Application of pyrolysis to remove hydrogen from an organic nuclear waste.

The work deals with the removal by slow pyrolysis of epoxy resin from samples of spent nuclear fuel embedded in this polymer. Beyond the nuclear field, epoxy resin removal by pyrolysis is a typical issue for the recovery of metals in electronic waste. The main objective is to find the optimal conditions to remove hydrogen in the residual solid waste, in order to avoid hydrogen production by radiolysis during storage and so to prevent any risk of overpressure and explosion. The condensable pyrolysis products (tar-water mixture) and the char were characterised and quantified by elemental analyses, while the permanent gases were quantified by gas chromatography. A data reconciliation method was applied to adjust the values of raw measurements in order to complete the mass balances for both C, H, O and N elements and pyrolysis products. After studying the impact of temperature on the pyrolysis balance, experiments on a pilot furnace were conducted at 450 °C, in the frame of a parametric study of the heating rate, argon gas flow rate, resin mass and plateau time. At fixed temperature, we show that the plateau time is the only significant parameter for minimizing the residual hydrogen content in the char.

A multi-analytical methodology for the characterization of industrial samples of spent Ni-MH battery powders.

A multi-analytical methodology is implemented to characterize several sieving fractions of industrial samples of Black Mass (BM) powders originating from the thermo-mechanical treatment of cylindrical and prismatic-type spent nickel metal-hydride (Ni-MH) batteries. Elemental analyses of 17 elements (including C and O) indicate that the elemental composition of the powders (greater than93 %wt) does not depend on the battery type nor on the sieving fraction. XRD analyses evidence several phases (including Ni, NiO, CeO2 and C) but their quantification is not possible. Beyond these standard characterisations, magnetic susceptibility measurements demonstrate that the amount of metallic nickel versus nickel oxide increases with the sieving fraction, and that powders from prismatic-type batteries contain twice as much metallic nickel than cylindrical ones. Thanks to statistical analysis (based on clustering algorithms) of an electron probe µ-analysis (EPMA) compositional map, the complete methodology allows us to propose a full phase distribution for the BM particles. Three types of particles are identified and quantified. They originate from the partial oxidation of the battery components (anode active mass, anode current collector, cathode active mass and cathode current collector). The whole picture highlights the joint importance of battery ageing mechanisms, thermal deactivation and BM sieving steps on powder composition.

Leaching Mechanisms of Industrial Powders of Spent Nickel Metal Hydride Batteries in a Pilot-Scale Reactor.

In view of a sustainable recycling process, the leaching mechanisms of nickel and rare-earth elements (REEs) contained within industrial samples of spent nickel metal hydride battery powders were investigated in HCl and H2 SO4 , under mild temperature (25-60 °C) and pH (3-5.5). First, in-depth characterization of the heterogeneous battery powder was carried out with powder XRD, SEM, electron probe microanalyzer wavelength-dispersive spectroscopy (EPMA-WDS) quantitative analyses of individual particles, and inductively coupled plasma optical emission spectrometry (ICP-OES) elemental analysis. An unusual result is the identification of particles that exhibit a core-shell structure, which is related to anode active mass aging mechanisms. Then, a leaching study in a 10 L pilot-scale reactor demonstrated the selective dissolution of REEs, with respect to nickel, at pH 3, which is attributed to 1) the kinetic inhibition of nickel metal dissolution, and 2) the specific core-shell structure of aged mischmetal particles. Furthermore, the use of H2 SO4 led to coprecipitation of lanthanide-alkali double sulfates and nickel salts.

Insights on the Stability and Cationic Nonstoichiometry of CuFeO2 Delafossite.

CuFeO2, the structure prototype of the delafossite family, has received renewed interest in recent years. Thermodynamic modeling and several experimental Cu-Fe-O system investigations did not focus specifically on the possible nonstoichiometry of this compound, which is, nevertheless, a very important optimization factor for its physicochemical properties. In this work, through a complete set of analytical and thermostructural techniques from 50 to 1100 °C, a fine reinvestigation of some specific regions of the Cu-Fe-O phase diagram under air was carried out to clarify discrepancies concerning the delafossite CuFeO2 stability region as well as the eutectic composition and temperature for the reaction L = CuFeO2 + Cu2O. Differential thermal analysis and Tammann's triangle method were used to measure the liquidus temperature at 1050 ± 2 °C with a eutectic composition at Fe/(Cu + Fe) = 0.105 mol %. The quantification of all of the present phases during heating and cooling using Rietveld refinement of the high-temperature X-ray diffraction patterns coupled with thermogravimetric and differential thermal analyses revealed the mechanism of formation of delafossite CuFeO2 from stable CuO and spinel phases at 1022 ± 2 °C and its incongruent decomposition into liquid and spinel phases at 1070 ± 2 °C. For the first time, a cationic off-stoichiometry of cuprous ferrite CuFe1- yO2-δ was unambiguous, as evidenced by two independent sets of experiments: (1) Electron probe microanalysis evidenced homogeneous micronic CuFe1- yO2-δ areas with a maximum y value of 0.12 [i.e., Fe/(Cu + Fe) = 0.47] on Cu/Fe gradient generated by diffusion from a perfect spark plasma sintering pristine interface. Micro-Raman provided structural proof of the existence of the delafossite structure in these areas. (2) Standard Cu additions from the stoichiometric compound CuFeO2 coupled with high-temperature X-ray diffraction corroborated the possibility of obtaining a pure Cu-excess delafossite phase with y = 0.12. No evidence of an Fe-rich delafossite was found, and complementary analysis under a neutral atmosphere shows narrow lattice parameter variation with an increase of Cu in the delafossite structure. The consistent new data set is summarized in an updated experimental Cu-Fe-O phase diagram. These results provide an improved understanding of the stability region and possible nonstoichiometry value of the CuFe1- yO2-δ delafossite in the Cu-Fe-O phase diagram, enabling its optimization for specific applications.