XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1265
REE+Y from coal byproducts, which include the passivated
IACs and unweathered primary REMs, e.g., monazite and
xenotime, shown in Figure 7.
Bryan et al. (2015) wrote that kaolinite in coal entraps
REEs by ionic bonding and that REE contents of alumi-
num-rich portions of coal deposits are 5–10 times larger
than the whole coal deposit, which suggests that most of the
rare earths in U.S. coal byproducts exist in the form of pas-
sivated IACs. It is possible, nevertheless, that a significant
portion of them may also exist as REMs. It would, there-
fore, be necessary to find ways of extracting REEs from both
the IACs and REMs, which is a challenge. First, IACs may
be passivated as discussed above. Second, REMs are small
in particle size, typically 5 mm, as shown in Figure 7, and
are also low in number densities. As has already been noted,
flotation has the lower particle size limit of ~20 mm (Wills
and Finch, 2016).
The authors further developed, therefore, the two-liq-
uid flotation (TLF) process, which has no lower particle size
limit. Lai and Fuerstenau (1968) developed the liquid-liq-
uid extraction process to recover 0.1 mm alumina (Al2O3)
dispersed in aqueous media using iso-octane. Shergold
and his colleagues (1976, 1981) suggested using the TLF
process, in which various organic solvents are used, for the
Figure 6. Results of leaching an Upper Freeport coal middlings sample during the
activation (first) and IEX leaching (second) steps
Figure 7. a) Monazite in a coal floatation tails, Ky b) xenotime in a low-temperature ash
in clean coal
REE+Y from coal byproducts, which include the passivated
IACs and unweathered primary REMs, e.g., monazite and
xenotime, shown in Figure 7.
Bryan et al. (2015) wrote that kaolinite in coal entraps
REEs by ionic bonding and that REE contents of alumi-
num-rich portions of coal deposits are 5–10 times larger
than the whole coal deposit, which suggests that most of the
rare earths in U.S. coal byproducts exist in the form of pas-
sivated IACs. It is possible, nevertheless, that a significant
portion of them may also exist as REMs. It would, there-
fore, be necessary to find ways of extracting REEs from both
the IACs and REMs, which is a challenge. First, IACs may
be passivated as discussed above. Second, REMs are small
in particle size, typically 5 mm, as shown in Figure 7, and
are also low in number densities. As has already been noted,
flotation has the lower particle size limit of ~20 mm (Wills
and Finch, 2016).
The authors further developed, therefore, the two-liq-
uid flotation (TLF) process, which has no lower particle size
limit. Lai and Fuerstenau (1968) developed the liquid-liq-
uid extraction process to recover 0.1 mm alumina (Al2O3)
dispersed in aqueous media using iso-octane. Shergold
and his colleagues (1976, 1981) suggested using the TLF
process, in which various organic solvents are used, for the
Figure 6. Results of leaching an Upper Freeport coal middlings sample during the
activation (first) and IEX leaching (second) steps
Figure 7. a) Monazite in a coal floatation tails, Ky b) xenotime in a low-temperature ash
in clean coal