This report contains the findings of detailed studies of process and waste flows at five typical uranium mills. The studies were initiated for the purpose of characterizing the liquid and solid wastes resulting from uranium milling processes. The five mills reported on here typify the processes normally encountered, i.e., acid or alkaline leaching of the ore, concentration and purification of the leach liquor by ion exchange or solvent extraction, and chemical precipitation of the dissolved uranium. Although the radioactive waste materials, especially Radium-226, were of primary interest in these studies, useful information regarding the chemical characteristics of milling wastes was also obtained.