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8 - Chromite/PGE Assay Package

Since other elements are required for the metallurgical use of chromite, chromite assays usually are combined with major oxide analysis. For example, Cr/Fe ratios are very important in assigning value to chromite as well as other deleterious elements.

 

8-Chromite XRF

Samples are dried at 105 °C prior to LOI or fusion as laterites can easily absorb water from air. To minimize the matrix effects of the samples, the heavy absorber fusion technique of Norrish and Hutton (1969, Geochim. Cosmochim. Acta, volume 33, pp. 431-453) is used for major element (oxide) analysis. Prior to fusion, the loss on ignition (LOI), which includes H2O+, CO2, S and other volatiles, is determined from the weight loss after roasting the sample at 1050°C for 2 hours. The fusion disk is made by mixing a 0.5 g equivalent of the roasted sample with 6.5 g of a combination of lithium metaborate and lithium tetraborate with lithium bromide as a releasing agent. Samples are fused in Pt crucibles using an automated crucible fluxer and automatically poured into Pt molds for casting. Samples are analyzed on a Panalytical Axios Advanced wavelength dispersive XRF.

 

The intensities are then measured and the concentrations are calculated against the Ausmon standard which adjusts the calibration. Control standards are run to verify the procedure. Matrix corrections are done by using the oxide alpha - influence coefficients provided also by Norrish and Hutton (1969). In general, the limit of detection is about 0.01 wt% for most of the elements.

 

Code 8-Chromite Oxides and Detection Limits (%)

Oxide

Detection

   Limit (%)

Al2O3

0.01

CaO

0.01

Co3O4

0.01

Cr2O3

0.01

CuO

0.01

Fe2O3

0.01

K2O

0.01

MgO

0.01

MnO

0.01

Na2O

0.01

NiO

0.01

P2O5

0.01

SiO2

0.01

TiO2

0.01

V2O5

0.01

LOI

0.01

 


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Code 1C-OES



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