In the alkali fusion process for the production of zirconium oxychloride, the formation of the water insoluble by-product, Na2ZrSiO5, largely affects NaOH recovery and results in the formation of silicon slags. Thus, controlling Na2ZrSiO5 formation is necessary. In this paper, we studied the effects of roasting temperature, NaOH/zircon mole ratio, and particle size of zircon sand on Na2ZrSiO5 formation. The optimum reaction parameters, when the roasting time was 1 h, were as follows: >= 95 mu m average particle size of zircon sand, 6:1 NaOH/zircon mole ratio, and 750 degrees C roasting temperature. To avoid an uneven roasting temperature during alkali fusion, the use of a rotary kiln reactor is recommended. The amount of Na2ZrSiO5 was significantly decreased under these optimum conditions, and the content of Na2O was reduced from 7.049% to only 2.21% after three water-leaching cycles. (C) 2015 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.