Method for determining content of hexavalent chromium in fingerprint-resistant waste liquid

Abstract

The invention discloses a method for determining the content of hexavalent chromium in fingerprint-resistant waste liquid, which comprises the following steps: heating and demulsifying a fingerprint-resistant waste liquid sample under an acidic condition to separate solid from liquid, and precipitating and separating hexavalent chromium by using zinc hydroxide; inductively coupled plasma emission spectrometry is adopted for detection, after a treated sample is added into an inductively coupled plasma emission spectrometer through a sample injector, the hexavalent chromium element is gasified, ionized and excited in a plasma torch, a characteristic spectral line is radiated, and the intensity of the characteristic spectral line is in direct proportion to the concentration of the element within a certain concentration range; and the concentration of the hexavalent chromium element is accurately determined by detecting the strength of the characteristic spectral line of the hexavalent chromium element. Compared with a diphenylcarbazide spectrophotometric method, the method for determining the hexavalent chromium in the fingerprint-resistant waste liquid by adopting the inductively coupled plasma emission spectrometry has the advantages of strong anti-interference capability, high sample adding standard recovery rate, simplicity and convenience in operation, high automation degree, capability of improving the detection precision and capability of saving the detection cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical component detection, and particularly relates to a method for determining the content of hexavalent chromium in fingerprint-resistant waste liquid. BACKGROUND

[0002] In industrial production, fingerprint-resistant liquid is mainly used to improve the anti-fingerprint, anti-oil and corrosion resistance of metal surfaces such as stainless steel and aluminum materials. Fingerprint-resistant treatment is divided into two types: chromium-containing and chromium-free. When switching between different treatment processes, some fingerprint-resistant liquid becomes waste liquid and is stored in a waste liquid barrel. Hexavalent chromium is a highly hazardous component in fingerprint-resistant waste liquid and is a class 1 carcinogen with persistence in the environment. In the treatment of fingerprint-resistant waste liquid, the detection of hexavalent chromium is a core control index. Through accurate detection, the treatment technology is iterated to achieve a balance between environmental benefits and production sustainability.

[0003] Fingerprint-resistant waste liquid contains resins, heavy metals and other substances, and cannot be separated into solid and liquid. It is a emulsion and contains chromium in different valence states, which brings great difficulty to the detection of the content of hexavalent chromium. At present, the wastewater detection method in the environmental detection industry only has the GB / T7467-1987 standard "Determination of Hexavalent Chromium in Water - Diphenylcarbazide Spectrophotometric Method". The diphenylcarbazide spectrophotometric method has no emulsion treatment method, is greatly affected by organic matter and heavy metals, and has a low sample standard recovery rate. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a method for determining the content of hexavalent chromium in fingerprint-resistant waste liquid. The method uses inductively coupled plasma emission spectrometry to determine the content of hexavalent chromium in fingerprint-resistant waste liquid. Compared with the diphenylcarbazide spectrophotometric method, the method has strong anti-interference ability, high sample standard recovery rate, simple operation, high automation degree, improves detection accuracy, and saves detection cost.

[0005] To solve the above technical problems, the method for determining the content of hexavalent chromium in fingerprint-resistant waste liquid includes the following steps: Step one, demulsification, 100mL of sample is taken in a 250mL triangular flask, 1mL of (1+1) sulfuric acid solution is added, shaken, the pH value of the sample is adjusted to below 2, and the sample is placed on an electric heating plate to heat until the sample is separated into solid and liquid. Stop heating, filter the sample after it cools slightly, and collect the filtrate; Step two, zinc salt precipitation separation, 50mL of the filtrate sample is taken in a 150mL beaker, sodium hydroxide solution is added dropwise to adjust the pH value to 7-8, and under constant stirring, zinc hydroxide co-precipitant is added dropwise until the pH value of the solution is 8-9. The solution is transferred to a 100mL volumetric flask, diluted with water to the mark, filtered with slow filter paper, 10mL-20mL of the initial filtrate is discarded, and 50.0mL of the filtrate is taken for determination; Step three, draw a standard curve, take the chromium element standard use liquid 20.00mg / L to prepare a standard curve, prepare the chromium standard curve concentration respectively 0.10mg / L, 0.20mg / L, 0.40mg / L, 0.6mg / L, 1.00mg / L, 2.00mg / L, with 1% nitric acid solution constant volume, using inductively coupled plasma emission spectrometry, according to the instrument analysis conditions, from low concentration to high concentration in turn, with the chromium element series mass concentration as the abscissa, and its corresponding emission intensity value as the ordinate, to establish the standard curve of the target element; Step four, sample determination, under the same conditions as establishing the standard curve, analyze the sample, and read the chromium content in the sample by inductively coupled plasma emission spectrometry.

[0006] Further, during the sample determination process, if the concentration of the sample to be measured exceeds the concentration range of the standard curve, the sample to be measured is appropriately diluted and re-measured.

[0007] Further, the test conditions of the inductively coupled plasma emission spectrometry instrument analysis are horizontal observation mode, emission power 1150W, carrier gas flow rate 0.7L / min, auxiliary gas flow rate 1.0L / min, and cooling gas flow rate 12.0L / min.

[0008] Further, the blank sample is prepared by replacing the sample with pure water, and the blank sample is prepared according to the same steps as the sample preparation, and the blank sample is measured under the same conditions as the sample determination. Since the method for measuring the content of hexavalent chromium in the fingerprint-resistant waste liquid adopts the above technical scheme, i.e., the method heats the fingerprint-resistant waste liquid sample under acidic conditions to break the emulsion, separates the solid and liquid, and then uses zinc hydroxide to precipitate and separate the hexavalent chromium; the inductively coupled plasma emission spectrometry is used for detection, after the treated sample is added to the inductively coupled plasma emission spectrometer through the sampler, the hexavalent chromium element is gasified, ionized, excited and radiates characteristic spectral lines in the plasma torch, and within a certain concentration range, the intensity of the characteristic spectral lines is proportional to the concentration of the element, and the concentration of the hexavalent chromium element is accurately determined by detecting the intensity of the characteristic spectral lines of the hexavalent chromium element. Compared with the diphenyl carbonyl hydrazine spectrophotometry, the method for measuring the hexavalent chromium in the fingerprint-resistant waste liquid by inductively coupled plasma emission spectrometry has strong anti-interference ability, high sample standard recovery rate, simple operation, high automation degree, improved detection precision and saved detection cost. DETAILED DESCRIPTION

[0009] The method for measuring the content of hexavalent chromium in the fingerprint-resistant waste liquid includes the following steps: Step 1: Demulsification: Measure 100 mL of sample into a 250 mL Erlenmeyer flask, add 1 mL of (1+1) sulfuric acid solution, shake well, adjust the pH value of the sample to below 2, place on a hot plate and heat until the solid and liquid of the sample are separated, stop heating, cool slightly and filter the sample, and collect the filtrate; Step 2: Zinc salt precipitation and separation: take 50 mL of filtrate sample in a 150 mL beaker, add sodium hydroxide solution dropwise to adjust the pH value to 7-8, and under constant stirring, add zinc hydroxide coprecipitant dropwise until the pH value of the solution is 8-9. Transfer the solution to a 100 mL volumetric flask, dilute with water to the mark, filter with slow filter paper, discard 10 mL to 20 mL of the initial filtrate, and take 50.0 mL of the filtrate for determination; Step 3: Draw a standard curve. Prepare a standard curve with 20.00 mg / L of chromium standard solution. The concentrations of the chromium standard curve are 0.10 mg / L, 0.20 mg / L, 0.40 mg / L, 0.6 mg / L, 1.00 mg / L, and 2.00 mg / L, respectively. Use 1% nitric acid solution to make up the volume. Use inductively coupled plasma emission spectrometry. According to the instrument analysis conditions, inject samples from low concentration to high concentration in sequence. Use the mass concentration of the chromium element series as the abscissa and the corresponding emission intensity value as the ordinate to establish a standard curve for the target element. Step 4: Sample determination: Analyze the sample under the same conditions as those used to establish the standard curve, and use inductively coupled plasma optical emission spectrometry to read the chromium content in the sample.

[0010] Preferably, during the sample measurement process, if the concentration of the sample to be measured exceeds the concentration range of the standard curve, the sample to be measured is appropriately diluted and then re-measured.

[0011] Preferably, the test conditions of the inductively coupled plasma optical emission spectrometry instrument analysis are horizontal observation mode, emission power 1150W, carrier gas flow rate 0.7L / min, auxiliary gas flow rate 1.0L / min, and cooling gas flow rate 12.0L / min.

[0012] Preferably, the blank sample is measured by replacing the sample with pure water, preparing the blank sample according to the same steps as the sample preparation, and measuring the blank sample under the same conditions as the sample measurement.

[0013] This method adopts pretreatment methods such as acid heating for demulsification and zinc hydroxide precipitation for separation of hexavalent chromium, and then performs on-machine detection by inductively coupled plasma emission spectrometry, which effectively improves the accuracy of the measurement data. Compared with other methods, this method has strong anti-interference ability, high sample spike recovery rate, does not involve expensive materials, and reagents and consumables can be obtained locally without the need for special procurement, thus saving detection costs. The operation is simple and the degree of automation is high, providing an accurate and reliable basis for the treatment of fingerprint-resistant waste liquid.

Claims

1. A method for determining the content of hexavalent chromium in a fingerprint-resistant waste solution, characterized in that It comprises the following steps: Step one, demulsification, 100 mL sample is taken in a 250 mL flask, 1 mL of (1+1) sulfuric acid solution is added, the sample pH value is adjusted to below 2, and the sample is placed on an electric heating plate to separate the solid and liquid, heating is stopped, the sample is filtered slightly after cooling, and the filtrate is collected; Step two, zinc salt precipitation separation, 50 mL of the filtrate sample is taken in a 150 mL beaker, sodium hydroxide solution is added dropwise to adjust the pH value to 7-8, and zinc hydroxide co-precipitant is added dropwise under constant stirring until the solution pH value is 8-9, the solution is transferred to a 100 mL volumetric flask, diluted with water to the mark, filtered with slow filter paper, 10-20 mL of the initial filtrate is discarded, and 50.0 mL of the filtrate is taken for determination; Step three, standard curve preparation, a chromium element standard solution 20.00 mg / L is used to prepare a standard curve, chromium standard curve concentrations of 0.10 mg / L, 0.20 mg / L, 0.40 mg / L, 0.6 mg / L, 1.00 mg / L, and 2.00 mg / L are prepared, 1% nitric acid solution is used for constant volume, under the same conditions as the establishment of the standard curve, the sample is injected from low concentration to high concentration, the chromium element series mass concentration is used as the horizontal coordinate, and the corresponding emission intensity value is used as the vertical coordinate to establish the standard curve of the target element; Step four, sample determination, the sample is analyzed under the same conditions as the establishment of the standard curve, and the chromium content in the sample is read by inductively coupled plasma emission spectrometry.

2. The method of claim 1, wherein: During the sample determination process, if the concentration of the sample to be measured exceeds the standard curve concentration range, the sample to be measured is appropriately diluted and re-determined.

3. The method according to claim 1 or 2, wherein: The test conditions of the inductively coupled plasma emission spectrometry instrument analysis are horizontal observation mode, emission power 1150 W, carrier gas flow rate 0.7 L / min, auxiliary gas flow rate 1.0 L / min, and cooling gas flow rate 12.0 L / min.

4. The method of claim 1, wherein: The blank sample determination uses pure water instead of the sample, the blank sample is prepared according to the same steps as the sample preparation, and the blank sample is determined under the same conditions as the sample determination.