Spatial Separation of Copper and Cobalt Oxalate by Flow-Driven Precipitation

Abstract

A precipitation reaction is investigated far from equilibrium by introducing a continuous flow of the homogeneous mixture of water-soluble metal salts into sodium oxalate solution. The spreading gravity current maintained by the density difference between the solutions creates a radially symmetric precipitate pattern that contains spatially separated copper oxalate monohydrate and cobalt oxalate tetrahydrate, identified by X-ray diffraction measurements. In the transition zone, a unique crystalline composite containing copper oxalate plates with cobalt oxalate coating also forms.