Analysis of Trace Hazardous Elements and Halogens in Cement

With more and more use of alternate raw materials and fuels, it is becoming essential to monitor the trace elements in the final product and also in the finished goods produced using cement. X-Ray analysis is one such full proof method to analyse and detect the trace elements.

The role of the cement industry for effective utilization of waste materials and by-products has been growing. Slag from steel plant and coal fly ash from thermal power plant are typical by-products. Waste tyers, plastics and sludge are common waste materials. In addition, waste materials such as incinerated ashes of household waste and sewage sludge are also utilized. These waste materials and by-products are added as a part of raw material for cement production.

The rate of using the materials for cement production has increased over the years for environmental protection and effective utilization of resources.

Addition of waste materials and by-products can increase the contents of hazardous heavy elements in cement product and, therefore, can cause pollution of the hazardous heavy elements eluted from concrete. Accordingly, control of hazardous elements is essential for cement plant operation.

On the other hand, chlorine creates problem in kilns and also causes corrosion of rebar (reinforcing steel) in concrete while fluorine affects hydration reaction. These trace halogens are other important elements to be analyzed.

X-ray fluorescence spectrometry is widely used for chemical composition analysis of major components such as CaO, SiO2, Al2O3 and Fe2O3 of raw materials, raw meal, clinker and cement in each production process for process control owing to a rapid and precise analytical method. In recent cement production, the demand for analyzing trace hazardous heavy elements and halogens has increased for environmental protection and effective utilization of resources. Since the number of trace elements to be analyzed is increasing, high power wavelength dispersive XRF spectrometers, which have good sensitivity and spectral resolution for both heavy and light elements down to fluorine, are suitable for such applications.

The analysis of trace heavy elements in cement using unique correction methods was evaluated and accurate results were obtained.

Analysis examples of trace heavy elements and halogens in cement using a high-power wavelength-dispersive XRF spectrometer are presented.

Analysis results
In order to demonstrate that the ZSX PrimusIII+ meets the requirement of ASTM C114-11, a qualification test in ASTM C114-11 was carried out using NIST CRM?s of cement. The test results are shown in Table 1, which proves that the spectrometer meets the requirement. Refer to Table 1

For chlorine and heavy trace elements in cement, calibration curves were generated with cement reference materials. The calibration results are summarized in Table 2 and representative calibration curves are shown in Figure 1.

For Cl, Cr, and Ba, alpha correction (?alpha? in Table 2), where correction coefficients for absorption and enhancement by co-existing element are calculated theoretically by the fundamental parameter method, was applied.

For Co, Cu, Zn, As, Sr, Zr, Mo, and Pb, scatter ratio correction (?scatter ratio? in Table 2), where a scatter line, Rh-Ka Compton or background, is used as internal standard line, was applied. This correction also minimizes analysis error caused by variation in grain size or mineral composition for powder samples.

For V and Ni, the combination of the scatter ratio and alpha corrections (?scatter ratio + alpha? in Table 2) was applied. In this unique correction method, when theoretical alphas are calculated by the fundamental parameter method, scatter lines are also considered in the calculation to obtain theoretical alphas for calibration with scatter ratio method applied. Additionally, for V, Ni, As, and Zr, spectral overlap correction was applied.

Conclusion
The qualification test for ASTM C114-11 was demonstrated by the pressed powder method using a high-power sequential WD-XRF spectrometer. Using this spectrometer, calibration curves were generated with inter-element correction methods for trace elements in cement, including chlorine and hazardous elements of Cr, As, and Cd. Then, good accuracy was obtained for each element.

The analysis results show that trace elements in cement can be analyzed with high accuracy on high-power sequential WD-XRF spectrometers.

*In the columns of ?Result?, only the maximum values among the analysis results of the seven NIST CRMs are listed.
**The maximum difference for Cl is 0.005 mass%, which exceeds the limit 0.003 mass% while the differences of all the other CRMs are less than 0.003 mass%. The value 0.005 mass% is less than the double of the limit, 0.006 mass%.
***No value is given.
*Correction: each method is explained below
The accuracy of calibration is calculated by the following formula,
Importance of analysing halogens and hazardous elements in cement
Use of waste materials and by-products has increased substantially in cement production
Control of hazardous heavy elements and chlorides in finished cement and then in concrete is essential
Presence of halogens creates problem in manufacturing process as well as in concrete which promotes corrosion of re-bars
Demand for analysing hazardous heavy elements and halogens is warranted for environment protection
Presence of Co, Cu, Zn, Sr, Zr, Mo, V, Ni, Cr, As, Cd and halogens can be detected accurately by RigakuZSX Primus III + or equivalent XRF machine
The standard in reference is ASTM C114-II

Article by Hisashi Inoue, Yasujiro Yamada & Yoshiyuki Kataoka of Rigaku Corporation, Osaka, Japan In India Rigaku is represented through I R Technology Services Pvt.Ltd, Navi Mumbai.

Contact: N L Deshpande- Chief General Manager

Table 1. Qualification test result

Table 2. Calibration summary of trace elements in cement