The technology of ion exchange is applied in batch operation for removing potassium-40 as from liquid solutions (prepared in laboratory by solved known amount of KCl in known amount of distilled water. A measured quantity of the ion exchange medium (bentonite clays) is mixed with radioactive solution containing potassium-40 in a suitable mixing vessel. The activity concentrations of liquid solution containing potassium-40 in the influent and effluent samples are measured by gamma ray spectroscopy system composed of a high purity germanium detector with 40% efficiency coupled to an 8192 channel personal computer analyzer. The amount of exchanger media required and the rate of exchange is determined by laboratory tests. The distribution coefficient for bentonite clays for removing K-40 in batch operation (0.104815 l/gm) is estimated by correlation line method, with a correlation coefficient between the observed and the predicted data of 96%. To ensure accuracy and reliability of the collected data, the test is used to measure deviations between the observed and expected K-40 activity concentration captured by the bentonite clays and passed through it. No significant difference is observed between observed and expected data at 5% significant level. The results indicate that the distribution coefficient can be used in predicting the amount of an ion exchanger media needed to remove potassium-40 with a certain decontamination factor.