CHARACTERIZATION OF RESIDUAL MINERAL CONTENT IN BAUXITE PILES, SALINE COUNTY, ARKANSAS: AN XRF AND XRD ANALYSIS APPROACH

The Saline Mining District, located southwest of Little Rock, Arkansas, produced more alumina than any other bauxite mining districts in the United States during the late 19^th to mid- 20^th century. This area contains extensive deposits of bauxite ore and nepheline syenite previously mined by Aluminum Company of America using open pit and subsurface mining techniques. With the depletion of high-grade ore in the district, renewed interest in the mineral content of bauxite stockpiles has been the focus of several studies searching for critical minerals. Previous X-ray Fluorescence studies have identified critical elements in significant concentrations, including uranium, thorium, gallium, molybdenum and lanthanides.

This study incorporates five bauxite stockpiles (SP1, Clay, SP2, SP3, SP4) with varying alumina content situated on approximately 10 acres of land within an area of the former mine recognized as Section 20. This research was conducted, and X-ray Diffraction techniques to analyze the mineralogy of the elements of interest. Twenty-five samples were collected from each stockpile (n=125) to analyze and characterize elements of interest using X-ray Fluorescence to determine the elemental composition of the residual material. Five samples from each stockpile (n=25) were analyzed using X-ray Diffraction techniques to characterize the mineralogy of these elements of interest and determine the feasibility of extraction for commercial use.

Several samples had elements (Si, Ca, Rb, Sr, Zr, Nb, and Mo) that were determined to be enriched using XRF with respect to background concentrations in the Earth’s upper continental crust, including some which are on the 2022 List of Critical Minerals. The Clay stockpile exhibited the most diverse group of elements, including unique mineralogy associated with the cation-exchange capacity of the clay minerals. Other elements of interest are bound in the complex oxides and hydroxides associated with in-situ and detrital bauxite deposits. While current markets may not support the time and resource investment involved in mineral extraction, these stockpiles could be a potential source of critical minerals if the separation technology and mineral economics can be reconciled.