Membrane-Integrated Solvent Extraction Followed by Crystallization for Selective Removal and Recovery of Metal Ions as Crystals

Simultaneous solvent extraction-stripping was carried out with a membrane-integrated extractor. Crystalline CuSO4·5H2O was recovered from Cu-containing water by the extractor combined with a fluidized-bed crystallizer. Extraction tests were carried out, using SME-529 (a solvent from Shell Chem. Co.) with two apparatuses of different scale containing tubular fluoropolymer membranes (inner dia. 2 mm, pore dia. 0.1 μm); the inner surface area for the smaller one with 21 membrane tubes was 6.59 × 10-2m2, and that for the larger one with 528 tubes was 2.32 m2. Then we proposed a diffusion model by which Cu concentrations in a set of a feed solution, solvent and stripping solution can be calculated from the extraction equilibrium and the mass transfer coefficients available through simple experiments. The calculated values agreed well with the experimental values. A design method for a commercial-scale plant is proposed, based on the diffusion model.