in that: The following steps are involved: (1) After adjusting the pH of the fluorine-containing, chlorine-containing, sulfur-containing and phosphorus-containing wastewater to 4.5-9.0, the wastewater is separated by a nanofiltration membrane to obtain sulfur-containing and phosphorus-containing concentrated water and fluorine-containing and chlorine-containing brine; (2) subjecting the sulfur-phosphorus concentrated water and calcium chloride to phosphate-induced crystallization and solid-liquid separation to obtain superphosphate and phosphate crystallization mother liquor; the total molar ratio of calcium ions in the calcium chloride to sulfate and phosphate in the sulfur-phosphorus concentrated water is 1 to 1.5:1; and subjecting the fluorine-containing chlorinated salt water and calcium chloride to calcium fluoride-induced crystallization, and solid-liquid separation to obtain calcium fluoride crystals and calcium fluoride crystal mother liquor; wherein the molar ratio of calcium ions in the calcium chloride to fluoride ions in the fluorine-containing chlorinated salt water is 0.5-0.8:1; (3) The calcium fluoride crystallization mother liquor and the phosphate crystallization mother liquor are concentrated through a reverse osmosis membrane to obtain fresh water and concentrated water containing sodium chloride, and the concentrated water containing sodium chloride is crystallized by evaporation to obtain sodium chloride crystals and miscellaneous salts.

2. The method for treating fluorine-containing chlorophosphine wastewater according to claim 1, wherein: The nanofiltration membrane is a polypiperazineamide nanofiltration membrane. During the separation process using the nanofiltration membrane, the pressure is 3.0-5.0 MPa and the time is 0.5-4 h.

3. The method for treating wastewater containing fluorine, chlorine, sulfur and phosphorus according to claim 1 or 2, characterized in that: The volume ratio of the sulfur-phosphorus concentrated water to the fluorine-chloride-containing brine is 1:1.5-4.

4. The method for treating wastewater containing fluorine, chlorine, sulfur and phosphorus according to claim 1 or 2, characterized in that: The sulfur-phosphorus concentrated water has a fluoride ion concentration of 5-15 g / L, a chloride ion concentration of 1-5 g / L, a phosphate concentration of 3-25 g / L, and a sulfate concentration of 6-40 g / L.

5. The method for treating wastewater containing fluorine, chlorine, sulfur and phosphorus according to claim 1 or 2, characterized in that: The fluorine ion concentration in the fluorine-containing chlorosulfuric acid wastewater is 5-15 g / L, the phosphate concentration is 1-5 g / L, the sulfate concentration is 2-8 g / L, the sodium concentration is 12-25 g / L, and the chloride ion concentration is 1-5 g / L.

6. The method for treating wastewater containing fluorine, chlorine, phosphorus and sulfide according to claim 1 or 2, characterized in that: During the phosphate-induced crystallization process, the total molar ratio of calcium ions in the calcium chloride to sulfate and phosphate in the sulfur-phosphorus concentrated water is 1.1-1.3:

1.

7. The method for treating wastewater containing fluorine, chlorine, sulfur and phosphorus according to claim 1 or 2, characterized in that: During the calcium fluoride-induced crystallization process, the molar ratio of calcium ions in the calcium chloride to fluoride ions in the fluorine-containing chlorine brine is 0.55-0.65:

1.

8. The method for treating wastewater containing fluorine, chlorine, sulfur and phosphorus according to claim 1 or 2, characterized in that: During the phosphate-induced crystallization process and the calcium fluoride-induced crystallization process, the calcium chloride is added in the form of an aqueous solution, and the concentration of the calcium chloride solution is independently 50-250 g / L.

9. The method for treating wastewater containing fluorine, chlorine, phosphorus and sulfide according to claim 1 or 2, characterized in that: During the reverse osmosis membrane concentration process, the operating pressure is 3.0-6.0 MPa, the operating pH is 4.5-9.0, the concentration multiple is 30-80 times, and the sodium chloride concentration in the concentrated water is 90 g / L-120 g / L.

10. The method for treating wastewater containing fluorine, chlorine, sulfur and phosphorus according to claim 1 or 2, characterized in that: The temperature of the evaporation crystallization is 95-105° C., and the pressure is -20--90 kPa.

Images