Method for detecting ammonia-nitrogen content in waste sulfuric acid of sulfuric acid method titanium dioxide

Abstract

The application discloses a method for detecting ammonia-nitrogen content of waste sulfuric acid in a sulfuric acid method titanium white production process, and ammonia-nitrogen distillation equipment is composed of an electromagnetic stirring heater, a multi-mouth flask, a constant-pressure funnel (with a plug), a distillation condenser, a distillate pipe, a liquid receiving bottle, a micro-needle sampler and a glass syringe. 4+ , Fe 3+ ; after the iron powder is dissolved, sodium citrate is added; NaOH solution is added dropwise into the system until the pH value is 8-9; the heating intensity is controlled, and the mixed system is distilled to near dryness; pure water is injected into the flask through the rubber plug by using the glass syringe, and the ammonia-nitrogen is continuously released by repeated distillation; the ammonia-nitrogen gas and the distillate are absorbed by the absorption liquid; the distillate is neutralized to pH=6-8 and constant volume, the ammonia-nitrogen concentration in the absorption liquid is determined by using the Nessler reagent spectrophotometry, and the ammonia-nitrogen concentration in the waste acid is calculated. The application can simply and efficiently realize complete ammonia-nitrogen distillation release of the waste acid and avoid the interference of various impurities in the waste acid on the ammonia-nitrogen determination.

Description

Technical Field

[0001] This invention belongs to the field of detection, specifically relating to a method for detecting ammonia nitrogen content in waste acid from the sulfuric acid process for titanium dioxide production. Background Technology

[0002] Titanium dioxide is currently the white pigment with the best overall performance. It possesses stable physicochemical properties and excellent optical properties such as high refractive index, high hiding power, high whiteness, and high brightness. The main component of titanium dioxide is TiO2, and its production processes mainly include the chloride process and the sulfate process. The sulfate process has a history of nearly a century. Due to its mature technology, low equipment strength requirements, low raw material quality requirements, and ability to produce both anatase and rutile titanium dioxide crystals, it will coexist and complement the chloride process for a long time. A crucial step in the sulfate process is the "black titanium solution" hydrolysis. The black titanium solution is the leaching liquid from the solidified product of the acid hydrolysis reaction of ilmenite and sulfuric acid. Its main components include titanium oxysulfate, ferrous sulfate, free sulfuric acid, and sulfates of various heterometals. After boiling and heating, the titanium oxysulfate undergoes a hydrolysis reaction to form metatitanic acid precipitate. The residual liquid contains approximately 23% sulfuric acid (referred to in the industry as "23 acid"), approximately 9% ferrous sulfate, and unhydrolyzed Ti. 4+ The concentration of ions is approximately 4-6 g / L (calculated as TiO2). Due to the ammonia nitrogen carried by various raw materials and auxiliary materials during production, trace amounts of NH3 are also present in the waste acid. 4+ Ammonia nitrogen, an important environmental indicator, is introduced into downstream industries through the use of waste acid from the sulfuric acid process for titanium dioxide production, including the manufacture of polyferric sulfate and the neutralization of alkaline wastewater. Therefore, the ammonia nitrogen content in waste acid from the sulfuric acid process is a crucial indicator in the titanium dioxide industry. However, because this waste acid also contains impurities such as Mg, Ca, Zn, Mn, V, Al, Cu, Si, phosphate, and chloride ions, as well as unidentified impurities introduced from raw sulfuric acid, titanium ore, and auxiliary materials, ordinary ammonia nitrogen detection and pretreatment methods cannot avoid interference from these unidentified impurities. Currently, there is no authoritative standard for detecting ammonia nitrogen content in waste acid from the sulfuric acid process for titanium dioxide production.

[0003] The basic idea of ​​this invention is to neutralize the waste acid from the sulfuric acid process for titanium dioxide production to a pH of 8-9, distill off NH3 under alkaline conditions, absorb ammonia nitrogen with a dilute sulfuric acid solution, and then determine the ammonia nitrogen concentration in the absorbent using Nessler's reagent spectrophotometry, thereby obtaining the ammonia nitrogen content in the waste acid. However, because the waste acid contains Ti... 4+ Fe 2+ Fe 3+ (by Fe 2+ Metal ions (derived from oxidation), especially Ti 4+ Fe 3+Under purely alkaline and boiling conditions, hydrolysis inevitably occurs, forming a large amount of metal hydroxide precipitates that adsorb ammonia nitrogen. Furthermore, the precipitates formed are detrimental to the ammonia nitrogen distillation process. Additionally, NH3, as an nitrogen-containing ligand, has a strong ability to coordinate and complex metal ions, making complete removal during distillation difficult. In conclusion, directly neutralizing waste acid is highly unfavorable for the ammonia nitrogen distillation operation of this system. Summary of the Invention

[0004] The purpose of this invention is to overcome technical deficiencies and establish a method for determining the ammonia nitrogen content in waste acid from the sulfuric acid process of titanium dioxide by adding reduced iron powder and citric acid ligand, followed by neutralization and distillation.

[0005] This invention is achieved through the following technical solution:

[0006] A method for detecting ammonia nitrogen content in waste acid from the sulfuric acid process for titanium dioxide production includes the following steps:

[0007] (1) Add reduced iron powder to waste acid to reduce ferric ions and tetravalent titanium ions. After the reduced iron powder is completely dissolved in acid, add sodium citrate and dissolve it completely.

[0008] (2) Under stirring conditions, add 8% NaOH solution dropwise to the system, use a microneedle sampler to take a small amount of sample, and use precision pH test paper to detect the pH value of the system to neutralize it to 8-9;

[0009] (3) Turn on the heating and control the heating intensity so that the distillation rate is about 10 ml / min. Distill until the mixture is nearly dry. Use a glass syringe to inject pure water into the flask through the rubber stopper. Continue to distill repeatedly to fully release ammonia nitrogen. All ammonia nitrogen gas and distillate are absorbed by the absorbent.

[0010] (4) Neutralize the distillate to pH 6-8 and make up the volume. Determine the ammonia nitrogen concentration in the absorbent using Nessler's reagent spectrophotometry and calculate the ammonia nitrogen concentration in the waste acid.

[0011] Furthermore, the mass of iron powder added to 100ml of waste acid is 0.5g, and the mass of sodium citrate is 36g.

[0012] Furthermore, during the addition of NaOH and distillation, the overflowing gas or distillate is introduced into a receiving bottle containing the absorbent liquid to ensure that there is no gas leakage from the apparatus.

[0013] Furthermore, the absorbent was 0.01 mol / L dilute sulfuric acid.

[0014] The beneficial effects of this invention are as follows:

[0015] This invention pretreats the waste acid system as follows: first, a small amount of reduced iron powder is added to the waste acid, and a small amount of Fe... 3+Reduced to Fe 2+ Ti 4+ Restored to Ti 3+ Eliminate Fe 3+ Ti 4+ Compared to Fe 2+ Ti 3+ To mitigate the risk of hydrolysis, excess iron powder will dissolve in the waste acid, leaving no solid iron powder residue in the system. Adding sodium citrate provides citric acid ligands for coordinating and complexing Fe. 2+ The presence of metal ions can efficiently suppress the coordination of hydroxyl groups with metal ions, achieving a system free of metal hydroxide precipitates under boiling and alkaline conditions, thus eliminating the adsorption of ammonia nitrogen by metal hydroxides. Simultaneously, citric acid ligands and Fe... 2+ Fe ions form 2+ (L 4- The coordination stability constant of the complex is lgKn = 15.5, which is greater than that of NH3 and Fe. 2+ The coordination stability constants of the ions are 1.4 and 2.2, and the concentration of citric acid ligands is much greater than that of NH3. The strong competitive coordination of citric acid ligands with the central metal ion will "squeeze out" the NH3 ligands, releasing the "binding" effect of the metal ion on NH3, which is more conducive to the complete distillation of NH3. This invention can easily and efficiently realize the distillation and release of ammonia nitrogen from waste acid while avoiding the interference of various impurities in waste acid on ammonia nitrogen determination. Attached Figure Description

[0016] Figure 1 Linear fitting plots of ammonia nitrogen spiked in four batches of waste acid samples. Detailed Implementation

[0017] To enable those skilled in the art to better understand the present invention and to make the above-mentioned objectives, features and advantages of the present invention more apparent, the present invention will be further described in detail below with reference to embodiments.

[0018] Example 1

[0019] A method for detecting ammonia nitrogen content in waste acid from the sulfuric acid process for titanium dioxide production includes the following steps:

[0020] (1) The ammonia nitrogen distillation equipment mainly consists of an electromagnetic stirring heater, a multi-necked flask, a constant pressure funnel (with a stopper), a distillation condenser, a distillation tube, a receiving bottle, a microneedle sampler, and a glass syringe. The mouth of the flask is connected to the distillation condenser, the constant pressure funnel, and the rubber stopper, respectively. The microneedle sampler can be inserted into the rubber stopper to draw a small amount of solution and detect the pH value of the solution. The glass syringe can be inserted into the rubber stopper to inject pure water into the flask and add water to continue distillation. The rubber stopper can ensure that there is no gas leakage when the microneedle or syringe is used for sampling and water is added to continue distillation. The mouth of the distillation tube is below the liquid level of the absorbent in the receiving bottle.

[0021] (2) Add waste acid and reduced iron powder to the flask and start stirring. After the reduced iron powder is completely dissolved, add trisodium citrate and dissolve it completely. Install the ammonia nitrogen distillation equipment completely, and place the outlet of the distillation tube below the liquid level of the absorbent liquid (dilute sulfuric acid, c=0.01 mol / L) in the receiving bottle.

[0022] (3) Under stirring conditions, add the NaOH solution (8% by mass) dropwise from the constant pressure funnel to the system. Use a microneedle sampler to insert into the rubber stopper to draw a small amount of sample, and use precision pH test paper to detect the pH value of the system to neutralize it to 8-9. (Preliminary experiments can be conducted on the same batch of waste acid. The amount of NaOH solution used can be fixed to minimize the number of samplings.)

[0023] (4) Turn on the heating and condenser, control the heating intensity, and make the distillation rate about 10 ml / min. Distill until the mixture is nearly dry, use a glass syringe to inject pure water into the flask through the rubber stopper, and continue to distill repeatedly to fully release ammonia nitrogen. All ammonia nitrogen gas and distillate are absorbed by the absorbent.

[0024] (5) Neutralize the distillate to pH 6-8 and make up to volume. Determine the ammonia nitrogen concentration in the absorbent using Nessler's reagent spectrophotometry and calculate the ammonia nitrogen concentration in the waste acid.

[0025] During the experiment, the following should be noted: The blank sample is prepared with 25% sulfuric acid. After complete acid dissolution with reduced iron powder, trisodium citrate is added, and the pH is neutralized to 8-9 with NaOH solution. Then, the sample is distilled and the ammonia nitrogen value is determined following the steps described above. After multiple tests, the ammonia nitrogen content in the blank sample was almost zero.

[0026] No precipitation occurred in the pretreated system under boiling reflux conditions.

[0027] The accuracy of the method of the present invention was confirmed by spiking (NH4Cl, dried at 100-105℃ for 2 hours, ammonia nitrogen standard):

[0028] A series of different amounts of ammonia nitrogen standard solution were added to waste acid, and then distillation, measurement, and calculation were performed according to the basic steps. A linear fit was performed on the spiked data points, with the amount of ammonia nitrogen added to the waste acid as the x-axis and the actual measured total ammonia nitrogen as the y-axis. The intercept of the line was then used as the initial ammonia nitrogen content of the waste acid fitted by the spiking method. The initial ammonia nitrogen content of the waste acid obtained by the fitting method was compared with the ammonia nitrogen content measured by direct distillation (without adding ammonia nitrogen standard) to confirm accuracy. The ammonia nitrogen content detection results, linear equations, and other information for four batches of waste acid are shown in Tables 1 and 2. Figure 1 As shown in the figure. The results indicate that the spiking curve has good linearity, and the difference between the intercept ammonia nitrogen concentration and the direct distillation ammonia nitrogen concentration is small, demonstrating the accuracy and feasibility of the method. The method of this invention can be directly used to determine the ammonia nitrogen content of titanium dioxide waste acid.

[0029] Table 1. Determination parameters of acid composition and ammonia nitrogen in waste from four batches of sulfuric acid-process titanium dioxide, and results of ammonia nitrogen spiked analysis.

[0030]

[0031] *In the sulfuric acid process titanium dioxide industry, TiO2 concentration is commonly used to refer to titanium ion concentration.

[0032] Table 1 (continued)

[0033]

[0034] Table 2. Linear fitting equations for ammonia nitrogen spiking in four batches of waste acid samples.

[0035]

Claims

1. A method for detecting ammonia nitrogen content in waste acid from the sulfuric acid process for titanium dioxide production, characterized in that, Includes the following steps: (1) Add reduced iron powder to waste acid to reduce ferric ions and tetravalent titanium ions. After the reduced iron powder is completely dissolved in acid, add sodium citrate and dissolve it completely. The mass of iron powder added to 100ml waste acid is 0.5g and the mass of sodium citrate is 36g. (2) Under stirring conditions, add 8% NaOH solution dropwise to the system, use a microneedle sampler to take a small amount of sample, and use precision pH test paper to detect the pH value of the system to neutralize it to 8-9; (3) Turn on the heating and control the heating intensity so that the distillation rate is about 10 ml / min. Distill until the mixture is nearly dry. Use a glass syringe to inject water into the flask through the rubber stopper. Continue to distill repeatedly to fully release ammonia nitrogen. All ammonia nitrogen gas and distillate are absorbed by 0.01 mol / L dilute sulfuric acid absorbent. (4) Neutralize the distillate to pH 6-8 and make up the volume. Determine the ammonia nitrogen concentration in the absorbent using Nessler's reagent spectrophotometry and calculate the ammonia nitrogen concentration in the waste acid.

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