Zetium - Analysis of phosphates using the WROXI widerange oxides application

This data sheet demonstrates the performance of the Zetium - Minerals edition XRF spectrometer in providing accurate and precise phosphate analyses.

Phosphates occur as massive sediment-hosted phosphate rock, or as apatite minerals in igneous and metamorphic rocks. They are normally processed through phosphoric acid and super phosphoric acid intermediates to make ammonium phosphate fertilizers and elemental phosphorous. The presence of Fe2O3, Al2O3 and SiO2 need to be monitored because these affect the conversion of phosphates to super phosphoric acid

Zetium Minerals edition

Introduction

Phosphates occur as massive sediment-hosted phosphate rock, or as apatite minerals in igneous and metamorphic rocks. They are normally processed through phosphoric acid and super phosphoric acid intermediates to make ammonium phosphate fertilizers and elemental phosphorus. The presence of Fe2O3, Al2O3 and SiO2 needs to be monitored because these affect the conversion of phosphates to super phosphoric acid. This data sheet demonstrates the performance of the Zetium - Minerals edition XRF

spectrometer in providing accurate and precise phosphate analyses.

Instrumentation

The Minerals edition of the Zetium spectrometer is a fully integrated wavelength dispersive XRF spectrometer, complete with X-Y sample handler and state-of-the-art software. Engineered for excellence in terms of both analytical and operational performance, it has been configured specifically to meet the needs of users in the mining and minerals industries.

The Minerals edition of the Zetium spectrometer can be delivered with a set of 19 synthetic, multi-element wide- range oxides (WROXI) standards and an application template for the analysis of major and minor compounds in fused beads. Using PANalytical’s unique FP algorithm in our SuperQ analytical software, the WROXI application can determine concentrations of up to 21 common oxides in a wide range of rocks, ores and minerals. WROXI can be used either as a primary fused bead calibration or to verify customer in-house standards for pressed powder applications.

Figure 1. Comparison of certified and measured concentrations in phosphate samples 

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Sample and measurement details

Five certified reference materials (CRMs) from NIST, including SRM-120b, SRM-120c, SRM-694, BCR-32 and SARM-32, were prepared and analyzed as routine samples to test the accuracy of the WROXI calibrations.

The WROXI standards and CRMs used in this study were prepared using 0.9 g of sample fused in 9.0 g flux (66 % lithium tetraborate, 34 % lithium metaborate) and cast into 40 mm diameter fused beads.

The measurement program used to obtain the data presented had a total measurement time of nine minutes (Table 1). These times can, however, be adjusted according to the required precision.

Table 1. Total measurement time (peak + background) 

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Accuracy

The accuracy achieved with the Zetium spectrometer using WROXI standards and the SuperQ FP calibration model for major and minor element analyses in phosphate samples  is very good. This is illustrated in Figure  1  for  P2O5,  CaO  and SiO2 where measured values are compared with certified  values for all of the phosphate CRMs. A further comparison      of 12 oxides in a phosphate CRM (NIST SRM-694) is provided    in Table 2. Loss on ignition (LOI) is accurately determined as a balance compound by the SuperQ FP algorithm.

Table 2. A comparison of certified and measured concentrations for a phosphate rock CRM, NIST SRM-694

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Table 3. Reproducibility (10 measurements over 14 days) for phosphate rock (NIST SRM-120c) 

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Conclusion

Elemental analysis with XRF is already the key to the control of quality and production processes in the many industries analysing a wide range of oxide materials. The Minerals edition of the Zetium spectrometer with WROXI and the SuperQ FP approach further extends the advantages of XRF as the best analytical method for reliable phosphate analysis. It has been demonstrated that analyses are accurate and precise and the method benefits from a simple fusion sample preparation. Furthermore, the stability of the system is such that individual calibrations can be used for months. Time-consuming re-standardizations are unnecessary and the resultant data are highly consistent over time.

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