XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1835
The leaching test results in Figure 4 indicated that when the
weight ratio of sludge to carbon increased to 4.0 in RR pro-
cess, the roasting product had the best leaching efficiencies
of 98.38% and 99.04% for REEs and P2O5, respectively.
Further increasing the weight ratio of sludge to carbon, as
shown in Figure 6, caused the agglomeration of sludge,
which led to sharp drops of leaching efficiency for both
REEs and P2O5. So, the optimal sludge to carbon ratio for
RR should be 4:1. The contents of REEs and other main
chemical components in leachate are listed in Table 5.
Generation of Mixed REE Oxide (MREO)
The demonstration study of the REE recovery using digly-
colamide (DGA) solvent extraction technology was accom-
plished using the 5 M HNO3 sludge leachate directly as
feed solution. The extraction solvent formulation consisted
of tetraoctyl diglycolamide (TODGA) extractant and
Exxal C8 solvent modifier in Exxol D80 diluent. Batch
Figure 4. Change of REEs and P2O5 leaching efficiencies with addition of carbon
Table 5. Contents of REEs and other chemical components in leachate
Component Sc Y La Ce Pr Nd Sm Eu Gd
Content (ppm) 0.00 191.09 152.02 196.66 23.03 91.81 25.41 6.85 41.14
Component Tb Dy Ho Er Tm Yb Lu Total REE
Content (ppm) 5.57 32.45 5.45 11.81 0.84 2.79 0.38 787.30
Component P
2 O
5 MgO Al
2 O
3 Fe
2 O
3 CaO
Content (%)4.51 0.41 0.79 0.05 5.02
experiments were performed to evaluate overall feasibility
of the proposed approach including extraction, scrub and
strip steps. The experimental design included extraction (1
stage), scrub (2 stages), and strip (3 stages). Among REE
of interest, over 70% Pr, 90% Nd, and nearly 100% of
other lanthanides and Y were extracted by TODGA in a
single contact. All other major metal constituents including
U and Th were rejected. The purpose of scrub is to purify
organic product by removing residual unwanted metals
co-extracted with the target REE. It was performed using
1–2 M HNO3. Two-stage scrub removed major fractions
of La and Ce as well as other co-extracted metals, thus
purifying the loaded organic solvent. Three stage stripping
using dilute HNO3 quantitatively recovered target, other
heavy REE and Y generating highly pure aqueous REE
concentrate.
The solvent extraction aqueous concentrate was treated
with oxalic acid to obtain an REE oxalate precipitate. The
The leaching test results in Figure 4 indicated that when the
weight ratio of sludge to carbon increased to 4.0 in RR pro-
cess, the roasting product had the best leaching efficiencies
of 98.38% and 99.04% for REEs and P2O5, respectively.
Further increasing the weight ratio of sludge to carbon, as
shown in Figure 6, caused the agglomeration of sludge,
which led to sharp drops of leaching efficiency for both
REEs and P2O5. So, the optimal sludge to carbon ratio for
RR should be 4:1. The contents of REEs and other main
chemical components in leachate are listed in Table 5.
Generation of Mixed REE Oxide (MREO)
The demonstration study of the REE recovery using digly-
colamide (DGA) solvent extraction technology was accom-
plished using the 5 M HNO3 sludge leachate directly as
feed solution. The extraction solvent formulation consisted
of tetraoctyl diglycolamide (TODGA) extractant and
Exxal C8 solvent modifier in Exxol D80 diluent. Batch
Figure 4. Change of REEs and P2O5 leaching efficiencies with addition of carbon
Table 5. Contents of REEs and other chemical components in leachate
Component Sc Y La Ce Pr Nd Sm Eu Gd
Content (ppm) 0.00 191.09 152.02 196.66 23.03 91.81 25.41 6.85 41.14
Component Tb Dy Ho Er Tm Yb Lu Total REE
Content (ppm) 5.57 32.45 5.45 11.81 0.84 2.79 0.38 787.30
Component P
2 O
5 MgO Al
2 O
3 Fe
2 O
3 CaO
Content (%)4.51 0.41 0.79 0.05 5.02
experiments were performed to evaluate overall feasibility
of the proposed approach including extraction, scrub and
strip steps. The experimental design included extraction (1
stage), scrub (2 stages), and strip (3 stages). Among REE
of interest, over 70% Pr, 90% Nd, and nearly 100% of
other lanthanides and Y were extracted by TODGA in a
single contact. All other major metal constituents including
U and Th were rejected. The purpose of scrub is to purify
organic product by removing residual unwanted metals
co-extracted with the target REE. It was performed using
1–2 M HNO3. Two-stage scrub removed major fractions
of La and Ce as well as other co-extracted metals, thus
purifying the loaded organic solvent. Three stage stripping
using dilute HNO3 quantitatively recovered target, other
heavy REE and Y generating highly pure aqueous REE
concentrate.
The solvent extraction aqueous concentrate was treated
with oxalic acid to obtain an REE oxalate precipitate. The