Beneficiation and hydrometallurgical treatment of Norra Kärr eudialyte mineral

Abstract

Due to the demand for rare earth elements for everyday technology and applications, there has been much research initiated into the extraction and recovery of rare earth elements. An otherwise unknown mineral, eudialyte, is a zirconium silicate consisting of rare earth oxides, specifically the heavy rare earth oxide yttrium (III), with only trace amounts of thorium and uranium. The focus of this research project was to investigate and develop a beneficiation and leaching procedure for processing the Norra Kärr eudialyte ore. The development of the type of beneficiation and leaching experiments conducted was aided by a review of different physical separation methods and the treatment of iron and silica in other industries. After mineral characterization, a two-stage beneficiation process was developed, consisting of gravity and magnetic separation. The gravity separation portion comprised of preliminary heavy liquid separation tests done using both sodium polytungstate and methylene iodide at different size fractions. Different size fractions were studied for liberation purposes. This gravity separation step was implemented for the removal of the heavy iron-bearing mineral aegirine. This float product is then processed in a wet high-intensity magnetic separation (WHIMS) at 1 Tesla to separate the paramagnetic eudialyte from the non-magnetic gangue minerals. The implementation of this process resulted in limited success for a clear separation of eudialyte from its gangue. The overall results yielded no significant upgrade of eudialyte using the beneficiation process proposed. However, the proposed process did show that iron could be rejected through either gravity or magnetic separation, a definite benefit for further hydrometallurgical treatment. After the conclusion of the beneficiation tests, hydrometallurgical testing was done. The samples used in these leaching experiments were non-magnetic concentrates, where most of the iron was rejected via WHIMS. Two separate leaching processes were investigated to eliminate or minimize the formation of silica gel within the solution, while still recovering the total rare earth elements (TREEs). The first leaching process treated the concentrate in a 0.1 M solution of sulfuric acid at 25, 50 and 75°C at two and four-hour intervals. This leaching process resulted in gelation of the leach liquor as well as filtrate solution, but recovered the TREEs and Zr. The second leaching process limited the amount of water and acid available to the concentrate by only adding enough concentrated sulfuric acid to completely wet the sample. The acid-wet samples were then left for 30 minutes, one hour (then oven dried) or air dried before leached with DI water. While no gelation was observed during or after this leaching process, little to no rare earth elements and zirconium were recovered. It has become evident through these beneficiation and leaching experiments, that a generalized method, applicable in many other mineral processing industries for commonly known minerals, may not be the best method for processing eudialyte. In all, the mineralogy of eudialyte should be more heavily investigated so an appropriate mechanism can be applied. However, it is worth noting that due to the complex chemical composition of eudialyte, a specialization is required within the eudialyte mineral group.