Leaching of magnesium from asbestos processing wastes

摘要

Asbestos tailings consist of >90% serpentine, which has the formula Mg3Si_2O_2(OH)_4 and contains 26.3% Mg. The recently developed Magnola process recovers the magnesium content of the tailings using a flowsheet based on HC1 leaching, and the present report discusses some of the fundamental aspects of the leaching part of the process. Magnesium leaches rapidly from serpentine in hot HC1 media, and the resulting amorphous silica remains as an insoluble pseudomorph after the original serpentine particles. At 100℃ in 7.0 M HC1 media, the specific magnesium leaching rate is independent of the pulp density, although the total amount of magnesium dissolved increases linearly as the pulp density increases to 350 g/L solids. The rate of magnesium dissolution from 230 g/L of asbestos tailings in HC1 media at 100℃ increases as the 0.3 power of the HC1 concentration. The rate of magnesium dissolution in 7.0 M HC1 media increases moderately with increasing temperature; the apparent activation energy is 41.7 +- 4.3 kJ/mol. Surprising is the fact that the leaching rate is nearly independent of the particle size for serpentine particles < 1,000 μm in diameter, and this is a consequence of the diffuse nature of the reaction zone which extends over several hundred microns.