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Review

Phosphogypsum as the Secondary Source of Rare Earth Elements

by
Faizan Khalil
1,*,
Francesca Pagnanelli
2 and
Emanuela Moscardini
3
1
Department of Chemical Engineering, La Sapienza University of Rome, Via Eudossiana 18, 00184 Rome, Italy
2
Department of Chemistry, La Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Roma, Italy
3
Eco-Recycling, Viale Palmiro Togliatti 1639, 00155 Roma, Italy
*
Author to whom correspondence should be addressed.
Sustainability 2025, 17(19), 8828; https://doi.org/10.3390/su17198828
Submission received: 26 August 2025 / Revised: 19 September 2025 / Accepted: 22 September 2025 / Published: 2 October 2025
(This article belongs to the Section Waste and Recycling)

Abstract

Phosphogypsum (PG) is a byproduct of the wet phosphoric acid (WPA) production process. Since PG originates from phosphate rock (PR), it holds various concentrations of heavy metal and radionuclide, posing an environmental threat because of its large production and long-term accumulation. In addition to toxic heavy metals, PG may also be an alternative source of rare earth elements (REEs), since over 60% of REEs in PR transfer to PG during acid digestion. With the increasing demand of phosphoric acid (PA), global PG generation is approaching 300 million tons annually. Since 1994, an estimated 6.73 billion tons of PG has been produced worldwide, with approximately 58% (approx. 3.7 billion tons) ending up in stacks. Assuming a conservative REE content of 0.1%, these stacks may hold over 3.7 million tons of REEs. This review discusses phosphoric acid production processes and the transfer of REEs from PR to PG. In addition, it also discusses the current REEs world reserves, their presence in primary and secondary sources, and their uses. The review critically evaluates the research that has been conducted so far and the recent innovations in REE recovery from PG, and discusses the challenges associated with scalability and raw material variability.
Keywords: rare earth elements; phosphogypsum; phosphate rock; REE’s recovery; scale up challenges; REEs occurrence in phosphogypsum; wet phosphoric acid process; secondary resources; industrial waste valorization; hydrometallurgy; resin in leach rare earth elements; phosphogypsum; phosphate rock; REE’s recovery; scale up challenges; REEs occurrence in phosphogypsum; wet phosphoric acid process; secondary resources; industrial waste valorization; hydrometallurgy; resin in leach

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MDPI and ACS Style

Khalil, F.; Pagnanelli, F.; Moscardini, E. Phosphogypsum as the Secondary Source of Rare Earth Elements. Sustainability 2025, 17, 8828. https://doi.org/10.3390/su17198828

AMA Style

Khalil F, Pagnanelli F, Moscardini E. Phosphogypsum as the Secondary Source of Rare Earth Elements. Sustainability. 2025; 17(19):8828. https://doi.org/10.3390/su17198828

Chicago/Turabian Style

Khalil, Faizan, Francesca Pagnanelli, and Emanuela Moscardini. 2025. "Phosphogypsum as the Secondary Source of Rare Earth Elements" Sustainability 17, no. 19: 8828. https://doi.org/10.3390/su17198828

APA Style

Khalil, F., Pagnanelli, F., & Moscardini, E. (2025). Phosphogypsum as the Secondary Source of Rare Earth Elements. Sustainability, 17(19), 8828. https://doi.org/10.3390/su17198828

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