Co-processing method of heavy metals in residual liquid of potassium dichromate method for measuring COD and residual liquid of nessler's reagent spectrophotometry for measuring ammonia nitrogen

Abstract

The present application relates to a kind of heavy metal in the synergic treatment method of potassium dichromate method residual liquid and Nash reagent spectrophotometry residual liquid of COD, the synergic treatment method, its processing steps are as follows: (1) a certain volume of ammonia nitrogen detection residual liquid and a certain volume of COD detection residual liquid are quickly mixed, after mixing, the supernatant Y1 of generating precipitate a is obtained, and precipitate a is mainly yellow four iodomercurate silver precipitate;(2) the supernatant Y1 and a certain volume of ammonia nitrogen detection residual liquid are quickly mixed, after mixing, the supernatant Y2 of generating carmine iodide mercury precipitate is obtained, and the initial total iodine mercury ratio range of mixed solution is 1.02-1.23;(3) a certain amount of sodium hydroxide or slaked lime is added to the supernatant Y2, and bright red precipitate mercuric oxide and grey green precipitate chromium hydroxide are generated, and the supernatant Y3 of precipitate filtration is obtained.The above-mentioned processing method, not only has higher heavy metal recovery rate, and has the advantages of simple steps, low energy consumption, and less additional ions are introduced.

Description

Technical Field

[0001] This invention relates to the field of waste liquid treatment, and in particular to a synergistic treatment method for heavy metals in residual liquids of COD determination by potassium dichromate method and ammonia nitrogen determination by Nessler's reagent spectrophotometry. Background Technology

[0002] In environmental monitoring, Chemical Oxygen Demand (COD) is an important indicator for measuring the degree of pollution from reducing substances and organic matter in industrial wastewater and environmental water bodies. Therefore, many water samples require COD testing. The potassium dichromate method is one method for detecting COD content in wastewater. It uses reagents such as silver sulfate, sulfuric acid, and mercuric sulfate for determination. The residual liquid after testing contains excessive levels of heavy metals such as silver, mercury, and chromium. Direct discharge of the testing residual liquid results in the waste of heavy metals and environmental pollution.

[0003] Ammonia nitrogen wastewater contains free ammonia and ammonium ions, which have an impact on human health and the ecosystem. Currently, Nessler's reagent spectrophotometry is often used to detect the ammonia nitrogen content in wastewater. The principle of the determination is that Nessler's reagent reacts with ammonia nitrogen to form a light reddish-brown colloidal compound, and the absorbance of this compound is then measured to determine the ammonia nitrogen content. The residual liquid after the determination contains an excess of Nessler's reagent, which is a solution composed of mercuric iodide, potassium iodide, sodium hydroxide, and water. Mercury in Nessler's reagent is a heavy metal, and direct discharge of the residual liquid will pollute the environment.

[0004] Currently, the focus of public attention on the treatment of the aforementioned waste liquids is mainly on the joint treatment of COD waste liquid and ammonia nitrogen waste liquid. There are few reports on the treatment of residual test liquids. Most existing treatment methods for residual test liquids are separate treatments, with few combined treatments. Even those that are combined treatments have drawbacks such as complex treatment steps, high energy consumption, and the introduction of more additional ions. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, this invention provides a synergistic treatment method for heavy metals in COD residues determined by the potassium dichromate method and ammonia nitrogen residues determined by Nessler's reagent spectrophotometry. This method not only has a high heavy metal recovery rate, but also has the advantages of simple steps, low energy consumption, and virtually no introduction of additional ions.

[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0007] A synergistic treatment method for heavy metals in residual liquid from COD determination using the potassium dichromate method and ammonia nitrogen determination using Nessler's reagent spectrophotometry is provided, comprising the following steps:

[0008] (1) A certain volume of ammonia nitrogen detection residue and a certain volume of COD detection residue are rapidly mixed. After mixing, precipitate a is generated. After standing and filtering, supernatant Y1 is obtained. Precipitate a includes yellow silver tetraiodomercurate precipitate a1 and vermilion mercuric iodide precipitate a2, and the precipitate content a1>>a2.

[0009] (2) Quickly mix the supernatant Y1 with a certain volume of ammonia nitrogen detection residue. After mixing, a red mercuric iodide precipitate is generated. After standing and filtering, the supernatant Y2 is obtained. According to mass, the total iodine-mercury ratio of the two residues should be in the range of 1.02-1.23.

[0010] (3) Add sodium hydroxide or quicklime to the supernatant Y2 to adjust the pH to 6-8, and precipitate c will be generated. Precipitate c includes bright red mercuric oxide, gray-green chromium hydroxide, and reddish-brown ferric hydroxide. After no more precipitates are generated, let it stand and filter to obtain supernatant Y3.

[0011] In the above processing steps, step (1) can basically precipitate the silver ions in the COD detection residue. Specifically, since the ammonia nitrogen detection residue contains an excess of Nessler's reagent, and Nessler's reagent is prepared with water in the ratio of 16g ​​mercuric iodide, 7g potassium iodide, and 50ml sodium hydroxide solution, the mercury in Nessler's reagent mainly exists in the form of tetraiodmercuric ions (HgI2+2I). - →[HgI4] 2- This compound combines with silver ions in the COD detection residue to form a yellow precipitate of silver tetraiodomercurate, thus precipitating silver. After mixing, the silver ions in the COD detection residue preferentially combine with mercuric tetraiodomercurate ions to form silver tetraiodomercurate precipitate (the stability of silver tetraiodomercurate precipitate, mercuric iodide, and silver iodide precipitate decreases in that order), which can be used as a temperature indicator. The amount of mercuric iodide precipitate can be controlled by the volume ratio of the two residues.

[0012] The supernatant Y1 contains a large amount of untreated mercury ions. Through step (2), the mercury in the mixed solution can be precipitated out as much as possible in the form of mercuric iodide. Specifically, when the iodine-mercury ratio in the mixed solution is reduced to a certain value, [HgI4] 2- The following ionization process occurs: [HgI4] 2- →[HgI3] 2- +I - [HgI3] 2- →HgI2+I-, therefore, in addition to the ionized mercuric iodide precipitate, the mercury ions in the supernatant Y1 will combine with the ionized iodide ions to form mercuric iodide precipitate, thus allowing the heavy metal mercury in the mixed solution to be precipitated out as much as possible. The precipitated mercuric iodide can be purified and used as a raw material for Nessler's reagent.

[0013] The supernatant Y2 also contains a small amount of mercury ions and untreated trivalent chromium ions. The remaining mercury and chromium can be precipitated through step (3).

[0014] By treating the two types of residual liquids in synergy, heavy metals such as silver, mercury, and chromium can be largely removed, which is conducive to achieving the standard discharge of heavy metals in the residual liquids, and the precipitated substances are also easy to reuse.

[0015] Furthermore, in step (2), the total iodine-mercury ratio when the two residual liquids are mixed is required to be in the range of 1.02-1.23 by mass, which is more conducive to improving the precipitation rate of mercury.

[0016] Furthermore, in step (3), the mass concentration of sodium hydroxide is 20%.

[0017] Furthermore, in step (1), the amount of mercuric tetraiodide ions in the ammonia nitrogen residue is n1, and the amount of silver ions in the COD detection residue is n2, based on 1 ml. The ammonia nitrogen residue and COD residue are mixed in a certain volume ratio of n1:n2 = (1-1.06):2.

[0018] Furthermore, the settling time in steps (1) and (2) is 0.8-1.5h, and the settling time in step (3) is at least 1 day.

[0019] The present invention employs the above-mentioned structure, which has the following advantages: the two residual liquids are treated synergistically, resulting in simple treatment steps, low energy consumption, minimal introduction of new ions, high heavy metal recovery rate, and easy reuse of precipitates. Specifically, the low energy consumption is reflected in the fact that no additional heating is required. Among them, the precipitates in steps (1) and (2) account for most of the total precipitate. The precipitate silver tetraiodomercurate from step (1) can be used as a temperature indicator material, and the precipitate mercuric iodide from step (2) can be used as a component of Nessler's reagent. The two materials are precipitated separately, making reuse convenient. Detailed Implementation

[0020] To clearly illustrate the technical features of this solution, the invention will be described in detail below through specific embodiments. Many specific details are set forth in the following description to provide a thorough understanding of this application; however, this application may also be implemented in other ways different from those described herein. Therefore, the scope of protection of this application is not limited to the specific embodiments disclosed below.

[0021] Example 1:

[0022] The company's laboratory has residual solution A for ammonia nitrogen detection, which uses Nessler's reagent spectrophotometry to determine the ammonia nitrogen content in ammonia nitrogen wastewater, and residual solution B for COD detection, which uses the potassium dichromate method to determine the COD content in COD wastewater. Take 50 ml of residual solution A and calculate its [HgI4] content. 2-The amount of ions is approximately 3.3 × 10⁻⁶. -4 mol; Take 50 ml of residual solution B, and calculate that the amount of silver ions it contains is 6.39 × 10⁻⁶. - 4 The amount of mercury ions is 4.4 × 10⁻⁶ mol. -4 The amount of chromium ions is 2.56 × 10⁻⁶ mol. -4 mol.

[0023] The heavy metals in the two residual liquids were synergistically treated using residual liquid A and residual liquid B. The treatment steps are as follows:

[0024] (1) According to Ag + and [HgI4] 2- Take residual liquids A and B in a molar ratio of (1-1.06):2. If possible, take 100ml of each of residual liquids A and B. Stir and mix the measured residual liquids to generate a yellow silver tetraiodomercurate precipitate, accompanied by a very small amount of vermilion precipitate. Let stand for 0.8-1.5h and filter to obtain supernatant Y1.

[0025] The supernatant Y1 was divided into two equal portions. One portion was kept aside, and sodium chloride was added to the other portion. The silver ion content was determined by whether silver chloride precipitate was formed and the amount of precipitate. Specifically, after the white silver chloride precipitate no longer increased, the mixture was filtered and dried to obtain a white powder. The white powder was about 0.02 mg, which is less than the total silver discharge limit of 0.5 mg / L required by the national standard "Integrated Wastewater Discharge Standard" (GB 8978-1996) and the Shandong provincial standard "Integrated Discharge Standard for Water Pollutants in Watersheds Part 1: Dongping Lake Basin of Nansi Lake".

[0026] (2) The prepared supernatant Y1 is approximately 100 ml, containing approximately 4.4 × 10⁻⁶ mercury ions. -4 mol, with a total iodine-mercury ratio of 1.2, take 60 ml of the ammonia nitrogen detection residue and mix it with the supernatant Y1 to form a reddish-brown mercuric iodide precipitate. Let it stand for 0.8-1.5 h and filter to obtain the supernatant Y2;

[0027] The obtained vermilion precipitate was washed with water and dried. The weight of the dried solid was approximately 0.354 g. The theoretical amount of mercury precipitate in the supernatant Y1 and the residual liquid from ammonia nitrogen detection was 0.36 g. Therefore, the precipitation rate was 98.3%.

[0028] (3) The supernatant Y2 is approximately 160 ml, and contains approximately 4.4 × 10⁻⁶ mercury ions. -5 mol, chromium ions are 2.56 × 10 -4mol, add sodium hydroxide or quicklime with a mass concentration of 20% to adjust the pH to 6-8, and a bright red precipitate of mercuric oxide and a gray-green precipitate of chromium hydroxide will be generated. After no more precipitation is generated, let stand for 1 day and then filter to obtain supernatant Y3.

[0029] The total chromium content in the supernatant Y3 was determined by diphenylcarbazide spectrophotometry. The chromium content was approximately 0.208 mg, which meets the emission limit of 1.5 mg / L for chromium in the "Integrated Wastewater Discharge Standard" (GB 8978-1996) and the Shandong Provincial Local Standard "Integrated Discharge Standard for Water Pollutants in Watersheds Part 1: Dongping Lake Basin of Nansi Lake".

[0030] If the chromium content does not meet the national standard requirements, sodium sulfide can be added to convert hexavalent chromium into trivalent chromium, and then sodium hydroxide or quicklime can be added to precipitate trivalent chromium, thereby reducing the chromium content in the residual liquid.

[0031] The above steps can essentially remove heavy metals such as silver, mercury, and chromium from the two residual liquids, thus meeting the heavy metal emission standards.

[0032] Example 2:

[0033] Based on Example 1, in step (2), 67 ml of ammonia nitrogen detection residue was taken with a total iodine-mercury ratio of 1.27 for the experiment. The experimentally obtained mercuric iodide precipitate was about 0.37 g, while the theoretically obtained precipitate was 0.4 g, with a precipitation rate of about 92.5%. This shows that an excessively high iodine-mercury ratio will affect precipitation.

[0034] Example 3:

[0035] Based on Example 1, in step (2), 44 ml of ammonia nitrogen detection residue was taken for the experiment with a total iodine-mercury ratio of 1. The experimentally obtained mercuric iodide precipitate was about 0.249 g, while the theoretically obtained precipitate was 0.264 g, with a precipitation rate of about 94.3%. This shows that an excessively high iodine-mercury ratio can also affect precipitation.

[0036] In the above processing steps, step (1) can basically precipitate the silver ions in the COD detection residue. Specifically, since the ammonia nitrogen detection residue contains an excess of Nessler's reagent, and Nessler's reagent is prepared with water in the ratio of 16g ​​mercuric iodide, 7g potassium iodide, and 50ml sodium hydroxide solution, the mercury in Nessler's reagent mainly exists in the form of tetraiodmercuric ions (HgI2+2I). - →[HgI4] 2-This compound combines with silver ions in the COD detection residue to form a yellow precipitate of silver tetraiodomercurate, thus precipitating silver. After mixing, the silver ions in the COD detection residue preferentially combine with mercuric tetraiodomercurate ions to form silver tetraiodomercurate precipitate (the stability of silver tetraiodomercurate precipitate, mercuric iodide, and silver iodide precipitate decreases in that order), which can be used as a temperature indicator. The amount of mercuric iodide precipitate can be controlled by the volume ratio of the two residues.

[0037] The supernatant Y1 contains a large amount of untreated mercury ions. Through step (2), the mercury in the mixed solution can be precipitated out as much as possible in the form of mercuric iodide. Specifically, when the iodine-mercury ratio in the mixed solution is reduced to a certain value, [HgI4] 2- The following ionization process occurs: [HgI4] 2- →[HgI3] 2- +I - [HgI3] 2- →HgI2+I - Therefore, in addition to the ionized mercuric iodide precipitate, the mercury ions in the supernatant Y1 will combine with the ionized iodide ions to form mercuric iodide precipitate, thus allowing the heavy metal mercury in the mixed solution to be precipitated out as much as possible. Within a certain iodine-mercury ratio range, the precipitation rate of mercury can reach more than 95%. If the iodine-mercury ratio is too high or too low, the precipitation rate of mercury will decrease. The precipitated mercuric iodide can be purified and used as a raw material for Nessler's reagent.

[0038] The supernatant Y2 also contains a small amount of mercury ions and untreated trivalent chromium ions. The remaining mercury and chromium can be precipitated through step (3).

[0039] By treating the two types of residual liquids in synergy, heavy metals such as silver, mercury, and chromium can be largely removed, which is conducive to achieving the standard discharge of heavy metals in the residual liquids, and the precipitated substances are also easy to reuse.

[0040] The specific embodiments described above should not be construed as limiting the scope of protection of this invention. Any alternative modifications or variations made to the embodiments of this invention by those skilled in the art will fall within the scope of protection of this invention. All aspects not detailed in this invention are well-known to those skilled in the art.

Claims

1. A synergistic treatment method for heavy metals in residual liquid from COD determination by potassium dichromate method and ammonia nitrogen determination by Nessler's reagent spectrophotometry, characterized in that... The processing steps are as follows: (1) A certain volume of ammonia nitrogen detection residue and a certain volume of COD detection residue are rapidly mixed. After mixing, precipitate a is generated. After standing and filtering, supernatant Y1 is obtained. Precipitate a includes yellow silver tetraiodomercurate precipitate a1 and vermilion mercuric iodide precipitate a2, and the precipitate content a1>>a2. (2) Quickly mix the supernatant Y1 with a certain volume of ammonia nitrogen detection residue. After mixing, a red mercuric iodide precipitate b is generated. After standing and filtering, the supernatant Y2 is obtained. According to mass, the total iodine-mercury ratio of the two residues should be in the range of 1.02-1.

23. (3) Add sodium hydroxide or quicklime to the supernatant Y2 to adjust the pH to 6-8, and precipitate c will be generated. Precipitate c includes bright red mercuric oxide, gray-green chromium hydroxide, and reddish-brown ferric hydroxide. After no more precipitates are generated, let it stand and filter to obtain supernatant Y3; In step (1), the amount of mercuric tetraiodide ions in the ammonia nitrogen residue is n1, and the amount of silver ions in the COD detection residue is n2, based on 1 ml. The ammonia nitrogen residue and COD residue are mixed in a certain volume ratio of n1:n2=(1-1.06):

2.

2. The synergistic treatment method for heavy metals in residual liquid from COD determination by potassium dichromate method and ammonia nitrogen determination by Nessler's reagent spectrophotometry as described in claim 1, characterized in that, In step (2), the total iodine-mercury ratio of the two residual liquids should be in the range of 1.14-1.21 when mixed by mass, which is more conducive to improving the precipitation rate of mercury.

3. The synergistic treatment method for heavy metals in residual liquid from COD determination by potassium dichromate method and ammonia nitrogen determination by Nessler's reagent spectrophotometry as described in claim 1, characterized in that, In step (3), the mass concentration of sodium hydroxide is 20%.

4. The synergistic treatment method for heavy metals in residual liquid from COD determination by potassium dichromate method and ammonia nitrogen determination by Nessler's reagent spectrophotometry as described in claim 1, characterized in that, The settling time in steps (1) and (2) is 0.8-1.5h, and the settling time in step (3) is at least 1 day.