Degree Granting Department
Robert H. Byrne, Ph.D.
Iron, pH, Carbonate, Ionic strength, ICP-MS
The sorption behavior of yttrium and the rare earth elements (YREEs) was investigated using a variety of hydroxide precipitates over a range of solution conditions. Experiments with amorphous hydroxides of Al, Ga, and In were conducted at constant pH (~6.0) and constant ionic strength (I = 0.01 M), while YREE sorption by amorphous ferric hydroxide was examined over a range of ionic strength (0.01 M <Ì² I <Ì² 0.09 M), pH (3.9 <Ì² pH <Ì² 7.1), carbonate concentration (0 M <Ì² [CO32-]T <Ì² 150 micro-M), and temperature (10Â°C <Ì² T <Ì² 40Â°C). Sorption results were quantified via distribution coefficients, expressed as ratios of YREE concentrations between the solid and the solution, and normalized to concentrations of the sorptive solid substrate. Distribution coefficient patterns for Al, Ga, and In hydroxides were well correlated with the pattern for YREE hydrolysis.
In contrast, amorphous ferric hydroxide developed a distinct pattern that was different than those for Al, Ga, and In precipitates but similar to the pattern predicted for natural marine particles. YREE sorption was shown to be strongly dependent on pH and carbonate concentration, significantly dependent on temperature, and weakly dependent on ionic strength. Distribution coefficients for amorphous ferric hydroxide (iKFe) were used to develop a surface complexation model that contained (i) two equilibrium constants for sorption of free YREE ions (M3+) by surface hydroxyl groups, (ii) one equilibrium constant for sorption of YREE carbonate complexes (MCO3+), (iii) solution complexation constants for YREE carbonates and bicarbonates, (iv) a surface protonation constant for amorphous ferric hydroxide, and (v) enthalpies for M3+ sorption. This quantitative model accurately described (i) an increase in iKFe with increasing pH, (ii) an initial increase in iKFe with increasing carbonate concentration due to sorption of MCO3+, in addition to M3+, (iii) a subsequent decrease in iKFe due to increasing YREE complexation by carbonate ions (especially extensive for the heavy REEs), and (iv) an increase in iKFe with increasing temperature.
Scholar Commons Citation
Quinn, Kelly Ann, "Influence of solution and surface chemistry on yttrium and rare earth element sorption" (2006). Graduate Theses and Dissertations.