Kinetics of Ge(IV) Extraction Using a Microstructured Membrane Contactor

For hydrometallurgical metal extraction, the mass transfer by diffusion is additionally coupled with a chemical reaction of the metal ion with the extractant molecule, usually at the interface. Consequently, the kinetics is either limited by diffusion or chemical reaction (or both, respectively, in a mixed regime). Conventional methods for determining the extraction kinetics often lead to a misinterpretation, especially for fast reactions, and an isolated view of the interfacial reaction is restricted. With a new microcontactor setup, it is possible to perform a comprehensive kinetic analysis with very low sample volumes compared to established methods. Additionally, it is possible to quantify all individual mass transfer resistances and identify the extraction regime with the developed mass transfer model. The chemical reaction part is investigated isolated, to derive rate laws and kinetic constants. The methodology is discussed for the extraction of Ge(IV) from aqueous solutions with the two extractants 5,8‐diethyl‐7‐hydroxydodecan‐6‐oxime (LIX 63) and 7‐(4‐ethyl‐1‐methyloctyl)‐8‐hydroxyquinoline (Kelex 100). It was found that the extraction with LIX 63 is reaction limited and with Kelex 100 the reaction resistance is in the same order of magnitude as the diffusion resistances. The obtained results provide fundamental kinetic data for the design of solvent extraction equipment.