水热法分解钾长石制备雪硅钙石的实验研究

采用CaO作为助剂，在低温、中压的水热条件下分解钾长石，继而合成一种水合硅酸钙--雪硅钙石，同时得到KOH稀溶液，可用于制备高纯碳酸钾。影响晶化反应的主要因素有n(Ca)/n(Al+Si)、晶化温度、晶化时间、水固比（质量比）、搅拌速度等。讨论了各因素对钾长石分解及雪硅钙石形成的影响，通过X射线粉末衍射、热重-差热分析、扫描电镜等手段对合成产物进行结构性能表征。实验结果表明，以CaO为助剂分解钾长石，同时合成雪硅钙石的工艺方法可行，资源利用率接近100%。实验得到的优化工艺条件为：晶化温度为220～250 ℃，n(Ca)/n(Al+Si)在0.8～1.0之间，晶化时间5～8 h，水固比为20～25，搅拌速度400 r/min。在此条件下，钾长石中K₂O的溶出率达80%以上，同时得到结晶良好的针状雪硅钙石晶体。

Experimental Study on Synthesis of Tobermorite by Decomposing Potassium Feldspar

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.