Method for removing calcium ions and iron ions in sewage

Abstract

The invention belongs to the technical field of sewage treatment, and particularly relates to a method for removing calcium ions and iron ions in sewage. The method for removing the calcium ions and the iron ions in the sewage comprises the following steps that seed crystals and sodium carbonate are added into the sewage containing the calcium ions and the iron ions to be mixed, the adding speed of the sodium carbonate is controlled to be 50-200 mg / h * L, and CaCO3-Fe crystal precipitates are formed. The method for removing the calcium ions and the iron ions in the sewage has the advantages that synchronous removal of the calcium ions and the iron ions can be achieved, generated CaCO3-Fe crystals are large in particle size and high in purity, compared with separated removal, the effect is better, the water content is lower, and follow-up treatment is easier and more convenient.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a method for removing calcium and iron ions from wastewater. Background Technology

[0002] Excessive accumulation of iron ions in water can react with elements such as phosphorus and nitrogen, promoting eutrophication, leading to rapid algal growth, oxygen depletion, and severely impacting water quality and ecological balance. Furthermore, excessive iron entering the human body through drinking water can easily accumulate in organs such as the liver and heart, damaging liver cell function and potentially causing cirrhosis or even liver cancer. Iron overload can also promote lipid peroxidation, leading to myocardial damage and arrhythmias.

[0003] Currently, the main methods for treating iron-containing wastewater include chemical precipitation, adsorption, and electrolysis. While chemical methods are simple to operate and low in cost, they generate a large amount of sludge during the process and have limited effectiveness in removing iron ions. Adsorption methods offer advantages such as good treatment efficiency, simple operation, and stable performance, but the adsorbents are expensive, require regular replacement, and have high water quality requirements. Electrolysis offers advantages such as good treatment efficiency and the ability to recover metallic iron, but it has high operating costs and may produce harmful gases during the electrolysis process. Summary of the Invention

[0004] This application provides a method for removing calcium and iron ions from wastewater, aiming to solve the problems of unsatisfactory treatment effect, high cost, and easy secondary pollution caused by existing technologies for treating iron-containing wastewater.

[0005] This application provides a method for removing calcium and iron ions from wastewater, comprising the following steps: adding seed crystals and sodium carbonate to wastewater containing calcium and iron ions, and controlling the addition rate of sodium carbonate to be 50-200 mg / h*L, to form CaCO3-Fe crystal precipitate.

[0006] According to some embodiments of the method for removing calcium and iron ions from wastewater described in this application, the molar ratio of calcium ions to iron ions in the wastewater is (10-20):1.

[0007] According to some embodiments of the method for removing calcium and iron ions from wastewater as described in this application, the seed crystals include calcite and / or garnet.

[0008] According to some embodiments of the method for removing calcium and iron ions from wastewater described in this application, the seed crystal is calcite.

[0009] According to some embodiments of the method for removing calcium and iron ions from wastewater described in this application, the amount of seed crystals added is 50-450 mg / L.

[0010] According to some embodiments of the method for removing calcium and iron ions from wastewater described in this application, the seed crystals have a particle size of 0.02-0.15 mm.

[0011] According to some embodiments of the method for removing calcium and iron ions from wastewater described in this application, the amount of sodium carbonate added is 50-600 mg / L.

[0012] According to some embodiments of the method for removing calcium and iron ions from wastewater described in this application, the mixing stirring speed is 10-45 r / min.

[0013] According to some embodiments of the method for removing calcium and iron ions from wastewater described in this application, the mixing temperature is 20-30°C and the mixing time is 15-30 min.

[0014] The beneficial effects of this application include: the method for removing calcium and iron ions from wastewater described in this application can achieve simultaneous removal of calcium and iron ions, and the generated CaCO3-Fe crystals have large particle size and high purity, which is better than separate removal, has lower water content, and is simpler for subsequent treatment. Detailed Implementation

[0015] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0016] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0017] This application provides a method for removing calcium and iron ions from wastewater, comprising the following steps: adding seed crystals and sodium carbonate to wastewater containing calcium and iron ions, and controlling the addition rate of sodium carbonate to be 50-200 mg / h*L, to form CaCO3-Fe crystal precipitate.

[0018] When Ca is present in the solution 2+ Fe 3+ and CO3 2-At that time, and with calcium carbonate precipitation being dominant, FeOOH will be dispersed or coated on the CaCO3 surface in the form of nanoparticles.

[0019] The reaction equation is:

[0020]

[0021] 2Fe 3+ +3CO3 2- +2H2O→2FeOOH↓+3CO2↑.

[0022] If sodium carbonate is added too quickly, the calcium carbonate and iron compounds may not co-precipitate or may form a doped structure.

[0023] The method for removing calcium and iron ions from wastewater described in this application can achieve simultaneous removal of calcium and iron ions, and the generated CaCO3-Fe crystals have large particle size and high purity. Compared with separate removal, the method is more effective, has lower water content, and is easier to dispose of.

[0024] In some embodiments of this application, the molar ratio of calcium ions to iron ions in the wastewater is (10-20):1, for example, 10:1, 12:1, 15:1, 18:1, 20:1, etc. Since the solubility product of calcium carbonate (CaCO3) is approximately 3.36 × 10⁻⁶, the ratio of calcium ions to iron ions is approximately 10:1. -9 (25℃), while the Ksp of iron hydroxides [such as Fe(OH)3] is approximately 2.79 × 10⁻⁶. -39 The solubility products of the two differ by more than 20 orders of magnitude. If Fe 3+ If the concentration is too high, the OH- in the solution will increase. - or CO3 2- The concentration increased slightly, Fe 3+ It will preferentially precipitate alone as Fe(OH)3 or Fe2(CO3)3, and cannot form a co-precipitate with CaCO3.

[0025] In some embodiments of this application, the seed crystals include calcite and / or garnet. Crystallization removal can improve precipitation separation efficiency, ultimately forming crystalline particles rather than flocculent precipitates. During solid-liquid separation, crystalline particles only require physical separation, while sludge precipitation requires the addition of coagulants and flocculants.

[0026] In some embodiments of this application, the seed crystal is calcite.

[0027] In some embodiments of this application, the amount of seed crystals added is 50-450 mg / L, such as 50 mg / L, 80 mg / L, 120 mg / L, 260 mg / L, 380 mg / L, 410 mg / L, 450 mg / L, etc.

[0028] In some embodiments of this application, the seed crystals have a particle size of 0.02-0.15 mm, such as 0.02 mm, 0.05 mm, 0.08 mm, 0.10 mm, 0.12 mm, 0.15 mm, etc.

[0029] In some embodiments of this application, the amount of sodium carbonate added is 50-600 mg / L, such as 50 mg / L, 80 mg / L, 200 mg / L, 260 mg / L, 380 mg / L, 430 mg / L, 510 mg / L, 600 mg / L, etc.

[0030] In some embodiments of this application, the mixing stirring speed is 10-45 r / min, for example 10 r / min, 18 r / min, 23 r / min, 35 r / min, 39 r / min, 43 r / min, 45 r / min, etc. Controlling the stirring speed can control the reaction rate. If the reaction rate is too fast, the calcium carbonate and iron compound may not be able to co-precipitate or may form a doped structure.

[0031] In some embodiments of this application, the mixing temperature is 20-30°C, such as 20°C, 22°C, 25°C, 28°C, 30°C, etc., and the mixing time is 15-30 min, such as 15 min, 18 min, 20 min, 26 min, 30 min, etc.

[0032] The technical solution of this application will be further described below with reference to specific embodiments.

[0033] Example 1

[0034] A method for removing calcium and iron ions from wastewater includes the following steps: adding calcite seed crystals with a particle size of 0.10 mm and sodium carbonate to wastewater with a calcium ion to iron ion molar ratio of 10:1, wherein the amount of calcite seed crystals added is 300 mg / L and the amount of sodium carbonate added is 200 mg / L, the sodium carbonate is added at a rate of 75 mg / h*L, and the mixture is stirred for 15 min at a temperature of 25℃ and a stirring speed of 30 r / min to form CaCO3-Fe crystal precipitate.

[0035] Example 2

[0036] The method for removing calcium and iron ions from wastewater described in Example 2 differs from that in Example 1 only in that the sodium carbonate is added at a rate of 50 mg / h*L during the implementation of the method for removing calcium and iron ions from wastewater described in Example 2.

[0037] Example 3

[0038] The method for removing calcium and iron ions from wastewater described in Example 3 differs from that in Example 1 only in that the sodium carbonate is added at a rate of 125 mg / h*L during the implementation of the method for removing calcium and iron ions from wastewater described in Example 3.

[0039] Example 4

[0040] The method for removing calcium and iron ions from wastewater described in Example 4 differs from that in Example 1 only in that the sodium carbonate is added at a rate of 200 mg / h*L during the implementation of the method for removing calcium and iron ions from wastewater described in Example 4.

[0041] Example 5

[0042] The method for removing calcium and iron ions from wastewater described in Example 5 differs from that in Example 1 only in that the mixing and stirring speed during the implementation of the method for removing calcium and iron ions from wastewater described in Example 5 is 10 r / min.

[0043] Example 6

[0044] The method for removing calcium and iron ions from wastewater described in Example 6 differs from that in Example 1 only in that the mixing and stirring speed during the implementation of the method for removing calcium and iron ions from wastewater described in Example 6 is 20 r / min.

[0045] Example 7

[0046] The method for removing calcium and iron ions from wastewater described in Example 7 differs from that in Example 1 only in that the mixing and stirring speed during the implementation of the method for removing calcium and iron ions from wastewater described in Example 7 is 45 r / min.

[0047] Example 8

[0048] The method for removing calcium and iron ions from wastewater described in Example 8 differs from that in Example 1 only in that the seed crystal used in the method for removing calcium and iron ions from wastewater described in Example 8 is garnet.

[0049] Comparative Example 1

[0050] The method for removing calcium and iron ions from wastewater described in Comparative Example 1 differs from that in Example 1 only in that the molar ratio of calcium ions to iron ions in the wastewater is 5:1 during the implementation of the method for removing calcium and iron ions from wastewater described in Comparative Example 1.

[0051] Comparative Example 2

[0052] The method for removing calcium and iron ions from wastewater described in Comparative Example 2 differs from that in Example 1 only in that the molar ratio of calcium ions to iron ions in the wastewater is 30:1 during the implementation of the method for removing calcium and iron ions from wastewater described in Comparative Example 2.

[0053] The effectiveness of the methods for removing calcium and iron ions from wastewater described in Examples 1-8 and Comparative Examples 1-2 of this application was studied, and the results are shown in Table 1.

[0054] Table 1

[0055]

[0056]

[0057] As can be seen from Table 1, the method for removing calcium and iron ions from wastewater described in this application can achieve simultaneous removal of calcium and iron ions, and the generated CaCO3-Fe crystals have large particle size and high purity, which simplifies the subsequent treatment process.

[0058] Comparing Examples 1-4, it can be seen that when the sodium carbonate addition rate during the implementation process is 50-75 mg / h*L, the removal rate of calcium and iron ions in wastewater is relatively high when the method described in this application is used.

[0059] Comparing Examples 5-7, it can be seen that when the mixing speed during implementation is 20-30 r / min, the removal rate of calcium and iron ions in wastewater is relatively high when the method described in this application is used.

[0060] Comparing Examples 1 and 8, it can be seen that when calcite is used as a seed crystal during the implementation process, the removal rate of calcium and iron ions in wastewater is higher than that of garnet.

[0061] Comparing Example 1 and Comparative Examples 1-2, it can be seen that the method for removing calcium and iron ions from wastewater described in this application is applicable to wastewater with a molar ratio of calcium to iron ions of (10-20):1.

[0062] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A method for removing calcium and iron ions from wastewater, characterized in that, Includes the following steps: Seed crystals and sodium carbonate are added to wastewater containing calcium and iron ions and mixed together. The addition rate of sodium carbonate is controlled at 50-200 mg / h*L to form CaCO3-Fe crystal precipitate.

2. The method for removing calcium and iron ions from wastewater according to claim 1, characterized in that, The molar ratio of calcium ions to iron ions in the wastewater is (10-20):

1.

3. The method for removing calcium and iron ions from wastewater according to claim 1, characterized in that, The seed crystals include calcite and / or garnet.

4. The method for removing calcium and iron ions from wastewater according to claim 1, characterized in that, The seed crystal is calcite.

5. The method for removing calcium and iron ions from wastewater according to claim 1, characterized in that, The amount of seed crystals added is 50-450 mg / L.

6. The method for removing calcium and iron ions from wastewater according to claim 1, characterized in that, The seed crystals have a particle size of 0.02-0.15 mm.

7. The method for removing calcium and iron ions from wastewater according to claim 1, characterized in that, The amount of sodium carbonate added is 50-600 mg / L.

8. The method for removing calcium and iron ions from wastewater according to claim 1, characterized in that, The mixing speed is 10-45 r / min.

9. The method for removing calcium and iron ions from wastewater according to claim 1, characterized in that, The mixing temperature is 20-30℃, and the mixing time is 15-30 minutes.

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