Solid polytitanium coagulant and its preparation method and application based on liquid phase dispersion

Abstract

The application discloses a solid polytitanium coagulant and a preparation method and application thereof based on liquid-phase dispersion, and the preparation method of the solid polytitanium coagulant comprises the following steps: firstly, mixing liquid organic dispersant and titanium tetrachloride to obtain a mixed solution, then adding a solvent into the mixed solution to perform a polymerization reaction, and finally performing suction filtration and drying on the obtained reaction solution to obtain the solid polytitanium coagulant; wherein the liquid organic dispersant is one or more of n-hexane, n-heptane, isooctane, 3-methylpentane and cyclopentane. By adding the organic dispersant and taking inorganic titanium salt-titanium tetrachloride as a titanium source precursor, the solid polytitanium coagulant with excellent coagulation performance is rapidly and stably prepared in a green, environmentally-friendly, economical and efficient manner, the prepared polytitanium coagulant has high polymerization degree and good storage performance, and can be widely applied to removal of turbidity, organic matters and heavy metals in drinking water, domestic sewage and industrial wastewater.

Description

Technical Field

[0001] This invention relates to the field of coagulants, specifically to a solid polytitanium coagulant and its preparation method and application based on liquid-phase dispersion. Background Technology

[0002] In recent years, titanium salt coagulants have gained increasing attention due to their outstanding performance, huge application potential, and promise to solve some of the problems encountered in the application of aluminum and iron salt coagulants. Compared with traditional aluminum and iron salt coagulants, titanium salt coagulants have stronger adsorption and charge neutralization capabilities and netting and sweeping abilities, resulting in larger flocs and faster settling, making them suitable for low-temperature and low-turbidity water bodies. Furthermore, titanium salt coagulants are less corrosive, do not cause color problems, and are safe and non-toxic, posing no potential harm to human health or the ecological environment. Moreover, the coagulated sludge, after high-temperature calcination, yields titanium dioxide photocatalysts with wide-ranging applications, effectively solving the problem of subsequent treatment of large quantities of coagulated sludge. Meanwhile, China is rich in ilmenite resources, ranking second in the world in reserves, making titanium salt coagulants extremely promising for application.

[0003] However, simple titanium salts such as titanium tetrachloride (TC) and titanium sulfate (TS) are strongly acidic and release large amounts of H+ during hydrolysis. + In practical applications, the rapid hydrolysis rate leads to numerous drawbacks, such as difficulty in controlling the effective hydrolysis form, excessively low pH of the effluent, and instability of the coagulant over long-term storage. These issues severely affect the coagulation performance and limit the application of titanium salt coagulants. To overcome these problems, the preparation of polytitanium coagulants has become a current research focus for titanium salt coagulants. Traditional polymerization methods, including alkali prepolymerization and silica copolymerization, have been explored in recent years for titanium salt coagulants. Patents CN102976462A and CN103011358B disclose inorganic polymeric flocculants of poly(titanium tetrachloride) (PTC) and poly(titanium sulfate) (PTS), respectively. However, both PTC and PTS are liquid coagulants with low polymerization degree, prone to aggregation and unstable performance, and they also introduce more NaCl or Na2SO4 components. Patent CN101979333B discloses a method for preparing a polysilicon-titanium composite flocculant. However, the coagulant obtained by this invention is still a liquid and will generate more COD during use, posing a potential problem of secondary pollution, which is not conducive to its application in drinking water treatment and other fields. The above-mentioned traditional polymerization methods do not fully consider the hydrolytic characteristics of titanium salts themselves. Although they improve the degree of polymerization of the coagulant to some extent, they still suffer from problems such as low degree of polymerization, poor stability, difficult transportation, and narrow applicable scenarios, resulting in limited improvement in the coagulation performance of the obtained polytitanium coagulant.

[0004] Given that traditional polymerization methods are not suitable for titanium salts, patent CN104944547B innovatively applies the sol-gel method to the preparation of polytitanium coagulants and discloses a TiO2-based coagulant (TXC). This method uses TC as a precursor, ethanol as a solvent, and acetylacetone as a hydrolysis inhibitor. The resulting coagulant is solid, effectively solving the problems of instability, difficulty in storage, and difficulty in transportation associated with titanium salt coagulants. Compared to TC and PTC prepared by traditional polymerization methods, it exhibits a higher degree of polymerization, superior coagulation performance, smaller pH changes in effluent, and a wider applicable pH range. However, the drying method in this patented preparation scheme has significant drawbacks: natural drying is not only time-consuming (15 days), but the drying process is also highly susceptible to environmental humidity and temperature, resulting in poor repeatability and a low success rate; oven drying still takes a long time (7 days), and the drying process wastes a large amount of solvent and consumes a large amount of energy, making it unclean and environmentally unfriendly, which is detrimental to the mass production of coagulants and thus limits the widespread application of this product.

[0005] Therefore, there is an urgent need to develop other preparation methods to quickly, stably, environmentally friendly, economically and efficiently prepare solid polytitanium coagulants with excellent coagulation performance, so that they can better meet the needs of modern water treatment technology and mass production. Summary of the Invention

[0006] Purpose of the invention: The present invention aims to provide a solid polytitanium coagulant with excellent coagulation performance, high stability and environmental friendliness. The present invention also provides a method for preparing the solid polytitanium coagulant based on liquid phase dispersion and the application of the solid polytitanium coagulant.

[0007] Technical solution: The preparation method of the solid polytitanium coagulant based on liquid phase dispersion according to the present invention includes the following steps:

[0008] First, the liquid organic dispersant is mixed with titanium tetrachloride to obtain a mixture. Then, a solvent is added to the mixture to carry out a polymerization reaction. The resulting reaction solution is filtered and dried to obtain a solid titanium polycoagulant.

[0009] Further, the molar ratio of titanium tetrachloride to solvent is 1:1-10; the solvent includes water, and preferably, the molar ratio of titanium tetrachloride to solvent is 1:2-4.

[0010] Furthermore, the solvent also includes an organic chelating agent, and the molar ratio of titanium tetrachloride to the organic chelating agent is 1:0.025-0.1.

[0011] Furthermore, the organic chelating agent is one or more of acetylacetone, acetic acid, citric acid, tartaric acid, maleic acid, and succinic acid, preferably acetylacetone.

[0012] Furthermore, the liquid organic dispersant is one or more of n-hexane, n-heptane, isooctane, 3-methylpentane, and cyclopentane, preferably n-heptane.

[0013] Furthermore, the volume ratio of the liquid organic dispersant to titanium tetrachloride is 2-100:1, preferably 40:1.

[0014] Furthermore, the polymerization reaction conditions are as follows: stirring speed of 100-1000 rpm, reaction at 0-30℃ for 0.5-8 h; the drying method is vacuum drying or rotary evaporation drying, with drying parameters of 30-80℃ for 0.25-4 h; the solvent is added to the mixture by dripping the solvent dropwise at a rate of 0.1-10 mL / min or spraying the solvent into the mixture at a rate of 0.1-10 mL / min.

[0015] The present invention also provides the application of the above-mentioned solid polytitanium coagulant in water treatment. Specifically, the dosage of the solid polytitanium coagulant is 2-12 mg Ti / L, and the water body to be treated includes drinking water, domestic sewage or industrial wastewater.

[0016] Invention Principle: This invention utilizes a liquid-phase dispersion method to prepare solid polytitanium coagulants. By adding a liquid organic dispersant, the polymerization rate of titanium salts is controlled; furthermore, by adding an organic chelating agent, the hydrolysis rate of titanium salts is controlled, which is beneficial to the formation of effective titanium hydroxyl hydrolysis products during coagulation and significantly enhances the stability of the polytitanium coagulant. The liquid-phase dispersion method of this invention is simple, feasible, rapid, stable, uses readily available raw materials, and is low in cost, aligning with the concept of sustainable green development.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0018] (1) This invention proposes for the first time to prepare solid polytitanium coagulant by liquid phase dispersion method. By adding organic dispersant, the polytitanium coagulant has a high degree of polymerization, excellent coagulation performance, rapid floc sedimentation, and retains the advantages of low metal residue and low organic residue in the effluent of titanium salt coagulant.

[0019] (2) The preparation method of the present invention is fast and simple, which greatly shortens the time for preparing solid polytitanium coagulant using inorganic titanium salt as titanium source precursor. In comparison, the natural drying time of the coagulant in the existing patent CN104944547B is about 15 days, while the heating drying time of the present invention is only about 7 days. The preparation method is safe and stable, with mild conditions, simple operation, high repeatability, and easy to quantify and produce.

[0020] (3) The solid polytitanium coagulant prepared by the present invention is environmentally friendly in preparation process. By first filtering and then drying, not only is the energy required for drying reduced, but the material is also recycled through the recovery of organic dispersant. In addition, compared with the existing polytitanium coagulants prepared with organic titanium salt as precursor, the solid polytitanium coagulant of the present invention has lower organic residue in the coagulated water and less ecological impact and health risk.

[0021] (4) The polytitanium coagulant prepared by the present invention is a solid material, which is a white or yellow powder particle at room temperature. It has high stability, can be stored for a long time and transported over long distances, and can be widely used in the removal of turbidity, organic matter and heavy metals in drinking water, domestic sewage and industrial wastewater. Attached Figure Description

[0022] Figure 1 This is a schematic diagram illustrating the treatment effect of solid polytitanium coagulants prepared under different H2O / Ti molar ratios in Example 1 on three types of humic acid-kaolin simulated wastewater.

[0023] Figure 2 This is a schematic diagram of the solid materials of the solid polytitanium coagulant prepared under different AcAc / Ti molar ratios in Example 2.

[0024] Figure 3 This is a schematic diagram showing the solubility and basicity of solid polytitanium coagulants prepared at different AcAc / Ti molar ratios under different storage times in Example 2.

[0025] Figure 4 This is a schematic diagram illustrating the treatment effect of solid polytitanium coagulants prepared at different AcAc / Ti molar ratios in Example 2 on natural river water at Nanjing University under different storage times. Detailed Implementation

[0026] The present invention will now be further described in conjunction with specific embodiments and accompanying drawings.

[0027] Example 1: This example describes the preparation of solid polytitanium coagulants using n-heptane as a liquid organic dispersant at different H2O / Ti molar ratios without the addition of organic chelating agents. The preparation steps are as follows:

[0028] (1) Mix 400 mL of n-heptane and 10 mL of titanium tetrachloride to form a homogeneous mixture for later use; wherein the volume ratio of n-heptane to titanium tetrachloride is 40:1.

[0029] (2) Set the reaction temperature to 0℃ and the stirring speed to 300 rpm; add 3.28-6.56 mL of ultrapure water dropwise into the mixture at a dropping rate of 0.2 mL / min; wherein the molar ratio of titanium tetrachloride to ultrapure water is 1:2-4; continue stirring for 1 h to allow it to react fully;

[0030] (3) Filter the mixed liquid after the reaction to obtain a solid material containing a small amount of dispersant;

[0031] (4) The solid material containing a small amount of dispersant was vacuum dried at 50°C for 1 hour to obtain solid polytitanium coagulants prepared with different H2O / Ti molar ratios.

[0032] The titanium yield of solid polytitanium coagulants prepared with different H2O / Ti molar ratios was determined, and the steps are as follows:

[0033] A certain mass of solid titanium coagulant was taken, added with 50% nitric acid, allowed to stand and diluted, and the titanium content was determined by inductively coupled plasma atomic emission spectrometry (ICP-OES). The titanium yield of titanium coagulants with different H2O / Ti molar ratios was calculated by formula 1.

[0034] Titanium yield (%) = (Mass of titanium in titanium-titanium coagulant / Mass of titanium in precursor) × 100% (Formula 1)

[0035] The titanium yield of solid polytitanium coagulants under different H2O / Ti molar ratios is shown in Table 1 below. The titanium yield of solid polytitanium coagulants prepared under different H2O / Ti conditions is all above 95%. The titanium yield is little affected by the H2O / Ti factor. Considering the transfer loss caused by human operation during the measurement process, the preparation method of this invention has almost no titanium element loss and the titanium yield is close to 100%, indicating that this method can stably prepare solid polytitanium coagulants.

[0036] Table 1. Titanium yield of preparation methods under different H2O / Ti conditions

[0037]

[0038] Application Example 1: Solid polytitanium coagulants prepared at different H2O / Ti molar ratios in Example 1 were used to treat three types of humic acid-kaolin simulated wastewater.

[0039] Simulated wastewater with low turbidity and low humic acid concentration: initial turbidity 10±0.5 NTU, DOC 2±0.1 mg / L, pH 7.00±0.1; Simulated wastewater with medium turbidity and medium humic acid concentration: initial turbidity 20±1.0 NTU, DOC 10±0.5 mg / L, pH 7.30±0.1; Simulated wastewater with high turbidity and high humic acid concentration: initial turbidity 100±5.0 NTU, DOC 20±1.0 mg / L, pH 7.60±0.1.

[0040] The solid polytitanium coagulant prepared under different H2O / Ti conditions in this embodiment was added to three types of humic acid-kaolin simulated wastewater. Specifically, the dosage for low-turbidity, low-humic acid concentration simulated wastewater was 0.5-5 mg Ti / L, the dosage for medium-turbidity, medium-humic acid concentration simulated wastewater was 2-12 mg Ti / L, and the dosage for high-turbidity, high-humic acid concentration simulated wastewater was 5-30 mg Ti / L. The coagulation procedure was as follows: stirring at 200 rpm for 1 min, stirring at 40 rpm for 15 min, and standing for 20 min. The residual turbidity was then measured using a turbidimeter (2100N HACH, USA).

[0041] CJJ58-2009 Technical Regulations for Operation, Maintenance and Safety of Urban Water Supply Plants stipulates that the turbidity of the effluent from the coagulation sedimentation tank should not exceed 3 NTU, and the turbidity of the final water supply to the pipeline network should not exceed 1 NTU. In this invention, 1 and 2 NTU are taken as the effluent turbidity standards for judging the quality of turbidity removal, and are referred to as turbidity dosages of 1 and 2 NTU, respectively.

[0042] Coagulation results as follows Figure 1 As shown, (a)-(c) represent the coagulation of simulated wastewater at low, medium, and high concentrations, respectively. The solid polytitanium coagulants prepared under different H2O / Ti molar ratios exhibit slightly different coagulation performances. The coagulation performance is relatively small under H2O / Ti molar ratios of 2-3.5, while the coagulation performance is slightly worse under an H2O / Ti molar ratio of 4. This may be related to the morphology of titanium hydroxyl hydrolysis products resulting from different H2O / Ti molar ratios and the reaction uniformity caused by the stirring speed in the specific experiment. Specifically, for simulated wastewater with low turbidity and low humic acid concentration, and for simulated wastewater with medium turbidity and medium humic acid concentration, the turbidity dosage of 1 NTU is approximately 3 mg Ti / L and 6 mg Ti / L, respectively. For simulated wastewater with high turbidity and high humic acid concentration, only about 10 mg Ti / L is needed to reduce the initial turbidity of the simulated wastewater from 100 NTU to 2 NTU. At all three concentrations, the residual turbidity can be reduced to below 1 NTU by adding a certain dosage of coagulant, and no particle re-stabilization phenomenon occurs. These results demonstrate that the solid polytitanium coagulant prepared by this invention has good coagulation effect on wastewater with different turbidity and different organic matter concentrations.

[0043] Example 2: This example provides a method for preparing solid polytitanium coagulants using n-heptane as a liquid organic dispersant and acetylacetone (AcAc) as a chelating agent at different AcAc / Ti molar ratios. The liquid-phase dispersion method is employed, and the steps are as follows:

[0044] (1) Mix 400 mL of n-heptane and 10 mL of titanium tetrachloride to obtain a mixed solution for later use; wherein the volume ratio of n-heptane to titanium tetrachloride is 40:1.

[0045] (2) Mix 0-0.93 mL AcAc and 4.92 mL of ultrapure water until AcAc is fully dissolved to obtain a solvent for later use; wherein, the molar ratio of titanium tetrachloride, ultrapure water and AcAc is 1:3:0-0.1;

[0046] (3) Set the reaction temperature to 0℃ and the stirring speed to 300 rpm; add the solvent dropwise into the mixture at a dropping rate of 0.2 mL / min; continue stirring for 1 h to allow it to react fully;

[0047] (4) Filter the mixed liquid after the reaction to obtain a solid material containing a small amount of dispersant;

[0048] (5) The solid material containing a small amount of dispersant is vacuum dried at 50°C for 1 hour to obtain solid polytitanium coagulant.

[0049] Based on different AcAc / Ti molar ratios, they are numbered 1-4 sequentially, and detailed ratios are shown in Table 2.

[0050] Table 2. Solid polytitanium coagulants prepared under different AcAc / Ti molar ratios.

[0051]

[0052] Figure 2 The images show actual photographs of the solid polytitanium coagulant prepared in this embodiment, from left to right: polytitanium coagulant 1-4. Figure 2 As shown, when AcAc / Ti is 0, the polytitanium coagulant is a white powder; when AcAc / Ti is greater than 0, the polytitanium coagulant is an orange-yellow powder, and the larger the AcAc / Ti, the darker the material color. This is because AcAc chelates with some of the titanium hydrolysates and is embedded in the titanium-oxygen skeleton structure of the polytitanium coagulant.

[0053] The steps for determining the solubility and basicity of solid polytitanium coagulants at different AcAc / Ti molar ratios are as follows:

[0054] The solubility of a coagulant affects its coagulation performance, and a decrease in solubility reflects whether it has deteriorated. This invention references the American ANSI / AWWAB408-2010 standard for liquid polyaluminum chloride, using the turbidity of a 1g Ti / L polytitanium coagulant stock solution as the standard for evaluating the solubility of polytitanium coagulant. The turbidity of 1g Ti / L stock solutions of polytitanium coagulant prepared immediately after preparation and after 7 and 14 days of sealed storage was measured under different AcAc / Ti molar ratios.

[0055] The results are as follows Figure 3As shown in (a), after 14 days of sealed storage, the turbidity of the 1 g Ti / L stock solutions of No. 1-4 was not higher than 2.0, indicating that the above polytitanium coagulants did not show obvious deterioration. However, the turbidity of the stock solutions of polytitanium coagulants prepared under different AcAc / Ti conditions increased to different degrees. Among them, the turbidity of No. 1 stock solution increased most significantly from 0.4 NTU to about 2.0 NTU because no organic chelating agent AcAc was added. The turbidity of No. 4 stock solution was the most stable, indicating that the addition of AcAc significantly inhibited the deterioration trend of polytitanium coagulants.

[0056] Figure 3 (b) shows the results of basicity determination of fresh polytitanium coagulants prepared under different AcAc / Ti molar ratios and after 7 and 14 days of sealed storage. Similar to the results of solubility determination, the larger the AcAc / Ti ratio, the greater the variation in basicity of the polytitanium coagulant. This is due to the continued self-polymerization of the coagulant during sealed storage, while the presence of AcAc inhibits its self-polymerization.

[0057] Application Example 2: The solid polytitanium coagulant prepared at different AcAc / Ti molar ratios in Example 2 was used to treat natural river water (taken from Xiangxuehai Lake, Xianlin Campus of Nanjing University) under different storage times. The steps are as follows:

[0058] Natural river water quality indicators: initial turbidity 4.0±0.2 NTU, UV254 0.085±0.01, pH 7.50±0.1.

[0059] The solid polytitanium coagulant prepared under different AcAc / Ti molar ratios in this embodiment was added to natural river water at a dosage of 2-12 mg Ti / L. The coagulation procedure was as follows: stirring at 200 rpm for 1 min, stirring at 40 rpm for 15 min, and then standing for 20 min before measuring the residual turbidity using a turbidimeter.

[0060] Depend on Figure 4 It can be seen that in Example 2, all four types of polytitanium coagulants (numbered 1-4) can reduce the turbidity of low-turbidity natural water to below 1 NTU. In fresh conditions, the turbidity dosage of the four polytitanium coagulants for this natural river water is around 4 mg Ti / L, demonstrating outstanding coagulation performance. After 7 days of sealed storage, the turbidity dosage of number 1 increased by approximately 175%, indicating a significant decrease in the coagulation performance of this coagulant, which may be due to the high Ti / C ratio in number 1. The turbidity dosage of numbers 2 and 3 increased by 75% and 50% respectively, showing some improvement compared to number 1, while the turbidity dosage of number 4 increased by only about 10%. Comparing number 2-4 with number 1 in Table 2 shows that the addition of organic chelating agents significantly enhances the stability of the polytitanium coagulant, enabling it to be stored for extended periods and transported over long distances.

Claims

1. A method for preparing a solid polytitanium coagulant based on liquid phase dispersion, characterized by, The method comprises the following steps: The liquid organic dispersant is mixed with titanium tetrachloride to obtain a mixed solution, and then a solvent is added to the mixed solution to perform a polymerization reaction, and the obtained reaction solution is filtered and dried to obtain a solid polytitanium coagulant; the liquid organic dispersant is one or more of n-hexane, n-heptane, isooctane, 3-methylpentane and cyclopentane; the solvent comprises water; the solvent is added to the mixed solution in the form of drops at a drop rate of 0.1-10 mL / min or in the form of spray at an atomization rate of 0.1-10 mL / min.

2. The production method according to claim 1, characterized by, The molar ratio of the titanium tetrachloride to the solvent is 1:1-10.

3. The production method according to claim 2, characterized by, The solvent further comprises an organic chelating agent, and the molar ratio of the titanium tetrachloride to the organic chelating agent is 1:0.025-0.

1.

4. The production method according to claim 3, characterized by, The organic chelating agent is one or more of acetylacetone, acetic acid, citric acid, tartaric acid, maleic acid and succinic acid.

5. The preparation method according to claim 1, characterized in that, The volume ratio of the liquid organic dispersant to the titanium tetrachloride is 2-100:

1.

6. The method of claim 1, wherein, The polymerization reaction is performed at a stirring speed of 100-1000 rpm at 0-30 ℃ for 0.5-8 h, and the drying method is vacuum drying or rotary evaporation drying, and the drying parameters are as follows: drying at 30-80 ℃ for 0.25-4 h.

7. A solid polytitanium coagulant prepared by the liquid dispersion-based preparation method of claim 1.

8. Application of the solid polytitanium coagulant of claim 7 in water treatment.

9. Use according to claim 8, characterized in that, The dosage of the solid polytitanium coagulant is 2-12 mgTi / L, and the water body for water treatment comprises drinking water, domestic sewage or industrial wastewater.

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