Method for recycling hydrolyzed scale to produce titanium dioxide

Abstract

This invention discloses a method for recovering and utilizing hydrolyzed scale to produce titanium dioxide, relating to the field of titanium dioxide technology. It solves the problems of high difficulty in recovering hydrolyzed scale, significant waste of titanium resources in conventional treatments, and low economic returns. The invention includes: S1, crushing hydrolyzed scale using a jaw crusher; S2, mixing the crushed hydrolyzed scale material with ball milling media, adding water, and performing wet ball milling; S3, sending the deagglomerated material to a water washing section, where it is washed to obtain a metatitanic acid filter cake; S4, slurrying the metatitanic acid filter cake, and then sequentially passing it through a salt treatment section and a calcination section to obtain crude titanium dioxide; S5, feeding the crude titanium dioxide into a Raymond mill for further pulverization, adding demineralized water and a dispersant to the pulverized titanium dioxide, dispersing and slurrying the slurry, pumping it into a sand mill for deagglomeration and classification, and then sending it to subsequent processing to obtain rutile titanium dioxide. This invention improves the recovery rate of titanium resources, achieves equal economic value between hydrolyzed scale and titanium dioxide, and increases economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of titanium dioxide technology, specifically relating to a method for producing titanium dioxide by recycling scale through hydrolysis. Background Technology

[0002] The main production processes for titanium dioxide are the sulfuric acid process and the chloride process, with the sulfuric acid process being the primary method used in China. The sulfuric acid process typically uses sulfuric acid to convert titanium in titanium concentrate into soluble titanium oxysulfate through a vigorous chemical reaction. This is followed by a series of impurity removal processes, including sedimentation, crystallization, filtration to separate acid-insoluble substances and ferrous sulfate, resulting in a high-purity titanium oxysulfate solution. This solution is then hydrolyzed to produce metatitanic acid. After impurity removal, the metatitanic acid undergoes calcination, intermediate grinding, and post-processing to obtain the titanium dioxide product. The advantages of the sulfuric acid process are the availability of inexpensive and readily available ilmenite and sulfuric acid as raw materials, mature technology, and simple equipment. Its disadvantages include a long process, a significant amount of waste and byproducts, and greater difficulty in treatment. Therefore, reducing waste emissions has always been a crucial issue for my country's titanium dioxide industry.

[0003] During the hydrolysis of titanium solution, metatitanic acid is generated and adsorbed onto the edges and bottom of the hydrolysis pot. Fine calcium sulfate residue from the impurity removal process and material detached from the pot walls also adhere to the bottom along with the metatitanic acid. Although the production workshop rinses the pot after each batch of hydrolysis, scale accumulates at the bottom over time. This type of scale has a high impurity content due to its hard structure, high iron content, and high calcium content, making it difficult to depolymerize and recycle.

[0004] Conventional methods for treating hydrolyzed scale include: dumping it in landfills with titanium gypsum for direct disposal; or selling it cheaply to downstream industries with low titanium quality requirements, reducing environmental pressure and achieving some economic benefits, but it's difficult to achieve the same economic benefits as titanium dioxide. Existing recycling technologies include drying and crushing the hydrolyzed scale, mixing it with titanium concentrate for acid hydrolysis to prepare titanium liquid and recover some of the titanium. However, this method suffers from low acid hydrolysis rates and requires sophisticated equipment, resulting in a long process flow, low titanium recovery rates, and potential safety hazards. Summary of the Invention

[0005] This invention discloses a method for recycling hydrolyzed scale to produce titanium dioxide, aiming to solve the technical problems of high difficulty in recycling hydrolyzed scale, large waste of titanium resources in conventional treatment, and low economic benefits.

[0006] To solve the aforementioned technical problems, the present invention adopts the following technical solution:

[0007] A method for recycling scale from hydrolysis to produce titanium dioxide includes the following steps:

[0008] S1. The hydrolyzed scale is crushed into smaller hydrolyzed scale materials using a jaw crusher;

[0009] S2. Mix the crushed hydrolyzed scale material with ball milling media, add water and perform wet ball milling. After the material is finely ground in the ball mill, it overflows into the post-milling slurry storage tank for temporary storage, thus obtaining the deagglomerated material.

[0010] S3. The depolymerized material is sent to the washing section and washed to obtain metatitanic acid filter cake.

[0011] S4. After the qualified metatitanic acid filter cake is washed and pulped, it is successively passed through the salt treatment section and the calcination section to obtain crude titanium dioxide.

[0012] S5. After the coarse titanium dioxide is fed into the Raymond mill for crushing, the crushed titanium dioxide is added with demineralized water and dispersant. The slurry after dispersion and pulping is pumped into the sand mill for deagglomeration and classification. The sand mill slurry with qualified particle size distribution is sent to subsequent processing after density adjustment to obtain rutile titanium dioxide.

[0013] Preferably, the milling media is at least one of zirconium silicate beads and zirconium oxide beads, and the diameter of the milling media is 6-20 mm.

[0014] Preferably, the mass ratio of the hydrolyzed scale to the ball milling media is 1:3-2:1; more preferably, the mass ratio of the hydrolyzed scale to the ball milling media is 1:1.

[0015] Preferably, step S3 specifically includes:

[0016] S3.1. The depolymerized material is sent to a primary diaphragm filter press for filtration. After filtration, it is washed once with water to obtain a first-wash filter cake.

[0017] S3.2. After the washed filter cake is dispersed in the pulping tank, it is pumped into the bleaching tank, sulfuric acid, trivalent titanium and calcined seed crystals are added to react and obtain the bleached material.

[0018] S3.3. The bleached material is sent to a secondary diaphragm filter press for filtration. After filtration, it is washed a second time to obtain the second-washed filter cake.

[0019] Preferably, step S3.2 specifically includes: based on the mass of titanium dioxide, the first-washed filter cake that has passed the water washing is slurried into a slurry with a concentration of 300-350 g / L in a slurry tank, and then the slurry is pumped into a bleaching tank, heated to 55-60°C with direct steam, sulfuric acid is added, and the sulfuric acid concentration of the slurry is controlled to be 65-150 g / L. Based on the amount of titanium dioxide, 0.3-0.5 wt% of trivalent titanium and 1-3 wt% of calcined seed crystals are added, and the mixture is stirred and reacted for 60-80 min.

[0020] Preferably, the filtrate and washing waste liquid in step S3.3 are recycled and used as washing water for the primary washing in step S3.1, and the washing water for the secondary washing is demineralized water. By recycling the filtrate filtered by the secondary diaphragm filter press and the washing waste liquid from the secondary washing, and using it as washing water for the primary washing, the utilization rate is improved and the production cost is reduced.

[0021] Preferably, in step S5, the mass ratio of the dispersant, desalinated water, and titanium dioxide is 1:1:6 to 1:1:2; more preferably, the mass ratio of the dispersant, desalinated water, and titanium dioxide is 1:1:6 to 1:1:4.

[0022] Preferably, in step S5, the slurry concentration pumped into the sand mill is 700-800 g / L.

[0023] Preferably, in step S5, the grinding media inside the sand mill are 0.6-0.8 mm zirconium beads.

[0024] Preferably, in step S5, the subsequent processing includes coating, pressure filtration and washing, flash drying, vapor pulverization and packaging.

[0025] The process parameters not specified in this invention are all performed using conventional methods in the field.

[0026] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0027] 1. This invention recycles hydrolyzed scale for use in the production of titanium dioxide by crushing, depolymerizing, washing, salting, calcining, sand milling, and subsequent processing. This not only reduces the difficulty of recycling and the environmental pressure, but also improves the recovery rate of titanium resources and increases economic benefits.

[0028] 2. The metatitanic acid filter cake that has passed the washing process of this invention can be directly subjected to salt treatment, calcination and subsequent processing. Alternatively, it can be mixed with the hydrolyzed secondary washing cake in any proportion and then subjected to salt treatment, calcination and subsequent processing. In all cases, qualified rutile titanium dioxide can be obtained, realizing the same economic value of hydrolyzed scale and titanium dioxide, and maximizing its value. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Therefore, the detailed description of the embodiments of this application provided below is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0030] Example 1:

[0031] This embodiment provides a method for recycling scale through hydrolysis to produce titanium dioxide, including the following steps:

[0032] S1. The hydrolyzed scale is crushed into hydrolyzed scale material with a particle size of about 20mm using a jaw crusher;

[0033] S2. The crushed hydrolyzed scale material is mixed with ball milling media using 10mm diameter zirconia beads at a ratio of 1:1. After adding water, the mixture is wet-milled for 100 minutes. After the material is finely ground in the ball mill, it overflows into the post-milling slurry storage tank for temporary storage, thus obtaining the deagglomerated material.

[0034] S3. The depolymerized material is sent to the washing section, where it is washed to obtain metatitanic acid filter cake; specifically, this includes the following steps:

[0035] S3.1 The depolymerized material is sent to the primary diaphragm filter press for filtration by the primary washing feed pump. After filtration, it is washed once to obtain the primary washing filter cake. The qualified primary washing filter cake is blown by air and pressed again to further squeeze out the water and then discharged to the pulping tank for pulping and supply to the bleaching section.

[0036] S3.2. The washed filter cake is dispersed in a pulping tank and then pumped to a bleaching tank. Sulfuric acid, trivalent titanium, and calcined seed crystals are added to react and obtain bleached material. Specific operations include: The washed filter cake, based on the mass of titanium dioxide, is pulped in a pulping tank to a concentration of 350 g / L. The slurry is then pumped to a bleaching tank, heated to 60°C with direct steam, and sulfuric acid is added, controlling the sulfuric acid concentration in the slurry to 150 g / L. Based on the amount of titanium dioxide, 0.5 wt% trivalent titanium and 3 wt% calcined seed crystals are added, and the mixture is stirred and reacted for 60 minutes before being transferred to the bleaching section. Through bleaching, ferric iron is further converted to ferrous iron, and some heavy metal ions are converted into soluble salts, which are further removed during bleaching to obtain high-quality metatitanic acid, ensuring the production of high-grade titanium dioxide products.

[0037] S3.3 The bleached material is sent to a secondary diaphragm filter press for filtration. After filtration, a secondary water wash is performed to obtain a secondary wash filter cake. The washing water used for the secondary water wash is demineralized water. The filtrate filtered by the secondary diaphragm filter press and the waste water used for the secondary water wash are recycled and used as washing water for the primary water wash, which improves the utilization rate and reduces the production cost.

[0038] S4. After the qualified metatitanic acid filter cake is slurried, it is passed through the salt treatment section and the calcination section in sequence to obtain crude titanium dioxide; specifically, the concentration of slurry before the salt treatment section is 350g / L.

[0039] S5. After the coarse titanium dioxide is fed into a Raymond mill for pulverization, demineralized water and a dispersant are added to the pulverized titanium dioxide. The mass ratio of the dispersant, demineralized water and titanium dioxide is 1:1:6. The dispersant is sodium polycarboxylate. Then, the mixture is dispersed and pulped at a pulping concentration of 800 g / L. The pulped slurry is pumped into a sand mill for deagglomeration and classification to further ensure fineness. The grinding media in the sand mill are 0.6 mm zirconium beads. After the sand mill slurry with qualified particle size distribution is adjusted in density, it is sent to subsequent processing to obtain rutile titanium dioxide. The subsequent processing is a conventional processing method in this field, including coating, pressure filtration and washing, flash drying, vapor jet pulverization and packaging.

[0040] The process parameters not specified in this invention are all performed using conventional methods in the field.

[0041] Example 2:

[0042] The pulping concentration is 700 g / L.

[0043] Example 3:

[0044] The pulping concentration is 750 g / L.

[0045] Comparative Example 1:

[0046] Step S5 is omitted.

[0047] The titanium dioxide obtained in each embodiment and comparative example was tested for whiteness and brightness using conventional methods in the art, and the results are shown in Table 1.

[0048] Table 1

[0049] brightness Whiteness 20° gloss Example 1 95.3 98.3 97.5 Example 2 95.2 98.2 96.9 Example 3 95.2 98.3 97.1 Comparative Example 1 95.1 97.8 96.6

[0050] This invention, through the above-mentioned treatment, recycles hydrolyzed scale for use in the production of titanium dioxide. This not only reduces the difficulty of recycling and the environmental pressure, but also improves the recovery rate of titanium resources and increases economic benefits. Furthermore, the rutile titanium dioxide obtained from this treatment meets high requirements in terms of brightness, whiteness, and 20° gloss, achieving the same economic value for hydrolyzed scale and titanium dioxide, thus maximizing their value.

[0051] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for producing titanium dioxide by recovering and utilizing scale from hydrolysis, characterized in that, Includes the following steps: S1. The hydrolyzed scale is crushed into smaller hydrolyzed scale materials using a jaw crusher; S2. Mix the crushed hydrolyzed scale material with ball milling media, add water and perform wet ball milling. After the material is finely ground in the ball mill, it overflows into the post-milling slurry storage tank for temporary storage, thus obtaining the deagglomerated material. S3. The depolymerized material is sent to the washing section and washed to obtain metatitanic acid filter cake. S4. After the qualified metatitanic acid filter cake is washed and pulped, it is successively passed through the salt treatment section and the calcination section to obtain crude titanium dioxide. S5. After the coarse titanium dioxide is fed into the Raymond mill for crushing, the crushed titanium dioxide is added with demineralized water and dispersant. The slurry after dispersion and pulping is pumped into the sand mill for deagglomeration and classification. The sand mill slurry with qualified particle size distribution is sent to subsequent processing after adjusting the density to obtain rutile titanium dioxide. Step S3 specifically includes: S3.

1. The depolymerized material is sent to a primary diaphragm filter press for filtration. After filtration, it is washed once with water to obtain a first-wash filter cake. S3.

2. After the washed filter cake is dispersed in the pulping tank, it is pumped into the bleaching tank, sulfuric acid, trivalent titanium and calcined seed crystals are added to react and obtain the bleached material. S3.

3. The bleached material is sent to a secondary diaphragm filter press for filtration. After filtration, it is washed a second time to obtain the second-washed filter cake. Step S3.2 specifically includes: based on the mass of titanium dioxide, the first-washed filter cake that has passed the first water washing is pulverized into a slurry with a concentration of 300-350 g / L in a slurry tank, and then the slurry is pumped into a bleaching tank, heated to 55-60°C with direct steam, sulfuric acid is added, and the sulfuric acid concentration of the slurry is controlled to be 65-150 g / L. Based on the amount of titanium dioxide, 0.3-0.5 wt% of trivalent titanium and 1-3 wt% of calcined seed crystals are added, and the mixture is stirred and reacted for 60-80 min. In step S3.3, the filtrate and washing waste liquid are recycled and used as washing water for the first washing in step S3.

1. The washing water for the second washing is demineralized water. In step S5, the mass ratio of the dispersant, desalinated water, and titanium dioxide is 1:1:6 to 1:1:

2. In step S5, the slurry concentration pumped into the sand mill is 700-800 g / L for dispersion and pulping. In step S5, the grinding media inside the sand mill are 0.6-0.8mm zirconium beads.

2. The method for producing titanium dioxide by recycling hydrolyzed scale according to claim 1, characterized in that, The milling media is at least one of zirconium silicate beads and zirconium oxide beads, and the diameter of the milling media is 6-20 mm.

3. The method for producing titanium dioxide by recycling hydrolyzed scale according to claim 1, characterized in that, The mass ratio of the hydrolyzed scale to the ball milling media is 1:3-2:

1.

4. The method for producing titanium dioxide by recycling hydrolyzed scale according to claim 1, characterized in that, In step S5, the subsequent processing includes coating, pressure filtration and washing, flash drying, vapor pulverization and packaging.