he performance of an isotope dilution–precipitate flotation process for Cs-137 removal from low-level liquid radioactive waste is evaluated in this study using sodium tetraphenylborate (NaTPB) as the precipitating agent. In absence of Fe(III), neither the anionic sodium lauryl sulfate (SLS) nor the cationic cetylpyridinium chloride (CPC) could float the CsTPB precipitate over the studied pH range of 2.5–11.9. It is proposed that iron oxide coated CsTPB particles are formed upon addition of Fe(III) solution and their floatability is greatly dependent on the solution pH and the Fe(III) content. At the optimum conditions, remaining Cs-137 activity values