This report introduces a novel method of separating potassium from sodium by synthesizing K-alunite using activated aluminum hydroxide (Al(OH)(3)). A two-step operation, consisting of the mechanochemical activation of Al(OH)(3) and subsequent hydrothermal processing at a low temperature of 80 degrees C with Al-2(SO4)(3) 18H(2)O and K(2)SO4 or Na(2)SO4, was conducted. K-alunite but not Na-alunite at this low temperature was successfully formed, leading to the possible separation of potassium sulfate from sodium sulfate more easily. The process may serve the purpose of recovering potassium from some aqueous alkali sources for providing potash fertilizer in agricultural application.