Recycling of black dross containing rare earths originating from melting and recycling of magnesium alloys

The process of melting and recycling magnesium alloys using fluxes produces a residue termed black dross. The black dross investigated contained metal and non-metallic phases with a considerable content of rare earth metals (REEs). The black dross was separated by crushing and screening into metal and non-metallic fractions. The non-metallic fraction was further processed by water and acid leaching. In the water leach, NaCl, KCl and CaCl2 were separated for crystallisation. In the acid leach the residue was treated with hydrochloric acid in order to dissolve the rare earth elements Ce, La, Nd and Pr. Selective precipitation by oxalic acid and solvent extraction using D2EHPA or PC88A enables a recovery of up to 92.6% of the REEs from the oxide-salt-fraction. The equilibrium isotherms of the solvent extraction operation indicate the potential for further separating the rare earth elements. A flow sheet of the whole processes was developed in order to guide industrial application.