Nucleation granulation process for simultaneously removing calcium and fluorine in high-calcium low-fluorine wastewater

Abstract

The invention relates to the technical field of wastewater treatment, in particular to a nucleation granulation process for simultaneously removing calcium and fluorine in high-calcium low-fluorine wastewater. The nucleation energy barrier of the calcium fluoride is reduced by adopting a nucleation granulation process, utilizing high-concentration calcium ions coexisting in the fluorine-containing wastewater and inducing the seed crystal, so that the calcium fluoride in a metastable region is separated out, nucleated and grown under the induction of the seed crystal, and phase reconstruction and water purification of fluorine ions in a water body are realized. In the process, a crystal inducing agent does not need to be additionally added, efficient recovery of fluorine resources is realized only by utilizing calcium ions coexisting in the water body through induction of the added crystal seeds, the treatment cost is greatly reduced, the efficiency is high, the flow is short, and the occupied area of equipment is small; in addition, the produced calcium fluoride granules are high in purity, and extra economic benefits can be created for enterprises.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and in particular to a nuclear crystal granulation process for removing calcium and fluoride from high-calcium and low-fluoride wastewater. Background Art

[0002] Fluoride is widely present in natural water and groundwater around us. It is one of the essential trace elements in the human body. Drinking water with a fluoride ion concentration of 0.5-1.0 mg / L can effectively prevent dental caries and osteoporosis, promote the metabolism of calcium and phosphorus, and promote the conduction of nerve excitement and the metabolism of the enzyme system; but when drinking water with a fluoride ion concentration higher than 5-10 mg / L for a long time, it will cause serious harm to the development of human teeth, bones and infant brains. At present, due to the large-scale discharge of industrial fluoride wastewater from mining and smelting, coal chemical industry, electroplating, photovoltaics, fertilizers, semiconductors and other industries, fluoride poisoning has seriously threatened human health.

[0003] The treatment methods for fluoride-containing wastewater mainly include adsorption, ion exchange, precipitation, membrane separation and electrodialysis. Adsorption is the most commonly used water treatment method in industrial production. It uses adsorbents such as activated alumina, activated carbon, metal oxides, zeolites, etc. to effectively remove fluoride ions from the solution through adsorption, ion exchange or complexation. The precipitation method usually adds a large amount of calcium salt to the fluoride-containing wastewater to form calcium fluoride precipitate, thereby removing fluoride ions; in fact, fluoride-containing wastewater itself contains a high concentration of calcium ions, but due to the high nucleation barrier of calcium fluoride, it is generally necessary to add additional calcium salts to the wastewater to promote the formation of calcium fluoride precipitate, so the cost of the reagents invested in this method is relatively high.

[0004] In summary, how to provide a method for simultaneously removing calcium and fluoride by utilizing the coexisting calcium ions in fluoride-containing wastewater to generate calcium fluoride precipitate without the need for additional addition of calcium salts has become a problem that needs to be solved urgently. Summary of the invention

[0005] In order to solve the above technical problems, the present disclosure provides a nuclear crystal granulation process for removing calcium and fluoride from high-calcium and low-fluoride wastewater. The present disclosure adopts the nuclear crystal granulation process and utilizes the calcium ions coexisting in the fluoride-containing wastewater. It achieves the purpose of simultaneously removing calcium and fluoride from high-calcium and low-fluoride wastewater without adding additional crystal inducers. It has low cost and high efficiency, and is conducive to industrial application.

[0006] The present invention provides a nuclear crystal granulation process for simultaneously removing calcium and fluoride from high-calcium and low-fluoride wastewater, comprising the following steps:

[0007] Mixing high-calcium and low-fluorine wastewater with a pH of 6-8 with seed crystals, and making the seed crystals fluidized by controlling the hydraulic parameters of the high-calcium and low-fluorine wastewater;

[0008] The seed crystals induce calcium ions and fluoride ions in the water to precipitate and nucleate on the surface of the seed crystals in the form of calcium fluoride and grow to form calcium fluoride granules;

[0009] In the high-calcium, low-fluoride type wastewater, the concentration of calcium ions is more than twice the concentration of fluoride ions.

[0010] The present invention utilizes the high concentration of calcium ions coexisting in fluorine-containing wastewater, and reduces the nucleation barrier of calcium fluoride through the induction of crystal seeds, so that calcium fluoride in the metastable zone precipitates, nucleates and grows under the induction of crystal seeds, and enhances mass transfer under the auxiliary regulation of hydraulics, thereby achieving the physical phase reconstruction of fluoride ions in the water body and water quality purification. In this process, there is no need to add additional crystal inducing agents (i.e. calcium salts), and only calcium ions coexisting in the water body are used to achieve efficient recovery of fluorine resources under the induction of crystal seeds, which greatly reduces the processing cost, and has high efficiency, short process, and small equipment footprint; in addition, the generated calcium fluoride granulation has high purity, which can create additional economic benefits for the enterprise.

[0011] Among them, in the high-calcium, low-fluoride wastewater, the concentration of calcium ions can be 2 times, 5 times, 10 times, 12 times, 15 times, 20 times or 50 times the concentration of fluoride ions, but is not limited to the listed values, and other unlisted values ​​within the above range are also applicable.

[0012] In the present disclosure, hydraulic parameters such as flow rate can be adjusted by those skilled in the art according to relevant parameters such as seed dosage and wastewater quality.

[0013] The following are preferred technical solutions of the present disclosure, but are not intended to be limitations of the technical solutions provided by the present disclosure. Through the following technical solutions, the technical objectives and beneficial effects of the present disclosure can be better achieved and realized.

[0014] As a preferred technical solution of the present invention, in the high-calcium, low-fluoride wastewater, the concentration of calcium ions is 100-500 mg / L, for example, 100 mg / L, 150 mg / L, 200 mg / L, 250 mg / L, 300 mg / L, 350 mg / L, 400 mg / L, 450 mg / L or 500 mg / L, etc.; the concentration of fluoride ions is 10-50 mg / L, for example, 10 mg / L, 20 mg / L, 30 mg / L, 40 mg / L or 50 mg / L, etc., but is not limited to the listed values, and other values ​​not listed within the above range are equally applicable.

[0015] As a preferred technical solution of the present disclosure, alkali or acid is used to adjust the pH of the high-calcium and low-fluoride wastewater.

[0016] Preferably, the base comprises sodium hydroxide.

[0017] Preferably, the acid comprises hydrochloric acid.

[0018] As a preferred technical solution of the present disclosure, the seed crystal includes one or more of quartz sand, garnet or fluorite, such as a combination of quartz sand and garnet, a combination of garnet and fluorite, a combination of quartz sand, garnet and fluorite, etc.

[0019] As a preferred technical solution of the present disclosure, the particle size of the seed crystal is 0.18-0.25 mm, such as 0.18 mm, 0.20 mm, 0.22 mm or 0.25 mm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0020] Appropriate seed particle size helps improve the removal effect of calcium and fluoride ions. If the seed particle size is too small, although the specific surface area increases, it will lead to a decrease in the take-out rate and a decrease in the water treatment volume; if the seed particle size is too large, the specific surface area will be too small, and there will be fewer active sites for surface nucleation, thereby reducing the water treatment load.

[0021] As a preferred technical solution of the present disclosure, the core crystal granulation process is carried out in a core crystal granulation reactor;

[0022] The core crystal granulation reactor is provided with a water inlet, a water outlet and a granulation body discharge outlet.

[0023] As a preferred technical solution of the present disclosure, the core crystal granulation process comprises the following steps: filling the seed crystal into the core crystal granulation reactor, and then introducing high-calcium and low-fluoride wastewater with a pH of 6-8 into the core crystal granulation reactor to make the seed crystal in a fluidized state;

[0024] The seed crystals induce calcium ions and fluoride ions in the water to precipitate and nucleate on the surface of the seed crystals in the form of calcium fluoride and grow to form calcium fluoride granules.

[0025] As a preferred technical solution of the present disclosure, the filling height of the seed crystal is 20-35% of the effective height of the nuclear crystal granulation reactor, for example, 20%, 22%, 25%, 28%, 30%, 33% or 35%, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0026] As a preferred technical solution of the present invention, the hydraulic retention time of the high-calcium and low-fluoride wastewater in the nuclear crystal granulation reactor is ≥5 min, for example, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min or 12 min, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0027] In the present disclosure, the flow rate of high-calcium and low-fluorine type wastewater into the nuclear crystal granulation reactor can be adjusted by those skilled in the art according to the actual conditions such as the calcium and fluorine concentrations in the wastewater, the filling amount of the seed crystals, the volume and height of the nuclear crystal granulation reactor, etc. The present disclosure does not make specific limitations.

[0028] Compared with the prior art, the technical solution provided by the embodiments of the present disclosure has the following advantages:

[0029] (1) The present invention utilizes the high concentration of calcium ions coexisting in fluorine-containing wastewater, and reduces the nucleation barrier of calcium fluoride through the induction of crystal seeds, so that calcium fluoride in the metastable zone precipitates, nucleates and grows under the induction of crystal seeds, thereby achieving the physical phase reconstruction of fluoride ions in the water body and water purification. In this process, no additional crystal inducing agent (i.e., calcium salt) is required, and only calcium ions coexisting in the water body are used to achieve efficient recovery of fluorine resources under the induction of crystal seeds, which greatly reduces the processing cost, and has high efficiency, short process, and small equipment footprint; in addition, the generated calcium fluoride granules are of high purity, which can create additional economic benefits for the enterprise.

[0030] (2) By adopting the core crystal granulation process disclosed in the present invention, the removal rate of fluoride ions in high-calcium and low-fluoride wastewater reaches more than 90%, the purity of the obtained calcium fluoride granules reaches more than 90%, and the cost of reagents is saved by more than 20%. DETAILED DESCRIPTION

[0031] In order to more clearly understand the above-mentioned objectives, features and advantages of the present disclosure, the scheme of the present disclosure will be further described below. It should be noted that the embodiments of the present disclosure and the features in the embodiments can be combined with each other without conflict.

[0032] In the following description, many specific details are set forth to facilitate a full understanding of the present disclosure, but the present disclosure may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present disclosure, rather than all of the embodiments.

[0033] Example 1

[0034] This embodiment provides a nuclear crystal granulation process for simultaneously removing calcium and fluoride from high-calcium and low-fluoride wastewater, comprising the following steps:

[0035] (1) filling the core crystal granulation reactor with quartz sand having a particle size of 0.18 mm, the filling height of which is 25% of the effective height of the core crystal granulation reactor;

[0036] (2) Using sodium hydroxide to adjust the pH of high-calcium, low-fluoride wastewater with a fluoride ion concentration of 10 mg / L and a calcium ion concentration of 100 mg / L to 6;

[0037] The adjusted high-calcium and low-fluorine wastewater is introduced into the nuclear crystal granulation reactor at a flow rate of 20 L / h to fully fluidize the quartz sand;

[0038] Quartz sand induces calcium ions and fluoride ions in the water to precipitate and nucleate on the surface of the seed crystals in the form of calcium fluoride and grow to form calcium fluoride granules;

[0039] In the nuclear crystal granulation reactor, the hydraulic retention time of the wastewater is 5 minutes.

[0040] Example 2

[0041] This embodiment provides a nuclear crystal granulation process for simultaneously removing calcium and fluoride from high-calcium and low-fluoride wastewater, comprising the following steps:

[0042] (1) filling garnet with a particle size of 0.22 mm into a core crystal granulation reactor, the filling height being 30% of the effective height of the core crystal granulation reactor;

[0043] (2) introducing high-calcium, low-fluoride wastewater having a fluoride ion concentration of 50 mg / L, a calcium ion concentration of 500 mg / L, and a pH of 8 into the nuclear crystal granulation reactor at a flow rate of 25 L / h to fully fluidize the garnet;

[0044] Garnet induces calcium ions and fluoride ions in the water to precipitate and nucleate on the surface of the seed crystal in the form of calcium fluoride and grow to form calcium fluoride granules;

[0045] In the nuclear crystal granulation reactor, the hydraulic retention time of the wastewater is 10 minutes.

[0046] Example 3

[0047] This embodiment provides a nuclear crystal granulation process for simultaneously removing calcium and fluoride from high-calcium and low-fluoride wastewater, comprising the following steps:

[0048] (1) filling a nucleus crystal granulation reactor with fluorite having a particle size of 0.25 mm, the filling height of which is 35% of the effective height of the nucleus crystal granulation reactor;

[0049] (2) introducing high-calcium, low-fluorine wastewater having a fluoride ion concentration of 30 mg / L, a calcium ion concentration of 400 mg / L, and a pH of 7 into the nuclear crystal granulation reactor at a flow rate of 30 L / h to fully fluidize the fluorite;

[0050] Fluoroborite induces calcium ions and fluoride ions in the water to precipitate and nucleate on the surface of the seed crystal in the form of calcium fluoride and grow to form calcium fluoride granules;

[0051] In the nuclear crystal granulation reactor, the hydraulic retention time of the wastewater is 8 minutes.

[0052] The fluoride ion concentration, calcium ion concentration and purity of the obtained granules in the water after treatment by the core crystal granulation process described in the present disclosure in Examples 1-3 were measured, and the removal rates of fluoride ions and calcium ions were calculated. The results are shown in Table 1.

[0053] Table 1

[0054] Fluoride ion removal rate Calcium ion removal rate Granulation purity Example 1 98.5％ 25.6％ 92.4％ Example 2 95.0％ 36.8％ 91.8％ Example 3 93.2％ 43.2％ 90.2％

[0055] It can be seen from Table 1 that the core crystal granulation process disclosed in the present invention can effectively and simultaneously remove fluorine and calcium ions in water without adding additional crystal inducing agents, the fluorine ion removal rate is over 93.2%, and the purity of the obtained calcium fluoride granules is over 90.2%.

[0056] Moreover, compared with the precipitation method, the cost of the crystal-inducing agent can be saved by more than 20%, and since no dosing device is required, the equipment floor space is greatly saved.

[0057] The above description is only a specific embodiment of the present disclosure, so that those skilled in the art can understand or implement the present disclosure. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure will not be limited to the embodiments described herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A nuclear crystal granulation process for simultaneously removing calcium and fluoride from high-calcium and low-fluoride wastewater, characterized in that: The following steps are involved: Mixing high-calcium and low-fluorine wastewater with a pH of 6-8 with seed crystals, and making the seed crystals fluidized by controlling the hydraulic parameters of the high-calcium and low-fluorine wastewater; The seed crystals induce calcium ions and fluoride ions in the water to precipitate and nucleate on the surface of the seed crystals in the form of calcium fluoride and grow to form calcium fluoride granules; In the high-calcium, low-fluoride type wastewater, the concentration of calcium ions is more than twice the concentration of fluoride ions.

2. The core crystal granulation process according to claim 1, characterized in that: In the high-calcium, low-fluoride wastewater, the concentration of calcium ions is 100-500 mg / L, and the concentration of fluoride ions is 10-50 mg / L.

3. The core crystal granulation process according to claim 1 or 2, characterized in that: Using alkali or acid to adjust the pH of the high-calcium, low-fluoride wastewater; Preferably, the base comprises sodium hydroxide; Preferably, the acid comprises hydrochloric acid.

4. The core crystal granulation process according to any one of claims 1 to 3, characterized in that: The seed crystals include one or more of quartz sand, garnet or fluorite.

5. The core crystal granulation process according to any one of claims 1 to 4, characterized in that: The particle size of the seed crystal is 0.18-0.25 mm.

6. The core crystal granulation process according to any one of claims 1 to 5, characterized in that: The core crystal granulation process is carried out in a core crystal granulation reactor; The core crystal granulation reactor is provided with a water inlet, a water outlet and a granulation body discharge outlet.

7. The core crystal granulation process according to claim 6, characterized in that: The core crystal granulation process comprises the following steps: filling the seed crystal into the core crystal granulation reactor, and then introducing high-calcium and low-fluorine wastewater with a pH of 6-8 into the core crystal granulation reactor to make the seed crystal in a fluidized state; The seed crystals induce calcium ions and fluoride ions in the water to precipitate and nucleate on the surface of the seed crystals in the form of calcium fluoride and grow to form calcium fluoride granules.

8. The core crystal granulation process according to claim 7, characterized in that: The filling height of the seed crystals is 20-35% of the effective height of the nuclear crystal granulation reactor.

9. The core crystal granulation process according to claim 7 or 8, characterized in that: The hydraulic retention time of the high-calcium and low-fluoride wastewater in the nuclear crystal granulation reactor is ≥5 minutes.