Langmuir 1991, 7, 1453-1457
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Fourier Transform Infrared Spectroscopic Study of Adsorption of Oleic Acid/Oleate on Surfaces of Apatite and Dolomite D. E. Ince,tv* C. T. Johnston,s and B. M. Moudgil'nt Mineral Resources Research Center, Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611, and Department of Soil Science, University of Florida, Gainesville, Florida 3261 1 Received June 25, 1990. In Final Form: November 9,1990 The nature of the oleic acid species adsorbed on apatite and dolomite at pH 4 and pH 10 with and without NaCl was examined by Fourier transform infared (FT-IR) spectroscopy. In the case of apatite at pH 10,absence of the carboxyl stretching band at 1735 cm-1 and a moderate intensity of asymmetric carboxylate stretching band at 1560 cm-1 indicated that the predominant surfaces species is oleate. At pH 4,the intensity of the two bands reversed indicating oleic acid as the major adsorbed species. Intensity of the carbonyl stretching band increased in the presence of NaCl at pH 4. This is attributed to a shift in equilibrium toward oleic acid in the presence of sodium ions. In the case of dolomite at pH 10,none of the above bands were detected, presumably due to the small amount of oleate present at this pH value. At pH 4,although there is masking of the carboxylate band at 1560 cm-1 by the strong dolomite band in the 1350-1575 cm-l region, based on the intensity of the carboxyl stretching band at 1735 cm-1 it is indicated that the nature of the adsorbed species is similar to the apatite-oleate system. Adsorption of various species was estimated by integrated intensity of the bands in accordance with Beer's law and compared with macroscopic adsorption data. A good agreement between the two adsorption trends was obtained except for dolomite at pH 10. Flotation results correlate with the adsorption trends estimated by FT-IR spectroscopic measurements. Introduction Phosphate rock (apatite) is often separated from impurity minerals, such as silica, calcite, and dolomite, by the froth flotation technique before processing into phosphoric acid. Separation of dolomite from apatite, however, has been difficult because of similarities in the surface chemical properties of these minerals. This problem has attracted considerable interest during the past decade.'-ll It was determined in a recent studys that the flotation efficiency of dolomite from apatite at pH 4 with sodium oleate as the collector is significantly improved in the presence of sodium chloride. Correlation of adsorption and flotation data summarized in Table I revealed that sodium chloride depressed the flotation of apatite without affecting the dolomite flotation behavior. It is known that besides the amount of collector adsorbed, the nature of the adsorbed species also can have a major influence on the flotation of a given mineral. However, a recurring problem in the characterization of t
Department of Materials Science and Engineering.
t Current address: Pfizer Inc., Easton, PA.
I Department of Soil Science. (1) Moudgil, B. M.; Somasundaran, P. Advances in Phosphate Flotaiton; Advances in Mineral Processing; Somasundaran, p., Ed.; SME Littleton, CO, 1986; pp 426-441. (2) Houot, R.; et al. IntoJ.Mineral Process. 1985,14,245-264. (3) Lawver, J. E.; et al. Miner. Metall. Process. 1984, 1 , 89-106. (4) Moudgil,B. M.;Chanchani,R. Miner. Metall. Process. 1985,2, (2), 19-25. (5) Moudgil, B. M.;Chanchani, R. Miner. Metall. Process. 1985,2, (2), 13-19. (6) Llewellyn, T. O., Davis, B. E. and Sullivan,G. E., Miner. Metall. Process. 1984, I , 43-48. (7) Johnston,D. J.; Leja, J. Trans.-Znst. Min. Metall., Sect. C 1978, 87. C2.17-242. - -_. - __. I) Heieh, S. S. and Lehr, J. R., Miner. Metall. Process. 1985,2,10-13. 1) Moudgil, Brij M.; Ince, Dursun U.S. Patent 4,814,069, 1989. .O) Moudgil, B. M.;Ince, D. Znt. J.Mineral Process. 1988,24,47-54. .l)Moudgil, B. M.; Ince, D. Role of pH and Collector Concentration !parationof Phosphates from Dolomitic Gangue Using DDA-HCI; In actants in Solution Volume 10; Mittal, K. L., Ed.; Plenum Press: York, 1989; pp 457-466.
Table I. Adsorption and Flotation of Apatite and Dolomite with and without NaCP
mineral apatite dolomite
NaC1, kmol/m* none 2.0 x 10-2 none 2.0 X 1W2
amount adsorbed, pmol/g x 10+2 pH4 pH 10
3.3 1.8 5.8 5.8
6.1 8.1
amount floated, w t % pH4 pH 10
55-60 0-3 95-100 95-100
98
28
Total sodium oleate concentration = 4 X 10-5 kmol/ma.
the collector-surfactant systems has been the inability of the physical methods employed to determine the nature of the chemical species at the mineral surfaceaqueous solution interface. The chemical basis for the selectivity of the fatty acid for a particular surface is not fully understood at the present time. Although attempts have been made to identify the surface species on salt type minerals by IR spectroscopy, often masking by substrate made it difficult to obtain reliable data7J2-1Sin the IR region of interest. The objective of the present study was to examine the nature of the adsorbed species by using FT-IR spectroscopy. This is expected to help interpret the flotation behavior with and without NaCl using sodium oleate as the collector. Materials and Methods The apatite sample was obtained from Agrico Chemical Co. (Mulberry, FL) and was analyzed to contain 35.5% Pz05 and 2.1 % quartz impurities. The dolomite sample was supplied by (12) Chanchani,R. SelectiveFlotation of Dolomite from Apatite Using Sodium Oleate as the Collector;Ph.D.Dissertation, University of Florida, 1984. (13) Lovell, V. M.; Goold, L. A.; Finkelstein, N. P. I n t . J. Mineral Process. 1974, 1 , 183-192. (14) Peck, A. S. Infrared Studies of Oleic Acid and Sodium Oleate Adsorption on Fluorite, Barite and Calcite; USBM Report of Investigations, R.I. 6202; U.S. Bureau of Mines: Washington, DC, 1963; p 16. (15) Plit, L. R.; Kim, M. K. Trans. SOC.Min. Eng. AIME 1974,256. 188- 193.
0743-7463/91/2407-1453$02.50/0 0 1991 American Chemical Society
Znce et al.
1454 Langmuir, Vol. 7,No. 7, 1991 International Minerals and Chemicals Corp. (Bartow, FL). The analysis of the sample showed 18.9% MgO and 3.1% quartz impurities. The samples were ground and passed through a -325 mesh sieve. The BET N2 surface areas for apatite and dolomite were measured to be 18.4 and 10.1 m2/g, respectively. Adsorption of oleate on apatite and dolomite was determined by direct counts on the solids in the oleic acid precipitation region i.e. pH 8 and below. Above this pH, a solution depletion method was employed. At pH 4.5, solids were rinsed to remove any physically entrained oleic acid. Testa indicated that there was no significant desorption (
