Abstract:

Potassium feldspar was hydrothermally decomposed at low temperature and low pressure with CaO as additive, and then to synthesize a calcium silicate hydrate, i.e. tobermorite, meanwhile dilute KOH liquor was produced which could be used to prepare highly pure potassium carbonate.The factors affecting the crystallizing reaction include the mole ratio of Ca/(Al+Si), reaction temperature, reaction time, weight ratio of liquid to solid, and the rate of stirring. The experiments demonstrate that the process of decomposition of potassium feldspar and then synthesis of tobermorite are feasible, and the technique is near 100% in availability of the insoluble potassium resource From the experiments the optimal technical parameters are as follows: the temperature is 200-250 ℃, the mole ratio of Ca/(Al+Si) is 0.8-1.0, the reaction time is 5-8 hours, the weight ratio of liquid to solid is 20-25, and the rate of stirring is 400 r/min. With increasing temperature, the decomposing rate of potassium feldspar is enhanced.The higher value of Ca/(Al+Si) is propitious to the decomposition of potassium feldspar. The decomposing reaction can complete in 5-8 hours.The results indicate that the decomposing rate of potassium feldspar is over 80%, and the needle-like shape tobermorite is well synthesized in the experiments.

Key words: potassium feldspar, tobermorite, hydrothermal synthesis, potassium carbonate