Investigations on the process of dissolution and transformation of chloropinnoite in boric acid aqueous solution at 303 K by kinetics and Raman spectroscopy

Kinetics of dissolution and transformation of chloropinnoite (2MgO·2B2O3· MgCl2·14H2O) in 4.5% (wt%) boric acid aqueous solution at 303 K had been studied, and the kinetic process and mechanism were investigated by the Raman spectroscopy. According to the kinetic curve, the process of dissolution and phase transformation can be divided into three stages: dissolution stage, phase transformation induction period, and crystallization stage. The experimental results showed that when chloropinnoite dissolved in boric acid aqueous solution, MgCl2 was removed and midproduct (MgB2O(OH)6·H2O) dissolved at the same time, which was different from that of in water. Kurnakovite was a final product. The experimental data of the crystallization process have been fitted with the following mathematical modification with the aid of simplex optimum method and Runge–Kutta digital solution of differential equation system: −dc/dt = 6.31(c−0.3906)2 + 0.975(c−0.3906). Based on our experimental results and the Raman spectroscopy, kinetics and mechanism of dissolution, phase transformation, and crystallization of borate in chloropinnoite–boric acid water system are discussed. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 136–143, 2006