A method for purifying and increasing the acidity of waste acid in the titanium dioxide industry

Abstract

This invention discloses a method for purifying and increasing the acidity of waste acid in the titanium dioxide industry, belonging to the field of waste acid treatment. This invention aims to solve the problem of sulfuric acid waste caused by simple waste acid treatment, and the technical problem caused by precipitation during sulfuric acid concentration. The method of this invention is as follows: S1, cyclohexanol hexaphosphate, phosphate, and flocculant are mixed evenly in a certain proportion to obtain a purifying agent; S2, 30% of the total volume of waste acid is poured into the purifying agent and stirred; S3, the remaining waste acid is poured in and stirred; S4, the mixture is then filtered to complete the process. This invention avoids the waste of sulfuric acid caused by neutralization and precipitation methods; the activated acid has a low metal ion content, and precipitation during evaporation, concentration, and reuse effectively avoids the problems of regular management, cleaning, and equipment maintenance caused by precipitation.

Description

Technical Field

[0001] This invention belongs to the field of waste acid treatment, specifically, it relates to a method for purifying and increasing the acidity of waste acid in the titanium dioxide industry. Background Technology

[0002] The main components of waste acid from the titanium dioxide industry are titanium sulfate, ferrous sulfate, and sulfuric acid. The main treatment cost for this waste acid is approximately 100 yuan / ton. Treatment methods typically involve neutralizing the waste acid with alkaline chemicals, followed by precipitation and recovery of metal ions. Simply recovering the water for reuse requires purchasing new acid and evaporating and concentrating it before use. The cost of purchasing new acid and concentrating is approximately 900-1100 yuan / ton. This process can also incur additional operating costs due to the presence of impurities such as Fe and Ca ions in the newly purchased industrial-grade dilute sulfuric acid, which can cause precipitation during concentration, leading to pipeline blockages. Summary of the Invention

[0003] To address the aforementioned industry pain points and challenges, this invention proposes a method for purifying impurity metal ions such as Fe, Ti, and Ca from waste acid and, to a certain extent, increasing the acidity of the activated acid. This process has a lower cost than the purchase price of new acid, avoids the waste of sulfuric acid in waste acid due to simple treatment, and can obtain pure sulfuric acid with a concentration of 32wt%, reducing precipitation problems caused by the concentration process.

[0004] This invention aims to solve the problem of sulfuric acid waste caused by simple waste acid treatment, as well as the technical problem caused by precipitation during sulfuric acid concentration, and provides a method for purifying and increasing the acidity of waste acid in the titanium dioxide industry.

[0005] The purpose of this invention is to provide a method for purifying and increasing the acidity of waste acid in the titanium dioxide industry, comprising the following steps: S1, cyclohexanol hexaphosphate, phosphate and flocculant are mixed evenly in a certain proportion to obtain a purifying agent; S2. Pour 30% of the total volume of waste acid into the purification agent and stir for 15 minutes at room temperature. S3. Pour in the remaining waste acid and stir for 15 minutes at room temperature. S4. Then filter by pressure, and the process is complete.

[0006] Further specifying, in step S1, the mass ratio of cyclohexanol hexaphosphate, phosphate and flocculant is 1:0.6:0.1, and the molar ratio of phosphate to cyclohexanol hexaphosphate is 1:(1-3).

[0007] Further specifying, in step S1, the phosphate is one or any combination of two of the following: trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, diammonium hydrogen phosphate, diammonium dihydrogen phosphate, and hydroxyethylidene diphosphate.

[0008] Further specifying, in step S1, the flocculant is stearic acid.

[0009] Furthermore, the volume ratio of the purifying agent to the waste acid from the titanium dioxide industry is specified as 1:1000.

[0010] Further specifying, pressure filtration is performed under a pressure of 0.25 MPa to achieve a 65% reduction in metal waste volume; the liquid after pressure filtration is returned to the titanium dioxide production line. The precipitate after filtration mainly consists of iron phosphate.

[0011] Cyclohexanol hexaphosphate and phosphate form a multi-level reaction of phosphoric acid, which promotes the formation of colloids of Fe and Ti in the acid solution. These colloids need to be further precipitated by flocculants before filtration.

[0012] This invention uses pressure filtration, which allows the colloids produced by the purifying agent to come into contact with water, thereby increasing the acidity of the waste acid.

[0013] The purification agent must be used in the following manner: some of the waste acid must be poured into the purification agent first, and all of the waste acid must not be poured into the purification agent directly, nor can the purification agent be poured into the waste acid directly. This flocculation reaction requires a high concentration of linkage reaction, and some reactions need to occur first to trigger subsequent reactions, thereby reducing the amount of purification agent used.

[0014] The acidity is increased by the method of the present invention, with the mass fraction of sulfuric acid being 24% before treatment and 32% after treatment.

[0015] This invention utilizes the ionization equilibrium of cyclohexanol hexaphosphate and phosphate ions in solution to form an acid, as shown in Reaction 1, and shifts the equilibrium towards the production of cyclohexanol hexaphosphate, ensuring that cyclohexanol hexaphosphate is at a higher concentration.

[0016] Cyclohexanol hexaphosphate = ionization = phosphate ion + 6H+ + (1) Metal ions in the solution react with phosphate to produce a precipitate as shown in reaction (2). At this time, sulfuric acid is generated in the solution. Therefore, the present invention can increase the acid concentration while precipitating metal ions.

[0017] M2SO4 + cyclohexanol hexaphosphate = M3(PO4)2↓ + H2SO4 (M = Fe, Ti, Ca) (2) The resulting precipitate will produce a precipitation-dissolution equilibrium reaction in the solution as shown in (3). Therefore, through multi-stage filtration, the precipitate can be discharged, causing reaction (3) to shift to the positive direction, making the reaction more thorough and further reducing the metal ion content in the waste acid.

[0018] 3M 2+ +2PO4 3- (M=Fe, Ti, Ca) =M3(PO4)2(3) Compared with the prior art, the present invention has the following beneficial effects: (1) It avoids the waste of sulfuric acid caused by the neutralization precipitation method; (2) The activated acid has a low content of metal ions, which effectively avoids precipitation during evaporation, concentration and reuse, thus avoiding problems with regular management, cleaning and equipment maintenance. (3) The method of in-situ filtration in concentrated acid is used to recover and reuse acid, which is significantly different from the traditional neutralization method for treating waste acid and provides a new approach to waste acid treatment.

[0019] (4) Although multiple filtrations are required to fully treat the metal ions in the waste acid, and an appropriate amount of organic purifying agents such as cyclohexanol hexaphosphate will be introduced, these components will be removed in the subsequent evaporation and concentration process without causing new problems.

[0020] To further understand the features and technical content of this invention, please refer to the following detailed description and accompanying drawings. However, the accompanying drawings are for reference and illustration only and are not intended to limit the invention. Attached Figure Description

[0021] Figure 1 This is a picture of the waste acid solution after adding the purifying agent; Figure 2 This is a comparison image of the waste acid supernatant before (left) and after (right) precipitation; Figure 3 A photograph of the precipitate produced during the waste acid activation treatment of titanium dioxide. Detailed Implementation

[0022] The following examples are provided to better illustrate the present invention. However, the present invention is not limited to the specific embodiments described.

[0023] Example 1: The method for purifying and increasing the acidity of waste acid in the titanium dioxide industry in this example is carried out according to the following steps: S1. Mix 100g of cyclohexanol hexaphosphate, 60g of disodium hydrogen phosphate and 10g of stearic acid evenly and dissolve them in 1L of water. The molar ratio of phosphate to cyclohexanol hexaphosphate is 1:3 to obtain the purifying agent. S2. Add 30% of the total mass of waste acid to the purifying agent at a volume ratio of 1:1000, and treat at room temperature for 15 minutes at a speed of 100 r / min. S3. Pour in 70% of the total mass of waste acid and treat at room temperature for 15 minutes at a speed of 100 r / min. S4. Then, filter under pressure at 0.25 MPa to complete the process. The filtered liquid is returned to the titanium dioxide production line.

[0024] The following tests were used to verify the effectiveness of the invention. Using 1L of waste acid supernatant (the supernatant obtained after one filtration stage from waste acid from the titanium dioxide industry) as the treatment target, if simply adding purifying agent to the waste acid requires 54ml of purifying agent (as in Example 1), but if the waste acid is poured into the purifying agent, only 1ml of purifying agent is needed. After adding the purifying agent, a large amount of precipitate appears in the waste acid, such as... Figure 1 As shown in the figure, a comparison is made between samples of the filtered liquid and the supernatant of the acid solution before precipitation. Figure 2 As shown in Table 1, after adding the purifying agent, the solution changed from its original orange-red color (left) to light green (right). The Fe, Ti, and sulfate contents of the samples before and after treatment with the purifying agent were tested, and the results are shown in Table 1. The contents of FeSO4 and Ti(SO4)2 decreased from 8.36 wt.% and 1.56 wt.% to 2.14 wt.% and 0.44 wt.%, respectively, while the sulfuric acid mass fraction increased from 24 wt.% to 32 wt.%. This indicates that the purifying agent can not only treat metal ions in sulfuric acid and purify waste acid, but also increase the sulfuric acid content to a certain extent.

[0025] Table 1 Comparison of changes in various substances in the liquid before and after treatment The specific embodiments of the present invention have been described above. It should be noted that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for purifying and increasing the acidity of waste acid in the titanium dioxide industry, comprising the following steps: S1, cyclohexanol hexaphosphate, phosphate and stearic acid are mixed evenly in a certain proportion to obtain the purifying agent; S2. Pour 30% of the total volume of waste acid into the purification agent and stir for at least 15 minutes at room temperature. S3. Pour in the remaining waste acid and stir for at least 15 minutes at room temperature. S4. Then filter by pressure, and the process is complete.

2. The method according to claim 1, characterized in that, In step S1, the mass ratio of cyclohexanol hexaphosphate, phosphate and stearic acid is 1:0.6:0.1, and the molar ratio of phosphate to cyclohexanol hexaphosphate is 1:(1-3).

3. The method according to claim 1, characterized in that, Phosphate is one or a combination of two of the following: trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, diammonium hydrogen phosphate, diammonium dihydrogen phosphate, and hydroxyethylidene diphosphate.

4. The method according to claim 1, characterized in that, The volume ratio of the purifying agent to the waste acid from the titanium dioxide industry is 1:1000.

5. The method according to claim 1, characterized in that, Pressure filtration is filtration under a pressure of 0.25 MPa.

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