Bauxite: The Difficult Source of Aluminum Ore

Bauxite is an important mineral in the mining industry.  Globally, bauxite is the primary source of aluminum (Al) ore and a major industry in many countries including China, Australia, and Brazil. As such, grading Al concentration is of paramount interest in the mining process as is the need to determine concentrations of penalty elements. The desired goal is to conduct all the analysis in a way that maximizes productivity.

The United States Geological Survey defines bauxite as a “naturally occurring, heterogeneous material composed primarily of one or more aluminum hydroxide minerals, plus various mixtures of silica, iron oxide, titania, aluminosilicate, and other impurities in minor or trace amounts.  The principal aluminum hydroxide minerals found in varying proportions with bauxites are gibbsite and the polymorphs boehmite and diaspore.”

Bauxites are typically classified according to their intended commercial application:  abrasive, cement, chemical, metallurgical, refractory, etc. Determining the amount of those ‘impurities’ becomes just as important as the mineral itself. However, analysis of Al, silicon (Si), and iron (Fe) presents unique challenges. Accurate analysis of all three is critical for either ore grading or understanding their influence on the processing and production of the primary metal of interest. Previously, it was not possible to measure light elements such as Al and Si in the field without helium (He) or vacuum systems. This often meant costly time delays and reduced productivity while waiting for laboratory results.

Using  geometrically optimized large area drift detector technology makes bauxite analysis more accurate and efficient.  Recently, fourteen certified reference materials (CRM) and in-house standards were packed into standard XRF sample cups fitted with polypropylene film and measured for 120 seconds (on the light filter for Al and Si) and 30 seconds (on the main filter for Fe).

Take a look at this bauxite application note to see the correlation curves for Al, Si, and Fe, with certified results vs. the handheld XRF results. The coefficient of determination (R2) for each element is provided in the figures. The R2 value is a measure of how closely the data sets correlate with each other, where a perfect correlation would have an R2 of 1. The correlation coefficients and repeatability data for the key elements in bauxite analysis demonstrate the excellent accuracy and precision of the handheld XRF analyzer that utilized a geometrically optimized large area drift detector.

Are there any other elements that you are having trouble analyzing?  Comment below and let us know.