Recycling metals by controlled transfer of ionic species between complex fluids: en route to “ienaics”

Recycling chemistry of metals and oxides relies on three steps: dissolution, separation and material reformation. We review in this work the colloidal approach of the transfer of ions between two complex fluids, i.e. the mechanism at the basis of the liquid-liquid extraction technology. This approach allows for rationalizing in a unified model transformation such as accidently splitting from two to three phases, or uncontrolled viscosity variations, as linked to the transformation in the phase diagram due to ion transfer. Moreover, differences in free energies associated to ion transfer between phases that are the origin of the selectivity need to be considered at the meso-scale beyond parameterization of an arbitrary number of competing “complexes”. Entropy and electrostatics are taken into account in relation to solvent formulation. By analogy with electronics dealing about electrons transported in conductors and semi-conductors, this “ienaic” approach deals with ions transported between nanostructures present in colloidal fluids under the influence of chemical potential gradients between nanostructures coexisting in colloidal fluids. We show in this review how this colloidal approach generalizes the multiple chemical equilibrium models used in supra-molecular chemistry. Statistical thermodynamics applied to self-assembled fluids requires only a few measurable parameters to predict liquid-liquid extraction isotherms and selectivity in multi-phase chemical systems containing at least one concentrated emulsified water in oil (w/o) or oil in water (o/w) microemulsion.