A method for preparing pigment-grade titanium dioxide by adsorbing and removing phosphorus based on phosphorus-containing wastewater

Abstract

This invention discloses a method for preparing pigment-grade titanium dioxide based on phosphorus adsorption and dephosphorization of phosphorus-containing wastewater. The steps are as follows: 1) Drying metatitanic acid slurry to remove its free water, then grinding the dried product to obtain fine metatitanic acid powder; 2) Taking phosphorus-containing wastewater, adjusting the pH to 2-6, placing it in a shaker for vibration, and adding the fine metatitanic acid powder at a certain temperature for adsorption; 3) After adsorption, recovering the fine metatitanic acid powder, drying it, and then calcining it in a muffle furnace in stages to obtain titanium dioxide. This method uses the dried and ground fine metatitanic acid powder as an adsorbent to treat phosphorus-containing wastewater, improving the pigment properties of titanium dioxide while treating the wastewater. The treated phosphorus-containing wastewater meets the standards for direct discharge. The resulting titanium dioxide exhibits significantly improved blue phase and tinting strength, effectively broadening the application range of titanium dioxide. The method is simple to operate, low in cost, and environmentally friendly, possessing significant industrial application value.

Description

Technical Field

[0001] This invention belongs to the field of chemical materials and relates to a method for preparing pigment-grade titanium dioxide based on phosphorus adsorption and dephosphorization of phosphorus-containing wastewater. Background Technology

[0002] Direct calcination of the hydrolysis product, metatitanic acid, easily leads to drawbacks such as sintering, numerous surface defects, and uneven particle size distribution. Adding salt treatment agents before calcination can catalyze and promote crystal transformation, significantly improving the quality of the calcined product. Many factors influence the production of pigment-grade titanium dioxide, and salt treatment is one of the key processes. Currently, widely used industrial salt treatment agents include oxides or salts of Zn, K, P, and Al.

[0003] Adding phosphoric acid or phosphate to metatitanic acid slurry before calcination can effectively improve the weather resistance of the product and enhance the softness of the particles. Furthermore, during the production process, metatitanic acid, even after impurity removal treatment, may still contain trace amounts of iron impurities. Iron reacts at high temperatures to form reddish-brown iron oxide, significantly reducing the whiteness of titanium dioxide. Ferric phosphate is pale yellow and does not decompose even at high temperatures, so using phosphoric acid or phosphate as a salt treatment agent can also eliminate the influence of non-ferrous metals on the performance of titanium dioxide. However, directly adding high concentrations of phosphoric acid or phosphate to the metatitanic acid slurry cannot guarantee a completely uniform distribution of phosphorus on the metatitanic acid, resulting in insufficient uniformity of particle morphology after calcination, affecting pigment performance and thus limiting the application of titanium dioxide.

[0004] Pigment-grade titanium dioxide can be used in papermaking, chemical fiber and ink industries. The better the pigment performance of the titanium dioxide used, the smoother, glossier, stronger, more stable and longer the service life of the corresponding products. Therefore, improving the pigment performance of titanium dioxide is an urgent task. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing pigment-grade titanium dioxide based on phosphorus adsorption and dephosphorization of phosphorus-containing wastewater. This method improves the pigment performance of titanium dioxide while treating phosphorus-containing wastewater. It is simple to operate, low in cost, and environmentally friendly.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing pigment-grade titanium dioxide based on phosphorus adsorption and dephosphorization from phosphorus-containing wastewater is provided, comprising the following steps:

[0008] 1) Dry the metatitanic acid slurry to remove its free water, and then grind the dried product to obtain fine metatitanic acid powder;

[0009] 2) Take a certain amount of phosphorus-containing wastewater, adjust the pH to 2-6, place it in a shaker and shake, and add the metatitanic acid fine powder obtained in step 1) at a certain temperature for adsorption; pH value is one of the important indicators affecting adsorption behavior, and usually directly affects the physicochemical properties of the adsorbate and adsorbent to affect the adsorption process.

[0010] 3) After adsorption, the metatitanic acid fine powder is recovered, dried, and then calcined in stages to obtain pigment-grade titanium dioxide.

[0011] According to the above scheme, in step 1), the drying temperature of the metatitanic acid slurry is 60-110℃, and the time is 4-12h. If the drying temperature is too low or the time is too short, the free water will not be removed sufficiently, and if the temperature is too high, it will affect the specific surface area, pore volume and pore size of the sample, resulting in poor adsorption performance of the material.

[0012] According to the above scheme, in step 1), the dried metatitanic acid has a TiO2 content >95% and an iron content (calculated as TiO2) <60ppm.

[0013] According to the above scheme, in step 1), the primary particle size of the metatitanic acid fine powder obtained after grinding is 60-300 nm, and the agglomerated particle size is 1-5 μm.

[0014] According to the above scheme, in step 2), the phosphorus-containing substances in the phosphorus-containing wastewater are one or more of glyphosate or its salt, glyphosate or its salt, phosphorous acid or its salt, and phosphoric acid or its salt.

[0015] According to the above scheme, in step 2), HNO3 or NaOH is used to adjust the pH of the phosphorus-containing wastewater.

[0016] According to the above scheme, in step 2), the phosphorus concentration in the phosphorus-containing wastewater is 1-100 mg / L.

[0017] According to the above scheme, in step 2), the adsorption temperature is 20-50℃, the oscillation speed is 120-200rpm, and the adsorption time is 20-480min.

[0018] According to the above scheme, in step 2), the phosphorus content in the metatitanic acid fine powder after adsorbing phosphorus is 0.2-0.5%.

[0019] According to the above scheme, in step 2), the amount of metatitanic acid fine powder added is 0.01-0.5g / 50mL of phosphorus-containing wastewater.

[0020] According to the above scheme, in step 3), the drying conditions are: drying at 100-110℃ for 6-10 hours.

[0021] According to the above scheme, in step 3), the segmented calcination process is as follows: the temperature is raised from room temperature to 400-450℃ at a uniform rate for 30-60 minutes and held for 25-35 minutes; then the temperature is raised to 700-800℃ at a uniform rate for 60-120 minutes and held for 50-70 minutes; finally, the temperature is raised to 830-900℃ at a uniform rate for 90-120 minutes and held for 15-25 minutes.

[0022] The beneficial effects of this invention are as follows:

[0023] 1. This invention provides a method for preparing pigment-grade titanium dioxide based on phosphorus adsorption and dephosphorization of phosphorus-containing wastewater. The method uses dried and ground metatitanic acid fine powder as an adsorbent to treat phosphorus-containing wastewater. The phosphorus in the wastewater is effectively utilized as the phosphorus source for pigment-grade titanium dioxide. During the adsorption process, the metatitanic acid fine powder reacts with the low-concentration phosphorus-containing wastewater, resulting in a low solid content and a thorough reaction. The phosphorus element is evenly distributed on the surface of the metatitanic acid, and the titanium dioxide particles obtained after calcination are more regular and smooth, resulting in superior pigment performance. This method improves the pigment performance of titanium dioxide while treating phosphorus-containing wastewater. It is simple to operate, low in cost, environmentally friendly, and has broad industrial application value.

[0024] 2. In this invention, after adsorption treatment, the total phosphorus content in the phosphorus-containing wastewater solution is less than 0.3 mg / L, and in some cases, it is almost undetectable. According to the national standard GB 15580-2011, the treated phosphorus-containing wastewater meets the standard for direct discharge. Moreover, the adsorbent does not require regeneration and can be directly calcined to obtain high-performance pigment-grade titanium dioxide. This invention improves the performance of titanium dioxide while reducing the environmental harm of phosphorus and solves the problems of harsh regeneration conditions and high costs associated with ordinary adsorbents.

[0025] 3. The titanium dioxide samples processed by the method of the present invention have obvious grain boundaries, appropriate particle size and narrow grain distribution, smooth surface, and significantly improved properties such as blue phase and tinting strength. When applied to the fields of papermaking, chemical fiber and ink, it can effectively improve the performance of corresponding products and effectively broaden the application range of titanium dioxide, and has important industrial application value. Attached Figure Description

[0026] Figure 1 The images show the XPS full scan spectrum (left) and Ti 2p photoelectron spectrum (right) before and after phosphorus adsorption in Example 1 of this invention.

[0027] Figure 2 The X-ray powder diffraction patterns are those of the raw materials, products in Example 1 and Comparative Example 1 of this invention.

[0028] Figure 3 This is a scanning electron microscope image of the titanium dioxide in Example 1.

[0029] Figure 4 This is a scanning electron microscope image of titanium dioxide from Comparative Example 1.

[0030] Figure 5 This is a scanning electron microscope image of titanium dioxide from Comparative Example 2. Detailed Implementation

[0031] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below.

[0032] Example 1

[0033] A method for preparing pigment-grade titanium dioxide based on phosphorus adsorption and dephosphorization from phosphorus-containing wastewater is provided, comprising the following steps:

[0034] First, the metatitanic acid slurry was dried in an oven at 110℃ for 8 hours. The dried product was then ground to obtain fine metatitanic acid powder with a primary particle size of 200 nm and an agglomerate particle size of 2.3 μm. The XPS full-scan spectrum and Ti 2p photoelectron spectrum of the metatitanic acid at this point are shown below. Figure 1 The adsorption curve before adsorption is shown. A 25 mg / L glyphosate solution was adjusted to pH 3 using 0.05 mol / L HNO3. 50 mL of this solution was placed in a constant-temperature shaking bed and shaken at 150 rpm. When the solution temperature reached 30°C, 0.10 g of metatitanic acid powder was accurately weighed and added to the solution. After adsorption for 20 min, a sample was taken. The phosphorus concentration in the solution was below the detection limit (0 mg / L) of the Agilent 5800 inductively coupled plasma atomic emission spectrometer. The phosphorus content of metatitanic acid (calculated as TiO2) was calculated to be 0.20% (based on elemental phosphorus). After adsorption, the solution was filtered, washed with deionized water, and the solid adsorbent was recovered. The XPS full-scan spectrum of metatitanic acid and the Ti 2p photoelectron spectrum at this point are shown below. Figure 1 The adsorption curve is shown in the figure. The adsorbent was then dried at 105℃ for 8 hours, and then placed in a muffle furnace for segmented calcination. The calcination regime was as follows: the temperature was uniformly increased from room temperature to 420℃ over 30 minutes and held for 30 minutes; the temperature was uniformly increased from 420℃ to 780℃ over 60 minutes and held for 60 minutes; the temperature was uniformly increased from 780℃ to 830℃ over 120 minutes and held for 20 minutes.

[0035] The obtained product has a TiO2 mass fraction >99%, a blue hue value (SCX) of 4.3, and a chromatic tint (TCS) of 1380. The XRD pattern of titanium dioxide is shown below. Figure 2 As shown, the scanning electron microscope image is as follows: Figure 3 As shown.

[0036] Based on product characterization:

[0037] ①X-ray photoelectron spectroscopy (XPS)

[0038] Compared to before adsorption, the XPS full-scan spectrum of the product after glyphosate adsorption showed a stronger N1s peak at 401.62 eV and a P 2p peak at 133.34 eV, corresponding to the glyphosate group, indicating that glyphosate was adsorbed onto the adsorbent. The binding energy of Ti 2p3 / 2 decreased from 458.63 eV before adsorption to 458.36 eV after adsorption, while the binding energy of Ti 2p1 / 2 decreased from 464.32 eV before adsorption to 464.07 eV after adsorption. The changes in the binding energies of Ti 2p3 / 2 and Ti 2p1 / 2 reflect that Ti in the adsorbent participated in the adsorption process, and glyphosate interacted with the adsorbent through electrostatic forces. Compared with salt treatment by adding phosphoric acid to the slurry and then stirring, the adsorbed P was more uniformly distributed on the surface of the metatitanic acid.

[0039] ②Powder diffraction characterization of phases (XRD)

[0040] The XRD pattern of the product matched that of the anatase phase (JCPDS 21-1272). Compared with the raw material, the XRD pattern of the product showed sharper peaks and higher peak intensities, indicating that it had a higher degree of crystallinity.

[0041] ③ Scanning electron microscopy (SEM)

[0042] The titanium dioxide obtained by this invention has a uniform particle size distribution, obvious grain boundaries, smooth surface, and narrow grain distribution, which is beneficial to improving the pigment performance of titanium dioxide.

[0043] Example 2

[0044] A method for preparing pigment-grade titanium dioxide based on phosphorus adsorption and dephosphorization from phosphorus-containing wastewater is provided, comprising the following steps:

[0045] First, the metatitanic acid slurry was dried in an oven at 110℃ for 8 hours. The dried product was then ground to obtain fine metatitanic acid powder with a primary particle size of 200 nm and an agglomerated particle size of 2.3 μm. A 100 mg / L glyphosate solution was adjusted to pH 3 using 0.05 mol / L HNO3. 50 mL of this solution was placed in a constant-temperature shaking bed and shaken at 170 rpm. When the solution temperature reached 25℃, 0.20 g of the fine metatitanic acid powder was accurately weighed and added to the solution. After adsorption for 120 min, a sample was taken. The phosphorus concentration in the solution was below the instrument's detection limit. The phosphorus content of metatitanic acid (calculated as TiO2) was calculated to be 0.40% (based on elemental phosphorus). After adsorption, the solution was filtered, washed with deionized water, and the solid adsorbent was recovered. The adsorbent was then dried at 105℃ for 8 hours and then calcined in a muffle furnace in stages. The calcination process is as follows: the temperature is raised from room temperature to 420℃ at a constant rate over 60 minutes and held for 30 minutes; the temperature is raised from 420℃ to 800℃ at a constant rate over 120 minutes and held for 30 minutes; the temperature is raised from 800℃ to 850℃ at a constant rate over 90 minutes and held for 20 minutes.

[0046] The obtained product has a TiO2 mass fraction >99%, a blue hue value (SCX) of 4.7, and a tinting strength (TCS) of 1450.

[0047] Example 3

[0048] A method for preparing pigment-grade titanium dioxide based on phosphorus adsorption and dephosphorization from phosphorus-containing wastewater is provided, comprising the following steps:

[0049] First, the metatitanic acid slurry was dried in an oven at 110℃ for 8 hours. The dried product was then ground to obtain fine metatitanic acid powder with a primary particle size of 200 nm and an agglomerate particle size of 2.3 μm. A 25 mg / L glyphosate solution was adjusted to pH 4 using 0.05 mol / L NaOH, and 50 mL of the solution was placed in a constant-temperature shaking bed and shaken at 180 rpm. When the solution temperature reached 25℃, 0.08 g of the fine metatitanic acid powder was accurately weighed and added to the solution. After adsorption for 120 min, a sample was taken, and the phosphorus concentration of the solution was 0.2 mg / L. The phosphorus content of metatitanic acid (calculated as TiO2) was calculated to be 0.34% (based on elemental phosphorus). After adsorption, the mixture was filtered, washed with deionized water, and the solid adsorbent was recovered. The adsorbent was then dried at 105℃ for 8 hours and then calcined in a muffle furnace in stages. The calcination process is as follows: the temperature is raised from room temperature to 420℃ at a constant rate over 60 minutes and held for 30 minutes; the temperature is raised from 420℃ to 800℃ at a constant rate over 120 minutes and held for 30 minutes; the temperature is raised from 800℃ to 850℃ at a constant rate over 90 minutes and held for 20 minutes.

[0050] The obtained product has a TiO2 mass fraction >99%, a blue hue value (SCX) of 4.5, and a tinting strength (TCS) of 1360.

[0051] Example 4

[0052] A method for preparing pigment-grade titanium dioxide based on phosphorus adsorption and dephosphorization from phosphorus-containing wastewater is provided, comprising the following steps:

[0053] First, the metatitanic acid slurry was dried in an oven at 110℃ for 8 hours. The dried product was then ground to obtain fine metatitanic acid powder with a primary particle size of 200 nm and an agglomerated particle size of 2.3 μm. A 25 mg / L phosphorous acid solution was adjusted to pH 6 using 0.1 mol / L NaOH, and 50 mL of the solution was placed in a constant-temperature shaking bed and shaken at 170 rpm. When the solution temperature reached 35℃, 0.16 g of the fine metatitanic acid powder was accurately weighed and added to the solution. After adsorption for 60 min, a sample was taken, and the phosphorus concentration of the solution was 0.2 mg / L. The phosphorus content of metatitanic acid (calculated as TiO2) was calculated to be 0.24% (based on elemental phosphorus). After adsorption, the mixture was filtered, washed with deionized water, and the solid adsorbent was recovered. The adsorbent was then dried at 105℃ for 8 hours and then calcined in a muffle furnace in stages. The calcination process is as follows: the temperature is raised from room temperature to 420℃ at a constant rate over 30 minutes and held for 30 minutes; the temperature is raised from 420℃ to 750℃ at a constant rate over 60 minutes and held for 60 minutes; the temperature is raised from 750℃ to 820℃ at a constant rate over 120 minutes and held for 20 minutes.

[0054] The obtained product has a TiO2 mass fraction >99%, a blue phase value (SCX) of 4.2, and a tinting strength (TCS) of 1400.

[0055] Example 5

[0056] A method for preparing pigment-grade titanium dioxide based on phosphorus adsorption and dephosphorization from phosphorus-containing wastewater is provided, comprising the following steps:

[0057] First, the metatitanic acid slurry was dried in an oven at 110℃ for 8 hours. The dried product was then ground to obtain fine metatitanic acid powder with a primary particle size of 200 nm and an agglomerated particle size of 2.3 μm. A mixed solution of 25 mg / L glyphosate and 25 mg / L phosphorous acid was adjusted to pH 4 using 0.1 mol / L NaOH. 50 mL of this solution was placed in a constant-temperature shaking bed and shaken at 180 rpm. When the solution temperature reached 25℃, 0.2 g of fine metatitanic acid powder was accurately weighed and added to the solution. After adsorption for 120 min, a sample was taken. The phosphorus concentration of the solution was below the instrument's detection limit. The phosphorus content of metatitanic acid (calculated as TiO2) was calculated to be 0.29% (based on elemental phosphorus). After adsorption, the mixture was filtered, washed with deionized water, and the solid adsorbent was recovered. The adsorbent was then dried at 105℃ for 8 hours and then calcined in a muffle furnace in stages. The calcination process is as follows: the temperature is raised from room temperature to 420℃ at a constant rate over 60 minutes and held for 30 minutes; the temperature is raised from 420℃ to 800℃ at a constant rate over 120 minutes and held for 30 minutes; the temperature is raised from 800℃ to 860℃ at a constant rate over 90 minutes and held for 20 minutes.

[0058] The obtained product has a TiO2 mass fraction >99%, a blue hue value (SCX) of 4.4, and a tinting strength (TCS) of 1430.

[0059] Comparative Example 1

[0060] First, the metatitanic acid slurry was dried in an oven at 110℃ for 8 hours. The dried product was then ground to obtain fine metatitanic acid powder. The fine metatitanic acid powder was then calcined in a muffle furnace in stages. The calcination process was as follows: the temperature was uniformly increased from room temperature to 420℃ over 30 minutes and held for 30 minutes; the temperature was uniformly increased from 420℃ to 780℃ over 60 minutes and held for 60 minutes; and the temperature was uniformly increased from 780℃ to 830℃ over 120 minutes and held for 20 minutes.

[0061] The obtained product has a TiO2 mass fraction >99%, a blue hue value (SCX) of 2.8, and a tinting strength (TCS) of 1200. Scanning electron micrographs of titanium dioxide are shown below. Figure 4 As shown. With Figure 3 In contrast, the grain morphology is irregular and the grain size distribution is uneven.

[0062] Comparative Example 2

[0063] First, phosphoric acid (0.2% by mass of the product (based on TiO2) and phosphorus element) was added to the metatitanic acid slurry and stirred until homogeneous. The metatitanic acid slurry was then dried in an oven at 110℃ for 8 hours, followed by staged calcination in a muffle furnace. The calcination regime was as follows: a uniform temperature increase from room temperature to 420℃ over 30 minutes, held for 30 minutes; a uniform temperature increase from 420℃ to 780℃ over 60 minutes, held for 60 minutes; and a uniform temperature increase from 780℃ to 830℃ over 120 minutes, held for 20 minutes.

[0064] The obtained product has a TiO2 mass fraction >99%, a blue hue value (SCX) of 4.2, and a tinting strength (TCS) of 1340. Scanning electron micrographs of titanium dioxide are shown below. Figure 5 As shown. With Figure 4 In comparison, this product has a more uniform grain morphology, but the uniformity of particle size and roundness are not as good as... Figure 3 .

[0065] The above are merely specific embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing pigment-grade titanium dioxide based on phosphorus adsorption and dephosphorization from phosphorus-containing wastewater, characterized in that, Includes the following steps: 1) Dry the metatitanic acid slurry to remove its free water, and then grind the dried product to obtain metatitanic acid fine powder; wherein the drying temperature of the metatitanic acid slurry is 60-110℃ and the time is 4-12 h; the primary particle size of the metatitanic acid fine powder obtained after grinding is 60-300 nm and the agglomerated particle size is 1-5 μm. 2) Take phosphorus-containing wastewater, adjust the pH to 2-6, place it in a shaker and shake at a speed of 120-200 rpm, add the metatitanic acid fine powder obtained in step 1) at a temperature of 20-50℃ for adsorption; wherein the phosphorus concentration in the phosphorus-containing wastewater is 1-100 mg / L; 3) After adsorption, the metatitanic acid fine powder is recovered, dried, and then subjected to segmented calcination to obtain titanium dioxide. The segmented calcination process is as follows: the temperature is uniformly increased from room temperature to 400-450℃ in 30-60 min and held for 25-35 min; then the temperature is uniformly increased to 700-800℃ in 60-120 min and held for 50-70 min; finally, the temperature is uniformly increased to 830-900℃ in 90-120 min and held for 15-25 min.

2. The production method according to claim 1, characterized by, In step 2), the phosphorus-containing substances in the phosphorus-containing wastewater are one or more of glyphosate or its salts, glyphosate or its salts, phosphorous acid or its salts, and phosphoric acid or its salts.

3. The production method according to claim 1, characterized by, In step 2), the amount of metatitanic acid fine powder added is 0.01-0.5 g / 50 mL of phosphorus-containing wastewater.

4. The method of claim 1, wherein, In step 2), the phosphorus content in the metatitanic acid fine powder after adsorption of phosphorus is 0.2-0.5%.

5. The preparation method according to claim 1, characterized in that, In step 2), the adsorption time is 20-480 min.

6. The method of claim 1, wherein, In step 3), the drying conditions are: drying at 100-110℃ for 6-10 hours.

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