Kinetics study on the low-temperature soda roasting of boron-rich blast furnace slag

The method of preparing borax by low-temperature soda roasting and water leaching of boron-rich blast furnace slag (BRBFS) is a novel method for extracting boron from BRBFS. In order to further improve the water leaching rate of boron, this article mainly studied the low-temperature soda roasting kinetics of BRBFS. The effects of roasting temperature and Na₂CO₃ addition on the water leaching rate of boron were investigated. The results demonstrate that when the amount of Na₂CO₃ added is four times of the theoretical amount, the kinetics of NaBO₂ formation can be described by the Nucleation (Avrami) model in the temperature range of 600-700 °C. The corresponding apparent activation energy is 54.45 kJ/mol, and the apparent frequency factor is 215.16 h^-1. It was found that at a roasting temperature of 700 °C,when the amount of sodium carbonate added is twice, three times, and four times of the theoretical amount, the kinetics of NaBO₂ formation matches with 3-D Diffusion (Jander) model, Nucleation and Growth (Avrami-Erofeev) model, and Nucleation (Avrami) model, respectively. With an increase in the amount of Na₂CO₃ added, the rate-controlling step for the formation of NaBO₂ transitions from being diffusion-controlled to nucleation-controlled.