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Comparison of Two Processing Flowsheets for Production of
REEs Using Phosphoric Acid Sludge as a Feedstock
Haijun Liang, Patrick Zhang, and Aaron Medley
FIPR Institute, Florida Polytechnic University
Tatiana G. Levitskaia and Klemmer Nicodemus, Pacific Northwest National Laboratory
Gyoung Jang and Costas Tsouris, Oak Ridge National Laboratory
ABSTRACT: Under funding of U.S. Department of Energy (DOE) through the Critical Materials Innovation
(CMI) Hub and cooperative agreement DE-FE0032123, the Florida Industrial and Phosphate Research
(FIPR) Institute, Florida Polytechnic University developed two processing flowsheets for production of mixed
rare earth oxide/salt (MREO/MRES), or individual rare earth metals (REMs). Technological breakthroughs
were achieved in collaboration with Oak Ridge National Laboratory (ORNL), Pacific Northwest National
Laboratory (PNNL), the Mosaic Company, and Florida International University. The two processing flowsheets
include a hydrometallurgical approach and a thermal route. In both processes, phosphoric acid sludge was first
subject to some pretreatment steps including Solid-liquid (S-L) separation using a decanter centrifuge, washing
and filtration of the underflow product from the decenter using a filter press or a vacuum filter to obtain the
sludge solids. In the hydro process, the washed sludge solids were leached using 5 M nitric acid at about 75°C.
REE in the leachate was extracted using M N,N,N’,N’-tetraoctyl diglycolamide (TODGA), and REE in the
concentrate from solvent extraction was either processed into MREO through oxalic acid precipitation and
calcination or treated using different separation techniques to produce REE salts or metals. The thermal process
involved roasting of the pre-treated sludge to recover the phosphate value as elemental phosphorus (P) and to
render REE in the residue readily leachable. REE leaching recovery of over 97% was achievable with nitric
acid. This paper presents the major operating conditions, metallurgical performances, and preliminary TEA
information of the two processing flowsheets.
INTRODUCTION
Recently research on the recovery of REEs from uncon-
ventional resources has attracted more and more attention,
and phosphate rock is considered to be the most promising
unconventional REE resource [Zhang 2014 Zhang et al.,
2017 Pan, Fleet and Macrae, 1993 Schoneveld, Spandler
and Hussey, 2015]. It is estimated that each year in mined
phosphate rock there are more than 100,000 tons of REEs
around the world, and this amount meets the demand of
all the world [Kanazawa and Kamitani, 2016 Grosz et
al., 1995 Poul et al., 2015]. Yet, all of the REEs are still
being wasted in the phosphate processing streams includ-
ing phosphatic clay, flotation tails, phosphogypsum, phos-
phoric acid sludge and phosphate fertilizer. Investigations
indicated that in Florida the amount of REEs entering the
phosphate industry reached 30,000 tons, which exceeds
twice the demand of the USA, and moreover, the REE in
phosphate contains high proportions of heavy REEs, which
are scarcer and more critical for high-tech development,
than those in conventional resources [Giesekke, 1985
Comparison of Two Processing Flowsheets for Production of
REEs Using Phosphoric Acid Sludge as a Feedstock
Haijun Liang, Patrick Zhang, and Aaron Medley
FIPR Institute, Florida Polytechnic University
Tatiana G. Levitskaia and Klemmer Nicodemus, Pacific Northwest National Laboratory
Gyoung Jang and Costas Tsouris, Oak Ridge National Laboratory
ABSTRACT: Under funding of U.S. Department of Energy (DOE) through the Critical Materials Innovation
(CMI) Hub and cooperative agreement DE-FE0032123, the Florida Industrial and Phosphate Research
(FIPR) Institute, Florida Polytechnic University developed two processing flowsheets for production of mixed
rare earth oxide/salt (MREO/MRES), or individual rare earth metals (REMs). Technological breakthroughs
were achieved in collaboration with Oak Ridge National Laboratory (ORNL), Pacific Northwest National
Laboratory (PNNL), the Mosaic Company, and Florida International University. The two processing flowsheets
include a hydrometallurgical approach and a thermal route. In both processes, phosphoric acid sludge was first
subject to some pretreatment steps including Solid-liquid (S-L) separation using a decanter centrifuge, washing
and filtration of the underflow product from the decenter using a filter press or a vacuum filter to obtain the
sludge solids. In the hydro process, the washed sludge solids were leached using 5 M nitric acid at about 75°C.
REE in the leachate was extracted using M N,N,N’,N’-tetraoctyl diglycolamide (TODGA), and REE in the
concentrate from solvent extraction was either processed into MREO through oxalic acid precipitation and
calcination or treated using different separation techniques to produce REE salts or metals. The thermal process
involved roasting of the pre-treated sludge to recover the phosphate value as elemental phosphorus (P) and to
render REE in the residue readily leachable. REE leaching recovery of over 97% was achievable with nitric
acid. This paper presents the major operating conditions, metallurgical performances, and preliminary TEA
information of the two processing flowsheets.
INTRODUCTION
Recently research on the recovery of REEs from uncon-
ventional resources has attracted more and more attention,
and phosphate rock is considered to be the most promising
unconventional REE resource [Zhang 2014 Zhang et al.,
2017 Pan, Fleet and Macrae, 1993 Schoneveld, Spandler
and Hussey, 2015]. It is estimated that each year in mined
phosphate rock there are more than 100,000 tons of REEs
around the world, and this amount meets the demand of
all the world [Kanazawa and Kamitani, 2016 Grosz et
al., 1995 Poul et al., 2015]. Yet, all of the REEs are still
being wasted in the phosphate processing streams includ-
ing phosphatic clay, flotation tails, phosphogypsum, phos-
phoric acid sludge and phosphate fertilizer. Investigations
indicated that in Florida the amount of REEs entering the
phosphate industry reached 30,000 tons, which exceeds
twice the demand of the USA, and moreover, the REE in
phosphate contains high proportions of heavy REEs, which
are scarcer and more critical for high-tech development,
than those in conventional resources [Giesekke, 1985