Thermodynamic Analysis of Potassium Feldspar-CaCl2 Reaction System
A systematic thermodynamic analysis tovarious reactions occurred during potassium feldspar/CaCl2 calcinations in kilns was conducted.The results show that the extraction of potassium by roasting conversion of the potassium feldspar with CaCl2 was primarily through the reaction CaCl2 +2KAlSi3Os =CaAl2 Si2 O8 +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 3CaCl2+3H2O+ 3 SiO2 =Ca3 Si3 O9 +6HCl.With an inlet air to kilns of 25 ℃ and relative humidity 75 %,the equilibrium partial pressure of hydrogen chloride exceeded 10kPa at 1073K.The possible formation route for calcination product Ca12Al14 O33 was 14KAlSi3 O8 +54CaO =14Ca3 Si3 O9 +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.