Mechanism of the Effect of Hard Agglomeration on the Efficiency of Magnesium Oxide Acidizing Leaching Rate in Lightly Fired Powders
The leaching of magnesium from lightly fired powders obtained from low temperature calcination of magnesite by hydrochloric acid acidification was studied.The effects of addition method of hydrochloric acid,concentration of hydrochloric acid,liquid volume/solid mass ratio,external force way and reaction time on magnesium leaching rate were investigated.The leaching kinetics of lightly fired powders under ultrasonic condition was analyzed by using shrinkage core model.And the particle size distribution,mineral composition and mineral distribution characteristics of leaching residue were further analyzed.The results show that under the conditions of slowly adding hydrochloric acid,hydrochloric acid concentration of 14.8％,liquid volume/solid mass ratio of 9.8/1,stirring speed of 400 r/min and leaching time of 12.5 min,the leaching rate of magnesium can reach 70.48％.Using ultrasound can cause hard agglomeration to produce cracks or disintegration,which is beneficial to solid-liquid mass transfer,and the magnesium leaching rate is increased to 90.56％.The leaching process of lightly fired powders conforms to the mixed control model of surface chemical reaction and product layer diffusion.The ratio of magnesium to oxygen in the hard agglomeration is 1.33,the edge is 1.65,and there is a large amount of unreacted magnesium in the hard agglomeration.The particle size of the leaching slag is reduced from 42.61 μm to 24.39 μm by ultrasonic action.The ultrasonic bubble vibration force and the shock wave formed by the cavitation collapse can effectively prevent the formation of hard agglomeration or make the hard agglomeration re-disaggregate.
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