Thesis defence_Thomas MONOT

Abstract: Agromining is an environmentally friendly mining technique involving the growth ofhyperaccumulator plants on metal rich soils. Biomass is then harvested and treated bypyrometallurgical or hydrometallurgical processes to extract valuable metals. French Guyanahas an important mining potential, but also environmental specificities making agromining aviable way to valorize its resources. Two metals in particular have been identified as goodagromining candidates: gold and aluminium. In the first part of this work, the valorization ofaluminum from a plant endemic to French Guiana is studied. The hyperaccumulator Qualearosea was first characterized to quantify aluminum in the biomass, and its combustion wasstudied to estimate the energy produced. An acid process was then developed to extractaluminum from its ash and eliminate the main impurity, calcium. An aluminum salt was finallyproduced by precipitation of aluminum sulfate. The second part of this work studies thepotential development of gold agromining in French Guiana. The AGOR project aimed atfinding gold hyperaccumulators from this territory by analyzing plants in-situ and in museumand herbarium archives by field portable X ray fluorescence (FPXRF). Several plant specimensharvested on gold bearing soils in French Guiana were identified as hyperaccumulators by thismean, however FPXRF can be inaccurate and these results need to be verified by anotheranalysis technique. The ability of the FPXRF spectrometer NITON xl3t GOLDD to detect andquantify gold in biological matrixes has therefore been assessed by analyzing gold syntheticstandards ranging from 10 to 1000 mg/kg, and comparing the results to inductively coupledplasma atomic emission spectroscopy (ICP – AES) analysis. FPXRF performed well at goldconcentrations above 50 mg/kg, but an interference between gold and zinc was identified,leading to the detection of gold in synthetic standards rich in zinc. The analysis of thespecimens from French Guiana revealed that the same interference was responsible for thedetection of gold, therefore none of the plants harvested were gold hyperaccumulators.

The members of jury consist of:

Laurent CASSAYRE                Senior scientist, CNRS                                     ReviewerFabienne ESPITALIER             Professor, IMT Mines Albi                               ReviewerHervé MUHR                         Senior scientist, CNRS                                     ExaminerLenka SVECOVA                    Senior lecturer, INP Grenoble                          ExaminerBaptiste LAUBIE                    Senior lecturer, Université de Lorraine             SupervisorMarie-Odile SIMONNOT        Professor, Université de Lorraine                    Co-supervisorYann GUNZBURGER               Professor, Université de Lorraine                    InvitedClaire HAZOTTE                    Doctor, Econick                                              Invited