Adsorption of oleate on apatite studied by diffuse reflectance infrared Fourier transform spectroscopy

Abstract

The adsorption of oleate on apatite was studied at pH values from 6 to 9.8 and oleate concentrations from 2 X 10"5 6to 3 X 10~4 mol Lr1. Diffuse reflectance infrared Fourier transform spectroscopy has been found to be superior to the transmission infrared technique for detecting adsorbed oleate species. Confusion in previous studies is clarified and a better understanding of the adsorption mechanism obtained. Chemisorbed oleate corresponds to a single peak at 1550 cm"1 and probably comprises one oleate ion bonding with one lattice calcium ion on the surface. Surface calcium oleate precipitate showing peaks at 1574 and 1538 cm-1 has a structure similar to that of bulk calcium oleate and probably adsorbs through ion-dipole interaction and hydrocarbon chain association. Oleic acid dimer and monomer adsorb via hydrocarbon chain association onto underlying chemisorbed oleate and correspond to a sharp peak at 1713 cm'1 and a shoulder at 1732 cm"1, respectively. Chemisorption of oleate on apatite occurred under all conditions studied and was accompanied by physical adsorption of calcium oleate precipitate and/or oleic acid monomer and/or oleic acid dimer, depending on the pH and concentration of the solution.

Competition between sodium oleate and sodium silicate for a silicate/oleate modified magnetite surface studied by in situ ATR-FTIR spectroscopy

“…It has been shown by others that pH and silica concentration are two important factors affecting the efficiency of water-glass as depressant in selective separation of apatite from iron oxide [44,45]. However, at lower sodium silicate concentrations than 0.4 mM, the adsorbed silicate species seemed to work mainly as a dispersing agent [46].…”

“…The band assignments of oleate and oleic acid are well established in the literature [26]. There are four main regions in the IR spectrum of oleate which are commonly considered to determine and characterize the nature of adsorbed oleate at mineral surfaces:…”

Adsorption of Oleic Acid at Sillimanite/Water Interface

“…In the present study, a strong and intense band observed around 1586 cm −1 clearly suggests the presence of oleate, i.e., carboxylate ion on alumina and Al(OH) 3 . The asymmetric carboxylate vibration band has been attributed to chemisorbed oleate (21,22). If it is in the form of undissociated oleic acid (-COOH), the mean frequency of νC=O stretching vibration should appear around 1690 cm −1 for dimer and 1718 cm −1 for monomer.…”

A study of sodium silicate in aqueous solution and sorbed by synthetic magnetite using in situ ATR-FTIR spectroscopy

“…At higher pH values, however, polymeric silicates selectively adsorbed onto calcite surfaces rather than on apatite even at this low silicate concentration (1.3 × 10 −3 mol L −1 ). Gong et al concluded that the role of sodium silicate (10 −3 to 10 −2 mol L −1 ) in the selective flotation of apatite from iron oxides was attributed to the adsorption of moderately polymerized silicate species, which were responsible for the depression of the iron oxide [5,6]. However, in the reversed flotation of apatite from magnetite, Su et al observed that the selectivity of sodium silicate as depressant decreased when the dosage increased from 300 g t −1 (2.4 × 10 −4 mol L −1 ) to 500 g t −1 (4 × 10 −4 mol L −1 ) resulting in a less efficient dephosphorization of magnetite fines and proposed that the dispersion effect of sodium silicate played a key role at such a low concentration rather than the depressant effect [7].…”