Extraction of rare earth elements from bastnasite (REFCO3) and monazite (REPO4) after fluorine fixation was studied. Chlorination kinetics of fluorine-fixed flotation bulk concentrate with ammonium chloride was found to follow the regional reaction model. The chlorination was found to involve two series steps with nuclear growth occurred in normal to surface direction. Internal diffusion was identified to be the rate limiting step of the chlorination process and an apparent activation energy of 36.8 kJ mol was determined. (C) 2003 Elsevier Science Ltd. All rights reserved.