Method for softening sewage through co-crystallization

Abstract

The invention belongs to the technical field of sewage treatment, and particularly relates to a method for softening sewage through co-crystallization. The method for softening the sewage through co-crystallization comprises the following steps: adding a medicament into the sewage to be softened to enable substances to be removed in the sewage to be in a supersaturated state, then adding seed crystals into the sewage, and mixing and filtering. The method for softening the sewage through co-crystallization has the beneficial effects that according to the method for softening the sewage through co-crystallization, the removal object is in a supersaturated state by adding the agent, calcium fluoride or calcium fluorophosphate crystals are generated on the surface of the seed crystal in a heterogeneous crystallization mode under the action of external power, and the purpose of removing the fluorine ion concentration in the water is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage treatment, and in particular relates to a method for softening sewage through co-crystallization. Background Art

[0002] With the rapid development of industry, the discharge of various types of industrial wastewater has become increasingly prominent. Industrial wastewater is diverse and complex in composition. It contains a large number of impurities, such as fluoride and calcium ions. High concentrations of fluoride not only cause serious environmental pollution but can also be harmful to human health. High concentrations of fluoride can lead to eutrophication of water bodies, disrupting the ecological balance and affecting the survival of aquatic life. Long-term consumption of water with excessive fluoride content can cause dental fluorosis, and in severe cases, can even affect the nervous system and bone development.

[0003] At present, chemical precipitation and coagulation are mainly used to treat fluorine-containing wastewater. However, both chemical precipitation and coagulation have certain disadvantages. Therefore, an efficient and economical method for treating fluorine-containing wastewater is needed. Summary of the Invention

[0004] The present application provides a method for softening wastewater by co-crystallization, aiming to solve the problem of incomplete removal of existing fluoride-containing wastewater and relatively high cost.

[0005] The present application provides a method for softening sewage by co-crystallization, comprising the following steps: adding a reagent to the sewage to be softened to supersaturate the substance to be removed in the sewage, then adding crystal seeds to the sewage, mixing and filtering.

[0006] According to some embodiments of the method for softening sewage by co-crystallization described in the present application, the reagent includes sodium dihydrogen phosphate.

[0007] According to some embodiments of the method for softening sewage by co-crystallization described in the present application, phosphate in the sewage is supersaturated by adding sodium dihydrogen phosphate.

[0008] According to some embodiments of the method for softening wastewater by co-crystallization described in the present application, the concentration of fluoride ions in the wastewater is ≤20 mg / L.

[0009] According to some embodiments of the method for softening sewage by co-crystallization described in the present application, the seed crystals include dolomite, calcite or calcium fluorophosphate.

[0010] According to some embodiments of the method for softening sewage by co-crystallization described in the present application, the seed crystal is calcium fluorophosphate, and the particle size of the calcium fluorophosphate seed crystal is 0.15-0.6 mm.

[0011] According to some embodiments of the method for softening sewage by co-crystallization described in the present application, the particle size of the calcium fluorophosphate seed crystals is 0.2-0.3 mm.

[0012] According to some embodiments of the method for softening sewage by co-crystallization described in the present application, the amount of the calcium fluorophosphate seed crystals added is 100-500 mg / L.

[0013] According to some embodiments of the method for softening sewage by co-crystallization described in the present application, the amount of the calcium fluorophosphate seed crystals added is 400-450 mg / L.

[0014] According to some embodiments of the method for softening sewage by co-crystallization described in the present application, the mixing temperature is 20-30° C., and the mixing time is 10-30 min.

[0015] The beneficial effects of the present application include: the method for softening sewage by co-crystallization described in the present application makes the removal object in a supersaturated state by adding a reagent, and calcium fluoride or calcium fluorophosphate crystallizes on the surface of the seed crystal in a heterogeneous crystallization manner under the action of external power, thereby achieving the purpose of removing fluoride ion concentration in water. DETAILED DESCRIPTION

[0016] The embodiments of the present invention are described in detail below. The examples of the embodiments are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0017] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0018] An embodiment of the present application provides a method for softening sewage by co-crystallization, comprising the following steps: adding a reagent to the sewage to be softened to supersaturate the substance to be removed in the sewage, then adding crystal seeds to the sewage, mixing and filtering.

[0019] The method described in the present application achieves the purpose of removing fluoride ion concentration in water by adding a reagent to put the removal object into a supersaturated state, and calcium fluoride or calcium fluorophosphate crystallizes on the surface of the seed crystal in a heterogeneous crystallization manner under the action of external dynamics.

[0020] Induced crystallization is an improvement to traditional precipitation methods. This involves adding a specific crystal-inducing carrier and reagent to the raw water. Crystallization conditions are controlled to supersaturate, allowing the ions in the water to react with the reagent. The resulting precipitate forms new crystals on the surface of the seed crystals, which then grow continuously as the reaction proceeds. This is a fluoride removal method. Induced crystallization removes fluoride ions from fluoride-containing water by inducing the production of calcium fluoride and calcium fluorophosphate.

[0021] In some embodiments of the present application, the agent includes sodium dihydrogen phosphate.

[0022] In some embodiments of the present application, sodium dihydrogen phosphate is added to make the phosphate in the sewage supersaturated.

[0023] In some embodiments of the present application, the concentration of fluoride ions in the sewage is ≤20 mg / L, for example, 20 mg / L, 18 mg / L, 15 mg / L, 12 mg / L, 10 mg / L, 8 mg / L, etc.

[0024] In some embodiments of the present application, the seed crystal includes dolomite, calcite or calcium fluorophosphate.

[0025] In some embodiments of the present application, the seed crystal is calcium fluorophosphate, and the particle size of the calcium fluorophosphate seed crystal is 0.15-0.6 mm, for example, 0.15 mm, 0.2 mm, 0.26 mm, 0.32 mm, 0.43 mm, 0.47 mm, 0.50 mm, 0.53 mm, 0.60 mm, etc.

[0026] In some embodiments of the present application, the particle size of the calcium fluorophosphate seed crystals is 0.2-0.3 mm.

[0027] In some embodiments of the present application, the added amount of the calcium fluorophosphate seed crystals is 100-500 mg / L, for example, 100 mg / L, 120 mg / L, 180 mg / L, 230 mg / L, 260 mg / L, 330 mg / L, 370 mg / L, 400 mg / L, 460 mg / L, 500 mg / L, etc.

[0028] In some embodiments of the present application, the amount of calcium fluorophosphate seed crystals added is 400-450 mg / L.

[0029] In some embodiments of the present application, the mixing temperature is 20-30°C, for example, 20°C, 22°C, 25°C, 28°C, 30°C, etc., and the mixing time is 10-30min, for example, 10min, 12min, 15min, 20min, 25min, 30min, etc.

[0030] The technical solution of this application is further described below with reference to specific embodiments.

[0031] Example 1

[0032] A method for softening sewage by co-crystallization comprises the following steps: adding sodium dihydrogen phosphate to sewage to be softened (the concentration of fluoride ions in the sewage is 10 mg / L) to supersaturate phosphate in the sewage; then adding calcium fluorophosphate seed crystals with a particle size of 0.2-0.3 mm to the sewage, and controlling the amount of the calcium fluorophosphate seed crystals added to be 100 mg / L; mixing at a temperature of 25° C. for 10 minutes; and filtering.

[0033] Example 2

[0034] The method for softening sewage by co-crystallization described in Example 2 is different from that in Example 1 only in that the particle size of the calcium fluorophosphate seed crystals added in the method for softening sewage by co-crystallization described in Example 2 is 0.3-0.4 mm.

[0035] Specific operation methods include:

[0036] Sodium dihydrogen phosphate is added to the sewage to be softened (the concentration of fluoride ions in the sewage is 10 mg / L) to supersaturate the phosphate in the sewage. Then, calcium fluorophosphate seeds with a particle size of 0.3-0.4 mm are added to the sewage, and the amount of calcium fluorophosphate seeds added is controlled to be 100 mg / L. The mixture is mixed at a temperature of 25°C for 10 minutes and filtered.

[0037] Example 3

[0038] The method for softening sewage by co-crystallization described in Example 3 is different from that in Example 1 only in that the particle size of the calcium fluorophosphate seed crystals added in the method for softening sewage by co-crystallization described in Example 3 is 0.4-0.6 mm.

[0039] Specific operation methods include:

[0040] Sodium dihydrogen phosphate is added to the sewage to be softened (the concentration of fluoride ions in the sewage is 10 mg / L) to make the phosphate in the sewage supersaturated, and then calcium fluorophosphate seeds with a particle size of 0.4-0.6 mm are added to the sewage, and the amount of calcium fluorophosphate seeds added is controlled to be 100 mg / L. The mixture is mixed at a temperature of 25°C for 10 minutes and filtered.

[0041] Example 4

[0042] The method for softening sewage by co-crystallization described in Example 4 is different from that in Example 1 only in that the amount of calcium fluorophosphate seed crystals added in the method for softening sewage by co-crystallization described in Example 4 is 400 g / L.

[0043] Specific operation methods include:

[0044] Sodium dihydrogen phosphate is added to the sewage to be softened (the concentration of fluoride ions in the sewage is 10 mg / L) to supersaturate the phosphate in the sewage. Then, calcium fluorophosphate seeds with a particle size of 0.2-0.3 mm are added to the sewage, and the amount of calcium fluorophosphate seeds added is controlled to be 400 mg / L. The mixture is mixed at a temperature of 25°C for 10 minutes and filtered.

[0045] Example 5

[0046] The method for softening sewage by co-crystallization described in Example 5 is different from that in Example 1 only in that the amount of calcium fluorophosphate seed crystals added in the method for softening sewage by co-crystallization described in Example 5 is 500 g / L.

[0047] Specific operation methods include:

[0048] Sodium dihydrogen phosphate is added to the sewage to be softened (the concentration of fluoride ions in the sewage is 10 mg / L) to make the phosphate in the sewage supersaturated, and then calcium fluorophosphate seeds with a particle size of 0.2-0.3 mm are added to the sewage, and the amount of calcium fluorophosphate seeds added is controlled to be 500 mg / L. The mixture is mixed at a temperature of 25°C for 10 minutes and filtered.

[0049] Example 6

[0050] The method for softening sewage by co-crystallization described in Example 6 is different from that in Example 1 only in that the method for softening sewage by co-crystallization described in Example 6 uses calcite crystal seeds instead of calcium fluorophosphate crystal seeds.

[0051] The specific steps include:

[0052] Sodium dihydrogen phosphate is added to the sewage to be softened (the concentration of fluoride ions in the sewage is 10 mg / L) to supersaturate the phosphate in the sewage. Then, calcite seeds with a particle size of 0.2-0.3 mm are added to the sewage, and the amount of calcium fluorophosphate seeds added is controlled to be 100 mg / L. The mixture is mixed at a temperature of 25°C for 10 minutes and filtered.

[0053] Example 7

[0054] The method for softening sewage by co-crystallization described in Example 7 is different from that in Example 1 only in that the method for softening sewage by co-crystallization described in Example 7 uses dolomite crystal seeds instead of calcium fluorophosphate crystal seeds.

[0055] The specific steps include:

[0056] Sodium dihydrogen phosphate is added to the sewage to be softened (the concentration of fluoride ions in the sewage is 10 mg / L) to make the phosphate in the sewage supersaturated, and then dolomite seeds with a particle size of 0.2-0.3 mm are added to the sewage, and the amount of calcium fluorophosphate seeds added is controlled to be 100 mg / L. The mixture is mixed at a temperature of 25°C for 10 minutes and filtered.

[0057] Study on the effect of treating sewage by co-crystallization to soften sewage as described in Examples 1-7 of this application

[0058] The results are shown in Table 1.

[0059] Table 1

[0060]

[0061]

[0062] It can be seen from Table 1 that the method for softening sewage by co-crystallization described in the present application has a good effect of removing calcium ions and fluoride ions, and the effect is optimal when the addition amount of calcium fluorophosphate seed crystals is 400g / L and the particle size is 0.2-0.3mm.

[0063] Although the above embodiments have been shown and described, it is understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. Changes, modifications, substitutions and variations of the above embodiments by those skilled in the art are all within the scope of protection of the present invention.

Claims

1. A method for softening sewage by co-crystallization, characterized in that The following steps are involved: Add reagents to the sewage to be softened to make the substances to be removed in the sewage supersaturated, then add crystal seeds to the sewage, mix and filter.

2. The method for softening sewage by cocrystallization according to claim 1, characterized in that The agent includes sodium dihydrogen phosphate.

3. The method for softening sewage by cocrystallization according to claim 2, characterized in that: The phosphate in the wastewater is supersaturated by adding sodium dihydrogen phosphate.

4. The method for softening sewage by cocrystallization according to claim 1, characterized in that The concentration of fluoride ions in the sewage is ≤20 mg / L.

5. The method for softening sewage by cocrystallization according to claim 1, characterized in that: The seed crystals include dolomite, calcite or calcium fluorophosphate.

6. The method for softening sewage by co-crystallization according to claim 1, characterized in that: The seed crystal is calcium fluorophosphate, and the particle size of the calcium fluorophosphate seed crystal is 0.15-0.6 mm.

7. The method for softening sewage by co-crystallization according to claim 6, characterized in that: The particle size of the calcium fluorophosphate seed crystals is 0.2-0.3 mm.

8. The method for softening sewage by co-crystallization according to claim 6, characterized in that: The amount of the calcium fluorophosphate seed crystal added is 100-500 mg / L.

9. The method for softening sewage by co-crystallization according to claim 6, characterized in that: The amount of calcium fluorophosphate seed crystals added is 400-450 mg / L.

10. The method for softening sewage by co-crystallization according to claim 1, characterized in that: The mixing temperature is 20-30° C., and the mixing time is 10-30 min.

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