S. Veeramasuneni et al., THE INFLUENCE OF OXYGEN DEFECT STATES ON THE SURFACE-CHARGE OF ALKALI-HALIDES, Journal of colloid and interface science, 182(1), 1996, pp. 275-281
The sign of the surface charge for alkali halides in their saturated b
rines has been established from nonequilibrium electrophoresis measure
ments, and on this basis the flotation response of alkali halides was
explained based on the adsorption of oppositely charged collector coll
oids by heterocoagulation. These surface charge results for alkali hal
ides are generally as expected from simplified lattice ion hydration t
heory with some exceptions, specifically LiF, KCl, NaCl, KBr, RbBr, KI
, and RbI. The presence of natural oxygen defect states in the crystal
lattice and the inaccuracies involved in the gaseous ion hydration fr
ee energy values used appear, in the past, to be responsible for these
deviations. The presence of natural oxygen defect states in KCI, KBr,
RbBr, and RbI, as characterized by UV/Vis absorption, was found to ac
count for their anomalous surface charge. Further, other positively ch
arged alkali halides, LiF, NaCl, and KI, were found to be free of oxyg
en defect states. Nevertheless, oxygen defects can be created in these
alkali halides to make them negatively charged, and this has been dem
onstrated for NaCl. Such negatively charged NaCl can be readily floate
d with positively charged amine collector colloids, thus confirming th
e surface charge/collector colloid adsorption theory. (C) 1996 Academi
c Press, Inc.