The intensity of spontaneous surface convection in di-(2-ethylhexyl)phosphoric acid systems

The dependence of the rate of the arising and evolution of spontaneous surface convection (SSC) on various effects during the extraction of rare-earth metals (REMs) with heptane (or toluene) solutions of di-(2-ethylhexyl)phosphoric acid (D2EHPA) (HA) was studied. The intensity of SSC in heptane was higher than in toluene systems. In the same solvent, it was higher for the elements from the cerium subgroup. At low concentrations of a REM salt in the starting aqueous solution, the modulus of the surface rate of liquid flow in the dynamic interphase layer (DIL) was high because low-solubility salt particles experienced sedimentation, and the interphase surface was renewed. It was concluded that, at higher REM concentrations in the aqueous phase, the modulus of the surface flow rate was considerably higher because of the accumulation of LnA3 and structure formation in the interphase layer. For comparison, we give the moduli of surface flow rates of liquids during the re-extraction of acids in a toluene, HNO3/water system, in which the rate is higher than in aqueous REM(III) salt/D2EHPA solution in an organic diluent.