Sample preparation method for detecting ammonia nitrogen in high-sulfate wastewater and detection method

Abstract

The invention relates to the technical field of water quality detection, and particularly provides a sample preparation method and a detection method for detecting ammonia nitrogen in high-sulfate wastewater, the sample preparation method comprises the following steps: S1, mixing sodium thiosulfate, zinc sulfate, to-be-detected wastewater and a boric acid-sodium hydroxide buffer solution for the first time, and carrying out first standing to obtain a first mixture; s2, carrying out solid-liquid separation on the first mixture obtained in the step S1, and fixing the volume of a separated liquid phase to obtain a second solution; mixing potassium sodium tartrate, a Nessler reagent and the second solution for the second time, and standing for the second time to obtain a sample to be detected. According to the method, interference of high-content sulfate radicals and metal ions in the high-sulfate industrial wastewater can be effectively eliminated, the obtained color development system is high in stability, and the method has the advantages of being easy to operate, reliable in result and the like and has important significance on detection and treatment of the laterite-nickel ore hydrometallurgy wastewater.

Description

Technical Field

[0001] The invention relates to the technical field of water quality detection, and in particular to a sample preparation method and a detection method for detecting ammonia nitrogen in high-sulfate wastewater. Background Art

[0002] Ammonia nitrogen index is one of the important items of water quality control. Excessive ammonia nitrogen content will cause harm to human health and the ecological environment, so the monitoring of ammonia nitrogen index is very important in environmental quality and pollution control. Moreover, with the development of industrialization, the amount of industrial wastewater discharge is increasing, and the types of industrial wastewater are becoming more and more diverse, which brings more challenges to ammonia nitrogen detection.

[0003] Nickel in laterite nickel ore accounts for about 70% of the total land-based nickel reserves on Earth, and currently, laterite nickel ore is mostly extracted by hydrometallurgical process using sulfuric acid. In recent years, with the growth of nickel demand for stainless steel and new energy, the amount of industrial wastewater generated by the hydrometallurgical nickel extraction process has increased rapidly, and its detection and treatment have gradually attracted attention.

[0004] The industrial wastewater produced by the hydrometallurgical process of laterite nickel ore contains a large amount of sulfate ions and metal ions, which are difficult to test using traditional absorbance detection methods. There are problems such as inaccurate detection data and long detection time.

[0005] Therefore, it is necessary to develop a new method for detecting the ammonia nitrogen content in laterite nickel ore hydrometallurgical wastewater. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a sample preparation method and a detection method for ammonia nitrogen detection in high-sulfate wastewater, which has the advantages of being simple and easy to operate and having reliable results.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a sample preparation method for detecting ammonia nitrogen in high-sulfate wastewater, the sample preparation method comprising the following steps:

[0009] S1, first mixing sodium thiosulfate, zinc sulfate, wastewater to be tested and boric acid-sodium hydroxide buffer solution, and first standing to obtain a first mixture;

[0010] S2, step S1: the first mixture is subjected to solid-liquid separation, and the separated liquid phase is fixed to obtain a second solution; potassium sodium tartrate, Nessler's reagent and the second solution are mixed and allowed to stand for a second time to obtain a sample to be tested.

[0011] The sample preparation method for detecting ammonia nitrogen in high-sulfate wastewater provided by the present invention adopts a sodium thiosulfate solution to remove residual chlorine; then a zinc sulfate solution is added and mixed, so as to perform flocculation precipitation subsequently; and the boric acid-sodium hydroxide buffer solution is the key to the present invention. By adjusting the pH in the system by the boric acid-sodium hydroxide buffer solution, interference of sulfate radicals and metal ions in the wastewater to be detected can be avoided, so that the detection result can be accurate, and the color development system obtained by adding Nessler's reagent to the liquid phase after subsequent separation is more stable and clear, the detection speed is faster, and the application prospect is broad.

[0012] It should be further explained that the addition system of the boric acid-sodium hydroxide buffer solution in the present invention is matched with the zinc sulfate solution and the subsequent potassium sodium tartrate and Nessler's reagent. When these reagents are replaced by other reagents, it is difficult to exert the stable and efficient flocculation effect of the boric acid-sodium hydroxide buffer solution, and the test results are also greatly affected.

[0013] Preferably, the wastewater to be tested in step S1 is high sulfate wastewater, preferably laterite nickel ore hydrometallurgical wastewater.

[0014] It is worth mentioning that the difference between laterite nickel ore hydrometallurgical wastewater and conventional wastewater is that it contains a large amount of sulfate and metal ions. Sulfate can easily change the color intensity during the ammonia nitrogen detection process, resulting in inaccurate absorbance detection data and greater difficulty in detection.

[0015] Preferably, the sulfate content in the wastewater to be tested is 20-40 g / L, for example, it can be 20 g / L, 23 g / L, 25 g / L, 27 g / L, 29 g / L, 32 g / L, 34 g / L, 36 g / L, 38 g / L or 40 g / L, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0016] Preferably, the magnesium content in the wastewater to be tested is 6 to 8 g / L, for example, it can be 6 g / L, 6.3 g / L, 6.5 g / L, 6.7 g / L, 6.9 g / L, 7.2 g / L, 7.4 g / L, 7.6 g / L, 7.8 g / L or 8 g / L, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0017] Preferably, the sodium content in the wastewater to be tested is 2 to 4 g / L, for example, it can be 2g / L, 2.3g / L, 2.5g / L, 2.7g / L, 2.9g / L, 3.2g / L, 3.4g / L, 3.6g / L, 3.8g / L or 4g / L, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0018] Preferably, the manganese content in the wastewater to be tested is 2-50 mg / L, for example, it can be 2 mg / L, 3 mg / L, 5 mg / L, 10 mg / L, 12 mg / L, 15 mg / L, 20 mg / L, 25 mg / L, 28 mg / L, 30 mg / L, 32 mg / L, 35 mg / L, 40 mg / L, 45 mg / L or 50 mg / L, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0019] Preferably, the pH of the boric acid-sodium hydroxide buffer solution is 9.4-9.6, for example, 9.4, 9.5 or 9.6.

[0020] The pH of the boric acid-sodium hydroxide buffer solution in the present invention is very critical. Studies have shown that when the pH of the boric acid-sodium hydroxide buffer solution is not within the above range, it is difficult to obtain accurate detection results.

[0021] Preferably, the preparation of the boric acid-sodium hydroxide buffer solution comprises: dissolving boric acid in water to obtain a boric acid solution, and adjusting the pH of the boric acid solution to a target pH with a saturated sodium hydroxide solution to obtain the boric acid-sodium hydroxide buffer solution.

[0022] It should be further explained that, in the scheme of the present invention, by using a boric acid-sodium hydroxide buffer solution (pH=9.4-9.6) to make the volume constant, not only can various problems during simple sodium hydroxide adjustment be effectively solved, making the detection method easier to operate, but also the detection result is accurate and reliable. In addition, it should be noted that in the method of the present invention, in addition to being used to adjust and maintain the pH during flocculation in step S1, the type of the buffer solution is also one of the key factors affecting the sample to be tested obtained in step S2. The data of the present invention show that when the boric acid-sodium hydroxide buffer solution is replaced with other buffer solutions (such as borax-sodium hydroxide buffer solution and boric acid-potassium chloride-sodium carbonate buffer solution), the detection system may not develop color and / or be unstable, resulting in difficulty in calculating the ammonia nitrogen concentration by colorimetry.

[0023] Preferably, the sodium thiosulfate is added in the form of a sodium thiosulfate solution.

[0024] Preferably, the zinc sulfate is added in the form of a zinc sulfate solution.

[0025] Preferably, the mass concentration of the sodium thiosulfate solution is 3.0-4.0 g / L, for example, 3.0 g / L, 3.2 g / L, 3.3 g / L, 3.4 g / L, 3.5 g / L, 3.6 g / L, 3.7 g / L, 3.8 g / L, 3.9 g / L or 4.0 g / L, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0026] Preferably, the mass concentration of the zinc sulfate solution is 80-120 g / L, for example, 80 g / L, 85 g / L, 89 g / L, 94 g / L, 98 g / L, 103 g / L, 107 g / L, 112 g / L, 116 g / L or 120 g / L, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0027] Preferably, the volume ratio of the sodium thiosulfate solution to the zinc sulfate solution is (1.5-2.5):(0.8-1.5), wherein the number of parts of the sodium thiosulfate solution can be, for example, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4 or 2.5, etc. The number of parts of the zinc sulfate solution can be, for example, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 or 1.5, etc.

[0028] Preferably, the volume ratio of the sodium thiosulfate solution to the wastewater to be tested is (1.5-2.5):10, for example, it can be 1.5:10, 1.7:10, 1.8:10, 1.9:10, 2:10, 2.1:10, 2.2:10, 2.3:10, 2.4:10 or 2.5:10, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0029] Preferably, the volume ratio of the boric acid-sodium hydroxide buffer solution to the wastewater to be tested is (86-87.7):1, for example, it can be 86:1, 86.2:1, 86.4:1, 86.6:1, 86.8:1, 87:1, 87.2:1, 87.4:1, 87.6:1 or 87.7:1, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0030] Different from the existing detection scheme, the present invention does not add a trace amount of boric acid-sodium hydroxide buffer solution and then add water to make the volume, but directly uses boric acid-sodium hydroxide buffer solution to make the volume, which can greatly improve the stability of the element to be tested in the whole system and avoid the interference of sulfate and metal ions on the detection.

[0031] Preferably, the first mixing comprises: placing the wastewater to be tested in a volumetric flask, adding sodium thiosulfate solution and zinc sulfate solution, and then fixing the volume with a boric acid-sodium hydroxide buffer solution.

[0032] Preferably, the first standing time in step S1 is 15 to 30 min, for example, it can be 15 min, 17 min, 19 min, 20 min, 22 min, 24 min, 25 min, 27 min, 29 min or 30 min, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0033] Preferably, the solid-liquid separation in step S2 comprises filtration, preferably filtration using qualitative filter paper.

[0034] Preferably, the Nessler's reagent is mercuric iodide-potassium iodide-sodium hydroxide solution.

[0035] Preferably, the concentration of mercuric iodide in the Nessler's reagent is 9.5-10.5 g / L, for example, it can be 9.5 g / L, 9.7 g / L, 9.8 g / L, 9.9 g / L, 10 g / L, 10.1 g / L, 10.2 g / L, 10.3 g / L, 10.4 g / L or 10.5 g / L, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0036] Preferably, the concentration of potassium iodide in the Nessler's reagent is 5-10 g / L, for example, it can be 5 g / L, 5.6 g / L, 6.2 g / L, 6.7 g / L, 7.3 g / L, 7.8 g / L, 8.4 g / L, 8.9 g / L, 9.5 g / L or 10 g / L, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0037] Preferably, the concentration of sodium hydroxide in the Nessler's reagent is 12 to 20 g / L, for example, 12 g / L, 12.9 g / L, 13.8 g / L, 14.7 g / L, 15.6 g / L, 16.5 g / L, 17.4 g / L, 18.3 g / L, 19.2 g / L or 20 g / L, etc., but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0038] Preferably, the sodium potassium tartrate is added in the form of sodium potassium tartrate solution.

[0039] Preferably, the concentration of the potassium sodium tartrate solution is 450-500 g / L, for example, 450 g / L, 456 g / L, 462 g / L, 467 g / L, 473 g / L, 478 g / L, 484 g / L, 489 g / L, 495 g / L or 500 g / L, but is not limited to the listed values, and other unlisted values ​​within the range are equally applicable.

[0040] Preferably, the volume ratio of the sodium potassium tartrate solution to Nessler's reagent is (0.8-1.2):1, for example, it can be 0.8:1, 0.85:1, 0.89:1, 0.94:1, 0.98:1, 1.03:1, 1.07:1, 1.12:1, 1.16:1 or 1.2:1, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0041] Preferably, the volume ratio of the sodium potassium tartrate solution to the separated liquid phase is (0.8-1.2):20, for example, it can be 0.8:20, 0.85:20, 0.89:20, 0.94:20, 0.98:20, 1.03:20, 1.07:20, 1.12:20, 1.16:20 or 1.2:20, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0042] Preferably, the second mixing comprises: taking the separated liquid phase to a fixed volume in a colorimetric tube, and adding potassium sodium tartrate solution and Nessler's reagent.

[0043] Preferably, the second standing time is 10 to 20 min, for example, it can be 10 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min or 20 min, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0044] In a second aspect, the present invention provides a method for detecting ammonia nitrogen in laterite nickel ore hydrometallurgical wastewater, wherein the detection method uses the sample preparation method for detecting ammonia nitrogen in high sulfate wastewater described in the first aspect to test the sample to be tested.

[0045] The method for detecting ammonia nitrogen in laterite nickel ore hydrometallurgical wastewater provided in the second aspect of the present invention can realize rapid, efficient and accurate detection of ammonia nitrogen content, and has broad application prospects.

[0046] Preferably, the detection method is performed using absorbance.

[0047] Preferably, the wavelength detected in the detection method is 400-450nm, for example, it can be 400nm, 406nm, 412nm, 417nm, 423nm, 428nm, 434nm, 439nm, 445nm or 450nm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0048] Compared with the prior art, the present invention has at least the following beneficial effects:

[0049] The sample preparation method for detecting ammonia nitrogen in high-sulfate wastewater provided by the present invention is aimed at laterite nickel ore hydrometallurgical wastewater containing a large amount of sulfate, and a new method for determining ammonia nitrogen is developed, which is simpler to operate, does not require a distillation process, has more controllable operating errors, and has more accurate and reliable detection results. Specifically, the present invention adopts a boric acid-sodium hydroxide buffer solution with a specific pH value to directly react with the wastewater to be tested, sodium thiosulfate and zinc sulfate in a constant volume manner to form a reaction system, and the detection system after adding potassium sodium tartrate and Nessler's reagent to the liquid phase obtained after solid-liquid separation can be colored and stable. It can be seen that the method provided by the present invention can effectively eliminate the interference of high-content sulfate and metal ions in high-sulfate industrial wastewater, and realize accurate detection of ammonia nitrogen in wastewater. Under preferred conditions, the spiked recovery rate of ammonia nitrogen detection is between 97.2% and 101.1%, and the detection error for the standard solution is within 0.013 mg / L. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is a flow chart of the detection method for detecting ammonia nitrogen in high sulfate wastewater provided by the present invention.

[0051] Figure 2 This is a color diagram after adding mercuric iodide-potassium iodide-sodium hydroxide solution in step S2 of Example 1 of the present invention and allowing to stand for a second time.

[0052] Figure 3 This is a color diagram after adding mercuric iodide-potassium iodide-sodium hydroxide solution in step S2 of comparative example 2 of the present invention and letting it stand.

[0053] Figure 4 This is a color diagram after adding mercuric iodide-potassium iodide-sodium hydroxide solution in step S2 of comparative example 3 of the present invention and letting it stand. DETAILED DESCRIPTION

[0054] For the convenience of understanding the present invention, the present invention lists the following embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0055] It should be understood that the terms "first", "second", etc. are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly indicate the number of technical features indicated. Thus, a feature defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0056] As a specific embodiment of the present invention, a method for detecting ammonia nitrogen in high sulfate wastewater is provided, see Figure 1 , the detection method comprises the following steps:

[0057] S1. Firstly mix sodium thiosulfate, zinc sulfate, wastewater to be tested and boric acid-sodium hydroxide buffer solution, and then let it stand for a first time to obtain a first mixture.

[0058] S2, step S1: the first mixture is subjected to solid-liquid separation, and the separated liquid phase is fixed to obtain a second solution; potassium sodium tartrate, Nessler's reagent and the second solution are mixed and allowed to stand for a second time to obtain a sample to be tested.

[0059] S3. Determine the absorbance of the sample to be tested in step S2, and calculate the ammonia nitrogen concentration using the absorbance and the formula in formula (1).

[0060]

[0061] Where: N is the mass concentration of ammonia nitrogen in the water sample (mg / L), A s is the absorbance of the water sample, A b is the absorbance of the blank test, a is the intercept of the calibration curve, b is the slope of the calibration curve, and V is the volume of the water sample (mL). The calibration curve is drawn using an ammonia nitrogen standard solution (prepared by the ammonia nitrogen standard solution produced by Gangyan Nano-Gram). The drawing of the calibration curve is a prior art and will not be repeated here.

[0062] The present invention utilizes a specific buffer solution to achieve accurate control of pH in step (1), which is not only simple and easy to operate, but also can effectively eliminate human errors; at the same time, the buffer solution is beneficial to avoid interference of substances in the wastewater with the color development system, so that the detection result is accurate and reliable.

[0063] The technical solution of the present invention will be described clearly and completely below in conjunction with specific embodiments. It should be understood that the embodiments described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0064] The composition of the laterite nickel ore hydrometallurgical wastewater used in the following examples and comparative examples is shown in Table 1. Since wastewater is produced at different equipment and at different operating times during the hydrometallurgical process of laterite nickel ore, various indicators will fluctuate within the range of Table 1.

[0065] Table 1

[0066] project scope pH 7-8 Mn(mg / L) 2～50 Mg(g / L) 6.2-8.3 Na(g / L) 2-3.8 TSS (total suspended solids, mg / L) ＜20 <![CDATA[NH3-N(mg / L)]]> ＜10 <![CDATA[Cl - (mg / L)]]> 25-50 COD (chemical oxygen demand, mg / L) 20-45 <![CDATA[SO4 2- (g / L)]]> 20-40 TDS (total dissolved solids, g / L) 23-60

[0067] Unless otherwise specified in the present invention, in order to ensure the accuracy of ammonia nitrogen content detection, the water used is ammonia-free water.

[0068] The preparation methods of some reagents used in the following examples and comparative examples are as follows:

[0069] ① Boric acid-sodium hydroxide buffer solution with pH = 9.4-9.6: weigh 5g of boric acid and dissolve it in 1000mL of ammonia-free water, and adjust the pH to 9.4-9.6 with saturated sodium hydroxide;

[0070] ②3.0~4.0g / L sodium thiosulfate: weigh 3.0~4.0g sodium thiosulfate and dissolve it in 1000mL ammonia-free water;

[0071] ③80-120g / L zinc sulfate: weigh 80-120g sodium thiosulfate and dissolve it in 1000mL ammonia-free water;

[0072] ④450~500g / L potassium sodium tartrate: weigh 450~500g potassium sodium tartrate, dissolve in 500mL water, heat to boil to drive off ammonia, and dilute to 1000mL after sufficient cooling;

[0073] ⑤ Mercuric iodide-potassium iodide-sodium hydroxide solution: weigh 12-20g of sodium hydroxide and dissolve it in 50mL of water, and cool it to room temperature; weigh 5-10g of potassium iodide and 9.5-10.5g of mercuric iodide and dissolve them in water, then slowly pour this solution into the above 50mL of sodium hydroxide while stirring, and dilute it to 100mL with water.

[0074] If no specific techniques or conditions are specified in the following examples, all of them are carried out according to the techniques or conditions described in the literature in the field or according to the product instructions; if the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[0075] Example 1

[0076] This embodiment provides a sample preparation method for detecting ammonia nitrogen in high-sulfate wastewater, and the sample preparation method comprises the following steps:

[0077] S1. Take 10 mL of the wastewater to be tested in a 100 mL volumetric flask, add 2 mL of a 3.5 g / L sodium thiosulfate solution and 1 mL of a 100 g / L zinc sulfate solution, make up the volume with a boric acid-sodium hydroxide buffer solution of pH = 9.5, and let stand for 25 min to obtain a first mixture;

[0078] S2. Filter the first mixed material into a clean container with a qualitative filter paper washed with water, and discard 20 mL of the initial filtrate to obtain a separated liquid phase; dilute 20 mL of the separated liquid phase to a 50 mL colorimetric tube with ammonia-free water, add 1 mL of 500 g / L potassium sodium tartrate solution and 1 mL of mercuric iodide-potassium iodide-sodium hydroxide solution (16 g / L sodium hydroxide, 7 g / L potassium iodide, 10.0 g / L mercuric iodide), shake well, and let stand for a second 15 min to obtain a sample to be tested.

[0079] Example 2

[0080] This embodiment provides a sample preparation method for detecting ammonia nitrogen in high-sulfate wastewater, and the sample preparation method comprises the following steps:

[0081] S1. Take 10 mL of the wastewater to be tested in a 100 mL volumetric flask, add 2.5 mL of a 3.0 g / L sodium thiosulfate solution and 0.8 mL of an 80 g / L zinc sulfate solution, make up the volume with a boric acid-sodium hydroxide buffer solution of pH = 9.4, and let stand for 15 min to obtain a first mixture;

[0082] S2. Filter the first mixed material into a clean container with a qualitative filter paper washed with water, and discard 20 mL of the initial filtrate to obtain a separated liquid phase; dilute 20 mL of the separated liquid phase to a 50 mL colorimetric tube with ammonia-free water, add 0.8 mL of 450 g / L potassium sodium tartrate solution and 1 mL of mercuric iodide-potassium iodide-sodium hydroxide solution (12 g / L sodium hydroxide, 10 g / L potassium iodide, 10.5 g / L mercuric iodide), shake well, and let stand for a second 20 min to obtain a sample to be tested.

[0083] Example 3

[0084] This embodiment provides a sample preparation method for detecting ammonia nitrogen in high-sulfate wastewater, and the sample preparation method comprises the following steps:

[0085] S1. Take 10 mL of the wastewater to be tested in a 100 mL volumetric flask, add 1.5 mL of a 4.0 g / L sodium thiosulfate solution and 1.5 mL of a 120 g / L zinc sulfate solution, make up the volume with a boric acid-sodium hydroxide buffer solution of pH = 9.6, and let stand for 30 minutes to obtain a first mixture;

[0086] S2. Filter the first mixed material into a clean container with a qualitative filter paper washed with water, and discard 20 mL of the initial filtrate to obtain a separated liquid phase; dilute 20 mL of the separated liquid phase to a 50 mL colorimetric tube with ammonia-free water, add 1.2 mL of 500 g / L potassium sodium tartrate solution and 1 mL of mercuric iodide-potassium iodide-sodium hydroxide solution (20 g / L sodium hydroxide, 5 g / L potassium iodide, 9.5 g / L mercuric iodide), shake well, and let stand for a second 10 min to obtain a sample to be tested.

[0087] Example 4

[0088] The present embodiment provides a sample preparation method for detecting ammonia nitrogen in high-sulfate wastewater. The sample preparation method is the same as Example 1 except that in step S1, 50 mL of boric acid-sodium hydroxide buffer solution with pH = 9.5 is added for constant volume, and ammonia-free water is used for constant volume. The details are not repeated here.

[0089] According to the test in Example 4, the pH of the 1.0 mg / L ammonia nitrogen standard solution after filtration was 8.79, and the test result was 0.957 mg / L, which was low.

[0090] Example 5

[0091] This embodiment provides a sample preparation method for detecting ammonia nitrogen in high-sulfate wastewater. The sample preparation method is the same as that of Example 1 except that a boric acid-sodium hydroxide buffer solution with a pH of 10.0 is used for constant volume, and will not be described again.

[0092] According to the test in Example 5, the pH of the 1.0 mg / L ammonia nitrogen standard solution after filtration was 9.62, and the test result was 1.101 mg / L, which was high.

[0093] Example 6

[0094] This embodiment provides a sample preparation method for detecting ammonia nitrogen in high-sulfate wastewater. The sample preparation method is the same as that of Example 1 except that a boric acid-sodium hydroxide buffer solution with a pH of 8.8 is used for constant volume, and will not be described again.

[0095] According to the test in Example 6, the pH of the 1.0 mg / L ammonia nitrogen standard solution after filtration was 8.46, and the test result was 0.942 mg / L, which was low.

[0096] Comparative Example 1

[0097] This comparative example provides a sample preparation method for detecting ammonia nitrogen in high-sulfate wastewater. The sample preparation method is the same as Example 1 except that "constituting with boric acid-sodium hydroxide buffer solution with pH = 9.5" in step S1 is replaced by "adjusting the pH to 9.5 with a small amount of saturated sodium hydroxide, transferring to a 100mL volumetric flask, washing the beaker and pH meter and transferring the washing liquid to the volumetric flask, and then constant volume with ammonia-free water". It will not be repeated here.

[0098] Taking Example 1 and Comparative Example 1 as examples, the pH of the first mixture after the first standing was detected, and the pH of the wastewater at different locations in the laterite nickel ore hydrometallurgical process was tested, and the pH value results are shown in Table 2.

[0099] Table 2

[0100] Water sample source Example 1 Comparative Example 1 blank 9.15 8.34 1.0mg / L ammonia nitrogen standard solution 9.19 8.21 Discharge pool 9.01 8.14 Raw pool 9.04 8.07 B12 Overflow 9.10 8.64 Inlet-1.21 9.08 8.60 Out-1.21 9.12 8.68

[0101] The discharge pond, raw water pond, B12 overflow, Inlet-1.21 and Out-1.21 in Table 2 are wastewater discharged from different locations during the hydrometallurgical production of laterite nickel ore.

[0102] As can be seen from Table 2, the pH value after flocculation in the method provided by the present invention is normal. Although the detection result of Comparative Example 1 is not much different from that of the method of the present invention, the scheme has at least the problems of excessive addition of sodium hydroxide, slow adjustment, need to rinse the beaker and pH meter, etc., which makes the scheme complicated to operate, time-consuming and prone to human errors. In addition, the pH value changes greatly after flocculation, resulting in low accuracy of subsequent detection results.

[0103] Comparative Example 2

[0104] This comparative example provides a sample preparation method for detecting ammonia nitrogen in high-sulfate wastewater. The sample preparation method is the same as Example 1, except that the boric acid-sodium hydroxide buffer solution with a pH of 9.5 is replaced by a boric acid-potassium chloride-sodium carbonate buffer solution with a pH of 9.5, and will not be repeated here.

[0105] The boric acid-potassium chloride-sodium carbonate buffer solution with a pH of 9.5 in this comparative example is prepared by dissolving 6.18 g of boric acid and 15 g of potassium chloride in 1000 mL of ammonia-free water, and adjusting the pH to 9.5 with saturated sodium carbonate.

[0106] Comparative Example 3

[0107] This comparative example provides a sample preparation method for detecting ammonia nitrogen in high-sulfate wastewater. The sample preparation method is the same as Example 1, except that the boric acid-sodium hydroxide buffer solution with a pH of 9.5 is replaced by a borax-sodium hydroxide buffer solution with a pH of 10.5, and will not be repeated here.

[0108] The preparation of the borax-sodium hydroxide buffer solution in this comparative example includes: dissolving 9.5 g of borax in 1000 mL of ammonia-free water, and adjusting the pH to 10.5 with saturated sodium hydroxide. Since borax is alkaline, the pH is adjusted to 10.5 to avoid adding too little sodium hydroxide.

[0109] Taking Example 1 and Comparative Examples 2 to 3 as examples, the reaction conditions of different pH buffer solutions were analyzed. The wastewater from different locations in Example 1 and Comparative Examples 2 to 3 was treated and then the Nessler reagent was added to the solution. Figures 2 to 4 As shown, in Example 1, the boric acid-sodium hydroxide buffer solution is clear and transparent after adding Nessler's reagent. In Comparative Example 2, when the boric acid-sodium hydroxide buffer solution is replaced with a boric acid-potassium chloride-sodium carbonate buffer solution, when Nessler's reagent is added in step S2, the solution not only does not develop color, but also immediately produces a white precipitate, see Figure 3 In Comparative Example 3, when the boric acid-sodium hydroxide buffer solution is replaced with a borax-sodium hydroxide buffer solution, the solution is colored after adding Nessler's reagent in step S2, but gradually becomes turbid during the second standing process, see Figure 4This shows that boric acid-potassium chloride-sodium carbonate buffer solution and borax-sodium hydroxide buffer solution are difficult to be used for the detection of ammonia nitrogen in laterite nickel ore hydrometallurgical wastewater.

[0110] Comparative Example 4

[0111] This comparative example provides a sample preparation method for detecting ammonia nitrogen in high-sulfate wastewater. The sample preparation method is the same as Example 1, except that the mercuric iodide-potassium iodide-sodium hydroxide solution is replaced by mercuric chloride-potassium iodide-potassium hydroxide solution, and the rest is not repeated here.

[0112] Specifically, the preparation of the dimercuric chloride-potassium iodide-potassium hydroxide solution is as follows: 15.0g potassium hydroxide is taken, dissolved in 50mL water, and cooled to room temperature. 5.0g potassium iodide is weighed and dissolved in 10mL water. Under stirring, 2.50g of dimercuric chloride powder is added to the potassium iodide solution several times until the solution is dark yellow or a light red precipitate dissolves slowly, and the mixture is fully stirred and mixed, and a saturated solution of dimercuric chloride is added dropwise instead. When a small amount of vermilion precipitate no longer dissolves, the addition is stopped. Under stirring, the cooled potassium hydroxide solution is slowly added to the above-mentioned mixed solution of dimercuric chloride and potassium iodide, and diluted to 100mL, and left to stand in the dark for 24h, and the supernatant is poured out to obtain a dimercuric chloride-potassium iodide-potassium hydroxide solution.

[0113] Application Examples 1 to 6 and Comparative Application Examples 1 to 4

[0114] This application example provides a method for detecting ammonia nitrogen in high-sulfate wastewater, the detection method comprising: measuring the absorbance of the samples to be tested prepared in Examples 1 to 6 and Comparative Examples 1 to 4 at a wavelength of 420 nm, and calculating the ammonia nitrogen concentration using the absorbance and formula (1):

[0115]

[0116] Where: N is the mass concentration of ammonia nitrogen in the water sample (mg / L), A s is the absorbance of the water sample, A b is the absorbance of the blank test, a is the intercept of the calibration curve, b is the slope of the calibration curve, and V is the volume of the water sample (mL).

[0117] In application examples 2 to 3, the replacement of the buffer solution caused turbidity in the sample to be tested, which made it difficult to continue the test. In application example 4, although the boric acid-sodium hydroxide buffer solution was still used, the accuracy of the test data was not as good as that of Example 1 after the mercuric iodide-potassium iodide-sodium hydroxide solution was replaced with a mercuric chloride-potassium iodide-potassium hydroxide solution, indicating that the present invention preferably uses a boric acid-sodium hydroxide buffer solution and combines it with a specific reaction system to significantly improve the accuracy of the test results.

[0118] Taking Application Example 1 and Application Comparative Example 1 as examples, the ammonia nitrogen content of the wastewater in the discharge pool, raw water pool, B12 overflow, Inlet-1.21 and Out-1.21 at a certain moment was tested, and the results are shown in Table 3.

[0119] Table 3

[0120] Water sample source Example 1 Comparative Example 1 Difference 1.0mg / L ammonia nitrogen standard solution 0.987mg / L 0.952mg / L 0.035mg / L Discharge pool 6.41mg / L 6.08mg / L 0.33mg / L Raw pool 6.44mg / L 6.34mg / L 0.1mg / L B12 Overflow 6.32mg / L 5.55mg / L 0.77mg / L Inlet-1.21 25.4mg / L 25.53mg / L -0.13mg / L Out-1.21 3.40mg / L 3.28mg / L 0.12mg / L

[0121] As can be seen from Table 3, by comparing Application Example 1 with Application Comparative Example 1, it can be seen that the method provided by the present invention has significantly higher detection accuracy, the standard solution is closer to the actual result, and the buffer solution is directly used for constant volume, so the detection speed is faster.

[0122] Using the methods in Application Examples 1 to 6 and Comparative Example 1, the ammonia nitrogen concentration in the discharge pool, raw water pool and B12 overflow was detected at a certain moment, and the spiked recovery rate was tested. The results are shown in Table 4.

[0123] Table 4

[0124]

[0125]

[0126] From Table 4, we can see the following points:

[0127] (1) It can be seen from the comprehensive application examples 1 to 3 that the sample preparation method for detecting ammonia nitrogen in high-sulfate wastewater provided by the present invention can achieve a high detection accuracy, wherein the spike recovery rate is between 97.2% and 101.1%, and the sample preparation process is simple and fast, and has broad application prospects.

[0128] (2) It can be seen from the combined application examples 1 and application examples 4 to 6 that in application example 4, instead of using a boric acid-sodium hydroxide buffer solution with a pH of 9.5 for constant volume, 50 mL of a boric acid-sodium hydroxide buffer solution with a pH of 9.5 was added, and ammonia-free water was used for constant volume. The final spiked recovery rate was below 96.4%, and the spiked recovery rate was low. In application example 5, a boric acid-sodium hydroxide buffer solution with a pH of 10.0 was used for constant volume. The final spiked recovery rate was above 106.4%, and the spiked recovery rate was high. In application example 6, a boric acid-sodium hydroxide buffer solution with a pH of 8.8 was used for constant volume, resulting in a spiked recovery rate within 95.1%. This shows that the present invention preferably controls the pH of the boric acid-sodium hydroxide buffer solution within a reasonable range, and adopts a direct constant volume method, which can better ensure the accuracy of the detection and the spiked recovery rate.

[0129] (3) In Comparative Example 1, sodium hydroxide solution was used to adjust the pH. The final detected spike recovery rate was low, indicating that the detected data was low. This shows that the present invention preferably uses boric acid-sodium hydroxide buffer solution, which can significantly improve the accuracy of the test results.

[0130] In summary, the sample preparation method and detection method for ammonia nitrogen detection in high-sulfate wastewater provided by the present invention can be well applied to the detection of high-sulfate industrial wastewater, especially laterite nickel ore hydrometallurgical wastewater, the operation is simple and the results are reliable, which is of great significance for the detection and treatment of laterite nickel ore hydrometallurgical wastewater.

[0131] The present invention illustrates the detailed features of the present invention through the above embodiments, but the present invention is not limited to the above detailed features, that is, it does not mean that the present invention must rely on the above detailed features to be implemented. Those skilled in the art should understand that any improvement to the present invention, equivalent replacement of the technical features selected by the present invention, addition of auxiliary technical features, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A sample preparation method for detecting ammonia nitrogen in high sulfate wastewater, characterized in that: The sample preparation method comprises the following steps: S1, first mixing sodium thiosulfate, zinc sulfate, wastewater to be tested and boric acid-sodium hydroxide buffer solution, and first standing to obtain a first mixture; S2, step S1: the first mixture is subjected to solid-liquid separation, and the separated liquid phase is fixed to obtain a second solution; potassium sodium tartrate, Nessler's reagent and the second solution are mixed and allowed to stand for a second time to obtain a sample to be tested.

2. The sample preparation method according to claim 1, characterized in that: The wastewater to be tested in step S1 is high sulfate wastewater, preferably laterite nickel ore hydrometallurgical wastewater; Preferably, the sulfate content in the wastewater to be tested is 20-40 g / L; Preferably, the magnesium content in the wastewater to be tested is 6 to 8 g / L; Preferably, the sodium content in the wastewater to be tested is 2 to 4 g / L; Preferably, the manganese content in the wastewater to be tested is 2-50 mg / L.

3. The sample preparation method according to claim 1 or 2, characterized in that: The pH of the boric acid-sodium hydroxide buffer solution is 9.4-9.6; Preferably, the preparation of the boric acid-sodium hydroxide buffer solution comprises: dissolving boric acid in water to obtain a boric acid solution, and adjusting the pH of the boric acid solution to a target pH with a saturated sodium hydroxide solution to obtain the boric acid-sodium hydroxide buffer solution.

4. The sample preparation method according to any one of claims 1 to 3, characterized in that: The sodium thiosulfate is added in the form of a sodium thiosulfate solution; Preferably, the zinc sulfate is added in the form of a zinc sulfate solution; Preferably, the mass concentration of the sodium thiosulfate solution is 3.0-4.0 g / L; Preferably, the mass concentration of the zinc sulfate solution is 80-120 g / L.

5. The sample preparation method according to claim 4, characterized in that: The volume ratio of the sodium thiosulfate solution to the zinc sulfate solution is (1.5-2.5):(0.8-1.5); Preferably, the volume ratio of the sodium thiosulfate solution to the wastewater to be tested is (1.5-2.5):10; Preferably, the volume ratio of the boric acid-sodium hydroxide buffer solution to the wastewater to be tested is (86-87.7):

1.

6. The sample preparation method according to any one of claims 1 to 5, characterized in that: The first mixing comprises: placing the wastewater to be tested in a volumetric flask, adding a sodium thiosulfate solution and a zinc sulfate solution, and then fixing the volume with a boric acid-sodium hydroxide buffer solution; Preferably, the first standing time in step S1 is 15 to 30 minutes; Preferably, the solid-liquid separation in step S2 comprises filtration, preferably filtration using qualitative filter paper.

7. The sample preparation method according to any one of claims 1 to 6, characterized in that: The Nessler's reagent is mercuric iodide-potassium iodide-sodium hydroxide solution; Preferably, the concentration of mercuric iodide in the Nessler's reagent is 9.5-10.5 g / L; Preferably, the concentration of potassium iodide in the Nessler's reagent is 5 to 10 g / L; Preferably, the concentration of sodium hydroxide in the Nessler's reagent is 12 to 20 g / L; Preferably, the sodium potassium tartrate is added in the form of sodium potassium tartrate solution; Preferably, the concentration of the sodium potassium tartrate solution is 450-500 g / L.

8. The sample preparation method according to claim 7, characterized in that: The volume ratio of the sodium potassium tartrate solution to Nessler's reagent is (0.8-1.2):1; Preferably, the volume ratio of the sodium potassium tartrate solution to the separated liquid phase is (0.8-1.2):20; Preferably, the second mixing comprises: taking the separated liquid phase to a fixed volume in a colorimetric tube, and adding potassium sodium tartrate solution and Nessler's reagent; Preferably, the second standing time is 10 to 20 minutes.

9. A method for detecting ammonia nitrogen in laterite nickel ore hydrometallurgical wastewater, characterized in that: The detection method uses the sample preparation method for detecting ammonia nitrogen in high-sulfate wastewater described in any one of claims 1 to 8 to obtain the sample to be tested.

10. The detection method according to claim 9, characterized in that: The detection method is performed using absorbance.

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