Transuranic (TRU) waste that is being generated at Argonne National Laboratory has a TRU activity ranging from 10(2) to 10(7) nCi/g with a wide variety of chemical compositions. Currently, the waste is stored in highly acidic solutions that must be neutralized for intermediate storage. A magnetite carrier precipitation process has been adapted to concentrate TRU isotopes in a noncorrosive solid phase. In this paper, we report the results of a series of laboratory tests done to optimize the process. The parameters we optimized included (1) magnetite concentration used to precipitate plutonium from solution, (2) formation of magnetite (in situ or ex situ), (3) processing pH, and (4) temperature and mixing time of the carrier precipitation. We also studied the effects of anions, cations, and complexing agents in the waste solutions on the carrier precipitation and the effect of magnetite solids loading on the filtration equipment. An overview is given of the planned full-scale process, which will be operated in a glovebox.