Investigation of thermodynamic and kinetic regularities of asbestos waste leaching processes

The asbestos wastes were exploited for extraction of magnesium by agitation leaching process in atmospheric conditions, using hydrochloric acid as the leaching agent. The study was focused on investigating the kinetics of magnesium leaching. The effects of some variables, including stirring speed (150 – 300 r/min), leaching temperature (25 – 90 °C), leaching duration (10 – 60 min), the concentration of hydrochloric acid (150 – 300 g/L) and the solid-liquid ratio (1:2 – 1:5), on the leaching rate were carefully evaluated. It was found that increasing the stirring speed, leaching temperature, and concentration of hydrochloric acid can significantly increase the rate at which magnesium is leached. A comprehensive kinetic scrutinization was performed by fitting the experimental data with exponential kinetic equation, Yander diffusion equation, Drozdov-Rotinyan equation, and Prout-Tompkins equation. Amongst all these tested kinetic equations, the diffusion-controlled process showed a higher goodness-of-fit with experimental data. Thermodynamic aspects were also appraised carefully. The apparent activation energy for the process was calculated to be 19.8 kJ/mol, indicating a relatively low-level energy needed to initiate the process efficiently. Overall, the current study provided insight into how changing certain parameters can affect the overall performance when attempting to extract magnesium from the asbestos wastes by leaching process.