Potassium merlinoite was successfully synthesized from K-feldspar powder by microwave-assisted as well as conventional hydrothermal methods. Effects of aging, H2O/Al2O3 molar ratio, crystallization temperature, crystallization time, and mixed heating strategy on potassium merlinoite formation were systemically studied. It was observed that aging was not a necessary factor to the formation of merlinoite, and merlinoite was the unique crystalline product at a wide range of H2O/Al2O3 molar ratio, crystallization temperature and time. The reaction rate of microwave-assisted hydrothermal synthesis was 2-3 times as much as conventional method. The acceleration effect of microwave was proved to work only at the initial period of irradiation, and a mixed heating method was considered as an appropriate strategy to prepare merlinoite. A simple and economical chemical process has been proposed to convert the natural K-feldspar powder into merlinoite-type eco-fertilizer in this paper. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.