Method for measuring alkalinity in metallurgical industry circulating water in batches

Abstract

The invention discloses a method for batch determination of alkalinity in metallurgical industry circulating water. The method comprises the following steps: 1) electrode calibration; 2) setting titration parameters; 3) determination; 4) calculating data; a calculation formula is built in software, and a result is automatically calculated. The invention aims to provide a method for measuring the alkalinity of metallurgical industry circulating water in batches, which is realized as follows: the detection precision is as follows: the relative error is less than or equal to 1.5%, and the reproducibility RSD is less than or equal to 2%; the detection efficiency is as follows: single detection is less than or equal to 5 minutes, and continuous determination of more than 10 batches of samples is supported; the adaptability is as follows: the alkalinity range of 5-1000 mg / L (based on CaCO) is covered, the tolerance suspended matter is less than or equal to 50 mg / L, and the silicon content is less than or equal to 15% of circulating water.

Description

Technical Field

[0001] This invention belongs to the field of water quality analysis technology, and in particular relates to a method for batch determination of alkalinity in circulating water in metallurgical industries. Background Technology

[0002] Metallurgical industry circulating water (especially cooling circulating water) needs to be in continuous contact with high-temperature equipment (such as blast furnace cooling walls and continuous casting crystallizers). Alkalinity is a core indicator for controlling scaling and corrosion. Imbalance can directly threaten equipment lifespan and may also indirectly interfere with smelting processes through water migration, particularly affecting non-ferrous metal smelting and steel quality. It also impacts water quality management and smelting costs. To control circulating water alkalinity within a reasonable range, additional reagents, equipment, and manpower are required, and abnormal alkalinity directly increases smelting costs.

[0003] Currently, water alkalinity testing mainly employs manual titration and fully automated potentiometric titration. Manual titration uses phenolphthalein and methyl orange as indicators, with the endpoint determined by manually judging color changes. While the equipment cost is low, it is heavily influenced by the operator's subjective judgment, and a single test takes approximately 20-30 minutes, failing to meet the needs of batch sample testing. Fully automated potentiometric titration determines the endpoint by monitoring the potential jump using a pH electrode, avoiding human error. Existing technologies often employ a fixed titration rate (1 mL / min) and a single pH endpoint (4.5), combined with 0.1 mol / L hydrochloric acid titrant. The following shortcomings and defects exist in practical applications: For high-alkalinity water samples (>500mg / L, calculated as CaCO3), a fixed titration rate of 1mL / min leads to local excess hydrochloric acid, CO2 escape, and pH drift at the endpoint (deviation up to 0.3 pH units), resulting in a detection error >4%; the bicarbonate content varies greatly among different water samples (e.g., 80% bicarbonate in industrial circulating water and 60% in drinking water), and a single endpoint of pH=4.5 cannot ensure complete bicarbonate reaction; the detection results for low-alkalinity water samples (<50mg / L) are 10%-15% lower; the existing method uses 0.1mol / L hydrochloric acid regardless of the alkalinity of the water sample, and the hydrochloric acid consumption is <5mL for low-alkalinity water samples, resulting in a burette calibration error (±0.01mL) of up to 0.2%, affecting accuracy, and the fixed amount of reagent used per test leads to waste.

[0004] The aforementioned problems make it difficult for existing fully automated potentiometric titration methods to simultaneously achieve "high precision" and "high efficiency" in water alkalinity testing, especially in batch testing scenarios for industrial circulating water. These methods fail to meet the process requirements for detection accuracy (error ≤2%) and increase testing costs due to reagent waste. Therefore, it is necessary to develop a fully automated potentiometric titration method adapted to the characteristics of industrial circulating water to achieve high precision, high efficiency, and high adaptability in alkalinity determination. Summary of the Invention

[0005] In view of the characteristics of high alkalinity, high suspended solids, and large fluctuations in composition of industrial circulating water, the purpose of this invention is to provide a method for batch determination of alkalinity in metallurgical industrial circulating water, achieving the following: detection accuracy: relative error ≤1.5%, reproducibility RSD ≤2%; detection efficiency: single detection ≤5 minutes, supporting continuous determination of more than 10 batches of samples; adaptability: covering an alkalinity range of 5~1000 mg / L (calculated as CaCO3), and tolerant of circulating water with suspended solids ≤50 mg / L and silicon content ≤15%.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] This invention discloses a method for batch determination of alkalinity in circulating water in metallurgical industries, comprising the following steps:

[0008] 1) Electrode calibration: Select the calibration mode according to the instrument manual, and calibrate the pH electrode at three points using standard buffer solutions of pH 4.00, 6.86, and 9.18. The slope should be in the range of 0.95 to 1.05, and the error after calibration should be ≤0.02 pH.

[0009] 2) Titration Parameter Settings: 2.1) Titrant Concentration: 0.05 mol / L; 2.2) Dropping Rate Settings: In dynamic titration mode, under "Titration Parameters" → "Speed ​​Settings", click "Add Stage" and set the step rate: divided by pH range, first stage: when pH > 5.0, set a fast dropping rate of 1~2 mL / min; second stage: when pH < 5.0, set a slow dropping rate of 0.01~0.1 mL / step to accurately capture the endpoint jump of total alkalinity; select DET pH mode linked with step rate, and set "rapid addition when ΔpH / ΔV < 0.2pH / mL, > 0.2pH / mL". "Slowing down" balances efficiency and accuracy, allowing single-sample testing time to be controlled within 5 minutes; 2.3) Stirring speed setting: Set the stirring speed to 300~400 r / min, pre-stirring to 350 r / min, and slow dripping to 300 r / min to ensure thorough mixing of the water sample and hydrochloric acid, avoiding local pH unevenness that could cause abrupt shifts in the titration point; however, the speed should not be too fast to prevent solution splashing or excessive CO2 escape; 2.4) Titration endpoint setting: Instead of setting a fixed pH value in advance, the endpoint is automatically determined by monitoring the "rate of change of pH with titrant volume (ΔpH / ΔV)" during the titration process; the abrupt shift sensitivity is set to 0.5 pH / mL, and the minimum titration volume is 0.1 mL;

[0010] 3) Determination: Select according to the pre-detection alkalinity. For low alkalinity < 200 mg / L, take 50.0 mL of water sample, and for high alkalinity ≥ 200 mg / L, take 20.0 mL of water sample into the measuring cup. Place the measuring cup on the titration stage, insert the electrode and the burette head below the water sample surface, turn on the instrument and stirrer, and automatically titrate with hydrochloric acid standard titration solution until the reaction is complete.

[0011] 4) Data calculation: Total alkalinity = (V1 × c × 50.05 × 1000) / V 样 Where V1 is the volume of hydrochloric acid consumed at the total alkalinity endpoint, c is the hydrochloric acid concentration, and V 样 The volume is the water sample volume; the total alkalinity is expressed in mg / L as CaCO3; the calculation formula is built into the software, and the result is calculated automatically.

[0012] Furthermore, the electrode used in step 1) is an aqueous acid-base electrode.

[0013] Furthermore, in step 2), the titrant is a standard hydrochloric acid titration solution, calibrated with sodium carbonate as a reference, with a concentration error ≤ 0.0001 mol / L. The distilled or deionized water used for preparing the solution and for dilution is carbon dioxide-free water, which should be boiled for 15 minutes and cooled to room temperature before use. The pH value should be greater than 6.0 and the conductivity should be less than 0.2 μs / cm.

[0014] Furthermore, in step 3), the volumetric accuracy error of the burette is ≤0.01 mL.

[0015] Furthermore, the stirrer is a spiral stirrer.

[0016] Furthermore, through adaptive parameter setting and matrix pretreatment, the relative error of this method is reduced from 5% to below 1.5%, meeting the high-precision requirements of industrial circulating water process control.

[0017] Furthermore, this method reduces the single detection time from 20 minutes to 5 minutes.

[0018] Furthermore, this method supports continuous testing of more than 10 batches of samples, increasing the daily detection volume by more than 100%.

[0019] Furthermore, this method covers an alkalinity range of 5–1000 mg / L.

[0020] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0021] The advantages of this invention are that, through adaptive parameter settings and matrix pretreatment, the relative error is reduced from 5% to below 1.5%, meeting the high-precision requirements of industrial circulating water process control (such as metallurgical circulating water requiring an error of ≤2%); the single detection time is shortened from 20 minutes to 5 minutes, supporting continuous measurement of more than 10 batches of samples, increasing the daily detection volume by more than 100%; it covers an alkalinity range of 5~1000mg / L and is tolerant of complex circulating water with high suspended solids and high silica; the entire process requires no manual intervention, and the data is automatically stored and exported, meeting the intelligent requirements of "unattended operation" in industrial sites. Detailed Implementation

[0022] The technical solution of the present invention will be further described below with reference to examples, so that those skilled in the art can further understand the present invention.

[0023] Example 1:

[0024] A method for determining the total alkalinity of circulating water in metallurgical industries, the specific operation of which is as follows:

[0025] Accurately measure 13 aliquots of high-precision closed-loop cooling circulating water, 50.0 mL each, and place them in water sample measuring cups. Three aliquots are used for spiked recovery. Transfer 1.00 mL of 1000 mg / L sodium bicarbonate standard stock solution to each of the three 50.0 mL water samples, mix well, and proceed with the analysis. In dynamic titration mode, set the step rate: first stage (pH > 5.0), set a rapid dropping rate of 1.0 mL / min; second stage (pH < 5.0), set a slow dropping rate of 0.02 mL / step. Select the DET pH mode linked to the step rate, setting "rapid addition when ΔpH / ΔV < 0.2pH / mL, deceleration when > 0.2pH / mL". Set the pre-stirring speed to 350 rpm and the slow dropping speed to 300 rpm. Set the dynamic jump (DET) jump sensitivity to 0.5 pH / mL and the minimum titration volume to 0.1 mL. The measuring cup was placed on the titration stage, and the burette head, with the electrode and burette inserted, was submerged below the surface of the water sample. The instrument and stirrer were turned on, and the reaction was automatically titrated with a 0.0500 mol / L hydrochloric acid standard solution until completion. The total measurement time was approximately 12 minutes, with an average time of approximately 55 seconds per test. The results are shown in Table 1. The recovery rate was calculated as: (measured value after spiking - baseline value of the water sample) / theoretical spiking value × 100%.

[0026] Table 1. Experimental data on the accuracy and precision of high-precision closed-loop cooling water circulation.

[0027] Sample number project Measured value mg / L average value RSD% Theoretical dosage (mg / L) Recovery rate % IC1 (1-10) Total alkalinity 21.95，22.12，22.78，22.03，22.61，22.54，21.97，22.76，22.29，22.47 22.35 1.44 / / IC1 (11-13) Total alkalinity 41.81，42.47，42.25 42.18 0.80 20 99.2

[0028] As shown in the table above, the precision RSD of the total alkalinity of the high-precision closed-loop cooling water measured in 10 parallel trials is 1.44%, which is less than 5% and also less than the optimized preset target RSD ≤ 2%. The spike recovery rate is 99.2%, and the relative error is 0.8%. The recovery rate is between 95% and 105%, and the relative error reaches the optimized preset target of ≤ 1.5%, which verifies that this invention has good accuracy and precision.

[0029] Example 2:

[0030] A method for determining the total alkalinity of circulating water in metallurgical industries, the specific operation of which is as follows:

[0031] Accurately measure 13 portions of 20.0 mL of sintering waste heat circulating water and place them in water sample measuring cups. Three portions are used for spiked recovery. Transfer 10.00 mL of 1000 mg / L sodium bicarbonate standard stock solution and add it to each of the three 20.0 mL water samples, mix well, and prepare for analysis. In dynamic titration mode, set the step rate: first stage: when pH > 5.0, set a fast dropping rate of 1.5 mL / min; second stage: when pH < 5.0, set a slow dropping rate of 0.02 mL / step. Select DET mode linked with the step dropping rate and set "rapid addition when ΔpH / ΔV < 0.2pH / mL, deceleration when > 0.2pH / mL". Set the pre-stirring speed to 350 rpm and the slow dropping speed to 300 rpm. Set the dynamic jump (DET) jump sensitivity to 0.5 pH / mL and the minimum titration volume to 0.1 mL. The measuring cup was placed on the titration stage, and the burette head, with the electrode and burette inserted, was submerged below the surface of the water sample. The instrument and stirrer were turned on, and the reaction was automatically titrated with a 0.0500 mol / L hydrochloric acid standard solution until the reaction was complete. The total measurement time was approximately 38 minutes, with an average time of approximately 3 minutes per test. The measurement results are shown in Table 2. The recovery rate = (measured value after spiking - baseline value of water sample) / theoretical spiking value × 100%.

[0032] Table 2. Experimental data on the accuracy and precision of sintering waste heat circulating water.

[0033] Sample number project Measured value mg / L average value RSD% Theoretical dosage (mg / L) Recovery rate % Sintering residual heat (1-10) Total alkalinity 309.21，313.85，319.92，311.07，320.58，317.24，310.15，321.36，314.62，318.00 315.60 1.42 / / Sintering residual heat (11-13) Total alkalinity 813.11、820.02、830.48 821.20 1.07 500 101.1

[0034] As shown in the table above, the precision RSD of the total alkalinity of the sintering waste heat circulating water in 10 parallel measurements was 1.42%, which is less than 5% and also less than the optimized preset target RSD ≤ 2%. The spiked recovery rate was 101.1%, and the relative error was 1.1%. The recovery rate was between 95% and 105%, and the relative error reached the optimized preset target of ≤ 1.5%, which verifies that this invention has good accuracy and precision.

[0035] The example data demonstrates that this invention provides a reliable, accurate, and rapid method for batch determination of total alkalinity in circulating water in the metallurgical industry. The advantages of this invention lie in its ability to reduce the relative error to below 1.5% through adaptive parameter settings and matrix pretreatment, meeting the high-precision requirements (≤2%) for industrial circulating water process control; the maximum single detection time is less than 5 minutes, supporting continuous determination of more than 10 batches of samples, increasing the daily detection volume by more than 100%; it covers an alkalinity range of 5~1000 mg / L, requiring no sample pretreatment; and the entire process requires no manual intervention, with data automatically stored and exported, meeting the intelligent "unattended" requirements of industrial sites.

[0036] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for batch determination of alkalinity in circulating water in metallurgical industries, characterized in that: Includes the following steps: 1) Electrode calibration: Select the calibration mode according to the instrument manual, and calibrate the pH electrode at three points using standard buffer solutions of pH 4.00, 6.86, and 9.

18. The slope should be in the range of 0.95 to 1.05, and the error after calibration should be ≤0.02 pH. 2) Titration Parameter Settings: 2.1) Titrant Concentration: 0.05 mol / L; 2.2) Dropping Rate Settings: In dynamic titration mode, under "Titration Parameters" → "Speed ​​Settings", click "Add Stage" and set the step rate: divided by pH range. First stage: when pH > 5.0, set a fast dropping rate of 1~2 mL / min; Second stage: when pH < 5.0, set a slow dropping rate of 0.01~0.1 mL / step to accurately capture the endpoint jump of total alkalinity; Select DET pH mode linked with step rate, and set "Rapid addition when ΔpH / ΔV < 0.2pH / mL, > 0.2pH / mL". "Slowing down" balances efficiency and accuracy, and the testing time for a single sample can be controlled within 5 minutes; 2.3). Stirring rate setting: Set the stirring speed to 300~400 r / min, 350 r / min for pre-stirring, and 300 r / min for slow dripping to ensure that the water sample and hydrochloric acid are fully mixed and to avoid local pH unevenness that could cause abrupt shifts in the pH value; however, the speed should not be too fast to prevent solution splashing or excessive CO2 escape; 2.4) Titration endpoint setting: Instead of setting a fixed pH value in advance, the endpoint is automatically determined by monitoring the rate of change of pH with titrant volume (ΔpH / ΔV) during the titration process. The threshold value is set to 0.5 pH / mL and the minimum titration volume is 0.1 mL. 3) Determination: Select according to the pre-detection alkalinity. For low alkalinity < 200 mg / L, take 50.0 mL of water sample, and for high alkalinity ≥ 200 mg / L, take 20.0 mL of water sample into the measuring cup. Place the measuring cup on the titration stage, insert the electrode and the burette head below the water sample surface, turn on the instrument and stirrer, and automatically titrate with hydrochloric acid standard titration solution until the reaction is complete. 4) Data calculation: Total alkalinity = (V1 × c × 50.05 × 1000) / V 样 Where V1 is the volume of hydrochloric acid consumed at the total alkalinity endpoint, c is the hydrochloric acid concentration, and V 样 The volume represents the water sample; total alkalinity is expressed in mg / L as CaCO3. The calculation formula is built into the software, and the result is calculated automatically.

2. The method for batch determination of alkalinity in circulating water in metallurgical industries according to claim 1, characterized in that: The electrode used in step 1) is an aqueous acid-base electrode.

3. The method for batch determination of alkalinity in circulating water in metallurgical industries according to claim 1, characterized in that: In step 2), the titrant is a standard hydrochloric acid titration solution, standardized with sodium carbonate as a reference, with a concentration error ≤0.0001 mol / L. The distilled or deionized water used for preparing the solution and dilution is carbon dioxide-free. Boil for 15 minutes before use and cool to room temperature. The pH value should be greater than 6.0 and the conductivity should be less than 0.2 μs / cm.

4. The method for batch determination of alkalinity in circulating water in metallurgical industries according to claim 1, characterized in that: In step 3), the volumetric accuracy error of the burette is ≤0.01 mL.

5. The method for batch determination of alkalinity in circulating water in metallurgical industries according to claim 1, characterized in that: The agitator is a spiral agitator.

6. The method for batch determination of alkalinity in circulating water in metallurgical industries according to claim 1, characterized in that: This method, through adaptive parameter setting and matrix pretreatment, reduces the relative error from 5% to below 1.5%, meeting the high-precision requirements of industrial circulating water process control.

7. The method for batch determination of alkalinity in circulating water in metallurgical industries according to claim 1, characterized in that: This method reduces the single detection time from 20 minutes to 5 minutes.

8. The method for batch determination of alkalinity in circulating water in metallurgical industries according to claim 1, characterized in that: This method supports continuous testing of more than 10 batches of samples, increasing the daily detection volume by more than 100%.

9. The method for batch determination of alkalinity in circulating water in metallurgical industries according to claim 1, characterized in that: This method covers an alkalinity range of 5–1000 mg / L.