This paper describes the production of anhydrous puffed borax from borax pentahydrate (BPH) in a batch calcinator. The calcination of BPH is incomplete since agglomeration starts at 300degreesC. In order to avoid agglomeration at temperatures higher than 300degreesC, the surface of BPH particles have been covered with a CaO layer in aqueous media having a higher melting point than pure BPH. To investigate the effect of this CaO layer on the calcination of BPH, the samples were fed into the batch calcinator. During the calcination process, quantities such as the bulk density value, particle size distribution, sodium borate and calcium content of anhydrous borax have been determined as a function of temperature. It was found that the anhydrous borax can be obtained by calcination of BPH particles covered with CaO in 50, 20 and 5 min time intervals at a temperature range of 300, 400 and 500degreesC, respectively. As a result, puffed anhydrous borax of 99% purity with bulk density of 0.082 g cm(-3) and containing 0.670% Ca2+ has been produced by this method in 5 min interval at 500degreesC. (C) 2004 Elsevier B.V. All rights reserved.