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Extraction and separation of rare earth elements from hydrothermal metalliferous sediments

Extraction and separation of rare earth elements from hydrothermal metalliferous sediments
Extraction and separation of rare earth elements from hydrothermal metalliferous sediments

Rare earth elements (REE) can be efficiently extracted from umbers, ferromanganese metalliferous sediments of the Troodos ophiolite (Cyprus) by simple leaching and selective precipitation, without accumulation of radioactive by-products. Umbers are dominantly composed of amorphous Fe and Mn oxides with minor goethite, quartz and zeolites, and contain 350–500 mg kg−1 of rare earth elements and yttrium (REY), 200 times lower than many of the major REY source ores. To compensate for relatively low grades, a cost-effective extraction process was developed that utilises a weak lixiviant concentration (0.1–1.5 N) and short reaction times (5 min to 11 h). Acid solutions recover 70–85% of the initial sample REY content even at 20 °C. By contrast, extraction using ionic solutions of NaCl and ammonium sulphate proved ineffective. Acid recoveries of REY increase by nearly 10% at 70 °C and the use of different acids (HCl, HNO3, H2SO4) yields comparable results. The main impurities in the leachate include Ca and Na at even the weakest acid concentration (0.1 N). However, two-step leaching method greatly reduces concentrations of impurities in the REY-rich liquor, although with REY losses approaching 20%. Purification of the leach liquor via selective precipitation of REY as an oxalate is highly efficient although pH dependent. With maximum REY precipitation (96–99%) occurring between pH 1 and 2, the precise adjustment of pH allows separation of REY from other precipitating impurities (Ca). The maximum purity of the precipitate is achieved at pH 1.1 (>65%). Strong and consistent fractionation along the lanthanide series observed during the precipitation experiments has been successfully explained using a speciation modelling software (PHREEQC). The uptake of REY by oxalate in the experiments closely follows the bell-shape distribution of REY-oxalate solid complexes stability constant (−log β (RE2Ox3·nH2O)) replicating the fractionation trends observed at pH < 1.1. In addition, the modelling demonstrates that at equivalent REE concentration in solution, oxalate precipitates fractionate REY in the following order: middle REE > light REE ≫ heavy REE. This ordering and the variable degrees of uptake reflects the interplay of aqueous REY-oxalate complexes (log HOxβ1, Oxβ1 and Oxβ2) with the natural fractionation induced by solid REY-oxalate stability constant distribution. Overall, the combined leaching process and selective oxalate precipitation produces a total enrichment factor ranging between 1400 and 2400 for REY from the sample to the oxalate precipitate in a simple two-step process forming a high-purity end-product of mixed REY.

Leaching, Metalliferous sediments, Oxalate, PHREEQC, Rare earth elements, Speciation modelling, Umbers
0892-6875
106-121
Josso, Pierre
7da4acf5-b481-49df-931e-160d4ed199e5
Roberts, Steve
f095c7ab-a37b-4064-8a41-ae4820832856
Teagle, Damon A.H.
396539c5-acbe-4dfa-bb9b-94af878fe286
Pourret, Olivier
a89fcd5f-086a-4c86-8bfc-c0ef6d629b06
Herrington, Richard
6466a9c1-3e23-40a4-a1e5-a5ce15f5a43d
Ponce de Leon Albarran, Carlos
508a312e-75ff-4bcb-9151-dacc424d755c
Josso, Pierre
7da4acf5-b481-49df-931e-160d4ed199e5
Roberts, Steve
f095c7ab-a37b-4064-8a41-ae4820832856
Teagle, Damon A.H.
396539c5-acbe-4dfa-bb9b-94af878fe286
Pourret, Olivier
a89fcd5f-086a-4c86-8bfc-c0ef6d629b06
Herrington, Richard
6466a9c1-3e23-40a4-a1e5-a5ce15f5a43d
Ponce de Leon Albarran, Carlos
508a312e-75ff-4bcb-9151-dacc424d755c

Josso, Pierre, Roberts, Steve, Teagle, Damon A.H., Pourret, Olivier, Herrington, Richard and Ponce de Leon Albarran, Carlos (2018) Extraction and separation of rare earth elements from hydrothermal metalliferous sediments Minerals Engineering, 118, pp. 106-121. (doi:10.1016/j.mineng.2017.12.014).

Record type: Article

Abstract

Rare earth elements (REE) can be efficiently extracted from umbers, ferromanganese metalliferous sediments of the Troodos ophiolite (Cyprus) by simple leaching and selective precipitation, without accumulation of radioactive by-products. Umbers are dominantly composed of amorphous Fe and Mn oxides with minor goethite, quartz and zeolites, and contain 350–500 mg kg−1 of rare earth elements and yttrium (REY), 200 times lower than many of the major REY source ores. To compensate for relatively low grades, a cost-effective extraction process was developed that utilises a weak lixiviant concentration (0.1–1.5 N) and short reaction times (5 min to 11 h). Acid solutions recover 70–85% of the initial sample REY content even at 20 °C. By contrast, extraction using ionic solutions of NaCl and ammonium sulphate proved ineffective. Acid recoveries of REY increase by nearly 10% at 70 °C and the use of different acids (HCl, HNO3, H2SO4) yields comparable results. The main impurities in the leachate include Ca and Na at even the weakest acid concentration (0.1 N). However, two-step leaching method greatly reduces concentrations of impurities in the REY-rich liquor, although with REY losses approaching 20%. Purification of the leach liquor via selective precipitation of REY as an oxalate is highly efficient although pH dependent. With maximum REY precipitation (96–99%) occurring between pH 1 and 2, the precise adjustment of pH allows separation of REY from other precipitating impurities (Ca). The maximum purity of the precipitate is achieved at pH 1.1 (>65%). Strong and consistent fractionation along the lanthanide series observed during the precipitation experiments has been successfully explained using a speciation modelling software (PHREEQC). The uptake of REY by oxalate in the experiments closely follows the bell-shape distribution of REY-oxalate solid complexes stability constant (−log β (RE2Ox3·nH2O)) replicating the fractionation trends observed at pH < 1.1. In addition, the modelling demonstrates that at equivalent REE concentration in solution, oxalate precipitates fractionate REY in the following order: middle REE > light REE ≫ heavy REE. This ordering and the variable degrees of uptake reflects the interplay of aqueous REY-oxalate complexes (log HOxβ1, Oxβ1 and Oxβ2) with the natural fractionation induced by solid REY-oxalate stability constant distribution. Overall, the combined leaching process and selective oxalate precipitation produces a total enrichment factor ranging between 1400 and 2400 for REY from the sample to the oxalate precipitate in a simple two-step process forming a high-purity end-product of mixed REY.

Text Josso_etal_Extraction_Separation_REY_Umbers_reviewed_figures - Accepted Manuscript
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Text Josso_etal_Extraction_Separation_REY_Umbers_reviewed + figures (AM)
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More information

Accepted/In Press date: 17 December 2017
e-pub ahead of print date: 16 January 2018
Published date: 15 March 2018
Keywords: Leaching, Metalliferous sediments, Oxalate, PHREEQC, Rare earth elements, Speciation modelling, Umbers

Identifiers

Local EPrints ID: 417464
URI: https://eprints.soton.ac.uk/id/eprint/417464
ISSN: 0892-6875
PURE UUID: a908e9cb-ff44-458e-a311-719ffe9a5766
ORCID for Steve Roberts: ORCID iD orcid.org/0000-0003-4755-6703
ORCID for Damon A.H. Teagle: ORCID iD orcid.org/0000-0002-4416-8409

Catalogue record

Date deposited: 31 Jan 2018 17:30
Last modified: 14 Feb 2018 17:31

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Contributors

Author: Pierre Josso
Author: Steve Roberts ORCID iD
Author: Olivier Pourret
Author: Richard Herrington

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