Figure 1 : Compositions isotopiques du bore dans les principaux réservoirs terrestres.
Figure 2 : Cycle géochimique du bore, d’après (Lemarchand, 2001). Les masses sont exprimées en kg, les flux en kg/an, les concentrations, entre parenthèses, en ppm.
CHAPITRE I
Figure I-1 : Diagramme de rayons X de la birnessite synthétisée dans cette étude. Les chiffres au dessus des pics correspondent aux distances réticulaires en Å
Figure I-2 : Isotherme d’adsorption du bore sur l’acide humique Aldrich à T=25°C, I=0,15M et pH=9.
Figure I-3 : Courbe de titration par la soude d'une solution contenant 0.1 M de B(OH)3 et 0.2 M d'acide salicylique calculée sans pendre en compte la
complexation du bore par l’acide salicylique (pointillés), puis en prenant en compte cette complexation (trait plein).
Figure 1-4 : Spectres RMN 11B de l’acide borique et de l’ion borate en solution.
Figure I-5 : Nombre de coups mesurés à l’ICP-MS en fonction de la concentration en bore en utilisant une matrice contenant :
A- 0,1 mol/L de NH3 et 0,25 % massique de mannitol.
B- 2% de HNO3. 4 6 15 18 21 25 29
Liste des figures
170
Figure I-6 : Hauteur de pic mesurée en colorimétrie pour des solutions de concentrations comparables d’acide borique et de chlorure ferreux.
Figure I-7 : Représentation schématique des différents modèles surfaciques utilisés.
CHAPITRE II
Figure 1: Spectres de RMN 11B du bore libre (0,01mol/L) en solution (a: pH=11,4, b: pH=4,9), puis du bore complexé (0,01 mol/L) par le catéchol à pH=8 (c: [H2Cat]=0,01 mol/L, d: [H2Cat]=0,1 mol/L).
Figure 2 : Spectres RMN de 11B du bore complexé par l’acide salicylique.
A - pH=4,5, [B]tot = 0,01 mol/L, [H2Sal]tot = 0,02 mol/L (a), 0,05 mol/L
(b), 0,15 mol/L (c).
B - [B]tot = 0,01 mol/L, [H2Sal]tot = 0,1 mol/L, pH = 3,8 (a), 6,3 (b), 9,6
(c).
Figure 3 : Spectre RMN de 11B du bore complexé par l’acide tartrique.
[B]total =0,01 mol/L, [H4Tart]=0.1 mol/L (a, b, c d), 0,05 mol/L (e), 0,5
mol/L (f), pH=1,96 (a) , 5,45 (b), 9,32 (c), 13,02 (d), 11,37 (e) et 11,56 (f).
Figure 4 : Spectre RMN de 11B du bore complexé par l’acide citrique.
A - [B]tot = 0,01 mol/L, [H4Citr]tot = 0,1 mol/L, pH=1,99 (a), 3,41 (b),
5,13 (c), 9.2 (d), 10,88 (e).
B - [B]tot = 0.01 mol/L, [H4Citr]tot = 0,5 mol/L, pH=1,94 (a), 6,58 (b),
9,22 (c).
Figure 5 : Spéciation du bore (10-3 mol/L) en fonction du pH en présence de 10-1 mol/L de composé organique.
Figure 6 : Déplacements chimiques observés en RMN de 11B pour les complexes du bore avec différents types de ligands organiques.
31 34 53 55 57 59 61 62
Liste des figures
171 CHAPITRE III
Figure 1: Acid-base titration of the Aldrich humic acid at I=0.15M ant T=25°C. Circles and squares represent experimental titrations performed with and without CaCl2, respectively, but the dashed and dotted lines stand
for the two-sites and three-sites model fits, respectively.
Figure 2: Boron adsorption on humic acid: boron partition coefficient Kd (see definition in § 3.2.1.) between adsorbed and aqueous boron as function of pH at 25°C and I=0.15 M. Error bars were calculated taking account of concentration measurement uncertainties of 1%.
Figure 3: Boron concentration sorbed at the surface of the Ca-flocculated humic acid as a function of aqueous boron concentration (Langmurian adsorption isotherm) at pH=9, I=0.15M and T=25°C. The symbols represent the experimental data (errors bars take account of an uncertainty of 5% on boron chemical analyses). The solid line stands for the Langmuir equation fit whereas the dashed and dotted lines represent the surface complexation model fit with three and four complexes, respectively.
Figure 4: 11B MAS NMR spectra of boron adsorbed on humic acid at pH=6 and 9 in a suspension of 10g/L of humic acid in presence of [B]=0.1mol/L.
Figure 5: Boron isotopic fractionation during adsorption onto humic acid: variation of boron isotopes fractionation factor as a function of pH at 25°C. Boron isotopic composition was measured in solution at equilibrium. Isotopic composition of sorbed boron was deduced from its aqueous isotopic composition using eq.1. Error bars account for analytical uncertainty of 1% and 0.4 ‰ on boron concentration and isotopic measurements, respectively.
79
81
81
82
Liste des figures
172
Figure 6: Boron adsorption as function of pH modeled with three complexes formed on two carboxylic and one phenolic functions. Values of model parameters are listed in Tables 1 and 3.
Figure 7: Boron adsorption as function of pH modeled with four complexes formed on two carboxylic and two phenolic functions. Values of model parameters are listed in Tables 1 and 3.
Figure 8: Modeling of boron isotopic fractionation assuming it resulted solely from the fractionation between aqueous boric acid and borate ion (see § 4.2.1).
Figure 9: Modeling of sorption dependent boron isotopic fractionation with three and four surface complexes. Values of isotopic fractionations factors are listed in Table 3.
Figure 10: Schematic structures of boron surface complexes formed within the framework of the three-sites and four-sites models. It is assumed that the structures of boron surface complexes are the same in the two models with, in the case of the four-sites model, an additional BL-C
complex formed on weaker carboxylic functions.
CHAPITRE IV
Figure 1: Boron adsorption on goethite (A) and birnessite (B): boron partition coefficient Kd (Kd=(mBadsorbed/mgoethite)/(mBaq/msolution)) between
adsorbed and aqueous boron as function of pH at 25°C and I=0.1 M. Error bars were calculated taking account of concentration measurement uncertainties of 1%.
Figure 2: Boron concentration sorbed at the surface of goethite (A) and birnessite (B) as a function of aqueous boron concentration (Langmurian adsorption isotherm) at pH=8.2, I=0.1M and T=25°C. The symbols represent the experimental data (errors bars take account of an
84 85 86 87 88 107 108
Liste des figures
173
uncertainty of 1% on boron chemical analyses). The dashed and dotted lines represent the Langmuir equation fit of two hypothetical complexes, the solid line is the sum of dashed and dotted line. Values of fit parameters are K1=0.58, K2=0.0025, Γ1=8.5 mmol/kg, Γ2=141.7
mmol/kg for goethite and K1=0.12, K2=0.0045, Γ1=23.8 mmol/kg,
Γ2=102.7 mmol/kg for birnessite.
Figure 3: DRIFT spectra of boron adsorbed at 25°C on goethite (A) and birnessite (B) in presence of [B]=0.1mol/L in suspensions of 30 and 10 g/L for goethite and birnessite, respectively.
Figure 4: Boron isotopic fractionation following its adsorption at 25°C onto goethite (A) and birnessite (B): variation of boron isotopes fractionation factor as a function of pH. Error bars account for analytical uncertainty of 1% and 0.4 ‰ on boron concentration and isotopic measurements, respectively.
Figure 5: Modeling of boron sorption at the surface of goethite (A-B) and birnessite (C-D) at 25°C. Symbols represent experimental data but lines represent calculated Kd values. Values of models parameters are listed in Table 2.
Figure 6: Modeling at 25°C (solid line) of sorption dependent boron isotopic fractionation on goethite (A) and birnessite (B). Corresponding adsorption models are those where every constants were optimized (see table 2 and figure 5) Values of B isotopic fractionations factors are listed in Table 3.
Figure 7: Modeling (solid line) of boron isotopic fractionation at the surface of goethite (A) and birnessite (B) taking an αIV-III value equal to 0.965 at
25°C. 110 111 114 116 120
Liste des figures
174
Figure 8: Calculated B isotopic fractionation between bed rocks and soil solution (∆w-rock) as a function of the water/iron oxide ratio (WR) in the Nsimi
and Rio Icacos watersheds using with Kd and values determined in this study for B sorption on goethite surface at pH=5 (Nsimi) and pH=7 (Rio Icacos).
CHAPITRE V
Figure V-1 : Représentation schématique des transferts de bore dans les sols.
Figure V-2 : Modélisation des facteurs de fractionnement isotopiques entre bore adsorbé et bore dissous obtenus dans ce travail en considérant que les complexes surfaciques du bore ont une composition isotopique identique à celle de l’ion borate, et en optimisant uniquement αIV-III, le
facteur de fractionnement isotopique entre l’ion borate et l’acide borique.
Figure V-3 : Influence du pH (a), du taux de matière organique (b), du taux d’argiles (c) et du taux d’oxydes (d) sur la variation de composition isotopique du bore des eaux de sol.
Figure V-4 : Compositions isotopiques des grands fleuves mondiaux. D’après (Lemarchand et al., 2002b). 122 135 142 147 147