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.

Abstract: A gas siphon type reactor (10) is used to carry out a three phase chemical reaction under pressure, such as the reduction of uranyl nitrate to uranous nitrate by hydrogen, in the presence of a catalyst made up of platinum on a silica carrier. The control of the pressure in the reactor (10) is provided by regulating the liquid and gas flow rates from separator (52), into which the liquid and the gas leaving the reactor (10) are routed. The liquid in the reactor (10) is tapped from a lateral branch pipe (32) fitted with a filter (36) and emerging in the upper area (30), behind a profiled wall (34).

Abstract: A gas siphon type reactor (10) is used to carry out a three phase chemical reaction under pressure, such as the reduction of uranyl nitrate to uranous nitrate by hydrogen, in the presence of a catalyst made up of platinum on a silica carrier. The control of the pressure in the reactor (10) is provided by regulating the liquid and gas flow rates from a high-pressure separator (52), into which the liquid and the gas leaving the reactor (10) are routed. The liquid in the reactor (10) is tapped from a lateral branch pipe (32) fitted with a filter (36) and emerging in the upper area (30), behind a profiled wall (34).

Abstract: A gas siphon type reactor (10) is used to carry out a three phase chemical reaction under pressure, such as the reduction of uranyl nitrate to uranous nitrate by hydrogen, in the presence of a catalyst made up of platinum on a silica carrier. The control of the pressure in the reactor (10) is provided by regulating the liquid and gas flow rates from a high pressure separator (52), into which the liquid and the gas leaving the reactor (10) are routed. The liquid in the reactor (10) is tapped from a lateral branch pipe (32) fitted with a filter (36) and emerging in the upper area (30), behind a profiled wall (34).