Copper was adsorbed onto Ca-exchanged montmorillonite (Cheto clay) under basic conditions. Differential thermogravimetric analysis (DTGA) combined with mass spectroscopy (MS) was employed as the principal technology to study the distributions and structures of adsorbed copper species on Cheto clay. The results showed that the original Cheto clay was easily rehydrated. After copper adsorption, a step-by-step replacement of hydrated calcium ions by copper-ammonia complex was observed through the gradual decrease of the first DTGA dehydration peak intensity with the increasing copper loading amount. Compared with the original Cheto clay, copper-loaded samples showed new DTGA peaks assigned to NH3 and N2O. The presence of N2O peak suggested that the loaded copper species were in agglomerated copper oxide form, which dispersed well over the edge and external surface of the clay layers. (C) 2003 Elsevier B.V. All rights reserved.