Thermodynamic Analysis for Decomposition of Calcium Fluoride by Sodium Hydroxide

Diagrams of lgc-pH for dissolving components in the system of Ca-F-H2 O where sodium hydroxide decomposed calcium fluoride at 25 ℃ were drawed based on thermodynamic calculation data.According to the calculation results and the thermodynamic equilibrium diagram,the behavior of sodium hydroxide decomposing calcium fluoride was analyzed.The results show that at pH4,Fdecreased rapidly,Ca^2+increased rapidly,and calcium fluoride is not stable,and at 4≤pH≤12,calcium fluoride can exist stably,and at pH12,Ca^2+ reduced quickly,F^-increased rapidly,calcium fluoride started to decompose to generate Ca(OH)2(aq).When the pH rises up to 14.4,Ca(OH)2(aq)saturates and Ca(OH)2(s)precipitates.