Youssef Lamwati’s thesis: «A physiological and metabolomic study of Phytolacca americana’s response to rare earth elements and an investigation into its potential for phytoextraction from bauxite residues»

Mr Youssef Lamwati PhD student at the IMBE (POPCO team – Populations, Landscapes, Communities & Conservation), will defend his PhD thesis in public on Thursday 18 June 2026, at 10.00 am in the CEREGE lecture theatre at ARBOIS.

For those who won’t be able to make it on the day, don’t miss out and Watch the thesis defence online!

In front of a jury made up of :

• Claudia Cosio (University of Reims Champagne-Ardenne) – Rapporteur
• Ali BOULARBAH (Cadi Ayyad University, Marrakesh) – Rapporteur
• Imane WAHBY (Mohammed V University, Rabat) – Rapporteur
• Philippe BINET (University of Franche-Comté) – Examiner
• Abdallah OUKARROUM (Mohammed VI Polytechnic University) –
• Stéven CRIQUET (IMBE, AMU) – PhD supervisor
• Mouna FAHR (Mohammed V University, Rabat) – PhD supervisor
• Blanche COLLIN (CEREGE, AMU) – PhD supervisor

Summary of work:

Rare earth elements are metals that are essential to the functioning of modern technologies, particularly those linked to the energy transition, such as wind turbines, batteries and electric vehicles. However, their extraction currently poses serious problems: it is highly polluting and heavily reliant on just a few countries, which creates major economic and geopolitical challenges.

In view of these limitations, This thesis explores a more sustainable alternative: using plants to extract these metals from industrial waste, in particular bauxite residues from aluminium production. These residues contain rare earth elements, but in very stable and poorly soluble chemical forms, which makes them difficult to recover. The research has focused on a specific plant, Phytolacca americana, known for its ability to accumulate large quantities of metals. The aim was to understand whether this plant could be used to extract rare-earth elements and, above all, to unravelling the mechanisms that enable it to absorb and tolerate them. The results show that this plant reacts differently depending on the amount of metal present: at low concentrations, its growth is stimulated, but at high concentrations, the metals become toxic. A key element also emerges: phosphorus. Its presence or absence strongly influences the plant’s ability to absorb rare earth elements. By studying bauxite residues, the thesis demonstrates that the main obstacle to the extraction of rare earth elements is not the plant itself, but the chemical form of the metals in the soil. Some residues contain forms that are very poorly soluble, which prevents the plant from utilising them, whilst others are more readily available. Further experiments revealed an important mechanism. The plant is capable of locally modifying its environment at the root level to dissolve these highly stable mineral forms. It then converts the metals into organic forms that are easier to store in its tissues. Finally, a detailed analysis of the plant’s metabolism has identified specific molecules, notably glutamic acid derivatives, which play a central role in capturing and neutralising metals. These molecules could inspire new, cleaner extraction methods based on natural processes. This thesis shows that the direct extraction of rare earth elements by plants remains limited by the chemical constraints of the environment. However, understanding the biological mechanisms opens up concrete prospects for developing innovative extraction technologies, inspired by living organisms, which are more environmentally friendly and compatible with a circular economy.