High-purity ferric trichloride water purifying agent as well as preparation method and freezing recrystallization system thereof

Abstract

The invention discloses a preparation method of a high-purity ferric trichloride water purifying agent, which comprises the following steps: S1, dissolving a titanium dioxide byproduct ferrous sulfate in desalted water, then adding ammonium dihydrogen phosphate, controlling the pH value of the solution to 1.3, stirring to react until the reaction is finished, and filtering to obtain a ferrous sulfate solution; s2, adding hydrogen peroxide into the ferrous sulfate solution for oxidation, introducing industrial ammonia water to adjust the pH value of the solution to 2.0-5.0, and filtering to obtain ferric hydroxide colloid; s3, drying the ferric hydroxide colloid to obtain ferric hydroxide, and dissolving the ferric hydroxide in an industrial byproduct hydrochloric acid to obtain a ferric chloride solution; s4, sequentially carrying out evaporation concentration, freezing recrystallization and filtration on the ferric chloride solution to obtain ferric trichloride; compared with the prior art, the titanium dioxide byproduct ferrous sulfate is utilized and converted into high-purity ferric trichloride which can be used as a water purifying agent.

Description

Technical Field

[0001] The invention relates to the technical field of water purifier preparation, and in particular to a high-purity ferric chloride water purifier, a preparation method thereof and a freezing recrystallization system. Background Art

[0002] The domestic production capacity of ferrous sulfate, a byproduct of titanium dioxide production, is huge, and the output ratio of titanium dioxide to ferrous sulfate is usually about 1:3. Therefore, sulfuric acid-based titanium dioxide production enterprises produce a large amount of ferrous sulfate as a byproduct, but due to the poor crystal form of ferrous sulfate, the purity of ferrous sulfate is generally less than 90%, and it contains many impurities, mainly Ti, Mn, Mg, Al, Si, etc., and cannot be sold directly as a commodity. Most of the byproduct ferrous sulfate is treated as waste and piled up for a long time or discharged into rivers, lakes and seas, which not only wastes resources but also causes great harm to the environment.

[0003] In order to reduce the waste of resources, the by-product ferrous sulfate was recycled as follows.

[0004] CN117756189A discloses a method for preparing ferrous sulfate from ferrous sulfate, a byproduct of titanium dioxide, comprising the following steps: mixing ferrous sulfate, a byproduct of titanium dioxide, with water to obtain a mixed solution; filtering the mixed solution to obtain a filtrate and a filter residue; subjecting the filtrate to a reduction reaction with iron powder to obtain a slurry; reacting the slurry with an alkali, removing impurities through hydrolysis and filtering to obtain a purified ferrous sulfate solution and a de-impurity residue.

[0005] In this technology, the titanium dioxide by-product ferrous sulfate is removed by hydrolysis and filtration.

[0006] CN117303453A discloses a continuous refining method for ferrous sulfate produced as a byproduct of titanium dioxide, comprising the following steps:

[0007] S1: The raw materials are sent to the dissolving tank, hot water is introduced into the bottom of the dissolving tank, and the ferrous sulfate solution enters the buffer tank through the baffle tank of the dissolving tank, and water is added to the baffle tank to dilute the ferrous sulfate solution;

[0008] S2: The ferrous sulfate solution in the buffer tank is pumped into the impurity removal tank. Iron sheets are added to the impurity removal tank. The solution on the top of the impurity removal tank overflows to the ground sedimentation tank. The clear liquid on the top of the sedimentation tank overflows to the metal membrane filtration system. The clear liquid after metal membrane filtration is sent to the ferrous sulfate storage tank as a product.

[0009] S3: The concentrated liquid discharged from the metal membrane filtration system and the impurity removal tank is returned to the filter press buffer tank. The pump sends the liquid in the tank to the compressor, and the clear liquid in the filter press returns to the clear liquid buffer tank.

[0010] In this technology, the ferrous sulfate produced as a by-product of titanium dioxide is removed through sedimentation, membrane filtration and filter press.

[0011] CN110540247A discloses a method for recycling ferrous sulfate monohydrate, a byproduct of a titanium dioxide plant, comprising the following steps:

[0012] s1. Using ferrous sulfate monohydrate, a by-product obtained by concentrating the waste acid section of a titanium dioxide plant, as a raw material, mixing it with water to form a slurry, and then separating it to obtain a washing clear liquid and washed ferrous sulfate monohydrate;

[0013] s2, mixing the washed ferrous sulfate monohydrate in s1 with water, and stirring to carry out a hydration reaction; then adding concentrated sulfuric acid to obtain a reaction intermediate product; at the same time, preparing sodium nitrite, i.e., NaNO2, to prepare a sodium nitrite solution;

[0014] s3. Stir the reaction intermediate product and introduce oxygen, then add the sodium nitrite solution in batches, and circulate the catalytic oxidation reaction to obtain polyferric sulfate.

[0015] In this technology, the by-product ferrous sulfate is washed, oxidized and catalytically oxidized to prepare polyferric sulfate.

[0016] It can be seen that the current treatment of titanium dioxide by-product ferrous sulfate is mainly to remove impurities and convert it into polyferric sulfate, etc., and no information has been found that the titanium dioxide by-product ferrous sulfate is treated to obtain high-purity ferric chloride for use as a water purifier. Summary of the invention

[0017] In view of the deficiencies in the prior art, the object of the present invention is to provide a high-purity ferric chloride water purifier and a preparation method and a freezing recrystallization system thereof, so as to solve the problem in the prior art that there is no technology for treating the titanium dioxide by-product ferrous sulfate to obtain high-purity ferric chloride for use as a water purifier.

[0018] To achieve the above object, the first aspect of the present invention adopts the following technical scheme: a method for preparing a high-purity ferric chloride water purifier, comprising the following steps:

[0019] Step S1, dissolving the titanium dioxide by-product ferrous sulfate in desalted water, then adding ammonium dihydrogen phosphate and controlling the pH of the solution to be 1-1.4, stirring the reaction until the reaction is complete, and then filtering to obtain a ferrous sulfate solution;

[0020] Step S2, adding hydrogen peroxide to the ferrous sulfate solution for oxidation and introducing industrial ammonia water to adjust the solution pH to 2.0-5.0, and then filtering to obtain ferric hydroxide colloid;

[0021] Step S3, drying the iron hydroxide colloid to obtain iron hydroxide, and then dissolving the iron hydroxide in hydrochloric acid to obtain a ferric chloride solution;

[0022] Step S4, evaporating and concentrating the ferric chloride solution, freezing and recrystallizing it, and filtering it to obtain ferric chloride.

[0023] Furthermore, the mass ratio of the titanium dioxide by-product ferrous sulfate to the desalted water is 1 to 3:1, and the mass content of the titanium dioxide by-product ferrous sulfate is 80% to 92%.

[0024] Furthermore, the molar ratio of ferrous ions to hydrogen peroxide in the ferrous sulfate solution is 1:0.5-0.65, the mass content of industrial ammonia water is 14%-17%, and the molar ratio of industrial ammonia water to hydrogen peroxide is 1:3-3.3.

[0025] Furthermore, in step S2, the stirring speed is 50-500 rpm, the reaction temperature is 20-60° C., and the reaction time is 1-5 h.

[0026] Furthermore, the molar ratio of hydrochloric acid to ferric hydroxide is 3-3.3:1, and the mass content of hydrochloric acid is 15%-32%.

[0027] Furthermore, in the step S3, the stirring speed during the dissolution of iron hydroxide in hydrochloric acid is 50 to 500 rpm, the reaction temperature is 20 to 60° C., and the reaction time is 1 to 5 h.

[0028] The second aspect of the present invention adopts the following technical scheme: a high-purity ferric chloride water purifier is prepared by the preparation method of a high-purity ferric chloride water purifier described in the first aspect of the present invention.

[0029] The third aspect of the present invention adopts the following technical solution: a concentration crystallization system is used to complete step S4 in the method for preparing a high-purity ferric chloride water purifier described in the first aspect of the present invention.

[0030] Further, including:

[0031] A tank body, wherein a feed pipe, a compressed air inlet pipe and a water vapor extraction unit are arranged on the top of the tank body, a liquid discharge pipe and a crystal discharge pipe are arranged on the bottom of the tank body, and a precision filter screen is arranged at the inlet of the liquid discharge pipe;

[0032] A jacket, the jacket is arranged outside the tank body and is equipped with an inlet superheated steam pipe, an outlet superheated steam pipe, an inlet chilled water pipe and an outlet chilled water pipe;

[0033] A stirrer, the stirrer is rotatably disposed in the tank;

[0034] A regulating valve is provided on each of the feed pipe, the compressed air inlet pipe, the liquid discharge pipe, the crystal discharge pipe, the superheated steam inlet pipe, the superheated steam outlet pipe, the chilled water inlet pipe and the chilled water outlet pipe.

[0035] Furthermore, the compressed air pressure introduced by the compressed air inlet pipe is 0.1MPa~0.3MPa, the speed of the agitator is 50~500 rpm, the temperature of the tank body is controlled at 90℃~180℃ during evaporation and concentration, and the temperature of the tank body is controlled at 5℃~15℃ and the time is controlled at 0.5h~5h during freezing and recrystallization.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. The present invention uses extremely cheap titanium dioxide by-product ferrous sulfate as an iron source, and effectively utilizes industrial by-product hydrochloric acid as a chlorine source, making full use of two cheap by-products of the industrial system as main reaction raw materials, greatly reducing costs, and providing an important solution for the digestion and direction of titanium dioxide by-product ferrous sulfate and a large amount of by-product hydrochloric acid in my country's chemical production field, turning waste into treasure, which is of great significance;

[0038] 2. The present invention sequentially removes impurities from ammonium dihydrogen phosphate, converts to ferric hydroxide colloid, freezes and recrystallizes, and filters the ferrous sulfate produced as a byproduct of titanium dioxide to effectively convert the ferrous sulfate into ferric chloride and remove impurities, so that the purity of the prepared ferric chloride is as high as 99% or more; wherein, the addition of ammonium dihydrogen phosphate is to remove impurities such as Zn, Pb and Cr, which is beneficial to improving the purity of the final product, and the pH is controlled to be 1-1.4 to ensure that the ammonium dihydrogen phosphate does not react with the ferrous sulfate produced as a byproduct of titanium dioxide;

[0039] 3. The freezing recrystallization system can meet the requirements of evaporation concentration, freezing recrystallization and filtration of ferric chloride solution to obtain ferric chloride, which has the characteristics of low production cost, simple operation and small footprint. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The figure is a simplified process flow diagram of a concentration crystallization system in the present invention.

[0041] The figure marks in the drawings of the specification include: tank body 1, jacket 2, agitator 3, feed pipe 4, compressed air inlet pipe 5, liquid discharge pipe 6, crystallization discharge pipe 7, precision filter 8, superheated steam inlet pipe 9, superheated steam outlet pipe 10, chilled water inlet pipe 11, chilled water outlet pipe 12, steam outlet pipe 13, condenser 14, condensed water storage tank 15, vacuum pump 16, pressure relief pipe 17. DETAILED DESCRIPTION

[0042] The present invention is further described in detail below through specific embodiments:

[0043] like Figure 1As shown, an embodiment of the present invention proposes a concentration crystallization system, including a tank body 1, a jacket 2, an agitator 3 and a regulating valve, wherein a feed pipe 4, a compressed air inlet pipe 5 and a water vapor extraction unit are arranged on the top of the tank body 1, a liquid discharge pipe 6 and a crystallization discharge pipe 7 are arranged on the bottom of the tank body 1, and a precision filter screen 8 is arranged at the inlet of the liquid discharge pipe 6; the jacket 2 is arranged outside the tank body 1 and an inlet superheated steam pipe 9, an outlet superheated steam pipe 10, an inlet chilled water pipe 11 and an outlet chilled water pipe 12 are arranged on the jacket 2; the agitator 3 is rotatably arranged in the tank body 1; and one regulating valve is arranged on each of the feed pipe 4, the compressed air inlet pipe 5, the liquid discharge pipe 6, the crystallization discharge pipe 7, the inlet superheated steam pipe 9, the outlet superheated steam pipe 10, the inlet chilled water pipe 11 and the outlet chilled water pipe 12.

[0044] In this embodiment, the agitator 3 includes a stirring paddle rotatably arranged in the tank body 1 and a stirring motor arranged at the top outside the tank body 1 and connected to the stirring paddle; the water vapor extraction unit includes a water vapor outlet pipe 13 arranged at the top of the tank body 1 and a condenser 14 and a condensed water storage tank 15 connected to the water vapor outlet pipe 13 in sequence, and the regulating valve is arranged on the water vapor outlet pipe 13.

[0045] When in use, the regulating valves on the feed pipe 4, the inlet superheated steam pipe 9, the outlet superheated steam pipe 10 and the water vapor outlet pipe 13 are opened, and the other regulating valves are closed. The feed pipe 4 introduces the ferric chloride solution into the tank body 1, and then the regulating valve on the feed pipe 4 is closed; the inlet superheated steam pipe 9 introduces the superheated steam of 160°C into the jacket 2, and the flow rates of the inlet superheated steam pipe 9 and the outlet superheated steam pipe 10 are controlled to control the temperature in the tank body 1 to be 90°C to 180°C. At the same time, the stirring motor is started, and the stirring paddle is rotated at a speed of 50 to 500 rpm to evaporate and concentrate the ferric chloride solution. The water vapor generated by evaporation and concentration is discharged from the water vapor outlet pipe 13 and enters the condenser 14 for condensation to form condensed water, and the condensed water enters the condensed water storage tank 15 for storage. In order to improve the efficiency of evaporation and concentration, a vacuum pump 16 is also provided between the condenser 14 and the condensed water storage tank 15. The vacuum pump 16 is started to form a vacuum effect to achieve a pressure of -0.05MPa to -0.1MPa. Reduced pressure distillation can increase the distillation speed.

[0046] When the ferric chloride solution completes evaporation and concentration to form a saturated ferric chloride solution, close the regulating valves on the superheated steam inlet pipe 9, the superheated steam outlet pipe 10 and the steam outlet pipe 13, open the regulating valves on the chilled water inlet pipe 11 and the chilled water outlet pipe 12, and the chilled water inlet pipe 11 introduces 4-10°C chilled water into the jacket 2, and control the flow of the chilled water inlet pipe 11 and the chilled water outlet pipe 12 to control the temperature in the tank body 1 to 5-15°C, and cooperate with the stirring paddle to rotate at a speed of 50-500 rpm. The freezing time in the tank body 1 is 0.5h-5h to complete the freezing recrystallization.

[0047] After completing the freezing and recrystallization, close the regulating valves on the freezing water inlet pipe 11 and the freezing water outlet pipe 12, open the regulating valves on the compressed air inlet pipe 5 and the liquid discharge pipe 6, and the compressed air inlet pipe 5 introduces 0.1MPa~0.3MPa compressed air into the tank body 1 to squeeze out the liquid remaining in the ferric chloride that has completed the freezing and recrystallization. The liquid passes through the precision filter 8 and is discharged from the liquid discharge pipe 6. When the residual liquid in the frozen and recrystallized ferric chloride is squeezed and discharged, close the regulating valve on the liquid discharge pipe 6, open the regulating valve on the crystallization discharge pipe 7, discharge the frozen and recrystallized ferric chloride from the crystallization discharge pipe 7, and collect it to obtain the product.

[0048] Furthermore, a pressure relief pipe 17 is provided on the top of the tank body 1, and a pressure relief valve is installed on the pressure relief pipe 17 to avoid safety problems caused by overpressure in the tank body 1 during use.

[0049] Example 2

[0050] A method for preparing a high-purity ferric chloride water purifier comprises the following steps: adding 4083.6 g of ferrous sulfate produced as a byproduct of titanium dioxide with a mass content of 80% and 8004.8 g of desalted water into a reactor, heating to 60° C. to dissolve, then adding 40 g of ammonium dihydrogen phosphate with a mass content of 99%, wherein the pH value of the solution is 1.3, stirring for 1 hour, and filtering to obtain a ferrous sulfate solution after the reaction is completed;

[0051] 3L of ferrous sulfate solution was placed in a reactor, and then 1218.7g of 30% hydrogen peroxide was added for oxidation, followed by 406g of 15% industrial ammonia water. During this period, the temperature in the reactor was controlled at 20°C and stirred at a stirring speed of 50 rpm. The pH of the solution was 3.2. After reacting for 5 hours, filtration was performed to obtain ferric hydroxide colloid.

[0052] The ferric hydroxide colloid was placed in a drying oven at 105° C. and dried for 5 h, obtaining 467 g of ferric hydroxide, which was dissolved by 2393 g of industrial byproduct hydrochloric acid with a mass content of 20% at 20° C. and a stirring speed of 50 rpm for 5 h to obtain a ferric chloride solution;

[0053] The ferric chloride solution is distilled at 160°C using the above-mentioned concentrated crystallization system to form a saturated ferric chloride solution, and then frozen recrystallized at 15°C for 5 hours. After the freeze-recrystallization is completed, it is separated by filtration to obtain ferric chloride.

[0054] Table 1 Impurity content changes in Example 2 during the preparation of ferric chloride

[0055]

[0056]

[0057] Example 3

[0058] A method for preparing a high-purity ferric chloride water purifier comprises the following steps: adding 4023.6 g of ferrous sulfate produced as a byproduct of titanium dioxide with a mass content of 85% and 4028.8 g of desalted water into a reactor, heating at 60° C. to dissolve, and then adding 36 g of ammonium dihydrogen phosphate with a mass content of 99%; at this time, the pH value of the solution is 1; stirring the reaction for 1 hour; after the reaction is completed, filtering to obtain a ferrous sulfate solution;

[0059] 3L of ferrous sulfate solution was placed in a reactor, and then 1583.83g of 30% hydrogen peroxide was added for oxidation, followed by 447g of 17% industrial ammonia water. During this period, the temperature in the reactor was controlled at 60°C and stirred at a stirring speed of 500 rpm. The pH of the solution was 3.1. After reacting for 1h, the solution was filtered to obtain ferric hydroxide colloid.

[0060] The ferric hydroxide colloid was placed in a drying oven at 105° C. and dried for 5 h to obtain 467 g of ferric hydroxide, which was dissolved by 2632 g of industrial byproduct hydrochloric acid with a mass content of 15% at 60° C. and at a stirring speed of 500 rpm for 1 h to obtain a ferric chloride solution;

[0061] The ferric chloride solution is distilled at 90°C using the above-mentioned concentrated crystallization system to form a saturated ferric chloride solution, and then frozen recrystallized at 5°C for 30 minutes. After the freezing recrystallization is completed, it is separated by filtration to obtain ferric chloride.

[0062] Table 2 Impurity content changes in Example 3 during the preparation of ferric chloride

[0063]

[0064]

[0065] Example 4

[0066] A method for preparing a high-purity ferric chloride water purifier comprises the following steps: adding 4083.6 g of ferrous sulfate produced as a byproduct of titanium dioxide with a mass content of 87% and 12246.8 g of desalted water into a reactor, heating at 60° C. to dissolve, then adding 38 g of ammonium dihydrogen phosphate with a mass content of 99%, wherein the pH value of the solution is 1.4, stirring for 1 hour, and filtering to obtain a ferrous sulfate solution after the reaction is completed;

[0067] 3L of ferrous sulfate solution was placed in a reactor, and then 1413.3g of 30% hydrogen peroxide was added for oxidation, followed by 420g of 14% industrial ammonia water. During this period, the temperature in the reactor was controlled at 40°C and stirred at a stirring speed of 260 rpm. The pH of the solution was 3.2. After reacting for 3h, the solution was filtered to obtain ferric hydroxide colloid.

[0068] The ferric hydroxide colloid was placed in a drying oven at 105° C. and dried for 5 hours to obtain 500.8 g of ferric hydroxide, which was dissolved by 1276 g of industrial byproduct hydrochloric acid with a mass content of 32% at a temperature of 45° C. and a stirring speed of 320 rpm for 2.8 hours to obtain a ferric chloride solution;

[0069] The ferric chloride solution is distilled at 180°C using the above-mentioned concentrated crystallization system to form a saturated ferric chloride solution, and then the solution is frozen and recrystallized at 10°C for 2.5 hours. After the freezing and recrystallization is completed, the solution is separated by filtration to obtain ferric chloride.

[0070] Table 3 Impurity content changes in Example 4 during the preparation of ferric chloride

[0071]

[0072] Example 5

[0073] A method for preparing a high-purity ferric chloride water purifier comprises the following steps: adding 4083.6 g of ferrous sulfate produced as a byproduct of titanium dioxide with a mass content of 82% and 7504.8 g of desalted water into a reactor, heating at 60° C. to dissolve, then adding 40 g of ammonium dihydrogen phosphate with a mass content of 99%, wherein the pH value of the solution is 1.3, stirring the reaction for 1 hour, and filtering to obtain a ferrous sulfate solution after the reaction is completed;

[0074] 3L of ferrous sulfate solution was placed in a reactor, and then 1218.7g of 30% hydrogen peroxide was added for oxidation, followed by 406g of 15% industrial ammonia water. During this period, the temperature in the reactor was controlled at 20°C and stirred at a stirring speed of 50 rpm. The pH of the solution was 3.2. After reacting for 4 hours, filtration was performed to obtain ferric hydroxide colloid.

[0075] The ferric hydroxide colloid was placed in a drying oven at 105° C. and dried for 5 h to obtain 488.4 g of ferric hydroxide, which was dissolved by 2502 g of industrial byproduct hydrochloric acid with a mass content of 18% at 30° C. and at a stirring speed of 100 rpm for 4 h to obtain a ferric chloride solution;

[0076] The ferric chloride solution is distilled at 150°C using the above-mentioned concentrated crystallization system to form a saturated ferric chloride solution, and then the solution is frozen and recrystallized at 5°C for 30 minutes. After the freezing and recrystallization is completed, the solution is separated by filtration to obtain ferric chloride.

[0077] Table 4 Impurity content variation table of Example 5 in the process of preparing ferric chloride

[0078]

[0079] Example 6

[0080] A method for preparing a high-purity ferric chloride water purifier comprises the following steps: adding 4062.6 g of ferrous sulfate produced as a byproduct of titanium dioxide with a mass content of 81% and 7923.8 g of desalted water into a reactor, heating at 60° C. to dissolve, then adding 40 g of ammonium dihydrogen phosphate with a mass content of 99%, wherein the pH value of the solution is 1.3, stirring the reaction for 1 hour, and filtering to obtain a ferrous sulfate solution after the reaction is completed;

[0081] 3L of ferrous sulfate solution was placed in a reactor, and then 1206.1g of 30% hydrogen peroxide was added for oxidation, followed by 420g of 15% industrial ammonia water. During this period, the temperature in the reactor was controlled at 35°C and stirred at a stirring speed of 150 rpm. The pH of the solution was 3.2. After reacting for 3h, filtration was performed to obtain ferric hydroxide colloid.

[0082] The iron hydroxide colloid was placed in a drying oven at 105° C. and dried for 5 h to obtain 477.8 g of iron hydroxide, which was dissolved by 2447.8 g of industrial byproduct hydrochloric acid with a mass content of 19% at 50° C. and at a stirring speed of 300 rpm for 1.5 h to obtain a ferric chloride solution;

[0083] The ferric chloride solution is distilled at 120°C using the above-mentioned concentrated crystallization system to form a saturated ferric chloride solution, and then the solution is frozen and recrystallized at 10°C for 30 minutes. After the freezing and recrystallization is completed, the solution is separated by filtration to obtain ferric chloride.

[0084] Table 5 Impurity content variation table of Example 6 in the process of preparing ferric chloride

[0085]

[0086] Example 7

[0087] A method for preparing a high-purity ferric chloride water purifier comprises the following steps: adding 4083.6 g of ferrous sulfate produced as a byproduct of titanium dioxide with a mass content of 80% and 8004.8 g of desalted water into a reactor, heating at 60° C. to dissolve, then adding 42 g of ammonium dihydrogen phosphate with a mass content of 99%, wherein the pH value of the solution is 1.3, stirring for 1 hour, and filtering to obtain a ferrous sulfate solution after the reaction is completed;

[0088] 3L of ferrous sulfate solution was placed in a reactor, and then 1201.1g of 30% hydrogen peroxide was added for oxidation, followed by 426g of 15% industrial ammonia water. During this period, the temperature in the reactor was controlled at 40°C and stirred at a stirring speed of 180 rpm. The pH of the solution was 3.2. After reacting for 2.8h, filtration was performed to obtain ferric hydroxide colloid.

[0089] The ferric hydroxide colloid was placed in a drying oven at 105° C. and dried for 5 hours to obtain 502.8 g of ferric hydroxide, which was dissolved by 2575.8 g of industrial byproduct hydrochloric acid with a mass content of 19% at 28° C. and a stirring speed of 400 rpm for 2 hours to obtain a ferric chloride solution;

[0090] The ferric chloride solution is distilled at 170°C using the above-mentioned concentrated crystallization system to form a saturated ferric chloride solution, and then the solution is frozen and recrystallized at 5°C for 30 minutes. After the freezing and recrystallization is completed, the solution is separated by filtration to obtain ferric chloride.

[0091] Table 6 Impurity content changes in Example 7 during the preparation of ferric chloride

[0092]

[0093] Example 8

[0094] A method for preparing a high-purity ferric chloride water purifier comprises the following steps: adding 4081.6g of ferrous sulfate produced as a byproduct of titanium dioxide with a mass content of 83% and 8001.2g of desalted water into a reactor, heating at 60°C to dissolve, and then adding 43g of ammonium dihydrogen phosphate with a mass content of 99%, wherein the pH value of the solution is 1.3, stirring for 1h, and filtering to obtain a ferrous sulfate solution after the reaction is completed;

[0095] 3L of ferrous sulfate solution was placed in a reactor, and then 1204.2g of 30% hydrogen peroxide was added for oxidation, followed by 428g of 15% industrial ammonia water. During this period, the temperature in the reactor was controlled to be 25°C and stirred at a stirring speed of 320 rpm. The pH of the solution was 3.2. After reacting for 3.5h, filtration was performed to obtain ferric hydroxide colloid.

[0096] The iron hydroxide colloid was placed in a drying oven at 105° C. and dried for 5 h to obtain 495.6 g of iron hydroxide, which was dissolved by 2539 g of industrial byproduct hydrochloric acid with a mass content of 20% at 30° C. and a stirring speed of 300 rpm for 3 h to obtain a ferric chloride solution;

[0097] The ferric chloride solution is distilled at 160° C. using the above-mentioned concentrated crystallization system to form a saturated ferric chloride solution, and then the solution is frozen and recrystallized at 10° C. for 30 minutes. After the freezing and recrystallization is completed, the solution is separated by filtration to obtain ferric chloride.

[0098] Table 7 Impurity content changes in Example 8 during the preparation of ferric chloride

[0099]

[0100] Example 9

[0101] A method for preparing a high-purity ferric chloride water purifier comprises the following steps: adding 4080.6g of ferrous sulfate produced as a byproduct of titanium dioxide with a mass content of 83% and 8004.8g of desalted water into a reactor, heating at 60°C to dissolve, and then adding 40g of ammonium dihydrogen phosphate with a mass content of 99%, wherein the pH value of the solution is 1.3, stirring for 1h, and filtering to obtain a ferrous sulfate solution after the reaction is completed;

[0102] 3L of ferrous sulfate solution was placed in a reactor, and then 1204g of 30% hydrogen peroxide was added for oxidation, followed by 425g of 15% industrial ammonia water. During this period, the temperature in the reactor was controlled at 40°C and stirred at a stirring speed of 230 rpm. The pH of the solution was 3.2. After reacting for 4 hours, the solution was filtered to obtain ferric hydroxide colloid.

[0103] The iron hydroxide colloid was placed in a drying oven at 105° C. and dried for 5 h, and 519.6 g of iron hydroxide was obtained. 2662 g of industrial byproduct hydrochloric acid with a mass content of 20% was used to dissolve the colloid at 25° C. and at a stirring speed of 360 rpm for 3.2 h to obtain an iron chloride solution.

[0104] The ferric chloride solution is distilled at 160° C. using the above-mentioned concentrated crystallization system to form a saturated ferric chloride solution, and then the solution is frozen and recrystallized at 5° C. for 30 minutes. After the freezing and recrystallization is completed, the solution is separated by filtration to obtain ferric chloride.

[0105] Table 8 Impurity content changes in Example 9 during the preparation of ferric chloride

[0106]

[0107] Example 10

[0108] A method for preparing a high-purity ferric chloride water purifier comprises the following steps: adding 4080.6g of ferrous sulfate produced as a byproduct of titanium dioxide with a mass content of 83% and 8004.8g of desalted water into a reactor, heating at 60°C to dissolve, and then adding 42g of ammonium dihydrogen phosphate with a mass content of 99%, wherein the pH value of the solution is 1.3, stirring the reaction for 1h, and filtering to obtain a ferrous sulfate solution after the reaction is completed;

[0109] 3L of ferrous sulfate solution was placed in a reactor, and then 1204g of 30% hydrogen peroxide was added for oxidation, followed by 428g of 15% industrial ammonia water. During this period, the temperature in the reactor was controlled at 30°C and stirred at a stirring speed of 280 rpm. The pH of the solution was 5.2. After reacting for 3.8h, filtration was performed to obtain ferric hydroxide colloid.

[0110] The iron hydroxide colloid was placed in a drying oven at 105° C. and dried for 5 h, and 519.6 g of iron hydroxide was obtained. 2662 g of industrial byproduct hydrochloric acid with a mass content of 20% was used to dissolve the colloid at 25° C. and at a stirring speed of 360 rpm for 3.2 h to obtain an iron chloride solution.

[0111] The ferric chloride solution is distilled at 160° C. using the above-mentioned concentrated crystallization system to form a saturated ferric chloride solution, and then the solution is frozen and recrystallized at 10° C. for 30 minutes. After the freezing and recrystallization is completed, the solution is separated by filtration to obtain ferric chloride.

[0112] Table 9 Impurity content variation table of Example 10 in the process of preparing ferric chloride

[0113]

[0114] Comparative Example 1

[0115] The only difference from Example 10 is that 4080.6 g of ferrous sulfate produced as a by-product of titanium dioxide with a mass content of 83% and 8004.8 g of desalted water are added to the reactor, heated to 60° C. to dissolve, stirred for 1 hour, and after the reaction is completed, filtered to obtain a ferrous sulfate solution; the remaining steps are the same.

[0116] Table 10 Impurity content changes in comparative example 1 during the preparation of ferric chloride

[0117]

[0118] The impurity content and purity of ferric chloride prepared in Example 2-Example 10 and Comparative Example 1 are summarized in Table 11.

[0119] Table 11

[0120]

[0121]

[0122] According to Table 10, compared with the industry standard GB / T 4482-2018, the impurity content of the ferric chloride product prepared in Examples 2-10 of the present application is within the range of the industry standard, and the arsenic, lead, mercury, and cadmium elements in the raw materials have been completely removed in the prepared product. From the impurity content of the ferric chloride product in Examples 2-10, it can be seen that the core factors affecting the impurity content of the product in the process of preparing the ferric chloride product are the pH in the formation of ferric hydroxide colloid and the temperature regulation of the ferric chloride solution during the freezing and recrystallization process. The content of impurities in the generated ferric chloride product increases with the increase of pH in the formation of ferric hydroxide colloid. The core reason is that the increase of pH in the formation of ferric hydroxide colloid will cause other elements to precipitate in this precipitation range, and the free heavy metal elements will be adsorbed on the surface of the ferric hydroxide colloid. At the same time, the content of impurities in the ferric chloride product will increase as the temperature of the ferric chloride solution decreases during the freezing and recrystallization process. The reason is that the lower the freezing and recrystallization temperature, when the solution reaches saturation, more elements will precipitate at low temperatures, and free heavy metal elements will be adsorbed on the surface of ferric chloride crystals.

[0123] It should be noted that the contents of impurities such as Zn, As, Pb, Hg, Cd and Cr in the above table are detected by existing IPC detection technology, among which, "raw material" is ferrous sulfate, a by-product of titanium dioxide, "before filtration" is the mixed solution after adding ammonium dihydrogen phosphate to complete the reaction, "after filtration" is the ferrous sulfate solution obtained by filtration, "Fe(OH)3 filtrate" is the iron hydroxide colloid formed after filtration, "FeCl3 liquid" is the ferric chloride solution obtained by dissolving iron hydroxide in industrial by-product hydrochloric acid, and the "product" is the ferric chloride obtained after filtration and separation.

[0124] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a high-purity ferric chloride water purifier, characterized in that: The following steps are involved: Step S1, dissolving the titanium dioxide by-product ferrous sulfate in desalted water, then adding ammonium dihydrogen phosphate and controlling the pH of the solution to be 1-1.4, stirring the reaction until the reaction is complete, and then filtering to obtain a ferrous sulfate solution; Step S2, adding hydrogen peroxide to the ferrous sulfate solution for oxidation and introducing industrial ammonia water to adjust the solution pH to 2.0-5.0, and then filtering to obtain ferric hydroxide colloid; Step S3, drying the iron hydroxide colloid to obtain iron hydroxide, and then dissolving the iron hydroxide in industrial by-product hydrochloric acid to obtain a ferric chloride solution; Step S4, evaporating and concentrating the ferric chloride solution, freezing and recrystallizing it, and filtering it to obtain ferric chloride.

2. A method for preparing a high-purity ferric chloride water purifier according to claim 1, characterized in that: The mass ratio of the titanium dioxide byproduct ferrous sulfate to the desalted water is 1 to 3:

1.

3. A method for preparing a high-purity ferric chloride water purifier according to claim 1, characterized in that: The molar ratio of ferrous ions to hydrogen peroxide in the ferrous sulfate solution is 1:0.5-0.65, the mass content of industrial ammonia water is 14%-17%, and the molar ratio of industrial ammonia water to hydrogen peroxide is 1:3-3.

3.

4. A method for preparing a high-purity ferric chloride water purifier according to claim 1 or 3, characterized in that: The stirring speed in step S2 is 50-500 rpm, the reaction temperature is 20-60° C., and the reaction time is 1-5 h.

5. A method for preparing a high-purity ferric chloride water purifier according to claim 1, characterized in that: The molar ratio of hydrochloric acid to ferric hydroxide is 3-3.3:1, and the mass content of hydrochloric acid is 15%-32%.

6. A method for preparing a high-purity ferric chloride water purifier according to claim 1 or 5, characterized in that: In the step S3, the stirring speed during the dissolution of iron hydroxide in hydrochloric acid is 50-500 rpm, the reaction temperature is 20-60° C., and the reaction time is 1-5 h.

7. A high-purity ferric chloride water purifier, characterized in that: The high-purity ferric chloride water purifier is prepared by the preparation method of any one of claims 1 to 6.

8. A concentration crystallization system, characterized in that: Used to complete step S4 in the method for preparing a high-purity ferric chloride water purifier according to any one of claims 1 to 6.

9. A freezing recrystallization system according to claim 8, characterized in that: include: A tank body, wherein a feed pipe, a compressed air inlet pipe and a water vapor extraction unit are arranged on the top of the tank body, a liquid discharge pipe and a crystal discharge pipe are arranged on the bottom of the tank body, and a precision filter screen is arranged at the inlet of the liquid discharge pipe; A jacket, the jacket is arranged outside the tank body and is equipped with an inlet superheated steam pipe, an outlet superheated steam pipe, an inlet chilled water pipe and an outlet chilled water pipe; A stirrer, the stirrer is rotatably disposed in the tank; A regulating valve is provided on each of the feed pipe, the compressed air inlet pipe, the liquid discharge pipe, the crystal discharge pipe, the superheated steam inlet pipe, the superheated steam outlet pipe, the chilled water inlet pipe and the chilled water outlet pipe.

10. A freezing recrystallization system according to claim 9, characterized in that: The compressed air pressure introduced by the compressed air inlet pipe is 0.1MPa-0.3MPa, the rotation speed of the agitator is 50-500 rpm, the temperature in the tank body is controlled at 90°C-180°C during evaporation and concentration, and the temperature in the tank body is controlled at 5°C-15°C and the time is controlled at 0.5h-5h during freezing and recrystallization.

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