Synchysite is a rare mineral which has potential as a new source of rare earth elements. The influence of roasting temperature and time on the solubility of rare earth elements from a synchysite concentrate is examined. The maximum solubility of rare earth oxides in 57% HNO3 was 97% in a sample roasted at 700 degrees C for 120 min. Increasing the roasting temperature decreased solubility due to formation of cerium (IV) and calcium oxides. (c) 2007 Elsevier Ltd. All rights reserved.