Continuous Determination of Zinc and Copper in Electroplating Sewage by AA-1800 Flame Atomic Absorption Spectrometry

Continuous Determination of Zinc and Copper in Electroplating Sewage by Flame Atomic Absorption Spectrometry

Key words: flame atomic absorption spectrophotometry; electroplating wastewater; zinc; copper; analysis instrument ; AA-1800 In the analysis of electroplating wastewater, it is often necessary to simultaneously determine zinc and copper. The atomic absorption spectrophotometry has the advantages of simple operation, rapid analysis, strong anti-interference ability, etc., and has become a national standard analytical method for determining zinc and copper. In the flame atomic absorption spectrophotometric analysis, the light source used is mostly a single element hollow cathode lamp. Therefore, when measuring various elements, it is necessary to frequently change different hollow cathode lamps. After replacing the new hollow cathode lamp, it is necessary to readjust the wavelength of the lamp, the lamp current, the spectral width, the negative high voltage and the position of the lamp, and the hollow cathode lamp must be preheated for at least 20 minutes before the luminous intensity of the lamp is stabilized. The sample was measured. Therefore, the operation is troublesome and time consuming. Since the cathode of the zinc hollow cathode lamp is mostly made of zinc-copper alloy, the zinc lamp is scanned by the method of calibrating the wavelength of the energy maximum, and it is found that there is a resonance line of zinc not only at 213.9 nm but also copper at 324.8 nm. The resonance line has sufficient emission intensity. Therefore, the zinc lamp not only emits the spectrum of zinc, but also emits the spectrum of copper. According to this, the zinc hollow cathode lamp is used to determine the zinc in the sewage, and the wavelength is adjusted to 324.8 nm, and then the copper in the sewage is measured, which saves time and labor and improves work efficiency. At the same time, the copper standard curve and its detection limit were compared with the actual electroplating wastewater samples by zinc lamp and copper lamp. 1 Test 1.1 Main instruments and reagents Atomic absorption spectrophotometer (MEC China), zinc hollow cathode lamp, copper hollow cathode lamp. Zinc standard solution (500mg/L) and copper standard solution (500mg/L): all purchased by the State Environmental Protection Administration Standards Institute. Nitric acid: GR. 1.2 Instrument working conditions (Table 1) Table 1 Analysis of instrument working conditions for zinc and copper determination Lamp electrical negative hyperspectral passband air flow acetylene flow element line / nm flow / mA pressure / V width / nm / L ? min -1 /L ? min -1 zinc 213.9 3. 0 353. 2 0.4 6. 0 0. 6 copper 324. 8 3. 0 254. 4 0. 4 5. 5 0. 5 1.3 Test method 1.3.1 Pretreatment of samples Electroplated sewage samples, such as turbidity and precipitation, require pretreatment. After shaking the sewage sample, take 100ml into a 200ml beaker, add 5ml of nitric acid, and digest it on a hot plate at low temperature. After the precipitate is dissolved, the water sample is clear and transparent, then stop heating. After cooling, the volume is reduced to 100ml. Machine analysis. 1.3.2 Preparation of standard curve and determination of zinc and copper in the sample Open the instrument, install the zinc hollow cathode lamp, debug the instrument according to the working conditions of the instrument in Table 1. After preheating the zinc lamp for 20 minutes, determine the zinc standard curve and zinc in the sewage. The content, then the zinc lamp analysis line was adjusted to 324. 8nm, the copper standard curve and the copper content in the sewage were determined. 2 Results and discussion 2.1 Continuous determination of zinc and copper in electroplating wastewater by zinc hollow cathode lamp Test Zinc hollow cathode lamp was used for four parallel determinations of zinc and copper in electroplating wastewater with sample number SFR148 (see Table 2). The results showed that the relative standard deviation (RSD) of the assay was <2.52%. 2.2 Determination of the Accuracy of Zinc and Copper in Electroplating Sewage by Zinc Hollow Cathode Lamps. Zinc Hollow Cathode Lamps were used to test the recovery of zinc and copper in electroplating wastewater with sample No. SFR148 (the sample was diluted 5 times when zinc was determined) ( Table 3), the results show that the spiked recovery range is 95.6% ~ 104% Table 3 zinc lamp determination of zinc and copper in the electroplating wastewater test recovery rate of 4%. Determination of elemental background value / μg Sampling amount / μg spiked sample measured value / μg recovery rate /% 25.0 48. 2 97. 2 25. 0 47. 8 95. 6 zinc 23. 9 25. 0 49. 5 102 25 0 50. 0 104 50. 0 92. 8 104 50. 0 89. 2 96. 4 copper 41. 0 50. 0 91. 6 101 50. 0 90. 2 98. 4 2. 3 zinc and copper lamps The copper standard curve and the detection limit were respectively measured. The copper standard curve was determined by zinc lamp and copper lamp respectively. The blank solution of copper was measured 20 times in parallel, the absorbance was recorded, and the standard deviation S was calculated. The slope of the standard curve was divided by 3S. R. The detection limit is calculated. The results are shown in Table 4. The slopes of the standard curves are very close, the correlation coefficients are good, and the detection limits are less than the standard method of 0.05 mg/L. Table 4 Determination of copper standard curve and detection limit copper content of zinc lamp and copper lamp / μg 0. 00 0. 25 0. 50 1. 00 1. 50 2. 00 Standard curve correlation coefficient Y Detection limit P / mg ? L -1 Zinc lamp for measuring absorbance 0. 000 0. 044 0. 087 0. 175 0. 260 0. 355 y = 0. 176x-0.0008 0. 9998 0. 0122 copper lamp for measuring absorbance 0. 000 0. 046 0. 091 0. 178 0. 264 0. 363 y = 0. 179x-0.0002 0. 9997 0. 0048 2.4 Comparison of zinc and copper lamps for zinc plating and copper lamps, respectively. SFR163, SFR175, SFR188 The copper in the electroplating sewage of SFR202 was measured (Table 5), and the relative error of the two was <3.45%. Table 5 Comparison of results of zinc lamp and copper lamp in the determination of copper in electroplating wastewater. Sample No. Copper lamp Zinc lamp relative error /% SFR163 0. 58 0.56 3. 45SFR175 2. 62 2. 58 1. 53SFR188 8. 48 8. 22 3. 07SFR202 12. 5 12. 1 3. 203 Conclusion The zinc hollow cathode lamp was used as the light source. After the zinc in the electroplating wastewater was determined by flame atomic absorption spectrophotometry, the wavelength was adjusted to the resonance line of copper, and then the copper in the sewage was measured. The precision (RSD) of the zinc and copper was determined to be <2.52%, and the recoveries were between 95.6% and 104%. The copper standard series and its detection limit and the copper in the electroplating sewage were respectively determined by zinc lamp and copper lamp. It was found that the slopes of the standard curves of the two were very consistent, the correlation coefficients were good, and the detection limits were all smaller than the standard method. The requirement of 05mg/L, the relative error of the actual water sample measurement is <3.45%. Therefore, it is feasible to continuously measure zinc and copper in the electroplating sewage by using a zinc lamp, thereby avoiding frequent replacement of the hollow cathode lamp, saving time and labor, and improving work efficiency.