Ferrate-calcium salt enhanced turbidity removal and water purification method based on ferrous ion activation

Abstract

The invention relates to a ferrate-calcium salt enhanced turbidity removal and water purification method based on ferrous ion activation, and aims to solve the technical problems that the effluent quality is difficult to guarantee when a traditional coagulant is used for treating low-temperature low-turbidity water or algae-laden water, and particularly the turbidity is easy to exceed the standard. The invention discloses a ferrate-calcium salt enhanced turbidity removal and water purification method, which comprises the following steps of: adding a ferrous compound, a calcium salt and ferrate into low-turbidity or high-algae raw water, uniformly stirring, controlling the molar ratio of the ferrous compound to the ferrate to the calcium salt to be (0.5-1.5): 1: (2-10), and standing and precipitating to complete the enhanced turbidity removal and water purification method of the low-turbidity or high-algae raw water. Calcium ions are introduced through calcium salt so as to effectively compress double electric layers on the surface of colloid and promote destabilization and coagulation, multiple synergistic effects of oxidation, coagulation, adsorption and coprecipitation are constructed through directional activation of ferrous ions on ferrate and synergistic interaction of the calcium ions, and therefore when complex water with low temperature, low turbidity, high algae and the like is treated, the treatment effect is good, and the treatment cost is low. The deep and efficient removal of turbidity and organic matters can be synchronously realized.

Description

Technical Field

[0001] This invention belongs to the field of water treatment, and particularly relates to a method for enhanced turbidity removal and water purification based on ferrous ion activation of ferrate-calcium salt. Background Technology

[0002] In traditional drinking water treatment processes, coagulation and sedimentation are the core steps in removing turbidity. However, their effectiveness is often significantly reduced when dealing with low-temperature, low-turbidity water or water with high algae content. At lower water temperatures, the Brownian motion of water molecules weakens, and the Zeta potential stability of colloidal particles in the water increases. This results in slow hydrolysis of conventional aluminum or iron salt coagulants, forming small, loose flocs with extremely poor settling performance. Meanwhile, high algae content presents a double challenge: on the one hand, algal cells themselves have low density and are difficult to settle; on the other hand, extracellular polymers secreted by living algal cells and algal-derived organic matter can encapsulate colloidal particles and increase water viscosity, severely interfering with the hydrolysis and charge neutralization processes of coagulants. This leads to a surge in dosage without achieving the desired effect, resulting in persistently high turbidity and organic load in the effluent, posing a significant challenge to the stable operation of water treatment plants.

[0003] Ferrate, as a green water treatment agent, has attracted much attention due to its combined strong oxidizing and flocculating properties. It can directly oxidize and degrade various organic substances and kill microorganisms over a wide pH range, and its reduction product, Fe(III), can generate ferric hydroxide colloids with adsorption and flocculation functions in situ. However, its commercial application faces significant bottlenecks: the preparation and storage costs of ferrate itself are high, and large-scale use alone is not economically viable. More importantly, its turbidity removal essentially relies on the entrapment and sweeping action of Fe(III) flocs, a relatively simple mechanism. For highly stable fine colloids in low-temperature, low-turbidity water, this single subsequent flocculation is often not efficient or rapid enough, and its ability to remove subsequent oxidation byproducts is limited, indicating that there is still significant room for improvement in overall purification efficiency. Summary of the Invention

[0004] The purpose of this invention is to solve the technical problem that the effluent quality is difficult to guarantee when traditional coagulants are used to treat low-temperature, low-turbidity water or high-algae water, especially the turbidity is easy to exceed the standard. The invention provides a method for enhanced turbidity removal and water purification based on ferrous ion activation of ferrate-calcium salt.

[0005] The present invention provides a method for enhanced turbidity removal and water purification based on ferrous ion activation using ferrate-calcium salts, implemented according to the following steps:

[0006] Add ferrous compounds, calcium salts, and ferrates to low-turbidity or high-algae raw water, stir evenly, and control the molar ratio of ferrous compounds, ferrates, and calcium salts to (0.5~1.5):1:(2~10). After static sedimentation, the enhanced turbidity removal and purification method for low-turbidity or high-algae raw water is completed.

[0007] This invention introduces ferrous compounds, which serve as activators to reduce high-valence iron to generate intermediate-valence iron with higher reactivity, thereby enhancing the overall oxidation efficiency. On the other hand, the newly generated Fe(III) reacts with Fe(III) produced after the reaction of ferrates to form more compact Fe(OH)3 flocs.

[0008] This invention introduces calcium ions through calcium salts. On the one hand, the positive charge of calcium ions can effectively compress the electric double layer on the surface of colloids, promoting destabilization and coagulation. On the other hand, calcium ions can undergo complexation or precipitation reactions with carbonate, phosphate and organic carboxyl groups in water to generate micro-calcium salt crystal nuclei, providing an interface for heterogeneous deposition of iron hydroxide flocs. Furthermore, the bridging network between flocs is strengthened through ion bridging, thereby constructing composite flocs with higher density, denser structure and faster settling speed.

[0009] This invention constructs a multi-layered synergistic effect of oxidation, coagulation, adsorption, and co-precipitation by directional activation of ferrates by ferrous ions and synergistic enhancement by calcium ions. This enables the simultaneous deep and efficient removal of turbidity and organic matter when treating complex water qualities such as low temperature, low turbidity, and high algae content. Its overall purification efficiency far exceeds that of single-agent or simple mixed systems. While improving performance, it significantly reduces the unit water treatment cost by partially replacing expensive ferrates with inexpensive ferrous and calcium salts. Furthermore, all components are environmentally friendly and pose no risk of secondary pollution. The proposed optimized reagent ratio and intelligent control strategy make the system highly adaptable to water quality fluctuations, especially changes in temperature, turbidity, and algae content, solving the core problem of unstable performance of traditional processes under such conditions. In addition, the technical solution has clearly defined parameters, making it easy to integrate with online monitoring and automatic control systems, providing a reliable path for achieving precise and intelligent operation of the water treatment process. Attached Figure Description

[0010] Figure 1 The graphs show the comparison of effluent turbidity and UV254 removal rate of the ferrous ion-activated ferrate-calcium salt enhanced turbidity removal water purification agents in Examples 1-3. The straight line represents the UV254 removal rate, and the bar graph represents the effluent turbidity removal rate.

[0011] Figure 2 The graphs show the comparison of effluent turbidity and UV254 removal rate of the ferrous ion-activated ferrate-calcium salt enhanced turbidity removal water purification agents in Examples 1, 4, and 5. The straight line represents the UV254 removal rate, and the bar graph represents the effluent turbidity removal rate.

[0012] Figure 3 The graph shows a comparison of the effluent turbidity and UV254 removal rate of the ferrous ion-activated ferrate-calcium salt enhanced turbidity removal water purification agents of Examples 4, 1, and 2. The straight line represents the UV254 removal rate, and the bar graph represents the effluent turbidity removal rate. Detailed Implementation

[0013] Specific Implementation Method 1: This implementation method, based on ferrous ion-activated ferrate-calcium salt enhanced water purification, is carried out according to the following steps:

[0014] Add ferrous compounds, calcium salts, and ferrates to low-turbidity or high-algae raw water, stir evenly, and control the molar ratio of ferrous compounds, ferrates, and calcium salts to (0.5~1.5):1:(2~10). After static sedimentation, the enhanced turbidity removal and purification method for low-turbidity or high-algae raw water is completed.

[0015] In this embodiment, the amount of ferrous compound is calculated as Fe(II), the amount of ferrate is calculated as Fe(VI), and the amount of calcium salt is calculated as Ca(II).

[0016] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the water temperature of the low-turbidity or high-algae raw water is 2~10℃ and the pH is 6.5~8.5.

[0017] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that the turbidity of the low-turbidity raw water is 4~15 NTU.

[0018] Specific Implementation Method Four: This implementation method differs from Specific Implementation Method One or Two in that the concentration of algae in the high-algae raw water is 10~20 μg / L (calculated as chlorophyll a).

[0019] Specific Implementation Method 5: This implementation method differs from one of the specific implementation methods 1 to 4 in that the ferrous compound is ferrous sulfate.

[0020] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the calcium salt mentioned is one or a mixture of several of calcium chloride, calcium sulfate, calcium nitrate, or calcium hydroxide.

[0021] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One through Six in that when the turbidity of the low-turbidity raw water is 4~12.0 NTU, the concentrations of ferrous compounds, calcium salts, and ferrates in the water are controlled to be 2.5 × 10⁻⁶. -5 ~1.5×10 -4 mol / L, 5.0×10 -5 ~1.0×10 -4 mol / L and 1.0×10 -5 ~1.0×10 -4 mol / L.

[0022] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the stirring process is to first stir at a speed of 150 to 250 r / min for 1 to 3 minutes, and then stir at a speed of 30 to 50 r / min for 10 to 15 minutes.

[0023] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the molar ratio of ferrous compound, ferrate and calcium salt is controlled to be 1:1:(4~6).

[0024] This implementation optimizes the molar ratio of ferrous compounds, ferrates, and calcium salts.

[0025] Specific Implementation Method 10: This implementation method differs from Specific Implementation Methods 1 to 9 in that the static sedimentation treatment time is 15 to 30 minutes.

[0026] Specific Implementation Method Eleven: This implementation method differs from Specific Implementation Methods One through Ten in that after static precipitation treatment, calcium ions are removed by ion exchange, addition of sodium carbonate, or membrane softening.

[0027] Example 1: This example describes a method for enhanced turbidity removal and water purification based on ferrous ion-activated ferrate-calcium salts, implemented according to the following steps:

[0028] Calcium chloride solution, ferrous sulfate solution, and ferrate were added sequentially to 1.0 L of low-turbidity raw water. The mixture was stirred rapidly (200 r / min) for 1 minute, followed by slow stirring (40 r / min) for 10 minutes. After settling for 20 minutes, the enhanced turbidity removal and purification method for low-turbidity or high-algae raw water was completed. The supernatant was collected at 2 cm below the liquid surface, and the residual turbidity and UV were immediately measured. 254 and COD Mn .

[0029] The raw water used in this embodiment was an artificially prepared simulated low-temperature, low-turbidity, high-organic-content water sample to ensure the uniformity and comparability of experimental conditions. The specific preparation method is as follows: a certain amount of kaolin and sodium humate were added to each liter of tap water, and after thorough mixing, the mixture was allowed to stand for 24 hours to mature, thus obtaining the reserve raw water. Before the experiment, the reserve raw water was cooled to the target temperature (e.g., 5±1℃) using a cold water bath, and the pH value was adjusted to the required value using a 0.1 mol / L hydrochloric acid or sodium hydroxide solution. The typical water quality indicators of this raw water were measured as follows: initial turbidity of 9.87 NTU, pH value of 7.5±0.3, and UV254 (characterizing aromatic organic matter in water) of 0.29 cm⁻¹. -1 Between, permanganate index (COD) Mn The concentration was 3.9 mg / L. This water quality effectively simulates the characteristics of water bodies commonly found in reservoirs or lakes during winter, characterized by low temperature, low turbidity, and the presence of natural organic matter.

[0030] In this embodiment, 1.0 ml of 0.1 mol / L calcium chloride solution was added, and after mixing, the [Ca] in the water sample was reduced. 2+ ] = 1.0 × 10 -4 mol / L; add 0.5 ml of 0.1 mol / L ferrous sulfate solution, mix well, and the [Fe] in the water sample will be reduced. 2+ ] = 5.0 × 10 -5 mol / L; ferrate was added at a dosage of 50 μmol / L (calculated as Fe).

[0031] In this embodiment, the residual turbidity of the water sample was measured to be 0.25 NTU, the UV254 removal rate was 78.5%, and the COD... Mn The removal rate was 73.1%.

[0032] Example 2: The difference between this example and Example 1 is that the volume of the 0.1 mol / L ferrous sulfate solution added is 0.25 ml, and other conditions remain unchanged. At this time, the initial molar ratio Fe(II):Fe(VI):Ca(II) = 0.5:1.0:2.0.

[0033] In this embodiment, the residual turbidity of the water sample was measured to be 0.52 NTU, UV... 254 The removal rate was 70.2%, COD Mn The removal rate was 65.8%.

[0034] Example 3: The difference between this example and Example 1 is that the volume of the 0.1 mol / L ferrous sulfate solution added is 0.75 ml, and other conditions remain unchanged. At this time, the initial molar ratio Fe(II):Fe(VI):Ca(II) = 1.5:1.0:2.0.

[0035] In this embodiment, the residual turbidity of the water sample was measured to be 0.38 NTU, UV... 254 The removal rate was 75.0%, COD Mn The removal rate was 69.5%.

[0036] Example 4: The difference between this example and Example 1 is that the volume of the 0.1 mol / L calcium chloride solution added is 2.5 ml, and other conditions remain unchanged. At this time, the initial molar ratio Fe(II):Fe(VI):Ca(II) = 1.0:1.0:5.0.

[0037] In this embodiment, the residual turbidity of the water sample was measured to be 0.18 NTU, UV. 254 The removal rate was 79.8%, COD Mn The removal rate was 74.2%, and this embodiment also showed the best effluent effect among all embodiments, making it the most suitable ratio for the water quality of this sample.

[0038] Example 5: The difference between this example and Example 1 is that the volume of the 0.1 mol / L calcium chloride solution added is 5.0 ml, and other conditions remain unchanged. At this time, the initial molar ratio Fe(II):Fe(VI):Ca(II) = 1.0:1.0:10.0.

[0039] In this embodiment, the residual turbidity of the water sample was measured to be 0.20 NTU, UV... 254 The removal rate was 78.9%, COD Mn The removal rate was 73.5%.

[0040] Comparative Example 1: This comparative example differs from Example 1 in that no calcium chloride solution was added, while other conditions remained unchanged.

[0041] In this embodiment, the residual turbidity of the water sample was measured to be 2.10 NTU, UV. 254 The removal rate was 71.0%, COD Mn The removal rate was 66.0%.

[0042] Comparative Example 2: This comparative example differs from Example 1 in that only polyaluminum chloride is added instead of the reagent, at a dosage of 8 mg / L, while other conditions remain unchanged.

[0043] In this embodiment, the residual turbidity of the water sample was measured to be 1.83 NTU, UV... 254 The removal rate was 32.3%, COD Mn The removal rate was 28.6%.

Claims

1. A method for the purification of water from turbidity by ferric iron activated ferrate-calcium salt intensification, characterized by The method for strengthening and removing turbidity of water by ferric ion activated high ferrate-calcium salt is realized according to the following steps: The ferrous compound, calcium salt and high ferrate are added into low turbidity or high algae raw water, and stirred uniformly, the molar ratio of the ferrous compound, high ferrate and calcium salt is controlled to be (0.5-1.5):1:(2-10), and after the standing and precipitation treatment, the method for strengthening and removing turbidity of low turbidity or high algae raw water is completed.

2. The method of ferric ion activation based on high ferrate-calcium salt enhanced turbidity removal for water purification according to claim 1, characterized in that The water temperature of low turbidity or high algae raw water is 2-10 DEG C, and pH is 6.5-8.

5.

3. The method of ferric ion activation based on high ferrate-calcium salt enhanced turbidity removal for water purification according to claim 1, characterized in that The turbidity of low turbidity raw water is 4-15 NTU.

4. The method of ferric ion activation based on high ferrate-calcium salt enhanced turbidity removal for water purification according to claim 1, characterized in that The concentration of algae in high algae raw water is 10-20 μg / L.

5. The method of ferric ion activation based on high ferrate-calcium salt enhanced turbidity removal for water purification according to claim 1, characterized in that The ferrous compound is ferrous sulfate.

6. The method of ferric ion activation based on high ferrate-calcium salt enhanced turbidity removal for water purification according to claim 1, characterized in that The calcium salt is one or mixture of several of calcium chloride, calcium sulfate, calcium nitrate or calcium hydroxide.

7. The method of ferric ion activation based ferrate-calcium enhanced turbidity removal for water purification as claimed in claim 1, wherein When the turbidity of low turbidity raw water is 4-12.0 NTU, the concentrations of ferrous compound, calcium salt and ferrate in water are controlled to be 2.5×10 -5 ~1.5×10 -4 mol / L, 5.0×10 -5 ~1.0×10 -4 mol / L and 1.0×10 -5 ~1.0×10 - 4 mol / L respectively.

8. The method of ferric ion activation based ferrate-calcium enhanced turbidity removal for water purification as claimed in claim 1, wherein The stirring process is first stirred at the speed of 150-250 r / min for 1-3 min, and then stirred at the speed of 30-50 r / min for 10-15 min.

9. The method of ferric ion activation based ferrate-calcium enhanced turbidity removal from water as claimed in claim 1, wherein The standing and precipitation treatment time is 15-30 min.

10. The method of ferric ion activation based ferrate-calcium enhanced turbidity removal from water as claimed in claim 1, wherein After the standing and precipitation treatment, the calcium ion is removed by ion exchange process, adding sodium carbonate or membrane softening process.

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