Influence of temperature and alkalinity on the hydrolysis rate of borohydride ions in aqueous solution

摘要

The paper studies the influence of temperature (50-100 ℃) and alkalinity (C_(OH) = 2.33-9.53 M) of aqueous solutions on the hydrolysis (self-destruction) kinetics of borohydride ions BHJ. Characteristic peculiarities of the kinetic curve have been established and formulae to approximate the temperature-concentration dependence of the hydrolysis rate are proposed. An increase in temperature leads to an increase in the rate constant k of borohydride hydrolysis, and the temperature dependence of fe satisfactorily obeys Arrhenius' equation. The influence of solution alkalinity on the borohydride hydrolysis rate was explored. Within the temperature range studied, the fe = f(C_(OH)) curve consists of two fragments, each with the prevalence of one of two different mechanisms (paths) of borohydride hydrolysis. In highly-alkaline aqueous solutions, non-catalytic hydrolysis mainly occurs, whose rate is determined by temperature, being pH-independent. At lower alkalinity, the hydrolysis rate sharply increases due to catalysis by H~+ ions. A power dependence of k on the H~+ concentration has been found; the point where the mechanisms are switched is determined by temperature.