Sfiso Mkhize Sfiso Mkhize

Abstract

Rare earth elements (REEs) are essential ingredients for the high-tech industry, especially in the manufacture of permanent magnets, laser and optical devices, and chemical catalysts. World production of REEs has been dominated by China over the past 2 decades where the largest reserves have been found; however, REE deposits exist all over the world, but have been under-exploited. Since around 2005, China has been enforcing export quotas for REE raw materials citing environmental concerns over their production by small-scale and illegal miners, although retaining the resources for its own hi-tech industries is also a significant factor [1,2]. Consequently, significant R&D efforts have commenced outside of China to re-develop REE mining and novel extractive technologies [3].

In-situ leaching is currently one of the promising technologies that is favourable in the production of REEs. To model in-situ leaching, agitated and diffusion tests were conducted using lixiviants of various concentrations. The lixiviants used in this study are artificial sea water (SW), 0,5M ammonium sulphate (AS) and artificial sea water (SW+AS) doped with 0,5M ammonium sulphate. The objectives of this study was to determine the diffusion coefficients of the REEs adsorbed in weathered crust elution-deposited rare earth ores. A 3g sample of this material used in this study has a total rare earth content of 7202 ppm REEs.

From the agitated tests, 26.27%, 46.22% and 54.25% total REEs were recovered from the ore using SW, SW+AS and AS, respectively in 15 minutes. Total REEs is the mean extraction from all the REEs excluding Ce, which showed poor extraction from the ion adsorbed phase.

From the diffusion tests, REEs recoveries followed a power law trend for all lixiviants. SW+AS recovered the most REEs in the first 4 days compared with the other lixiviants, reaching 72.03% total REEs. A degree of fractionation could be observed for different REEs. Various models would need to be derived to successfully exploit the fractionation of REEs for an in-situ leaching process.