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Selective leaching of rare earth elements (REEs) from eudialyte concentrate after sulfation and thermal decomposition of non-REE sulfates

Balinski, A.; Atanasova, P.; Wiche, O.; Kelly, N.; Reuter, M.; Scharf, C.


Eudialyte, a sodium rich zirconosilicate, is one of the promising sources for REEs, particularly for HREEs+Y. The key challenge by hydrometallurgical processing is the prevention of silica gel formation and REE separation from resulting multi-element leach solutions. This study deals with the selective leaching of REEs from eudialyte concentrate after sulfation and thermal decomposition of non-REE sulfates. We demonstrate how to select the parameters in each process stage to achieve high yields of REEs and to separate them from Zr⁴⁺(+Hf⁴⁺), Nb⁵⁺, Al³⁺ and Fe³⁺. The best result in terms of the separation and the REE yield was achieved with the following parameters: acid addition: 15 mmol/g; roasting temperature: 750 °C; roasting time: 2 h; pulp density: 25 kg/m³; leaching temperature: 20 °C; leaching time: 24 h; stirring speed: 300 rpm. For sufficient conversion of REEs into sulfates H₂SO₄ was added in excess, approximately twice as high as the acid consumption. Water leaching at high solid/liquid ratios caused decrease in the separation factor and REE losses resulting from formation of double sulfates and gypsum.

Keywords: eudialyte concentrate; rare earth elements; separation; sulfation; selective roasting; thermal stability of sulfates; leaching; silica stability during leaching


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