Derivative-atomic absorption method for determination of trace copper and chromium in fly ash

Abstract: A derivative-atomic absorption method for the determination of trace elements copper and chromium in fly ash using derivative technology and conventional flame atomic absorption method (FAAS) has been established
(D-FAAS). The sensitivity is improved by 15.9 times (cu) and 14.7 times (Cr) compared to conventional methods, and the detection limit is reduced by 4.3 times (Cu) and 3.2 times (Cr). This method was used to determine the fly ash standard samples and the five power plant ash samples, the relative standard deviations were 1.22 ~ 2.56 (Cu), 1.82 ~ 3.11 (Cr), and the recovery rate of the standard addition From 97.9 to 103.2 (Cu), 9.6% to 102.1% (Cr).

Keywords: derivative one atomic absorption; fly ash; trace elements; copper; chromium

Middle circle classification number: X132-1 Document identification code: B Article number: 1005-8249 (2005) 01—0048-02

In addition to the constant elements such as Si, A1 and Ca, fly ash also contains various trace and even trace harmful elements such as As, Cd, Cr, Cu and Pb. In the process of discharge storage and utilization, it is easy to enter the atmosphere, water and soil, causing serious negative effects on the environment and ecology. It is difficult to directly determine the content of trace or even trace elements in fly ash by conventional flame atomic absorption method (FAAS). In order to improve the sensitivity of the conventional flame method and expand its application range, FAAS is often used in conjunction with a variety of technologies. Sun Hanwen et al. Proposed a new technique of derivative atomic spectroscopy based on the rate of change of the measured signal strength over time. The author has successfully determined trace cadmium and lead in fly ash using derivative-atom trapping flame absorption method (I) IAT-FAAS), and its sensitivity has been improved by 2 to 3 orders of magnitude compared with conventional flame method. In this paper, the derivative-atomic atomic absorption method (I) IFAAS is used to determine the trace elements copper and chromium in fly ash, which provides a method for further studying the distribution of trace heavy metal elements in fly ash and its dissolution characteristics in the environment. Sensitivity and accurate measurement method.

1 Experiment:
The main instruments and reagents for the test are atomic absorption spectrophotometer; derivative measurement device; excellent grade pure nitric acid, hydrochloric acid, perchloric acid, hydrofluoric acid and GBW08401 standard fly ash. Weigh 0.2500g (± 0.000002g) of the fly ash sample into a polytetrafluoroethylene beaker, add 1ml HCl and 3ml HNO2, then add 1ml HClO3 and 10ml HF, and heat it to slightly dry on a hot plate at 120 ℃ ~ 150 ℃. Repeat the operation of the above added reagents once, then add 1ml of HC1O3 and steam until slightly dry. Add lmlHNO. And a small amount of deionized water, heated until the residue is dissolved, after cooling, transfer to a 100ml volumetric flask, dilute with deionized water to the mark and shake well. Do a blank test at the same time. Adjust the output signal of the atomic absorption to match the input of the derivative instrument, tap the output signal of the derivative instrument and another output signal of the original atomic absorption signal on the recorder, and record the changes of the atomic absorption and the combined signal simultaneously. Under the best conditions, the sensitivity and detection limit and linear range of conventional method and derivative-atom trapping were investigated simultaneously and step by step, and the standard fly ash sample GBW08401 was selected to verify the reliability of this method, and then respectively Ash samples from 5 power plants were measured.

2 Experimental results and discussion
2.1 Linearity and correlation of 1D-FAAS method: Take Cu standard solution (5 / g / m1) 0.00, 2.00, 4.00, 8.00, 10. OOml, Cr standard solution (5μg / m1) O0, 4. O0, 8. O0, 12. o0, 16.00, and 20.00ml, put them in 100ml volumetric flasks respectively, dilute with 1% nitric acid solution to the mark and shake well, measure the absorbance of the standard series, and draw the standard curve (see Figure 1, Figure 2). Regressing the data to get a linear equation in one yuan is shown in Table 2. The linear test, intercept and slope test show that the correlation coefficients of the two-element linear regression equation are ≥ 0.9990, the relative difference of the slope change is less than 10, and the intercept is not significantly different from zero, which fully meets the requirements of the standard curve.

2.2 Sensitivity, detection limit and precision: Through experiments, the sensitivity and detection limit of the conventional method and D-FAAS technology were investigated. The results are shown in Table 3. It can be seen from Table 3 that the sensitivity of the D-FAAS method for measuring Cu and Cr is improved by 15.9 times and 14.7 times compared with the conventional flame method; the detection limit is reduced by 4.3 times and 3.2 times compared with the conventional method; The relative standard deviations of 10 measurements were 1.5 (Cu) and 2.5 (Cr), respectively. It can be seen that this technique is used to determine trace elements Cu and Cr with satisfactory accuracy and precision.

2.3 Determination of fly ash samples: According to the working conditions in Table 1, the contents of Cu and Cr in the standard samples of fly ash GBW08401 were determined respectively, and the standard recovery experiment was performed. The results are shown in Table 4. It can be seen from the data in Table 4 that the measured value and the reference value have good consistency, and their precision and accuracy fully meet the technical requirements of the measurement, which is equivalent to the effect of the graphite furnace atomic absorption method, and the precision is better than the graphite furnace method. The D-FAAS technique is fully suitable for the determination of trace elements Cu and Cr in fly ash. Using this technology to measure the ash samples of the power plant, the results are shown in Table 4. The relative standard deviation and recovery rate of the 7 measurements were Cu: 1.22% to 2.56% and 97.9% to 103.2%, Cr: 1.82% to 3.1l% and 97.6% to 102.1%, satisfactory.

3. Conclusion HNO3-HCL-HCLO4-HF is used to digest the fly ash sample, and the use of derivative technology and flame atomic absorption method (D-FAAS) combined technology to determine trace Cu and Cr in fly ash has high accuracy And precision, so as to provide a more practical and convenient method for studying the distribution characteristics, dissolution characteristics and migration of trace heavy metals in coal ash.

1 Sun Hanwen · Atomic Absorption Analysis Technology [M] · Beijing Chongguo Science and Technology Press, 1992

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