KINETICS OF THE ACID DIGESTION OF SERPENTINE WITH CONCURRENT GRINDING FOR THE PURPOSE OF CARBON DIOXIDE SEQUESTRATION

Open Access
Author:
Van Essendelft, Dirk Thomas
Graduate Program:
Energy and Geo-Environmental Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
September 25, 2008
Committee Members:
  • Harold Harris Schobert, Committee Chair
  • Derek Elsworth, Committee Member
  • Mark Stephen Klima, Committee Member
  • James David Kubicki, Committee Member
  • Sridhar Komarneni, Committee Member
Keywords:
  • Chemical Kinetics
  • Computational Modeling
  • Serpentine
  • Carbon Dioxide Sequestration
  • Mineral Carbonation
  • Strong Acid Dissolution
Abstract:
The kinetics of the acid digestion of serpentine is an important scientific and industrial issue as pertains to carbon dioxide sequestration. Serpentine contains approximately 25% magnesium by weight and is prolific near most major population centers. These two properties make serpentine an ideal mineral carbonation feedstock. However, serpentine is a highly ordered ultramafic magnesium silicate structure consisting of alternating sheets of brucite-like material and silica-like material. This highly ordered structure causes the formation of a silica barrier around the mineral particles that can slow or even stop the kinetics as the particles dissolve. The physical behavior of this layer causes a shift in kinetic behavior from surface limited kinetics to diffusion limited kinetics. However, it has been shown that both behaviors are important at the same time and vary by particle size. Further, it has been shown that the kinetics can be greatly accelerated by incorporating concurrent, low energy, attrition-type grinding during the chemical reaction. A computational model based on surface kinetics, surface species distribution, surface charge, the electrical double layer, gel layer diffusion, solution thermodynamics, and particle size and shape was developed to describe the kinetics. It was demonstrated that the computational model can describe the experimental fractional magnesium extraction of magnesium from serpentine within ~3% in every case and within ~1% in most cases with reasonable understanding and characterization of the materials going into the system. It was found that particle shape as well as size plays a critical role in the kinetics. However, the tools to quickly and adequately characterize particle shape were not available during this study and represent a great opportunity for future research. The experiments performed in this study allowed the model to be predictive and be used to size and design of large scale industrial equipment and estimate the upper bound of the energy consumption for the system. It was found that the total parasitic energy loss for the large scale digestion system would be less than 6.1%, which is much less than competing technologies.