Method for detecting divalent sulfur in tungstate solution

Abstract

The invention discloses a method for detecting divalent sulfur in a tungstate solution, which comprises the following steps: providing a tungstate solution to be detected, adding acid to adjust the pH value of the tungstate solution to 3.0-5.5, and then adding citric acid and ammonia water to obtain the treated tungstate solution to be detected; providing an iodine standard titration solution, a sodium thiosulfate standard titration solution and a starch indicator; adding the excessive elemental iodine standard titration solution into the treated tungstate solution to be detected, enabling elemental iodine and divalent sulfur ions in the tungstate solution to be subjected to redox reaction, and remaining elemental iodine; and titrating the residual elemental iodine by using the sodium thiosulfate standard titration solution and the starch indicator to obtain the content of the residual elemental iodine, and obtaining the content of the elemental iodine reacting with the divalent sulfur ions according to the content of the residual elemental iodine, thereby calculating the content of the divalent sulfur ions.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical detection, and more specifically, to a method for detecting divalent sulfur in a tungstate solution. Background Art

[0002] Ammonium paratungstate is an important high-purity chemical with a wide range of applications in catalysts, electronics, optoelectronics, thermal materials, chemicals, metallurgy and other fields.

[0003] The raw materials for preparing ammonium paratungstate are sodium tungstate and ammonium salt. Since the purity of ammonium paratungstate is required to be high, sodium tungstate is also required to be of high purity.

[0004] The sodium tungstate solution obtained by recycling tungsten resources from waste cemented carbide will contain divalent sulfide ions due to insufficient oxidation, which will affect the purity of the sodium tungstate. If the content of divalent sulfide ions can be controlled through detection, the purity of the sodium tungstate will be improved. Summary of the invention

[0005] The purpose of the present invention is to overcome the above-mentioned defects of the prior art and provide a method for detecting divalent sulfur in a tungstate solution, which can accurately detect the content of divalent sulfide ions in a sodium tungstate solution.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A method for detecting divalent sulfur in a tungstate solution comprises the following steps:

[0008] Providing a tungstate solution to be tested, adding acid to adjust the pH value of the tungstate solution to 3.0-5.5, and then adding citric acid and ammonia water to obtain a treated tungstate solution to be tested;

[0009] Provide elemental iodine standard titration solution, sodium thiosulfate standard titration solution and starch indicator;

[0010] Adding an excess of the elemental iodine standard titration solution to the treated tungstate solution to be tested, the elemental iodine undergoes an oxidation-reduction reaction with the divalent sulfide ions in the tungstate solution, and the remaining part is elemental iodine;

[0011] The remaining elemental iodine is titrated with the sodium thiosulfate standard titration solution and the starch indicator to obtain the content of the remaining elemental iodine,

[0012] The content of the elemental iodine that reacts with the divalent sulfide ions is obtained according to the content of the remaining elemental iodine, thereby calculating the content of the divalent sulfide ions.

[0013] Implementing the embodiments of the present invention will have the following beneficial effects:

[0014] In the embodiment of the present invention, the pH value is first adjusted to be weakly acidic with acid, and the tungstate ions begin to undergo polymerization reaction to form a polyacid ion structure, and then citric acid and ammonia water are added, and the ammonia water is converted into ammonium ions. Tungstate, citric acid and ammonium react with each other to form a complex, thereby preventing tungstate from complexing with sodium thiosulfate and affecting the detection of divalent sulfide ions. DETAILED DESCRIPTION

[0015] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0016] The present invention discloses a method for detecting divalent sulfur in a tungstate solution, comprising the following process:

[0017] 1) providing a tungstate solution to be tested, adding acid to adjust the pH value of the tungstate solution to 3.0-5.5, and then adding citric acid and ammonia water to obtain a treated tungstate solution to be tested.

[0018] In the embodiment of the present invention, the pH value is first adjusted to be weakly acidic with acid, and the tungstate ions begin to undergo polymerization reaction to form a polyacid ion structure, and then citric acid and ammonia water are added, and the ammonia water is converted into ammonium ions. Tungstate, citric acid and ammonium react with each other to form a complex, thereby preventing tungstate from complexing with sodium thiosulfate and affecting the detection of divalent sulfide ions.

[0019] In a specific embodiment, the acid may include one or more of glacial acetic acid and carbonic acid.

[0020] In a specific embodiment, citric acid, ammonia water and water are first mixed into a mixed solution, and then the mixed solution is added to the tungstate solution, so that the citric acid and ammonia water react to generate ammonium ions first, thereby reducing the transition effect of ammonia water on the weakly acidic environment of the tungstate solution.

[0021] In a specific embodiment, the molar ratio of citric acid to ammonia water is preferably 1:1-2, so that the number of ammonium radicals is less than the number of acid radicals in citric acid, so that citric acid can continue to combine with tungstate radicals.

[0022] In one specific embodiment, the molar ratio of citric acid to tungstate is 1:0.5-1.

[0023] In a specific embodiment, the tungstate salt may include one or more of alkaline solutions of tungsten such as sodium tungstate, ammonium tungstate and potassium tungstate.

[0024] 2) Provide elemental iodine standard titration solution, sodium thiosulfate standard titration solution and starch indicator.

[0025] 3) Add an excess of elemental iodine standard titration solution to the treated tungstate solution to be tested, and the elemental iodine undergoes a redox reaction with the divalent sulfide ions in the tungstate solution, leaving the remaining elemental iodine.

[0026] 4) titrating the remaining elemental iodine with the sodium thiosulfate standard titration solution and the starch indicator to obtain the content of the remaining elemental iodine, and obtaining the content of the elemental iodine that reacts with the divalent sulfide ions according to the content of the remaining elemental iodine, thereby calculating the content of the divalent sulfide ions.

[0027] The following are specific embodiments.

[0028] Example 1

[0029] 1) Prepare the sodium tungstate solution to be tested, including 0.1 mol / L sodium tungstate and 0.05 mol / L sodium sulfide.

[0030] 2) Prepare a mixture of citric acid, ammonia water and water, including 0.1 mol / L citric acid and 0.2 mol / L ammonia water.

[0031] 3) Providing 0.1 mol / L elemental iodine standard titration solution, 5 wt% starch indicator and 0.1 mol / L sodium thiosulfate standard titration solution.

[0032] 4) Take 10mL of the sodium tungstate solution to be tested, adjust the pH to 3.1 with glacial acetic acid, add 10mL of the mixed solution prepared in step 2, and then add 10mL of the standard titration solution of elemental iodine. After sufficient reaction, titrate with the standard titration solution of sodium thiosulfate. When the solution turns light yellow, add 5mL of starch indicator and continue to titrate with the standard titration solution of sodium thiosulfate until the solution changes from blue to colorless. The titration is completed and the volume of the standard titration solution of sodium thiosulfate used is recorded as 10mL.

[0033] Example 2

[0034] 1) Prepare the sodium tungstate solution to be tested, including 0.1 mol / L sodium tungstate and 0.05 mol / L sodium sulfide.

[0035] 2) Prepare a mixture of citric acid, ammonia water and water, including 0.1 mol / L citric acid and 0.1 mol / L ammonia water.

[0036] 3) Providing 0.1 mol / L elemental iodine standard titration solution, 5 wt% starch indicator and 0.1 mol / L sodium thiosulfate standard titration solution.

[0037] 4) Take 10mL of the sodium tungstate solution to be tested, adjust the pH to 4.0 with glacial acetic acid, add 10mL of the mixed solution prepared in step 2, and then add 10mL of the standard iodine titration solution. After sufficient reaction, titrate with the standard sodium thiosulfate titration solution. When the solution turns light yellow, add 5mL of starch indicator and continue to titrate with the standard sodium thiosulfate titration solution until the solution changes from blue to colorless and the titration is completed. Record the volume of the standard sodium thiosulfate titration solution used as 10mL.

[0038] Example 3

[0039] 1) Prepare the sodium tungstate solution to be tested, including 0.05 mol / L sodium tungstate and 0.05 mol / L sodium sulfide.

[0040] 2) Prepare a mixture of citric acid, ammonia water and water, including 0.1 mol / L citric acid and 0.1 mol / L ammonia water.

[0041] 3) Providing 0.1 mol / L elemental iodine standard titration solution, 5 wt% starch indicator and 0.1 mol / L sodium thiosulfate standard titration solution.

[0042] 4) Take 10mL of the sodium tungstate solution to be tested, adjust the pH to 5.4 with glacial acetic acid, add 10mL of the mixed solution prepared in step 2, and then add 10mL of the standard titration solution of elemental iodine. After sufficient reaction, titrate with the standard titration solution of sodium thiosulfate. When the solution turns light yellow, add 5mL of starch indicator and continue to titrate with the standard titration solution of sodium thiosulfate until the solution changes from blue to colorless. The titration is completed and the volume of the standard titration solution of sodium thiosulfate used is recorded as 10mL.

[0043] Comparative Example 1

[0044] The difference between Comparative Example 1 and Example 1 is that the sodium tungstate is not treated with a mixture of citric acid and ammonia water, specifically as follows:

[0045] 1) Prepare the sodium tungstate solution to be tested, including 0.1 mol / L sodium tungstate and 0.05 mol / L sodium sulfide.

[0046] 2) providing a 0.1 mol / L elemental iodine standard titration solution, a 5 wt% starch indicator and a 0.1 mol / L sodium thiosulfate standard titration solution.

[0047] 3) Take 10mL of the sodium tungstate solution to be tested, adjust the pH to 2.3 with glacial acetic acid, add 10mL of elemental iodine standard titration solution, and after sufficient reaction, titrate with sodium thiosulfate standard titration solution. When the solution turns light yellow, add 5mL of starch indicator and continue to titrate with sodium thiosulfate standard titration solution until the solution changes from blue to colorless and the titration is completed. Record the volume of sodium thiosulfate standard titration solution used as 13mL.

[0048] The sodium thiosulfate consumed in Comparative Example 1 is significantly greater than its theoretical value, and the test result is inaccurate, which should be due to the reaction between thiosulfate and tungstate.

[0049] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for detecting divalent sulfur in a tungstate solution, characterized in that: The process includes: Providing a tungstate solution to be tested, adding acid to adjust the pH value of the tungstate solution to 3.0-5.5, and then adding citric acid and ammonia water to obtain a treated tungstate solution to be tested; Provide elemental iodine standard titration solution, sodium thiosulfate standard titration solution and starch indicator; Adding an excess of the elemental iodine standard titration solution to the treated tungstate solution to be tested, the elemental iodine undergoes an oxidation-reduction reaction with the divalent sulfide ions in the tungstate solution, and the remaining part is elemental iodine; The remaining elemental iodine is titrated with the sodium thiosulfate standard titration solution and the starch indicator to obtain the content of the remaining elemental iodine, The content of the elemental iodine that reacts with the divalent sulfide ions is obtained according to the content of the remaining elemental iodine, thereby calculating the content of the divalent sulfide ions.

2. The detection method according to claim 1, characterized in that: Firstly, the citric acid, the ammonia water and water are mixed into a mixed solution, and then the mixed solution is added into the tungstate solution.

3. The detection method according to claim 1 or 2, characterized in that: The molar ratio of the citric acid to the ammonia water is 1:1-2.

4. The detection method according to claim 1 or 2, characterized in that: The molar ratio of the citric acid to the tungstate in the tungstate is 1:0.5-1.

5. The detection method according to claim 1, characterized in that: The acid includes one or more of glacial acetic acid and carbonic acid.

6. The detection method according to claim 1, characterized in that: The tungstate includes one or more of alkaline solutions of tungsten such as sodium tungstate, ammonium tungstate and potassium tungstate.