1– The dissolution of rare earths as well as the
formation of gypsum or anhydrite depends on
both sulfuric acid concentration and leaching
temperature.
2– About 95.7% total rare earth were leached by
reacting 9 M sulfuric acid with yttrium fluorite at
100 °C for 2 h and a solids concentration of
200 g/L.
3– Solvent extraction was performed with 0.2 M
DEHPA/TBP to remove thorium and uranium
from the sulfate leach liquor of 3.0 M sulfate ion
concentration and pH 1.1.
4– The rare earths were precipitated from the raffinate
by oxalic acid after extracting the radioactive
impurities from the sulfate leach liquor. The recovery
of the rare earths as oxide was 89.9% with
96% purity.
5– Calcium fluoride was recovered from the evolved
hydrogen fluoride in water by reacting with calcium
carbonate in the pH range 1.0–4.0. It is
possible to obtain about 580 g CaF2 per kilogram
of El Missikat ore sample.