Liquid-Liquid Separation
Solvent extraction is the elegant heart of modern hydrometallurgy. Two immiscible liquids — an aqueous phase carrying dissolved metals and an organic phase containing a selective extractant — are mixed together, allowing the target metal to transfer from water to organic. The phases then separate by gravity in a settler, producing a purified aqueous raffinate and a metal-loaded organic. This deceptively simple principle enables the separation of elements that are chemically almost identical, such as adjacent rare earths or cobalt from nickel.
The McCabe-Thiele Diagram
Designing an SX circuit requires knowing how many mixer-settler stages are needed. The McCabe-Thiele graphical method plots the equilibrium isotherm (the curved line relating organic and aqueous concentrations at equilibrium) against the operating line (the straight line representing mass balance). Starting from the feed point, you step between these curves — each step represents one theoretical stage. When the steps reach the target raffinate concentration, you have your stage count. This simulation builds the diagram interactively as you adjust parameters.
The O/A Ratio Trade-off
The organic-to-aqueous volumetric flow ratio (O/A) is the key design variable. A higher O/A means more organic solvent contacts each volume of aqueous feed, improving extraction per stage but requiring more (expensive) organic inventory. A lower O/A concentrates the metal into less organic volume — desirable for downstream stripping — but needs more stages. The optimal O/A balances capital cost (more stages) against operating cost (more solvent) and is found at the intersection of economics and thermodynamics.
Industrial Practice
The world's copper supply depends on SX: over 25% of global copper is produced through leach-SX-electrowinning circuits. Rare earth separation requires dozens of SX stages in cascade due to similar K_D values between adjacent elements — a separation tour de force. Cobalt-nickel separation, uranium purification, and platinum group metal refining all rely on carefully engineered SX flowsheets. This simulator lets you explore the fundamental design principles that underpin these billion-dollar operations.