IMPURITY CATIONS IN THE BULK AND THE (001)SURFACE OF MUSCOVITE - AN ATOMISTIC SIMULATION STUDY

Solution energies are calculated for monovalent and divalent impuritie s in the bulk and the {001} surface of muscovite, using atomistic simu lation techniques and a consistent set of interatomic potentials. Csis the most soluble alkali metal cation. There are marked differences between the bulk and surface solution energies for the smaller univale nt cations, indicating appreciable segregation to the surface. Without deprotonation of an OH group, none of the Group 1 cations are able to enter the hexagonal cavity on the mica basal plane. Small divalent ca tions are predicted to substitute for octahedral Al with the most favo urable charge-balance mechanism involving the additional substitution of Al for Si. The solution mechanism for larger, less soluble divalent cations involves substitution for K+, with a compensating Al/Si excha nge. Where possible, results are calculated for two models, the first assuming complete ordering of Al and Si on the tetrahedral aluminosili cate sheets and the second completely random ordering. There is little difference between the values from the two models, with the exception of the {001} surface energy.