(253p) Evaluation of Effective Stacking Interactions of Kaolinite Nanoparticles in Aqueous and Organic Solvents By Molecular Theory of Solvation

Crucial for the understanding of the rich phase behavior of nanocolloidal systems is accurate determination of effective interactions between the nanoparticles. Evaluation of the interactions by conventional molecular simulation techniques generally requires costly free energy integration and therefore is usually avoided by adopting simple and often unrealistic semiempirical effective potentials. In order to efficiently obtain effective interactions in a nanocolloidal system, we employ the three-dimensional reference interaction site model with the Kovalenko-Hirata closure relation (3D-RISM-KH) molecular theory of solvation [1-3]. 3D-RISM-KH molecular theory of solvation offers fully atomistic description with all-atom force-fields and notable performance advantages over molecular simulations. In addition, this modeling approach predicts the adsorption structure and thermodynamics of multicomponent systems and allows comparison of the interactions among solvent components with the adsorbent.

The approach is applied to study the effective interactions between kaolinite clay platelets, which serve as a simple model of Mature Fine Tailing (MFT). MFT is a gel-like colloidal suspension of clay nanoparticles and residual bitumen in water with electrolytes produced by aqueous process of extraction of bitumen from oil sands. Efficient dewatering and densification of the MFT are of great importance for decreasing the environmental footprint of the oil sands industry. Currently, efforts are undertaken to introduce a process of non-aqueous extraction of bitumen from oil sands, which would raise the energetic efficiency and avoid the water pollution of the conventional process. However, regardless of the extraction method, oil sands bitumen froth contains fines (clay particles coated with bitumen) above the 0.5% limit required for pipeline transportation.

Potential of mean force between kaolinite clay platelets with several mutual orientations as well as adsorption structure in different aqueous/organic solvents with additives/adjuvants is computed. The molecular insights provided by the 3D-RISM-KH molecular theory of solvation allow us to better understand the mechanisms of bitumen desorption and clay nanoparticle flocculation in aqueous and organic solvents, and should facilitate the rational design of adjuvants/flocculants specifically tailored for these purposes.

References

1. Kovalenko, A.; Hirata, F. J. Chem. Phys. 1999, 110, 10095-10112.

2. Kovalenko, A. In: Molecular Theory of Solvation; Hirata, F., Ed.; Kluwer Academic Publishers: Dordrecht, 2003; pp. 169-275.

3. Kovalenko, A. Pure Appl. Chem. 2013, 85, 159-199.