Abstract: When optimizing the conventional purification methods, by gas, of aluminum in a molten state, a negative effect of the temperature has been revealed surprisingly when using a mixture of noble gases and carbon dioxide. In the same way, it has been proved inadequate to use concentrations of carbon dioxide higher than 10% in volume. It is therefore proposed to use, at a temperature comprised between 730.degree. and 780.degree. C., a gaseous mixture comprised of at least an inert carrier gas and of 4 to 10% in volume of carbon dioxide in a ratio of 0.4 to 1.0 Nm.sup.3 per ton of molten material. The method is also appropriate for continuous and discontinuous operation plants. In the first case an optimum effect of the stay time for the molten particles of three minutes should be provided, whereas a total time of one hour should be provided in the second case. This method allows, supposing a pseudo-1 kinetic order, to reach a speed constant of 5.3 for sodium, 4.9 for lithium and 2.5.times.10.sup.-4 sec.sup.