A method for determining the acidity of an acidic iron-containing rare earth solution
Through the EDTA complex reaction and separation of iron ions and rare earth ions, combined with methyl orange indicator, the accurate determination of the acidity of high-iron ion rare earth solution is achieved, the titration error problem caused by iron hydroxide precipitation is solved, the production cost is reduced and the rare earth dissolution efficiency is improved.
Patent Information
- Application Number
- CN202310945881.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-07-31
- Publication Date
- 2025-09-30
- Estimated Expiration
- 2043-07-31
AI Technical Summary
In the prior art, during the acid-base neutralization titration process of a rare earth solution with a high iron ion content, the precipitation of iron hydroxide results in a large titration analysis error, making it impossible to accurately measure the acidity.
EDTA standard solution was used to complex with iron ions and rare earth ions in sequence. The acidity of the solution was determined by two titrations to eliminate the influence of ferric hydroxide precipitation. Methyl orange was used as the indicator to observe the titration end point and calculate the acidity.
The accurate determination of the acidity of high-ferric ion rare earth solution is achieved, the production cost is reduced, and the rare earth dissolution efficiency and the accuracy of the test results are improved.
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of separation and purification of rare earth elements, and particularly relates to a method for determining the acidity of an acidic iron-containing rare earth solution. Background Art
[0002] NFB rare earth waste contains approximately 30%-60% iron. After incineration, most of the iron is oxidized to ferric oxide. After hydrochloric acid dissolution, some of the ferric oxide dissolves into ferric chloride, bringing the iron ion content in the rare earth solution to as high as 0.1-1 mol / L.
[0003] During the control of the dissolution process, the acidity of the rare earth solution must be tested to understand whether there is enough hydrochloric acid to ensure complete dissolution of the rare earth and to improve the rare earth yield.
[0004] Acidity in solutions is commonly determined using acid-base neutralization titration. The endpoint pH of this titration, using methyl orange as an indicator, is 4.41. Due to the presence of a large amount of ferric chloride in the solution, using sodium hydroxide as a standard solution to titrate an acidic solution containing iron ions, at pH values between 2.1 and 3.0, sodium hydroxide reacts with the iron ions to form a ferric hydroxide precipitate, causing the solution to become turbid. This not only affects the operator's ability to observe the indicator color but also makes it impossible to calculate the consumption of the standard solution in the reaction with the iron ions. This results in significant errors in the titration analysis, hindering accurate analysis and control. Summary of the Invention
[0005] The technical problem to be solved by the present invention is to provide a method for determining the acidity of an acidic iron-containing rare earth solution. The method can simply and accurately determine the acidity in a high-iron salt rare earth solution, thereby solving the problem of large errors in the process of determining the acidity in a high-iron ion solution by the current acid-base neutralization titration method.
[0006] The technical solutions of the present invention are as follows:
[0007] A method for determining the acidity of an acidic iron-containing rare earth solution comprises:
[0008] S1. Place a volume V of acidic iron-containing rare earth solution in a container and add an appropriate amount of deionized water. The solution turns light yellow. After adding the ferric iron indicator, the solution turns reddish brown. Then add EDTA standard solution until the solution changes from reddish brown back to light yellow. At this time, the ferric iron has been completely complexed. Record the volume of EDTA standard solution consumed as V1.
[0009] S2. Take another volume of acidic iron-containing rare earth solution (V) and place it in a container. For color development, add an appropriate amount of deionized water; then add a volume of EDTA standard solution (V1), shake well, and drop methyl orange indicator. The solution turns red. Then titrate with a molar concentration of alkali standard solution (M). The titration endpoint is when the solution changes from red to yellow. The volume of the consumed alkali standard solution is recorded as V2.
[0010] S3, adding an appropriate amount of EDTA standard solution to the solution after titration in step S2 so that all EDTA is complexed with the rare earth element, the volume of the added EDTA standard solution is V4, and the solution is red at this time; then titrating with an alkali standard solution with a molar concentration of M, the titration end point is when the solution changes from red to yellow, and the volume of the alkali standard solution consumed is recorded as V3;
[0011] S4. Calculate the acidity of the acidic iron-containing rare earth solution using the following formula:
[0012] Acidity C = (M × V2 - M × V1 × V3 / V4) ÷ V
[0013] in:
[0014] C——the acidity of the target solution iron-containing rare earth solution (mol / L);
[0015] M——molar concentration of alkali standard solution (mol / L);
[0016] V——the volume of the target solution acidic iron-containing rare earth solution (mL);
[0017] V1——the consumed volume of EDTA standard solution in step S1 (mL);
[0018] V2——the consumed volume of alkali solution in step S2 (mL);
[0019] V3——the consumed volume of alkali solution in step S3 (mL);
[0020] V3 - the volume of EDTA standard solution added in step S3 (mL).
[0021] Preferably, the acidity of the acidic iron-containing rare earth solution is 0.1-1 mol / L.
[0022] Preferably, the iron ion content in the acidic iron-containing rare earth solution is 5-30 mg / mL, and the sum of the rare earth element concentrations is 0.3-1.6 mol / L.
[0023] Preferably, the volume ratio of the acidic iron-containing rare earth solution used in steps S1 and S2 to the added deionized water is 1-5:5-10.
[0024] Preferably, the ferric iron indicator in step S1 is an ammonium thiocyanate solution with a mass concentration of 0.5-2%.
[0025] Preferably, the mass concentration of the EDTA standard solution in steps S1, S2 and S3 is 3-8%.
[0026] Preferably, the mass concentration of the methyl orange indicator in step S1 is 0.1-0.5%, and the dosage is 2-3 drops.
[0027] Preferably, the alkali standard solution used for titration in steps S2 and S3 is NaOH solution.
[0028] Preferably, the concentration of hydroxide ions in the alkali standard solution used for titration in steps S2 and S3 is 0.1-0.5 mol / L.
[0029] The amount V4 of the EDTA standard solution added in step S3 should not be excessive to ensure that all the added EDTA is complexed with the rare earth element and there is no uncomplexed EDTA.
[0030] The present invention is applied to the detection of the acidity of an iron-containing salt solution, and utilizes the preferential complexation effect of EDTA on trivalent iron ions to solve the problem of precipitation of iron salts during the titration process, so that during the analytical titration analysis operation, the color change at the titration endpoint is clear and obvious, avoiding the error of unclear color development.
[0031] Disodium ethylenediaminetetraacetic acid, commonly known as EDTA, can form stable, water-soluble complexes with most metal ions. Under certain conditions, the thermodynamic equilibrium constant for the complexation reaction between metal ions and EDTA anions is also known as K (complexation stability constant). A larger K value indicates a more stable complex and the easier it is for EDTA to complex with it. According to literature (reference: Luo Shoukuan, "An Empirical Formula for Calculating the Complex Stability Constant of EDTA," Journal of Chongqing Iron and Steel College, 1999, 3: Vol. 14, No. 1), the K values for EDTA with trivalent rare earth ions are 15.2-16.9 (La to Lu), while the K value for EDTA with trivalent ferric ions is 24.5. This indicates that the K value for EDTA with trivalent ferric ions is greater than that with trivalent rare earth ions. Therefore, when EDTA is added to an acidic rare earth solution containing iron salts, EDTA preferentially complexes with trivalent ferrous ions. Only when EDTA is in excess will it complex with rare earth ions. Therefore, it is only necessary to add EDTA solution sufficient to complex the iron ions into the high iron salt rare earth solution to be determined. After the iron ions are complexed, no iron hydroxide precipitation and no consumption of standard solution will be produced during the acid-base titration process using methyl orange as an indicator, making it convenient to observe the color changes at the starting and end points of the titration, thereby improving the accuracy of the acidity titration.
[0032] In an acidic, high-iron salt rare earth solution, a certain amount of EDTA completely complexes with iron ions, releasing a certain amount of hydrogen ions. This increases the solution's acidity. Using methyl orange as an indicator, titration with a standard sodium hydroxide solution results in a higher calculated result. However, after titration, uncomplexed rare earth ions remain in the residual solution. Adding a further amount of EDTA solution allows the EDTA to complex with a sufficient amount of rare earth ions to produce hydrogen ions. At this point, the residual solution turns red due to the presence of methyl orange indicator. Titration with a standard sodium hydroxide solution is then performed. The total amount of hydrogen ions produced by the EDTA complexation reaction is determined through a second acid-base titration, addressing the issue of hydrogen ions produced by the EDTA complexation reaction affecting acidity determination.
[0033] Beneficial effects:
[0034] (1) The present invention utilizes a quantitative EDTA complex reaction to release a quantitative hydrogen ion, and adopts a secondary titration method to subtract the total amount of hydrogen ions produced by the complex reaction to eliminate the influence. In the high-iron salt rare earth solution, the concentration of iron ions varies, and the amount of EDTA used cannot be determined. The present invention uses a trivalent iron indicator to indicate whether the iron ions in the determination solution are completely complexed. There is no need to use high-cost precision instruments such as ICP to analyze the iron ions, and the operating cost is low.
[0035] (2) The acidity determination method of the present invention uses conventional titration analysis equipment and conventional chemical analysis reagents, is easy to operate, and has the advantage of data accuracy over the pH test paper detection method.
[0036] (3) The present invention is applicable to the detection of the acidity of high-iron salt rare earth solutions such as NFB rare earth waste dissolution liquid, and the detection results are digitized to provide an accurate reference for the control of rare earth dissolution process in the hydrochloric acid optimal dissolution method. Using this determination method, the acidity of the dissolution process and the volume of hydrochloric acid added can be accurately controlled, and the alkali solution used to adjust the pH value can be reduced. In the NFB waste optimal dissolution process, 0.2-0.8 tons of industrial concentrated hydrochloric acid and 0.2-0.6 tons of liquid caustic soda can be saved for each ton of rare earth (calculated as oxide), thereby reducing production costs while ensuring the efficiency of rare earth dissolution. DETAILED DESCRIPTION
[0037] The following further describes the embodiments of the present invention.
[0038] Example 1
[0039] Pour 81.175g of dried, dehydrated ferric chloride solid into a 2000mL beaker, add 500mL of 0.5mol / L hydrochloric acid solution, and 500mL of a 1mol / L rare earth solution (pH 5.0). This creates an acidic, high-ferric rare earth solution with an acidity of 0.25mol / L, a rare earth concentration of 0.5mol / L, and an iron ion concentration of 0.5mol / L.
[0040] Place 1 mL of acidic ferric salt rare earth solution (V = 1 mL) in a 250 mL conical flask and add 5 mL of deionized water. The solution will now appear light yellow. Add 2-3 drops of 0.1% ammonium thiocyanate solution, and the solution will appear reddish-brown. Add 5 mL of 5% EDTA standard solution (V1 = 5 mL), and the reddish-brown color will return to light yellow.
[0041] Place 1 mL of the acidic ferric salt rare earth solution (V = 1 mL) in a 250 mL conical flask. Add 5 mL of deionized water, which should result in the solution appearing light yellow. Add 5 mL of a 5% EDTA standard solution, shake well, and then add 2-3 drops of a 0.1% methyl orange indicator (shake well again). The solution should appear red. Titrate with a 0.2102 mol / L NaOH standard solution. The endpoint is when the solution turns from red to yellow. Record the volume of standard solution consumed (V2 = 5.7 mL).
[0042] Add V4 = 1 mL of 5% EDTA standard solution to the solution after titration in the previous step. The solution will now turn red. Titrate with 0.2102 mol / L NaOH standard solution. The endpoint is when the solution turns from red to yellow. Record the volume of standard solution consumed, V3 = 0.9 mL.
[0043] Acidity of acidic iron-containing rare earth solution C = (M × V2 - M × V1 × V3 / V4) ÷ V = (0.2102 mol / L × 5.7 mL - 0.2102 mol / L × 5 mL × 0.9 mL ÷ 1 mL) ÷ 1 mL = 0.2522 mol / L
[0044] This confirms that the calculated acidity of the target solution is 0.2522 mol / L, which is close to the initial acidity of the target solution, 0.25 mol / L. This error is within 0.8%, which is consistent with the analytical error of the titration.
[0045] Example 2
[0046] Take 100 ml of the acidic ferric salt dilute solution prepared in Example 1, which has an acidity of 0.25 mol / L, a rare earth concentration of 0.5 mol / L, and an iron ion concentration of 0.5 mol / L, and add 100 mL of 0.75 mol / L hydrochloric acid solution to prepare an acidic ferric salt rare earth solution with an acidity of 0.5 mol / L, a rare earth concentration of 0.25 mol / L, and an iron ion concentration of 0.25 mol / L.
[0047] Place 1 mL of acidic ferric salt rare earth solution (V = 1 mL) in a 250 mL conical flask and add 5 mL of deionized water. The solution will now appear light yellow. Add 2 to 3 drops of 0.1% ammonium thiocyanate solution, and the solution will turn reddish brown. Add 2.5 mL of 5% EDTA standard solution (V1 = 2.5 mL), and the reddish brown color will return to light yellow.
[0048] Place 1 mL of the acidic ferric salt rare earth solution (V = 1 mL) in a 250 mL conical flask. Add 5 mL of deionized water, which should result in the solution appearing light yellow. Add 2.5 mL of a 5% EDTA standard solution, shake well, and then add 2-3 drops of a 0.1% methyl orange indicator (shake well again). The solution should appear red. Titrate with a 0.2102 mol / L NaOH standard solution. The endpoint is when the solution turns from red to yellow. Record the volume of standard solution consumed (V2 = 4.6 mL).
[0049] Add V4 = 1 mL of 5% EDTA standard solution to the solution after titration in the previous step. The solution will now turn red. Titrate with 0.2102 mol / L NaOH standard solution. The endpoint is when the solution turns from red to yellow. Record the volume of standard solution consumed, V3 = 0.9 mL.
[0050] Acidity of acidic iron-containing rare earth solution C = (M × V2 - M × V1 × V3 / V4) ÷ V = (0.2102 mol / L × 4.6 mL - 0.2102 mol / L × 2.5 mL × 0.9 mL ÷ 1 mL) ÷ 1 mL = 0.4940 mol / L
[0051] This verifies that the calculated acidity of the target solution is 0.4940 mol / L, which is close to the initial configuration acidity of the target solution of 0.5 mol / L.
[0052] Example 3
[0053] Take 100 ml of the acidic ferric salt rare earth solution prepared in Example 1 with an acidity of 0.25 mol / L, a rare earth concentration of 0.5 mol / L, and an iron ion concentration of 0.8 mol / L, and add 100 mL of 1.35 mol / L hydrochloric acid solution to prepare an acidic ferric salt rare earth solution with an acidity of 0.8 mol / L, a rare earth concentration of 0.25 mol / L, and an iron ion concentration of 0.25 mol / L.
[0054] Place 1 mL of acidic ferric salt rare earth solution (V = 1 mL) in a 250 mL conical flask and add 5 mL of deionized water. The solution will now appear light yellow. Add 2 to 3 drops of 0.1% ammonium thiocyanate solution, and the solution will turn reddish brown. Add 2.5 mL of 5% EDTA standard solution (V1 = 2.5 mL), and the reddish brown color will return to light yellow.
[0055] Place 1 mL of the acidic ferric salt rare earth solution (V = 1 mL) in a 250 mL conical flask. Add 5 mL of deionized water, which should result in the solution appearing light yellow. Add 2.5 mL of a 5% EDTA standard solution, shake well, and then add 2-3 drops of a 0.1% methyl orange indicator (shake well again). The solution should appear red. Titrate with a 0.2102 mol / L NaOH standard solution. The endpoint is when the solution turns from red to yellow. Record the volume of standard solution consumed (V2 = 6.0 mL).
[0056] Add V4 = 1 mL of 5% EDTA standard solution to the solution after titration in the previous step. The solution will now turn red. Titrate with 0.2102 mol / L NaOH standard solution. The endpoint is when the solution turns from red to yellow. Record the volume of standard solution consumed, V3 = 0.9 mL.
[0057] Acidity of acidic iron-containing rare earth solution C = (M × V2 - M × V1 × V3 / V4) ÷ V = (0.2102 mol / L × 6.1 mL - 0.2102 mol / L × 2.5 mL × 0.9 mL ÷ 1 mL) ÷ 1 mL = 0.4940 mol / L
[0058] This verifies that the calculated acidity value of the target solution is 0.8092 mol / L, which is very close to the initial configuration acidity of the target solution of 0.8 mol / L.
[0059] Example 4
[0060] Take 100 mL of NFB waste dissolution solution and acidic high iron salt rare earth solution with a rare earth concentration of 0.63 mol / L.
[0061] Place 1 mL of acidic ferric salt rare earth solution (V = 1 mL) in a 250 mL conical flask and add 5 mL of deionized water. The solution will now appear light yellow. Add 2-3 drops of 0.1% ammonium thiocyanate solution, and the solution will appear reddish-brown. Add 5 mL of 5% EDTA standard solution (V1 = 5 mL), and the reddish-brown color will return to light yellow.
[0062] Place 1 mL of the acidic ferric salt rare earth solution (V = 1 mL) in a 250 mL conical flask. Add 5 mL of deionized water, which should result in the solution appearing light yellow. Add 5 mL of a 5% EDTA standard solution, shake well, and then add 2-3 drops of a 0.1% methyl orange indicator (shake well again). The solution should appear red. Titrate with a 0.2102 mol / L NaOH standard solution. The endpoint is when the solution turns from red to yellow. Record the volume of standard solution consumed (V2 = 6.3 mL).
[0063] Add V4 = 1 mL of 5% EDTA standard solution to the residual solution after the previous titration. The solution will turn red. Titrate with 0.2102 mol / L NaOH standard solution. The endpoint is when the solution turns from red to yellow. Record the volume of standard solution consumed, V3 = 0.9 mL.
[0064] The acidity of the acidic iron-containing rare earth solution is C = (M×V2-M×V1×V3 / V4)÷V = (0.2102mol / L×6.3mL-0.2102mol / L×5mL×0.9mL÷1mL)÷1mL = 0.3784mol / L.
[0065] While the specific embodiments of the present invention have been described in detail above, these are merely exemplary and the present invention is not limited thereto. It will be apparent to those skilled in the art that any equivalent modifications and substitutions to the present invention fall within the scope of the present invention. Therefore, any equivalent changes and modifications made without departing from the spirit and scope of the present invention are encompassed within the scope of the present invention.
Claims
1. A method for determining the acidity of an acidic iron-containing rare earth solution, comprising: S1. Place a volume V of acidic iron-containing rare earth solution in a container and add an appropriate amount of deionized water. The solution turns light yellow. After adding a trivalent iron indicator, the solution turns reddish brown. Then add EDTA standard solution until the solution changes from reddish brown to light yellow. The volume of EDTA standard solution consumed is recorded as V1. S2. Take another volume of acidic iron-containing rare earth solution (V) and place it in a container. Add an appropriate amount of deionized water. Then add a volume of EDTA standard solution (V1). Shake well and then drop methyl orange indicator. The solution turns red. Then titrate with a molar concentration of alkali standard solution (M). The titration endpoint is when the solution changes from red to yellow. The volume of the consumed alkali standard solution is recorded as V2. S3, adding an appropriate amount of EDTA standard solution to the solution after titration in step S2 so that all EDTA is complexed with the rare earth element, the volume of the added EDTA standard solution is V4, and the solution is red at this time; then titrating with an alkali standard solution with a molar concentration of M, the titration end point is when the solution changes from red to yellow, and the volume of the alkali standard solution consumed is recorded as V3; S4. Calculate the acidity of the acidic iron-containing rare earth solution using the following formula: Acidity C = (M×V2-M×V1×V3 / V4) ÷ V.
2. The method for determining the acidity of an acidic iron-containing rare earth solution according to claim 1, wherein: The acidity of the acidic iron-containing rare earth solution is 0.1-1 mol / L.
3. The method for determining the acidity of an acidic iron-containing rare earth solution according to claim 1, wherein: The iron ion content in the acidic iron-containing rare earth solution is 5-30 mg / mL, and the sum of the rare earth element concentrations is 0.3-1.6 mol / L.
4. The method for determining the acidity of an acidic iron-containing rare earth solution according to claim 1, wherein: The volume ratio of the acidic iron-containing rare earth solution used in steps S1 and S2 to the added deionized water is: 1-5:5-10.
5. The method for determining the acidity of an acidic iron-containing rare earth solution according to claim 1, wherein: The ferric iron indicator in step S1 is an ammonium thiocyanate solution with a mass concentration of 0.5-2%.
6. The method for determining the acidity of an acidic iron-containing rare earth solution according to claim 1, wherein: The mass concentration of the EDTA standard solution described in steps S1, S2 and S3 is 3-8%.
7. The method for determining the acidity of an acidic iron-containing rare earth solution according to claim 1, wherein: The mass concentration of the methyl orange indicator described in step S2 is 0.1-0.5%, and the dosage is 2-3 drops.
8. The method for determining the acidity of an acidic iron-containing rare earth solution according to claim 1, wherein: The alkali standard solution used for the titration in steps S2 and S3 is NaOH solution.
9. The method for determining the acidity of an acidic iron-containing rare earth solution according to claim 1, wherein: The concentration of hydroxide ions in the alkali standard solution used for the titration in steps S2 and S3 is 0.1-0.5 mol / L.