Experimental Studies of Barite (001) Growth in Alkali Metal Salt Solutions at 108 °C

Barite (BaSO4) growth on the (001) surface was studied using Hydrothermal Atomic Force Microscopy under solutions of alkali metal chloride salts (LiCl, NaCl, KCl, RbCl, and CsCl) as a function of saturation index and ionic strength of the salts at 108 °C. When LiCl, NaCl, and KCl were used as the background electrolyte, growth hillocks on the Barite surface consisted of both 010 steps and ⟨120⟩ steps at ionic strengths of 0.05 and 0.1 M, but 010 steps were not observed at lower ionic strength. From the saturation-state-dependent studies, it was found that the kinetic coefficient for ⟨120⟩ step growth increased with increasing ionic strength in LiCl and NaCl solutions, whereas KCl showed a more complex effect on ⟨120⟩ step velocities. When RbCl or CsCl was used as the background electrolyte, the growth of hillocks was partially or completely inhibited. The results suggest that the smaller ionic radii ions of Li+, Na+, and K+ become incorporated into the growing Barite lattice, whereas the larger cations Rb+ and Cs+ do not become incorporated into the lattice but instead behave as interferences to growth by interacting with sites along ⟨120⟩ steps and blocking the attachment of barium ions.