The surface chemistry of the calcite/oleate flotation system was examined b
y in situ FT-NIR/IRS. Spectra of combination and overtone bands of aliphati
c stretching vibrations revealed gauche/trans conformational changes that o
ccurred solely as a function of temperature. The conformational changes wer
e attributed to the simple "melting" behavior associated with phase transit
ions. It was concluded that chemisorbed oleate at calcite surfaces is gel-l
ike at temperatures below 22 degreesC, resembles a coagel between 22 degree
sC and 31 degreesC, and becomes micelle-like at temperatures above 31 degre
esC. By comparison, chemisorbed oleate at fluorite surfaces also undergoes
these phase transitions but is additionally dependent on adsorption density
. The conformational changes were observed at high chemisorption densities
(>2.0x10(-10) mol/cm(2)) and attributed to molecular forces, primarily van
der Waal's interactive forces, among neighboring chemisorbed oleate molecul
es. Similar analysis of in situ FT-NIR/IRS spectra of surface-precipitated
calcium dioleate at calcite surfaces did not exhibit this behavior thereby
confirming that surface-precipitated calcium dioleate remains in an all-tra
ns conformation. The results help explain why surface polymerization is not
observed at calcite surfaces but is observed at fluorite surfaces.