Abstract: New compounds which meet general formula (I): where: m=0, 1 or 2; R1 and R2=a C6 to C12, straight-chain or branched, hydrocarbon group; R3=H, a C1 to C12, straight-chain or branched, hydrocarbon group, optionally comprising one or more heteroatoms; a C3 to C8 monocyclic hydrocarbon group, optionally comprising one or more heteroatoms, or a monocyclic (hetero)aryl group; or else R2 and R3 together form a —(CH2)n— group where n=1 to 4; R4=a C2 to C8, straight-chain or branched, hydrocarbon group, or a monocyclic aromatic group; R5=H, or a C1 to C12, straight-chain or branched, hydrocarbon group.

Abstract: New compounds which meet general formula (I): where: m=0, 1 or 2; R1 and R2=a C6 to C12, straight-chain or branched, hydrocarbon group; R3=H, a C1 to C12, straight-chain or branched, hydrocarbon group, optionally comprising one or more heteroatoms; a C3 to C8 monocyclic hydrocarbon group, optionally comprising one or more heteroatoms, or a monocyclic (hetero)aryl group; or else R2 and R3 together form a —(CH2)n— group where n=1 to 4; R4=a C2 to C8, straight-chain or branched, hydrocarbon group, or a monocyclic aromatic group; R5=H, or a C1 to C12, straight-chain or branched, hydrocarbon group.

Abstract: The main subject-matter of the present invention is a process for the dissolution of at least one element chosen from niobium and tantalum and at least one other element chosen from uranium and the rare earth elements, advantageously for the dissolution of niobium, tantalum, uranium and rare earth elements, present in an ore or an ore concentrate. Said process comprises: the roasting of a material, comprising said elements, which material is mixed, dry or/in the presence of water, with an acid roasting agent in order to obtain a calcine; said material consisting of said ore or concentrate or having been obtained from said ore or said concentrate and said acid roasting agent providing for roasting in a sulphate medium; and the dissolution in an aqueous solution of the calcine obtained in order to obtain a slurry, the liquid fraction of which includes iron, in the ferric state, at a concentration of at least 50 g/l, advantageously of at least 70 g/l and very advantageously of at least 120 g/l.