Inter-position repeatability study on TheOx® Advanced instrument using bauxite type samples followed by XRF analysis

Bauxite is one of the world’s sources of aluminum. Exploration, mine planning, processing and quality control require a constant monitoring of aluminum content and concentrations of other elements like silicon, iron and titanium, which are important to define the grade and value of the bauxite ore. This application note was made to evaluate the performance and rapidity of bauxite sample preparation by borate fusion followed by XRF analysis for the determination of major and minor elements.

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Introduction

Bauxite is one of the world’s sources of aluminum. Exploration, mine planning, processing and quality control require a constant monitoring of aluminum content and concentrations of other elements like silicon, iron and titanium, which are important to define the grade and value of the bauxite ore. This application note was made to evaluate the performance and rapidity of bauxite sample preparation by borate fusion followed by XRF analysis for the determination of major and minor elements.

A Claisse® TheOx® Advanced fusion instrument was used to prepare the glass disks. The instrument uses electric resistance heating and has six fusion positions enabling a throughput of 24 to 30 fusions per hour. It delivers fast fusion temperature ramp up for shorter fusion cycles and an increased sample throughput.

 XRF measurements were performed using a PANalytical Zetium sequential wavelength dispersive X-ray fluorescence spectrometer configured with a 2.4 kW Rh-anode Super Sharp Tube (SST R-mAX50).

Challenges

  • Rapid and accurate sample preparation and sample analysis to control exploration, mining and processing of the mineral.
  • High reproducibility and inter-position repeatability for sturdy and stable sample preparation.

Benefits

  • Easy and fast
  • Inter-position repeatability and stability
  • High throughput
  • Precise results

Global Sample Preparation Method

All samples were prepared using a 1:10 dilution ratio with a LiT/LiM 50/50 flux, pure grade (99.98+%) without non-wetting agents. The entire cold-to-cold process took 24 minutes.

To avoid any loss of material which could lead to unprecise results, the flux was weighed directly in the 95% Pt - 5% Au crucible in which was weighed the sample. A fully automatic TheOx Advanced instrument was used to fuse the sample.

Results

The stability of TheOx Advanced instrument has been verified by producing ten fused disks replicates on the same fusion position. This repeatability test was done using the certified reference material (CRM) NIST 698 (Table 1).

To study the inter-position repeatability of TheOx® Advanced fusion instrument during the borate fusion process, repeatability tests were done using CRM NIST 698. Two fused disks replicates were produced on each fusion position (for a total of twelve replicates).

The relative standard deviation (RDS) and average concentrations were then calculated and compared to the expected value of the CRM NIST 698 (Table 2).

Table 1: Results of the sample preparation repeatability test for CRM NIST 698 where 10 fused disk replicates were produced on the same fusion position
NIST 698Certified value (wt%)Average value (wt%)RSD (wt%)
Na2O (%)0.0150.0170.001
MgO (%)0.0580.0520.001
Al2O3 (%)48.248.300.03
SiO2 (%)0.690.6800.007
P2O5 (%)0.370.3800.001
SO3 (%)0.1430.1450.002
K2O (%)0.010.01000.0009
CaO (%)0.620.5700.003
TiO2 (%)2.382.3200.005
V2O5 (%)0.0640.0680.001
Cr2O3 (%)0.080.08000.0006
MnO (%)0.3830.38400.0008
Fe2O3 (%)19.619.600.02
ZnO (%)0.02919.600.0003
ZrO2 (%)0.0610.06600.0005
Table 2: Results of the sample preparation repeatability test for CRM NIST 698 where two fused disk replicates were produced on each fusion position – for a total of 12 replicates
NIST698Certified value (wt%)Average value (wt%)RSD (wt%)
Na2O (%)0.0150.0170.001
MgO (%)0.0580.0510.001
Al2O3 (%)48.248.310.02
SiO2 (%)0.690.6750.008
P2O5 (%)0.370.3830.002
SO3 (%)0.1430.1440.002
K2O (%)0.010.0110.001
CaO (%)0.620.5670.003
TiO2 (%)2.382.3210.006
V2O5 (%)0.0640.0660.002
Cr2O3 (%)0.080.0790.001
MnO (%)0.3830.3850.001
Fe2O3 (%)19.619.600.01
ZnO (%)0.0290.02800.0003
ZrO2 (%)0.0610.06600.0008

Conclusion

Considering that the standard deviation value includes not only sample preparation errors but also instrumental measurement errors, it can be demonstrated that TheOx Advanced instruments produces highly reproducible disks all along the six positions.

Therefore, elemental analysis with TheOx Advanced fusion instrument combined with a Zetium Minerals edition XRF spectrometer is the key to control mining, processing and quality of bauxite ores. The productivity and repeatability of TheOx Advanced instrument make fusion and the consequent benefits of an accurate XRF analysis easily achievable.

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