Mineralogical Studies in Assisting Beneficiation of Rare Earth Element Minerals from Carbonatite Deposits

Abstract

Rare earth elements (REE) are either housed in exotic REE minerals, which sporadically populate the host rock or they occur as ionic substitutions in the crystal structure of existing rock forming minerals. The genesis of REEs in carbonatite rocks can result in intricate mineralogical textures and the importance of mineralogy in disclosing these various associations is discussed. REE minerals in carbonatite rocks can occur in complex association with minerals such as calcite, strontianite, barite, apatite, and fluorite. Knowledge of gangue mineral size and association with REE minerals plays a critical role in the physical up-grading process, as this process is often based on firstly achieving the best possible liberation of required minerals, and secondly exploiting these minerals’ physical differences, to concentrate the REE minerals. A REE mineral concentrate where the total rare earth oxides (TREO) exceed 40% should be achieved in the physical up-grading process, and much of the time this is attempted by removing the gangue minerals for hydrometallurgical extraction of REEs. Numerous carbonatite deposits have been recorded as containing very high TREO values and REE mineralization is in the form of fluorocarbon minerals such as bastnasite, parisite, and synchisite or in the phosphate form of monazite and xenotime On the African continent these deposits occur prominently along the East African rift valley (Woolley & Kjarsgaard 2008). To date, few of these deposits have been taken through to production status, which may be an indication of the complexity of REE bearing carbonatite ores. The preliminary mineralogical study recommended in this study can provide answers for the metallurgist, at a relatively low cost. The instruments used are X-Ray diffraction (XRD), optical microscopy, and a conventional scanning electron microscope (SEM) with Energy dispersive spectroscopy (EDS). The designing of a suitable metallurgical extraction process is usually a multi-phase program, which should utilize information gleaned from the mineralogy. Some exploration programs today involve sophisticated techniques of mapping and modeling the resource but in many cases little or no budget is approved for a mineralogical study. In the case of REE deposits, it is critical to undertake upfront mineralogy to answer questions pertaining to the mode of occurrence of REE minerals, and to give insight into their texture and association with the various non economic minerals. The information gleaned will provide guidance to metallurgists in the upgrading scoping testwork, and in addition it will provide early predictions of potential REE mineral recoveries from the ore.