The coatings of ferromagnetic-charcoal-polymer microparticles (1-25 mu m) with organic extractants specific for actinides were optimized for use in the magnetically assisted chemical separation (MACS) process. The organic extractants, octyl (phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) dissolved in tributyl phosphate (TBP), coated the particles when a carrier organic solvent was evaporated. Coated particles were heated in an oven overnight to drive off any remaining carrier solvent and fix the extractants on the particles. Partitioning coefficients for americium obtained with the coated particles routinely reached 3000-4000 ml g(-1), approximately 10 times the separation efficiency observed with the conventional solvent extraction system using CMPO and TBP. (C) 1997 Elsevier Science B.V.