Leaching of rare Earth elements from an Illinois basin coal source

The existence of rare earth elements (REEs) in coal sources at elevated concentrations has been the focus of several studies over the past decade. However, limited research has been conducted on methods to recover and refine the REEs. This paper reports the results of a detailed study into the potential of selectively recovering REEs in an Illinois basin coal source by leaching. Leaching characteristics are obtained for several segments obtained from a core sample as well as three different reject materials collected at a coal processing plant. Using a 1.2 mol/L sulfuric acid solution at 75 °C, over 60% REE recovery is achieved from the direct floor and an inner parting material as well as the coal-rich core segments that are pretreated by low-temperature plasma oxidation to obtain access to the micro-dispersed mineral matter. In the leachable parting material, fluorapatite is detected by XRD analysis, which is one of the more soluble phosphate minerals with a documented association with REEs. For the three plant reject samples, the leaching recovery values obtained for the heavy REEs are higher than those obtained for the light REEs under the standard leaching conditions and when 0.1 mol/L (NH ₄ ) ₂ SO ₄ was used to extract REEs by an ion exchange mechanism. Thermal activation by roasting or chemical activation by pretreatment using 8 mol/L NaOH solution increases the total REE recovery with significantly higher gains obtained for the light REEs. Leaching kinetics are relatively fast within the first 2 h and then slow to provide relatively low overall recovery values under the standard test conditions for the coarse and fine reject samples. However, significantly higher recovery values are realized when treating mixed-phase (middling) particles existing within the coarse reject material.