钾长石-氯化钙高温反应体系热力学分析

Thermodynamic Analysis of Potassium Feldspar-CaCl2 Reaction System

对窑炉反应器中钾长石-氯化钙高温焙烧反应体系进行了系统的热力学分析。结果表明,在温度<1423K时钾长石转化提钾主要是通过反应Ca Cl_2+2KAl Si_3O_8=Ca Al2Si2O8+4Si O_2+2KCl实现的,按照氯化钙配料为化学计量比配料的5倍计算,当温度≥1073 K时钾长石的平衡转化率可达85%。标准状况下纯氯化钙在高温水蒸气中是稳定的,但当二氧化硅存在时氯化钙将按照反应3Ca Cl_2+3H_2O+3Si O_2=Ca_3Si_3O_9+6HCl发生显著水解,当入窑空气温度为25°C、相对湿度75%时,1073 K反应平衡时氯化氢分压>10k Pa;在钾长石-Ca Cl_2高温焙烧过程中少量产物七铝酸十二钙的形成途径可能是:14KAl Si_3O_8+54Ca O=14Ca_3Si_3O_9+Ca_(12)Al_(14)O_(33)+7K_2O;钠长石与氯化钙反应的热力学趋势远大于钾长石,因此应尽量选用低钠长石含量的钾长石矿为原料。

A systematic thermodynamic analysis tovarious reactions occurred during potassium feldspar/CaC12 calci- nations in kilns was conducted. The results show that the extraction of potassium by roasting conversion of the potas- sium feldspar with CaCl~ was primarily through the reaction CaCl2 ＋2KAlSi3O8 = CaAl2 Si20s ＋4SiO2 ＋2KCl at the temperatures lower than 1423K. The equilibrium conversion of potassium feldspar reached 85% at the temperatures higher than 1073K in accordance withthe ingredient of calcium chloride was 5 times as the stoichiometric ratio. Pure CaCl2 was high-temperature stable in a humid moisture atmosphere under standard condition. In the present of SiO2, however, a significant thermal hydrolysis of the calcium chloride occurred according to the reaction 3 CaC12 ＋3H2O＋ 3 SiO2 = Ca3 Si3 O9 ＋6HCl. With an inlet air to kilns of 25 o C and relative humidity 75 %, the equilibrium partial pres- sure of hydrogen chloride exceeded 10kPa at 1073K. The possible formation route for calcination product Ca12 Al14 033 was 14KAlSi3 O8 ＋54CAO = 14Ca3 Si3O9 ＋Ca12 Al14 O33 ＋7 K2O. The thermodynamic trend for the reaction of CaCl2 with sodium feldspar was stronger than that with potassium feldspar, thus the preferred potassium feldspar feedstock was the one with low content of sodium feldspar.