XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1289
REE-enriched strip was dried to produce the dry rare earth
concentrate evaluated in this program.
The chemical separation was qualified using a 0.5
kg/day production micropilot digestion system at PSI in
Andover, MA, shown in Figure 4. The micro-pilot diges-
tion system consists of 2 five-liter glass filter bottom reac-
tors for the REE leaching and filtration, and 2 five-liter
glass stirred tank reactors for REE enrichment through sol-
vent extraction.
Leaching was performed using a concentrated acid
solution and residence time was varied between 1 hour and
36 hours. Liquid-liquid extraction was performed using
an organic lixiviant diluted with a hydrocarbon blend.
Residence time in the extraction step was varied between
0.5 and 5 min. Organic to aqueous ratio was varied between
1:5 and 5:1 in order to achieve maximum REE extraction
yield and purity.
Because it was difficult to determine the exact gravi-
metric REE purity at each stage of the process, the team
developed a metric called “relative content” to track con-
centration increase. Relative content is defined by the total
concentration of REE at any stage of the process divided by
the total amount of metal. Both the numerator and denom-
inator were measured using an Agilent 5800 Inductively
Coupled Plasma with Optical Emission Spectroscopy (ICP-
OES). A method was developed quantifying 54 commonly
found metals in coal ash, including the rare earth elements:
Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb,
Lu. The team defined a purity metric of rare earth relative
content as the sum of the concentration of the rare earth
elements divided by the concentration of all 54 metal cat-
ions measured by ICP-OES. The mass balance and purity
measurements were used to assess elemental yields, purity
and selectivity at each processing step.
The project team designed, constructed and operated
a chemical processing pilot plant (0.5 tpd capacity) based
on the process development from the Phase I and micropi-
lot efforts. The chemical processing pilot is located at the
Winner Water Services (WWS) facility in Sharon, PA. The
chemical pilot plant contains all of the equipment neces-
sary to extract REE metals from coal ash and purify the
REEs to meet the target concentrations. The pilot plant
contained two liquid-liquid extraction (LLX) systems, a
bench top system (capacity of ~1 gal/hr), and a commercial
system (capacity ~50 gal/hr), denoted LLX1 and LLX2 in
Figure 5, respectively.
Post processing enrichment was performed using selec-
tive rare earth precipitation from aqueous solution as oxa-
lates. The rare earth oxalates were calcined at 800° C for 4
hours to produce a mixed rare earth oxide.
The ash cake materials resulting from the digestion step
were functionally qualified for use as a pozzolanic cement
Figure 4. Micropilot Plant (0.5 kg/day capacity)
REE-enriched strip was dried to produce the dry rare earth
concentrate evaluated in this program.
The chemical separation was qualified using a 0.5
kg/day production micropilot digestion system at PSI in
Andover, MA, shown in Figure 4. The micro-pilot diges-
tion system consists of 2 five-liter glass filter bottom reac-
tors for the REE leaching and filtration, and 2 five-liter
glass stirred tank reactors for REE enrichment through sol-
vent extraction.
Leaching was performed using a concentrated acid
solution and residence time was varied between 1 hour and
36 hours. Liquid-liquid extraction was performed using
an organic lixiviant diluted with a hydrocarbon blend.
Residence time in the extraction step was varied between
0.5 and 5 min. Organic to aqueous ratio was varied between
1:5 and 5:1 in order to achieve maximum REE extraction
yield and purity.
Because it was difficult to determine the exact gravi-
metric REE purity at each stage of the process, the team
developed a metric called “relative content” to track con-
centration increase. Relative content is defined by the total
concentration of REE at any stage of the process divided by
the total amount of metal. Both the numerator and denom-
inator were measured using an Agilent 5800 Inductively
Coupled Plasma with Optical Emission Spectroscopy (ICP-
OES). A method was developed quantifying 54 commonly
found metals in coal ash, including the rare earth elements:
Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb,
Lu. The team defined a purity metric of rare earth relative
content as the sum of the concentration of the rare earth
elements divided by the concentration of all 54 metal cat-
ions measured by ICP-OES. The mass balance and purity
measurements were used to assess elemental yields, purity
and selectivity at each processing step.
The project team designed, constructed and operated
a chemical processing pilot plant (0.5 tpd capacity) based
on the process development from the Phase I and micropi-
lot efforts. The chemical processing pilot is located at the
Winner Water Services (WWS) facility in Sharon, PA. The
chemical pilot plant contains all of the equipment neces-
sary to extract REE metals from coal ash and purify the
REEs to meet the target concentrations. The pilot plant
contained two liquid-liquid extraction (LLX) systems, a
bench top system (capacity of ~1 gal/hr), and a commercial
system (capacity ~50 gal/hr), denoted LLX1 and LLX2 in
Figure 5, respectively.
Post processing enrichment was performed using selec-
tive rare earth precipitation from aqueous solution as oxa-
lates. The rare earth oxalates were calcined at 800° C for 4
hours to produce a mixed rare earth oxide.
The ash cake materials resulting from the digestion step
were functionally qualified for use as a pozzolanic cement
Figure 4. Micropilot Plant (0.5 kg/day capacity)