Rapid online detection method for content of residual acid in multi-element metal salt solution and application of rapid online detection method

Abstract

The invention discloses a rapid online detection method for the content of residual acid in a multi-element metal salt solution and application of the rapid online detection method. The method comprises the following steps: preparing an alkali standard solution, and determining the titer of the alkali standard solution to the residual acid; the method comprises the following steps: preparing a pH meter, carrying out two-point correction on the pH meter, preparing a multi-element metal salt standard solution, dropwise adding an alkali standard solution in a stirring state, detecting the pH by using the corrected pH meter, recording the consumption of the alkali standard solution when the titration end point is reached, and calculating to obtain the content of the residual acid in the multi-element metal salt standard solution. According to the method, the pH value of metal ions which are firstly precipitated in a multi-element metal salt standard solution is taken as a titration key pH value, so that the problem that the acidity of a detection result is relatively high due to the fact that the metal salt ions which are easy to hydrolyze consume hydroxyl radicals in a precipitation process is avoided, and tests show that the relative error between the residual acid content measured by the method and a theoretical value is less than or equal to 2%, and the relative error is less than or equal to 2%. And the detection period is shortened to 5-10 minutes, so that the requirements of online detection on detection precision and speed can be met.

Description

Technical Field

[0001] The invention relates to a method for detecting residual acid content in a solution, in particular to a rapid online detection method for residual acid content in a polymetallic salt solution and application thereof, belonging to the technical field of analytical chemistry. Background Art

[0002] In the hydrometallurgical process of laterite nickel ore, sulfuric acid is needed to leach the ore pulp. The concentration of sulfuric acid not only affects the leaching rate of metals and the degree of corrosion of production equipment, but also affects the amount of limestone slurry required for subsequent neutralization of residual acid. Therefore, it is of great significance to quickly and accurately determine the residual acid concentration in acid solution containing multiple metal salts for the research and improvement of acid leaching effect and acid leaching process.

[0003] At present, acid-base titration or potentiometric titration is commonly used to determine the residual acid concentration. Acid-base titration is a method of determining the residual acid concentration by using the color change of the indicator to indicate the end point of the acid-base titration. Commonly used acid-base indicators include methyl red, methyl orange, bromocresol green, etc., but these will cause errors in the titration process due to subjective color judgment, and the solution often contains Fe 3+ , Fe 2+ 、A1 3+ Cr 3+ 、Ni 2+ , Mn 2+ When the easily hydrolyzed ions are directly titrated with sodium hydroxide standard solution, these hydrolyzed ions will hydrolyze to form metal hydroxides when the titration indicator changes color or before the color changes, or react with sodium hydroxide standard solution to form precipitation and consume the standard solution, causing errors in the measurement results. The potentiometric titration method is to titrate directly on the potentiometric titrator with an alkali standard solution. The results show that there are multiple equivalence points, and the difference between each equivalence point is not large. It is necessary to manually analyze the equivalence point of the residual acid, which is prone to systematic errors. Summary of the invention

[0004] In view of the problems existing in the prior art, the first object of the present invention is to provide a rapid online detection method for the residual acid content in a polymetallic salt solution. The method uses the pH value of the first precipitated metal ion in the polymetallic salt standard solution as the titration focus pH, avoiding the problem of excessive acidity in the test result caused by the consumption of hydroxide by the easily hydrolyzed metal salt ions during the precipitation process. After testing, the residual acid content in the polymetallic salt standard solution determined by the method has a relative error of ≤2% from the theoretical value, and the detection cycle is shortened to 5-10 minutes, which can meet the requirements of online detection for detection accuracy and speed.

[0005] The second object of the present invention is to provide an application of a rapid online detection method for residual acid content in a polymetallic salt solution, which is used for online detection of residual acid content in a liquid phase in laterite nickel ore hydrometallurgy. In the detection process, the present invention does not need to add any acid-base indicator except the alkali standard solution, thereby avoiding experimental errors caused by manual observation of the color change of the titration endpoint solution, and because the titration endpoint pH is low, the sampling amount and reagent consumption are small during the detection process, the operation is simple, fast and accurate, and can meet the requirements for online detection of residual acid content in the liquid phase in laterite nickel ore hydrometallurgy.

[0006] In order to achieve the above technical objectives, the present invention provides a rapid online detection method for residual acid content in a polymetallic salt solution, comprising: Step S1, preparing a standard alkali solution, and calibrating the actual concentration of the standard solution with a reference reagent to determine its titer for residual acid; Step S2, selecting two standard buffer solutions of 6.86 and 1.68 as calibration solutions, and performing two-point calibration on the pH meter; Step S3, preparing multi-metal salt standard solutions with different residual acid concentrations, selecting one of the multi-metal salt standard solutions with a determined concentration, adding a base standard solution dropwise under stirring, and detecting the pH value with a calibrated pH meter, and recording the consumption of the base standard solution when the titration endpoint is reached; Step S4, obtaining the residual acid content in the polymetallic salt standard solution according to the consumption of the alkali standard solution in step S4, the titration endpoint pH, and the concentration and volume of the polymetallic salt standard solution.

[0007] As a preferred solution, the polymetallic salt solution contains Fe 3+ , Fe 2+ 、A1 3+ Cr 3+ 、Ni 2+ and Mn 2 + .

[0008] As a preferred solution, the residual acid in the polymetallic salt solution is at least one of sulfuric acid, nitric acid and hydrochloric acid.

[0009] As a preferred solution, the alkali standard solution is sodium hydroxide and / or potassium hydroxide, and the concentration thereof is 0.5-1.0 g / L. Further preferably, the alkali standard solution is sodium hydroxide.

[0010] As a preferred solution, the reference reagent is potassium hydrogen phthalate.

[0011] As a preferred solution, the residual acid in the polymetallic salt standard solution is measured as sulfuric acid, with a concentration gradient of 8-10 g / L and a concentration range of 10-50 g / L.

[0012] As a preferred solution, the titration endpoint pH is the pH value of the first precipitated metal ion in the polymetallic salt standard solution.

[0013] As a preferred solution, the process of adding the alkali standard solution in step S3 is: accurately transfer a certain volume V of the polymetallic salt standard solution into a 50 mL beaker, add a stirrer, place it on a magnetic stirrer, insert the calibrated pH meter into the beaker against the wall, away from the stirrer, and add the alkali standard solution until the titration endpoint pH is reached.

[0014] As a preferred solution, the residual acid in the polymetallic salt standard solution is measured in terms of sulfuric acid, and the calculation process of its content is as follows: Formula 1: H 2 SO 4 (g / L)= ; In formula 1, T is the mass of sulfuric acid equivalent to 1.0L sodium hydroxide standard solution expressed in grams, i.e., the titer, with the unit of g / L; V is the volume of the standard liquid sample to be tested, with the unit of mL; V 1 It is the volume of sodium hydroxide standard solution consumed by the sample to be tested, with the dimension of mL.

[0015] As a preferred solution, after obtaining the residual acid content in the polymetallic salt standard solution, step S3 and step S4 need to be repeated 3 to 5 times for parallel sample calibration.

[0016] The present invention also provides an application of a rapid online detection method for residual acid content in a polymetallic salt solution, which is used for online detection of residual acid content in a liquid phase in laterite nickel ore hydrometallurgy.

[0017] Compared with the prior art, the beneficial technical effects of the technical solution of the present invention are: 1) The detection method provided by the present invention uses the pH value of the first precipitated metal ion in the multi-metal salt standard solution as the key pH for titration, thereby avoiding the problem of high acidity in the detection result caused by the consumption of hydroxide by the easily hydrolyzed metal salt ions during the precipitation process. After testing, the residual acid content in the multi-metal salt standard solution determined by this method has a relative error of ≤2% compared with the theoretical value, and the detection cycle is shortened to 5-10 minutes, which can meet the requirements of online detection for detection accuracy and rate.

[0018] 2) The technical solution provided by the present invention does not need to add any acid-base indicator except the alkali standard solution during the detection process, thereby avoiding the experimental error caused by manually observing the color change of the titration endpoint solution. In addition, since the pH value of the titration endpoint is low, the sampling amount and reagent consumption during the detection process are small, the operation is simple, fast and accurate, and can meet the online detection requirements of the liquid phase residual acid content in laterite nickel ore hydrometallurgy. DETAILED DESCRIPTION

[0019] In order to facilitate the understanding of the present invention, the present invention will be described in more comprehensive and detailed manner in combination with the specification and preferred embodiments. It should be noted that the described embodiments are only part of the embodiments of the present invention, rather than all 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.

[0020] In the following examples, the first metal ion precipitated from the polymetallic salt solution is Fe 3+ The precipitation pH value is about 2.80, which is the titration endpoint pH.

[0021] Example 1 1) Prepare a sodium hydroxide standard solution with a titer of T (NaOH) = 0.900 g / L, and calibrate it with potassium hydrogen phthalate standard reagent to obtain a titer of 0.890 g / L.

[0022] 2) Prepare 250 mL of standard sample so that Ni 2+ 6.0g / L, Fe 3+ 4.0g / L、Al 3+ 7.0g / L, Mn 2+ 5.0g / L, Co 2+ 0.5g / L, Mg 2+ 10.0g / L, the theoretical concentration of sulfuric acid is 45g / L.

[0023] 3) Calibrate the pH meter using 6.86 and 1.68 calibration solutions. The slope of the calibration curve should be greater than 95%.

[0024] 4) Take 2 mL of standard sample and record it as V 1 , put it in a 50mL beaker and add a stirrer, place it on a magnetic stirrer, and put the calibrated pH meter electrode into the beaker, try to stick it to the wall of the beaker to prevent the stirrer from breaking the glass bubble of the electrode. After placing it, start stirring and titrate with NaOH standard solution, and record the volume of NaOH consumed as V 2 , three sets of parallel samples were made, and the calculated result was 44.8g / L, which was 0.2g / L different from the theoretical result, and the average detection period was 5min.

[0025] Example 2 This example is exactly the same as Example 1, except that 250 mL of standard sample is prepared so that Ni 2+ 6.0g / L, Fe 3+ 4.0g / L、Al 3+ 7.0g / L, Mn2+ 5.0g / L, Co 2+ 0.5g / L, Mg 2+ 10.0g / L, the theoretical concentration of sulfuric acid is 30g / L. Based on 3 sets of parallel samples, the calculated result is 29.7g / L, which is 0.3g / L different from the theoretical result, and the average detection period is 5min.

[0026] Example 3 This embodiment is exactly the same as Embodiment 1, except that: 1) Prepare 250 mL of standard sample so that Ni 2+ 6.0g / L, Fe 3+ 4.0g / L、Al 3+ 7.0g / L, Mn 2+ 5.0g / L, Co 2 + 0.5g / L, Mg 2+ 10.0g / L, the theoretical concentration of sulfuric acid is 10g / L.

[0027] 2) Take 5 mL of standard sample and record it as V 1 , put it in a 50mL beaker and add a stirrer, place it on a magnetic stirrer, and put the calibrated pH meter electrode into the beaker, keeping it as close to the beaker wall as possible to prevent the stirrer from breaking the glass bubble of the electrode. After placing it in place, start stirring and titrate with NaOH standard solution, and record the volume of NaOH consumed as V 2 , three sets of parallel samples were made, and the calculated result was 9.8g / L, which was 0.2g / L different from the theoretical result. The average detection period was 5min.

[0028] Example 4 1) Calibrate the pH meter using 6.86 and 1.68 calibration solutions. The slope of the calibration curve should be greater than 95%.

[0029] 2) Take 2 mL of workshop samples with different acidity and record them as V 1 , put it in a 50mL small beaker and add a stirrer, place it on a magnetic stirrer, and put the calibrated pH meter electrode into the small beaker, try to stick it to the wall of the beaker to prevent the stirrer from breaking the glass bubble of the electrode. After placing it, start stirring and titrate with NaOH standard solution, and record the volume of NaOH consumed as V 2 Three parallel samples were made for each sample, and the calculated results were 48.7 g / L. The average detection cycle was 5 minutes. This method was used for the rapid determination of residual acid in the hydrometallurgical nickel leaching solution, and could provide timely and accurate data for subsequent production processes.

[0030] Example 5 1) Calibrate the pH meter using 6.86 and 1.68 calibration solutions. The slope of the calibration curve should be greater than 95%.

[0031] 2) Take 2 mL of workshop samples with different acidity and record them as V 1 , put it in a 50mL small beaker and add a stirrer, place it on a magnetic stirrer, and put the calibrated pH meter electrode into the small beaker, try to stick it to the wall of the beaker to prevent the stirrer from breaking the glass bubble of the electrode. After placing it, start stirring and titrate with NaOH standard solution, and record the volume of NaOH consumed as V 2 Three parallel samples were made for each sample, and the calculated results were 32.6 g / L. The average detection cycle was 5 minutes. This method was used for the rapid determination of residual acid in the hydrometallurgical nickel leaching solution, and could provide timely and accurate data for subsequent production processes.

[0032] Example 6 1) Calibrate the pH meter using 6.86 and 1.68 calibration solutions. The slope of the calibration curve should be greater than 95%.

[0033] 2) Take 5 mL of workshop samples with different acidity and record them as V 1 , put it in a 50mL small beaker and add a stirrer, place it on a magnetic stirrer, and put the calibrated pH meter electrode into the small beaker, try to stick it to the wall of the beaker to prevent the stirrer from breaking the glass bubble of the electrode. After placing it, start stirring and titrate with NaOH standard solution, and record the volume of NaOH consumed as V 2 Three parallel samples were made for each sample, and the calculated results were 12.5g / L respectively. The average detection cycle was 5min. This method was used for the rapid determination of residual acid in the hydrometallurgical nickel leaching solution, and could provide timely and accurate data for subsequent production processes.

[0034] In order to further illustrate the advantages of the detection method provided by the present invention, the present invention also performs a potassium ferrocyanide titration test on the pH value of the detection solution, and the process is as follows: 1) Use the standard sample provided in Example 1; 2) Take 20 ml of the sample and put it into four 100 ml volumetric flasks, leave one as a blank, and add 2 ml, 5 ml, and 10 ml of potassium ferrocyanide (200 g / L) to the other three, respectively, make up to volume, shake well, and precipitate overnight; 2) After confirming that no precipitation is produced in the above sample, filter it and measure the pH of the sample before and after filtration. The results are shown in Table 1. Then dilute the filtrate 500 times, transfer 10 ml to a 250 ml beaker, add 2 drops of methyl red indicator, and titrate to obtain the acidity result indicated by color change. The results are shown in Table 2.

[0035]

[0036]

[0037] It can be seen from Tables 1 and 2 that the amount of potassium ferrocyanide added cannot exceed 10 ml. Once it exceeds 10 ml, new precipitates will still be produced after multiple filtrations, thereby affecting the pH of the filtrate. In addition, since this method requires the preparation of the sample solution in advance, the precipitation process requires overnight precipitation for sufficient precipitation, which is difficult to meet the requirements of online detection, and the acidity is determined by the color change of the filtrate, which still has a large subjective characteristic, and its system error is large, and it is difficult to meet the accuracy requirements. It can be seen that the method provided by the present invention has the advantages of high test accuracy, short detection cycle and simple preparation process compared to the residual acid detection method in the prior art, and can meet the technical requirements for online detection of residual acid content in polymetallic salt solutions.

Claims

1. A rapid online detection method for residual acid content in a polymetallic salt solution, characterized in that: include: Step S1, preparing a standard alkali solution, and calibrating the actual concentration of the standard solution with a reference reagent to determine its titer for residual acid; Step S2, selecting two standard buffer solutions of 6.86 and 1.68 as calibration solutions, and performing two-point calibration on the pH meter; Step S3, preparing multi-metal salt standard solutions with different residual acid concentrations, selecting one of the multi-metal salt standard solutions with a determined concentration, adding a base standard solution dropwise under stirring, and detecting the pH value with a calibrated pH meter, and recording the consumption of the base standard solution when the titration endpoint is reached; Step S4, obtaining the residual acid content in the polymetallic salt standard solution according to the consumption of the alkali standard solution in step S4, the titration endpoint pH, and the concentration and volume of the polymetallic salt standard solution.

2. The rapid online detection method for residual acid content in a polymetallic salt solution according to claim 1, characterized in that: The polymetallic salt solution contains Fe 3+ , Fe 2+ 、A1 3+ Cr 3+ 、Ni 2+ and Mn 2+ ; The residual acid in the polymetallic salt solution is at least one of sulfuric acid, nitric acid and hydrochloric acid.

3. The rapid online detection method for residual acid content in a polymetallic salt solution according to claim 1, characterized in that: The alkali standard solution is sodium hydroxide and / or potassium hydroxide, and its concentration is 0.5-1.0 g / L; the reference reagent is potassium hydrogen phthalate.

4. The rapid online detection method for residual acid content in a polymetallic salt solution according to claim 1, characterized in that: The residual acid in the polymetallic salt standard solution is measured as sulfuric acid, and its concentration gradient is 8-10 g / L, and the concentration range is 10-50 g / L.

5. The rapid online detection method for residual acid content in a polymetallic salt solution according to claim 1, characterized in that: The titration endpoint pH is the pH value of the metal ions first precipitated in the polymetallic salt standard solution.

6. The rapid online detection method for residual acid content in a polymetallic salt solution according to claim 5, characterized in that: The process of adding the alkali standard solution in step S3 is: accurately transfer a certain volume V of the polymetallic salt standard solution into a 50 mL beaker, add a stirrer, place it on a magnetic stirrer, insert the calibrated pH meter into the beaker against the wall, away from the stirrer, and add the alkali standard solution until the titration endpoint pH is reached.

7. The rapid online detection method for residual acid content in a polymetallic salt solution according to claim 1, characterized in that: The residual acid in the polymetallic salt standard solution is measured in terms of sulfuric acid, and the calculation process of its content is as follows: Formula 1: H2SO4 (g / L) = ; In formula 1: T is the mass of sulfuric acid expressed in grams equivalent to 1.0L of sodium hydroxide standard solution, that is, the titer, with the dimension of g / L; V is the volume of the standard liquid sample to be tested, with the dimension of mL; V1 is the volume of the sodium hydroxide standard solution consumed by the sample to be tested, with the dimension of mL.

8. The rapid on-line detection method for residual acid content in a polymetallic salt solution according to claim 7, characterized in that: After obtaining the residual acid content in the polymetallic salt standard solution, step S3 and step S4 need to be repeated 3 to 5 times for parallel sample calibration.

9. Application of the method for rapid online detection of residual acid content in a polymetallic salt solution according to any one of claims 1 to 8, characterized in that: Used for online detection of residual acid content in liquid phase in laterite nickel ore hydrometallurgy.

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