XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1279
Investigations [Grosz et al., 1995 Jasinski, 2017] indicated
that phosphate rock usually contains, on average, 0.046
wt% of REEs, and about 250 million tons of phosphorite
are mined annually around the world. So, each year more
than 110,000 tons of REEs enter the phosphate industry,
and all of them are lost in the processing streams, In Florida
alone, annual REE loss includes about 5,800 tons in phos-
phatic clay, 3,400 tons in phosphogypsum, 1100 tons in
phosphoric acid sludge, 780 tons in flotation tails, and 620
tons in phosphate fertilizer. If the REEs in phosphate pro-
cessing can be recovered, the total amount could meet the
U.S. demand, with Y more than meeting the entire world
demand.
In central Florida there are many large sedimentary
phosphate rock deposits, which have been developed and
utilized for about 150 years. In the beneficiation plant,
phosphate ore is washed and classified first to remove the
micro-fine clay (–150 mesh) and get 3 fractions in different
size range: pebble (+16 mesh), coarse flotation feed (–16+35
mesh) and fine flotation feed (–35+150 mesh). The coarse
and fine flotation feeds go through a “Crago” double flota-
tion process (a direct flotation using fatty acid as collector to
concentrate phosphates, and then an inverse flotation using
amine to remove silica from the rougher phosphate con-
centrate) to concentrate phosphates [Zhang, Yu and Bogan
1997]. The phosphate concentrate is then transferred to
acid plant, where it is digested by sulfuric acid (dihydrate
wet-process) to produce phosphoric acid for fertilizer pro-
duction. During the beneficiation and wet-process, huge
amounts of wastes are produced, including phosphatic clay,
flotation tails (fatty acid flotation tails, and amine flotation
tails) and phosphogypsum [Liang et al., 2017].
Several researches have demonstrated the existence
of REEs in Florida phosphate resources [Zhang, 2014
Claude and Henry, 1954 Giesekke, 1985 Zhang, 2012].
As early as 1989 a comprehensive investigation was carried
out by Kremer and Chokshi [1989] of Mobile Research &
Development Corporation. The results indicated that the
phosphate ore (matrix) analyzed 282 ppm REEs. After ben-
eficiation and chemical processing the REEs are distributed
in various streams, with 40% in phosphatic clay, 37.5%
in phosphogypsum, 12.5% in phosphoric acid and 10%
in flotation tails. Reports by Zhang [2014] and Poul et al
[2015] showed that the total amount of REEs in Florida
phosphate ore annually mined mount to about 30,000 tons,
greatly exceeding the current demand of America. More
importantly, comparing with conventional REE resources
such as bastnaesite ore, REE in Florida phosphates contain
higher proportions of heavy REEs, which are scarcer but
more critical for high-tech development and green energy
industries. Therefore, recovering REEs from Florida phos-
phate resources could play a significant role in building a
resilient REE supply chain for the U.S.
As a founding member of the Critical Material
Institute (CMI) Hub funded by the U.S. Department of
Energy (DOE), FIPR Institute has been conducting a series
of research on recovering REEs from Florida phosphate
resources. This paper presents a processing scheme for
recovering both REEs and phosphate values from a amine
flotation tails in Florida, including gravitation separation
to pre-concentrate REE-containing minerals, flotation of
the gravity separation concentrate to further upgrade REEs
and phosphate, and concentrated sulfuric acid pyrolysis
– water leaching to recover REE and phosphate from the
final concentrate.
METHODOLOGY
Mineral Beneficiation
Investigation indicated that REEs in the flotation tails
existed mainly as monazite and xenotime, associated with
some heavy minerals, and most of the phosphorus was
hosted in francolite associated with gangue minerals in
coarse particles [Zhang et al., 2023 Hassan and Bogan,
1994]. Since the contents of REEs and P2O5 (usually
used to denote the phosphorus in minerals) in the tails
were very low, it was very important to select a low-cost
and highly efficient beneficiation method to discard most
of the gangue minerals. Gravity separation using a shaking
table was selected to accomplish pre-concentration of REE-
containing minerals as well as phosphate for the following
reasons: 1) the specific gravities of monazite, xenotime and
phosphate rock are 4.6 ~5.7, 4.4 ~5.1 and 3.16 ~3.22,
respectively, all of which are higher than that (2.65) of
quartz, which is the main gangue mineral in the tails 2)
the particle size range is suitable for gravity separation and
3) shaking table is one of the least methods for gravity sepa-
ration. So, a shaking table was used first to remove a large
amount of gangue from the tails, then the shaking table
concentrate was ground and upgraded through flotation.
REEs and Phosphorus Leaching
A process of concentrated sulfuric acid pyrolysis – water
leaching (CSAP – WL) was applied to recover REEs and
phosphorus from the final concentrate. The concentrate
was mixed with concentrated sulfuric acid first, then the
mixture was roasted at 350°C for 4 hours. After cooling
down, water was added into the mixture and stirred for
2 hours to leach REEs and phosphorus. During roasting,
REE minerals and phosphates (mainly fluorapatite) reacted
with sulfuric acid as follows:
Investigations [Grosz et al., 1995 Jasinski, 2017] indicated
that phosphate rock usually contains, on average, 0.046
wt% of REEs, and about 250 million tons of phosphorite
are mined annually around the world. So, each year more
than 110,000 tons of REEs enter the phosphate industry,
and all of them are lost in the processing streams, In Florida
alone, annual REE loss includes about 5,800 tons in phos-
phatic clay, 3,400 tons in phosphogypsum, 1100 tons in
phosphoric acid sludge, 780 tons in flotation tails, and 620
tons in phosphate fertilizer. If the REEs in phosphate pro-
cessing can be recovered, the total amount could meet the
U.S. demand, with Y more than meeting the entire world
demand.
In central Florida there are many large sedimentary
phosphate rock deposits, which have been developed and
utilized for about 150 years. In the beneficiation plant,
phosphate ore is washed and classified first to remove the
micro-fine clay (–150 mesh) and get 3 fractions in different
size range: pebble (+16 mesh), coarse flotation feed (–16+35
mesh) and fine flotation feed (–35+150 mesh). The coarse
and fine flotation feeds go through a “Crago” double flota-
tion process (a direct flotation using fatty acid as collector to
concentrate phosphates, and then an inverse flotation using
amine to remove silica from the rougher phosphate con-
centrate) to concentrate phosphates [Zhang, Yu and Bogan
1997]. The phosphate concentrate is then transferred to
acid plant, where it is digested by sulfuric acid (dihydrate
wet-process) to produce phosphoric acid for fertilizer pro-
duction. During the beneficiation and wet-process, huge
amounts of wastes are produced, including phosphatic clay,
flotation tails (fatty acid flotation tails, and amine flotation
tails) and phosphogypsum [Liang et al., 2017].
Several researches have demonstrated the existence
of REEs in Florida phosphate resources [Zhang, 2014
Claude and Henry, 1954 Giesekke, 1985 Zhang, 2012].
As early as 1989 a comprehensive investigation was carried
out by Kremer and Chokshi [1989] of Mobile Research &
Development Corporation. The results indicated that the
phosphate ore (matrix) analyzed 282 ppm REEs. After ben-
eficiation and chemical processing the REEs are distributed
in various streams, with 40% in phosphatic clay, 37.5%
in phosphogypsum, 12.5% in phosphoric acid and 10%
in flotation tails. Reports by Zhang [2014] and Poul et al
[2015] showed that the total amount of REEs in Florida
phosphate ore annually mined mount to about 30,000 tons,
greatly exceeding the current demand of America. More
importantly, comparing with conventional REE resources
such as bastnaesite ore, REE in Florida phosphates contain
higher proportions of heavy REEs, which are scarcer but
more critical for high-tech development and green energy
industries. Therefore, recovering REEs from Florida phos-
phate resources could play a significant role in building a
resilient REE supply chain for the U.S.
As a founding member of the Critical Material
Institute (CMI) Hub funded by the U.S. Department of
Energy (DOE), FIPR Institute has been conducting a series
of research on recovering REEs from Florida phosphate
resources. This paper presents a processing scheme for
recovering both REEs and phosphate values from a amine
flotation tails in Florida, including gravitation separation
to pre-concentrate REE-containing minerals, flotation of
the gravity separation concentrate to further upgrade REEs
and phosphate, and concentrated sulfuric acid pyrolysis
– water leaching to recover REE and phosphate from the
final concentrate.
METHODOLOGY
Mineral Beneficiation
Investigation indicated that REEs in the flotation tails
existed mainly as monazite and xenotime, associated with
some heavy minerals, and most of the phosphorus was
hosted in francolite associated with gangue minerals in
coarse particles [Zhang et al., 2023 Hassan and Bogan,
1994]. Since the contents of REEs and P2O5 (usually
used to denote the phosphorus in minerals) in the tails
were very low, it was very important to select a low-cost
and highly efficient beneficiation method to discard most
of the gangue minerals. Gravity separation using a shaking
table was selected to accomplish pre-concentration of REE-
containing minerals as well as phosphate for the following
reasons: 1) the specific gravities of monazite, xenotime and
phosphate rock are 4.6 ~5.7, 4.4 ~5.1 and 3.16 ~3.22,
respectively, all of which are higher than that (2.65) of
quartz, which is the main gangue mineral in the tails 2)
the particle size range is suitable for gravity separation and
3) shaking table is one of the least methods for gravity sepa-
ration. So, a shaking table was used first to remove a large
amount of gangue from the tails, then the shaking table
concentrate was ground and upgraded through flotation.
REEs and Phosphorus Leaching
A process of concentrated sulfuric acid pyrolysis – water
leaching (CSAP – WL) was applied to recover REEs and
phosphorus from the final concentrate. The concentrate
was mixed with concentrated sulfuric acid first, then the
mixture was roasted at 350°C for 4 hours. After cooling
down, water was added into the mixture and stirred for
2 hours to leach REEs and phosphorus. During roasting,
REE minerals and phosphates (mainly fluorapatite) reacted
with sulfuric acid as follows: