Dissolution made easy using peroxide fusions for ICP-OES analyses for chromite ores, ferrochromes and chromium slags

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(Free-Press-Release.com) August 26, 2011 -- Authors: Janice Pitre, C.S. Claisse, Inc. ; Mélanie Bédard . C.S. Claisse Inc. ; Aaron Hineman, PerkinElmer, Inc.

Introduction

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Dissolution made easy using peroxide fusions for ICP-OES analyses for chromite ores, ferrochromes and chromium slags

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Although there are more than ten known chromium minerals, only one is a source of commercial importance. This mineral is known as chromite and has the theoretical composition FeCr2O4 . The main product generated by chromite is ferrochrome, a major player in the steel industry and most particularly, in the stainless steel industry. The mining and steel industries must assess the quality of the chromite ore to optimize the grade of their stainless steel production.

Metal analysis traditionally uses AA or ICP-OES to measure the metal contents in the ores and industrial products. However, the traditional dissolution method for chromite and ferrochrome is a multi-step, multi-acid digestion which requires the use of HNO3, HF and HClO4 and can take between 1 to 3 hours. Knowing the risks associated with the use of HF and HClO4, many laboratories look for alternative methods to obtain full dissolution of their samples while optimizing their uptime and productivity. As will be demonstrated, sodium peroxide fusions are a quick, safe and efficient alternative for the dissolution of these specific samples.

Experimental

Peroxide fusions can be performed either manually or with automated systems. Although both methods are efficient, the automated systems have the advantage of increasing productivity, improving safety, maintaining repeatable preparation conditions, avoiding spattering as well as cross-contamination. In this project, fusions were performed using a Claisse Peroxide Fluxer. The Claisse Peroxide Fluxer is a 6 position gas Fluxer specifically designed to do multiple and repetitive peroxide fusions with excellent repeatability and reproducibility. Different samples and reference materials were used to validate the developed method

In a zirconium crucible, the samples were mixed with Sodium Carbonate and Sodium peroxide (Na2O2) and placed on the Claisse Peroxide Fluxer for 3.5 minutes, then cooled by the Fluxer fans for 4 minutes.
The content of the cooled zirconium crucible was then dissolved with a mix of HNO3 and HCl acids, diluted and brought to the ICP-OES for analysis. The measurements were performed using the PerkinElmer Optima 7300 DV ICP-OES instrument.

Results and Discussion

The following criteria were taken into consideration in selecting the wavelength: (a) the freedom from spectral interferences; (b) the different sensitivities and expected concentration in the samples. Observed interferences were compensated for by modifying the processing parameters (e.g. adjusting the background correction points, applying multi-component spectral fittings (MSF) or inter-elemental corrections (IEC)).

Method detection limits (MDLs) were based on ten replicate measurements of a series of low concentration or diluted sample solutions. The MDL was calculated by multiplying the standard deviation of the ten replicate measurements by 3 and the correction factor. The accuracy and precision of the method was evaluated. The accuracy was determined by calculating the elemental recovery of certified reference materials (CRMs). The precision was determined by preparing and measuring 10 replicates of the various CRMs. The accuracy and precision obtained demonstrates that the developed method performs very well. Pre-fusion spikes were performed on samples and CRMs to monitor the recovery of the elements and further validate the method.

Conclusion

Peroxide fusions combined with the simultaneous ICP-OES have the analytical capabilities to perform the analysis of chromite ore, ferrochrome and chromium slag samples with good accuracy, precision and speed of analysis. The analytical method developed is robust and fulfills the requirements normally set for the analysis of high matrix samples such as fusion samples. The sodium peroxide fusion approach to dissolution of chromite ore, ferrochrome and chromium slag samples is an excellent alternative to other harsh, incomplete and time-consuming acid digestions.

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chromite ores     claisse     ferrochromes     fusion xrf     PerkinElmer     peroxide fluxer     sample preparation by fusion