Kinetics of the Acid Digestion of Serpentine with Concurrent Grinding. 1. Initial Investigations

The rapid extraction of magnesium from serpentine is critical to novel low-pressure mineral carbonation methodology. Though almost any acid can dissolve the magnesium, the rate plays a critical role in the industrialization of the process. It has been demonstrated that including a low-energy, attrition-type grinding with the chemical attack of the acid can more than double the extraction rate. However, the dissolution mechanism and rate law were elusive. It was found that the dissolution mechanism changes through the reaction progress and with particle size. A model was developed that combines the effects of surface reaction, surface speciation, the electrical double layer, particle size distribution, and ash layer diffusion. Because of the highly irregular particle geometry, a semiempirical spherical particle size distribution was used. The resulting model was able to fit the data with reasonable parameters, and it was demonstrated that the effect of grinding is to change the diffusivity of the ash layer. Further development of the model is underway.