H2SO4, HCl, HNO3
|
20-80% REE extraction. Possibility to modify the recovery ratio of REE
and Fe depending on acid concentration and leaching steps. By-products
production (Orbite Patent, and HNO3 Pilot NTUA). |
Low
REE’s recovery. Large amounts of effluents and acid wastes. As acid
concentration increases, selectivity decreases. Special equipment for
corrosion resistance is needed in case of HCl. Silica gel formation at
low acid concentrations. |
H2SO3
|
Digestion in 2-3 stages of
selective dissolution of REE, up to 85% Y recovery (Patent Alcan). |
No
data available for the Sc extraction. |
Carboxylic acids such as formic, citric, acetic, methanesulfonic acid,
etc. |
Selective REE’s leaching (similar to mineral acids), Ca and Al
versus Fe. Bio-leaching (Rusal Patent). |
Difficulty in recycling
organic acids by distillation, producing large amounts of calcium
sulphate. In some cases, low REE extraction. More expensive solvents
than inorganic acids. |
CO2, NaΗCO3
|
Selective metals recovery such as Sc, Ti and Zr producing carbonate
complexes in the caustic solution. Large intake of CO2
in pulp (Rusal pilot plant for production of 2 tons per year
Sc2O3).
|
Low Sc recovery (<26%)
No REE recovery.
|
Ionic Liquid (HBET-TF2N) |
High selectivity of REE against Fe Si and Ti;
Similar to mineral acid recoveries; low acid consumption (regeneration
of IL), and purification and up concentration of REE solution. |
High
cost of IL (non commercial commodity-synthesized on demand), IL losses
in aqueous phases. |