阅读说明：本技术 一种含铁酸洗废液中硝酸根离子的检测方法 (method for detecting nitrate ions in iron-containing pickling waste liquid ) 是由 朱松锋 居银栋 蒋银峰 黄莉君 陈炎彬 朱芬 于 2019-09-04 设计创作，主要内容包括：本发明公开了一种含铁酸洗废液中硝酸根离子的检测方法。该方法包括如下步骤：将含铁酸洗废液絮凝沉淀,分离得到透明上清液,在上清液中加入锌粉和氯化镉溶液,搅拌混合均匀,搅拌反应,将反应溶液静止后取上清液加水稀释,加入对氨基苯磺酸溶液,混合均匀放置后加入盐酸萘乙二胺溶液,混合均匀后放置显色,采用紫外分光光度计测定吸光度值,计算得到硝酸根含量。本发明的检测方法通过控制还原锌粉等反应条件,达到了检测效果的协同最大化,降低了共存离子等杂质对检测结果的干扰,检测结果误差可控制在4.6％以下,实现了含铁酸洗废液中硝酸根离子的准确测定,操作简单,成本低廉,无需复杂的前处理,检测速度快,可以广泛应用于工业测定。(The invention discloses a method for detecting nitrate ions in iron-containing pickling waste liquid. The method comprises the following steps: flocculating and precipitating the iron-containing pickling waste liquid, separating to obtain transparent supernatant, adding zinc powder and cadmium chloride solution into the supernatant, stirring and mixing uniformly, stirring for reaction, standing the reaction solution, taking the supernatant, adding water for dilution, adding sulfanilic acid solution, mixing uniformly, placing, adding naphthylethylenediamine hydrochloride solution, mixing uniformly, placing for color development, measuring the absorbance value by adopting an ultraviolet spectrophotometer, and calculating to obtain the nitrate content. The detection method disclosed by the invention achieves the cooperative maximization of the detection effect by controlling the reaction conditions of the reduced zinc powder and the like, reduces the interference of impurities such as coexisting ions and the like on the detection result, can control the error of the detection result to be below 4.6%, realizes the accurate determination of the nitrate ions in the iron-containing pickling waste liquid, is simple to operate, low in cost, free of complex pretreatment, high in detection speed and capable of being widely applied to industrial determination.)

1. A method for detecting nitrate ions in iron-containing pickling waste liquid is characterized by comprising the following steps:

S1, flocculating and precipitating the iron-containing pickling waste liquid, and separating to obtain transparent supernatant;

S2, adding reducing agent zinc powder and cadmium chloride solution into the supernatant in the step S1, stirring and mixing uniformly, wherein the adding amount of the reducing zinc powder is 0.3-0.6% of the mass of the supernatant, the adding amount of the cadmium chloride solution is 5-15% of the mass of the supernatant, and stirring and reacting for 4-8 min;

S3, standing the reaction solution in the step S2, adding water into the supernatant for dilution, adding a sulfanilic acid solution, uniformly mixing, standing for 2min, adding a naphthyl ethylenediamine hydrochloride solution, uniformly mixing, standing for color development for 5-10 min, measuring an absorbance value by using an ultraviolet spectrophotometer, and calculating to obtain the nitrate content.

2. The detection method according to claim 1, wherein the flocculation precipitation in S1 is performed by: and adjusting the pH value of the iron-containing pickling waste liquid to 6-8, and adding polyacrylamide for flocculation and precipitation.

3. the detection method as claimed in claim 1, wherein the reduced zinc powder in S2 has a particle size of 100-200 meshes and a purity of 96% or more.

4. The detection method as claimed in claim 3, wherein the addition amount of the reduced zinc powder in S2 is 0.4-0.5% of the mass of the supernatant.

5. The detection method as claimed in claim 3, wherein the amount of the reduced zinc powder added in S2 is 0.4% of the mass of the supernatant, the particle size of the zinc powder is 200 mesh, and the purity is 97%.

6. The detection method according to claim 3, wherein the concentration of the cadmium chloride solution in S2 is 5-50 g/L.

7. The detection method according to claim 6, wherein the concentration of the cadmium chloride solution in S2 is 45g/L, and the addition amount is 6% of the mass of the supernatant.

8. The detection method according to claim 1, wherein the volume ratio of the supernatant to the water in S3 is 1:9(1: 3-1: 15).

9. The detection method according to claim 8, wherein the concentration of the sulfanilic acid solution in S3 is 5 to 20g/L, and the volume ratio of the supernatant to the sulfanilic acid solution is 5: 1.

10. The detection method according to claim 9, wherein the concentration of the naphthyl ethylenediamine hydrochloride solution in S3 is 1-5 g/L, and the volume ratio of the supernatant to the naphthyl ethylenediamine hydrochloride solution is 5: 1.

Technical Field

the invention relates to the technical field of chemical analysis and detection, and particularly relates to a method for detecting nitrate ions in iron-containing pickling waste liquid.

Background

The surfaces of stainless steel, alloy steel and the like in the steel industry produce a layer of oxides during machining, which are usually removed by mixed pickling. At present, manufacturers at home and abroad mostly adopt mixed acid washing containing nitric acid to remove oxides. The mixed acid containing nitric acid is adopted for pickling, so that the pickling speed is high, the over-pickling is not easy to occur, and the pickled steel keeps a good surface, which cannot be achieved by other pickling. After multiple times of pickling, the metal ions in the pickling solution are increased to a certain concentration, and the acid content is reduced to a certain percentage, namely the pickling solution loses the pickling capacity and becomes waste liquid. However, the total acidity of the waste liquid is still quite high, and the waste liquid contains a large amount of metallic iron, chromium, nickel, nitrate ions, sulfate ions, chloride ions and the like, and the waste liquid can cause serious pollution to the environment if not treated. Nitrate in the waste acid can be decomposed into toxic and harmful gases such as NO2 and NO when meeting strong acid or high temperature, and the mixed gas of NO2 and NO is also called nitrate gas. NO2 mainly damages respiratory tract, and long-term contact can cause respiratory diseases, and NO can combine with hemoglobin in human body to make blood lack of oxygen and cause damage to heart, liver, kidney and hematopoietic system. Yellow smoke is formed when a large amount of nitrate gas is generated, so that the problems of difficult waste acid treatment and high treatment cost are caused. Therefore, it is very important to accurately detect and control the nitrate content in the iron-containing pickling waste liquid.

At present, the nitrate in the aqueous solution is mainly determined by a phenol disulfonic acid method, a cadmium column reduction method, an ion chromatography method, a gas phase molecular absorption spectrometry method, a thymol (thymol) spectrophotometry method, an ultraviolet spectrophotometry method and the like. The method has complex measuring steps, particularly the cadmium column reduction method has harsh operating conditions, and each cadmium column needs to be manufactured again. In addition, the coexisting ions, especially the chloride ions in the sample can cause serious interference to the measurement of the phenol disulfonic acid method and the thymol spectrophotometry, and the iron-containing pickling waste liquid generally contains a large amount of chloride ions, so that the pretreatment needs to consume a large amount of medicaments, is complex and time-consuming, and is not beneficial to the rapid batch measurement of enterprises. Although the ultraviolet spectrophotometry is simple in pretreatment and simple and convenient to operate, the measurement accuracy cannot be guaranteed due to interference of various substances such as a surfactant, a soluble organic matter, iron ions, chlorate, hydroxide and the like. Therefore, it is important to develop a method for measuring the nitrate content in the iron-containing pickling waste liquid, which is simple in operation, low in cost, and less in interfering substances. The prior art CN106198693A discloses a method for detecting the concentration of nitrite ions in a solution, which mainly uses a carboxylated graphene-polypyrrole-chitosan three-electrode system to measure the concentration of nitrite ions by differential pulse voltammetry, and does not disclose the problem of specifically reducing impurity interference in the related iron-containing waste acid solution.

Disclosure of Invention

The invention aims to solve the technical problem of overcoming the defect and the defect of impurity interference in the detection of nitrate ions in the existing iron-containing waste acid and provides a method for detecting the nitrate ions in the iron-containing pickling waste liquid.

The above purpose of the invention is realized by the following technical scheme:

A method for detecting nitrate ions in iron-containing pickling waste liquid comprises the following steps:

s1, flocculating and precipitating the iron-containing pickling waste liquid, and separating to obtain transparent supernatant;

S2, adding reducing agent zinc powder and cadmium chloride solution into the supernatant in the step S1, stirring and mixing uniformly, wherein the adding amount of the reducing zinc powder is 0.3-0.6% of the mass of the supernatant, the adding amount of the cadmium chloride solution is 5-15% of the mass of the supernatant, and stirring and reacting for 4-8 min;

S3, standing the reaction solution in the step S2, adding water into the supernatant for dilution, adding a sulfanilic acid solution, uniformly mixing, standing for 2min, adding a naphthyl ethylenediamine hydrochloride solution, uniformly mixing, standing for color development for 5-10 min, measuring an absorbance value by using an ultraviolet spectrophotometer, and calculating to obtain the nitrate content.

Among them, it should be noted that:

The zinc powder in the S2 reacts with the cadmium chloride solution to generate cadmium powder, or the cadmium powder can be directly added, but the cadmium powder has higher price. The addition amount of the reduced zinc powder in the S2 can be 0.3, 0.4, 0.5 or 0.6 percent of the mass of the supernatant, and the addition amount of the cadmium chloride solution is 5, 6, 8, 10 or 15 percent of the mass of the supernatant.

In the S3, the supernatant of the reaction solution is diluted by water in order to reduce the concentration of nitrate in the solution, the concentration is too high to interfere the subsequent color development reaction, sulfanilic acid is added to provide an acid environment and diazotize with the nitrate, then azotize with naphthyl ethylenediamine hydrochloride for color development, and both the sulfanilic acid and the naphthyl ethylenediamine hydrochloride are color developers.

The nitrate content is measured by an ultraviolet spectrophotometer, the ultraviolet spectrophotometer is used for measuring the absorbance of the chromogenic solution at the wavelength of 540nm by taking pure water as reference, the absorbance of nitrate standard solutions with different concentrations is measured, an absorbance standard curve under different nitrate concentrations is obtained, and the nitrate content in the sample is calculated from the standard curve by the sample absorbance.

preferably, the flocculation precipitation method in S1 is: and adjusting the pH value of the iron-containing pickling waste liquid to 6-8, and adding polyacrylamide for flocculation and precipitation. The pH is adjusted to eliminate the acidity of the waste liquid and prevent the added reducing agent from reacting with acid, and to precipitate metal ions such as iron ions in the waste liquid and eliminate the interference of the iron ions on the oxidation-reduction reaction.

preferably, the particle size of the reduced zinc powder in S2 is 100-200 meshes, and the purity is more than or equal to 96%. The zinc powder has too low purity and low content of effective components, so that the reduction effect is reduced; the zinc powder has too large particle size, the specific surface area is reduced, and the reaction efficiency is reduced. The particle size is too small, and the reaction product is easily suspended in a solution and is difficult to settle down, so that the subsequent color reaction is interfered.

Preferably, the addition amount of the reduced zinc powder in S2 is 0.4-0.5% of the mass of the supernatant.

Preferably, the addition amount of the reduced zinc powder in S2 is 0.4% of the mass of the supernatant, the particle size of the zinc powder is 200 meshes, and the purity is 97%.

Preferably, the concentration of the cadmium chloride solution in the S2 is 5-50 g/L. Too high concentration of the cadmium chloride solution wastes the medicament, and too low concentration generates too little reduced cadmium which is not enough to completely reduce nitrate. For example, it may be 15g/L, 20g/L, 25g/L or 45 g/L.

Preferably, the concentration of the cadmium chloride solution in S2 is 45g/L, and the addition amount is 6% of the mass of the supernatant.

Preferably, the volume ratio of the supernatant to water in S3 is 1: 3-1: 15. The dilution factor determines the concentration of nitrate ions in the solution, too high dilution factor can cause too low nitrate concentration, the measurement error is large, and too low dilution factor can cause too high nitrate concentration to influence the subsequent color reaction.

For example, it may be 1:3, 1:9 or 1:15, preferably 1: 9.

Preferably, the concentration of the sulfanilic acid solution in S3 is 5-20 g/L, and the volume ratio of the supernatant to the sulfanilic acid solution is 5: 1. For example, it may be 5g/L, 10g/L or 20 g/L.

the nitrate and sulfanilic acid are firstly subjected to diazotization reaction, the reaction product and naphthyl ethylenediamine hydrochloride are subjected to azo color development reaction, the nitrate radical reaction is incomplete due to too low sulfanilic acid concentration, the measurement result is low, the reagent is wasted due to too high concentration, and the naphthyl ethylenediamine hydrochloride is treated in the same way.

Preferably, the concentration of the naphthyl ethylenediamine hydrochloride solution in S3 is 1-5 g/L, and the volume ratio of the supernatant to the naphthyl ethylenediamine hydrochloride solution is 5: 1. For example, it may be 1g/L, 3g/L or 5 g/L.

Compared with the prior art, the invention has the beneficial effects that:

(1) The invention provides a method for detecting nitrate ions in iron-containing pickling waste liquid, which achieves the cooperative maximization of the detection effect by controlling the reaction conditions of reduced zinc powder and the like, reduces the interference of impurities such as coexisting ions and the like on the detection result, can control the error of the detection result to be below 4.6 percent, and can realize the accurate determination of the nitrate ions in the iron-containing pickling waste liquid.

(2) The detection method disclosed by the invention is simple to operate, low in cost, free of complex pretreatment, high in detection speed and capable of being widely applied to industrial determination.

Detailed Description

The present invention will be further described with reference to specific embodiments, but the present invention is not limited to the examples in any way. The starting reagents employed in the examples of the present invention are, unless otherwise specified, those that are conventionally purchased.

The liquid to be tested is prepared according to the following method:

6.855g of dried analytically pure sodium nitrate solid is added into 1L of the iron-containing pickling waste liquid without nitrate ions, and the mixture is stirred and dissolved, so that the concentration of the nitrate ions in the pickling waste liquid is 5 g/L.