Determination of Silver and Volatile Elements in Metal Concentrates Samples Using Lithium Borate Fusion Followed by XRF Analysis

In the metal industry, some samples can be challenging to analyse. An inappropriate sample preparation method can lead to inconsistent analytical results and even render the samples impossible to analyse. For example, concentrates that contain partly reduced materials can cause problems when using lithium borate fusion. If this type of sample is not correctly oxidized during the sample preparation process, it can chemically alloy and attack the platinumware. Also, if the fusion method is not optimal, it can lead to the loss of volatile elements that are crucial to accurately determine the sample type and its characterizations.

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Introduction

In the metal industry, some samples can be challenging to analyse. An inappropriate sample preparation method can lead to inconsistent analytical results and even render the samples impossible to analyse. For example, concentrates that contain partly reduced materials can cause problems when using lithium borate fusion. If this type of sample is not correctly oxidized during the sample preparation process, it can chemically alloy and attack the platinumware. Also, if the fusion method is not optimal, it can lead to the loss of volatile elements that are crucial to accurately determine the sample type and its characterizations.

Challenges
• A partially oxidized sample can attack and damage the platinumware used in the sample preparation, thus increasing costs.
• Obtain a high reproducibility and inter-position repeatability for stable sample preparation.

Benefits
• Easy and fast sample preparation for tricky samples
• Avoid the loss of volatile elements in fusion
• Avoid chemical attacks on your platinumware
• Precise results.

Apparatus and Instrumental Conditions

An automatic Claisse TheOx Advanced fusion instrument was used to create 40 mm lithium borate glass disks. Its resistance-based electric system, excellent insulation properties and preset fusion programs allow a uniform heating, thus providing repeatable and reproducible fusion conditions as well as a perfect retention of volatile elements.

A PANalytical 4 kW MagiX PRO sequential WDXRF and a 37 mm collimator mask were used to analyse glass disks.

Global Sample Preparation Method

The concentrate samples were prepared using a 1:20 dilution ratio in a LiT/LiBr 99.5/0.5 flux, pure grade (99.98+%).

This flux was weighed in the same Pt/Au crucible in which was weighed the sample. A fully automatic TheOx Advanced instrument was used to fuse the sample.

A single fusion method was developed for all the different sample matrices. The fusion method used requires an additive to make sure the sulfur is retained and fully oxidized. The whole cold-to-cold fusion process took less than 24 minutes, including the oxidation step.

Once the sample was oxidized and diluted in the melted borate flux, it was automatically poured into a 40 mm diameter Pt/Au shallow mold.

Results

Six replicates were prepared. This application allows the analysis of many elements, but the table below shows the results obtained for five elements of interest. The chart shows the calibration range (in %) and the relative standard deviation (RSD) obtained on the replicates.

Table 1: Composition Ranges and Precision (in %)
Compound                               Range (%)RSD (%)
Ag2O                                           0-1.51.0
ZnO                                            15-250.5
PbO                                            15-250.6
CuO                                            15-250.6
SO3                                             25-451.2

Conclusion

The results presented in the previous table indicate that sample preparation by borate fusion followed by XRF analysis is an effective method to analyse concentrates for majors, silver and volatile elements.

The method showed good precision of sensitive elements such as silver, and an excellent retention of volatile elements such as sulfur, thus proving the quality of the method. This demonstrates that the use of TheOx Advanced fusion instrument leads to reproducible and efficient results despite the fact that the samples contained volatile and partially oxidized elements.

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