Study On The Phase Relation Of Chloropinnoite-Water Pesudobinary System And The Kinetics Of Dissolution And Phase Transformation Of Chloropinnoite In The Boric Acid Solution

Chloropinnoite is a double borate, which crystallizes out from concentrated salt lake brine. The forming relationship of Chlorpoinnoite double borate and hydrated magnesium borate in the salt lakes has been reported slightly. This paper has studied the dissolution and phase transformation of Chloropinnoite in aqueous solution using phase equilibrium and kinetics method.( 1 ) The phase relation of chlorpoinnoite-water pesudobinary system in the temperature range of 273K to 453K has been studied using phase equilibrium. The results show that the phase transformation products of Chloropinnoite in the water have clearly been influenced by temperature. From 273K to 314K the inderite has existed; from 314K to 360K the poinnoite has existed; and from 360k to 453k the new hydrated borate a -ascharite has existed respectively. The solubility of these magnesium borates has obtained at varied temperature. The mechanism of dissolution and phase transformation has proposed. The conclusion obtained has important significance to synthesize hydrated borates and to explain their forming in salt lakes.(2) The kinetics and mechanism of dissolution and phase transformation of Chloropinnoite in water at 87℃and in the boric acid solution at 30 ,40, 50 and 0℃ have been studied respectively. The transformation products are MgO 暋2O3 · 3H2O, 2MgO ·3B2O3 ·15H2O(Kurnakovite)and 2MgO ·3B2O3·15H2O(Inderite) respectively. With the aid of simplex optimum method and Runge-Kutta digital solution of differential equation system, the experimental data was fitted. The kinetic equations of the crystallization reactions have been given and the mechanism has been proposed on the basis of existing forms of boroxygen anion in the solution.(3 ) The influences of the third composition which is close to actual brine compositions, including NaCl, MgCl2· 6H2O, MgSO4 · 6H2O, LiCl, H3BO3, Na2B4O7 ·10H2O on the dissolution and phase transformation of the Chloropinnoite in water have studied using phase equilibrium method. The results show that thedissolution and phase transformation products of chloropinnoite have been clearly influenced by solution pH, temperature, and total boron in the solution, but the third composition except boric acid has barely influenced on the dissolution and phase transformation of chloropoinnoit. Some hydrated borates such as 2MgO ·3B2O3 · 15H2O(Kurnakovite), 2MgO · 3B2O3· 15H2O(Inderite) , MgO ·2B2O3 ·9H2O, MgO ·3B2O3 ·7.5H2O, MgO ·B2O3·3H2O have been obtained. The mechanisms of dissolution and phase transformation of chloropinnoite in the third composition solution have been proposed. The results have been important instructional meaning to the forming and utilizing of borate in the salt lakes.