This thesis contains an introduction to the surface chemistry of minerals in aqueous environment, and a summary of five manuscripts concerning adsorption reactions at the surfaces of nano-sized gibbsite (α-Al(OH)3), amorphous silica and kaolinite. Nano-sized gibbsite was synthesized and thoroughly characterized using X-ray diffraction, high-resolution transmission electron microscopy, atomic force microscopy and Fourier transform infrared spectroscopy. The adsorption of protons and the development of charge at the surfaces were studied using high precision potentiometry and zeta potential measurements. The results showed that singly coordinated surface sites at the particle edges protonate/deprotonate, while ion pairs with the medium ions are formed at doubly coordinated surface sites at the basal planes. This ion pair formation is a slow reaction, requiring long equilibrium times. The adsorption of o-phthalate, maleate, fumarate, malonate and oxalate onto gibbsite surfaces was studied using Fourier transform infrared spectroscopy, zeta potential measurements, adsorption measurements and theoretical frequency calculations. All ligands were found to form outer-sphere complexes at the basal planes. Significant amounts of inner-sphere complexes at the particle edges were found for malonate and oxalate only. The observed adsorption was described using surface complexation models. The proton reactions at the surface of amorphous silica were described using a two-site model. XPS indicated that Na+ is accumulated in the vicinity of the surface. Proton reactions at kaolinite surfaces were explained using a nonelectrostatic model, assuming that only the aluminol and silanol sites at the particle edges are reactive. Extensive modeling provided support for this assumption.

L'étude des mécanismes de sorption de l'ion uranyle sur le substrat SrTiO$_3$ en fonction de la température a fait l'objet de cette étude. Tout d'abord, une caractérisation physico¬chimique a été réalisée à l'aide de plusieurs techniques structurales (DRX, FTIR) et morphologique (MEB). La spectroscopie XPS a permis d'identifier deux sites de surface (Ti¬OH et Sr-OH). En utilisant les titrages potentiométriques de SrTiO$_3$ à différentes températures, les caractéristiques acido-basiques ont été déterminées. Ensuite, la simulation des titrages potentiométriques, entre 25 et 90°C, a été réalisée à l'aide du code FITEQL, les constantes d'équilibre ainsi obtenues montrent une nette variation avec la température: la protonation du site $\equiv Sr – OH$ suit un processus endothermique tandis que la déprotonation du site $\equiv Ti – OH$ implique un processus exothermique. A partir de ces constantes d'équilibre, les grandeurs thermodynamiques, enthalpie et entropie de protonation/déprotonation ont été calculées en utilisant la relation de van't Hoff. Les études de sorption de l'ion uranyle sur le substrat SrTiO$_3$ ont été réalisées dans un intervalle de pH de 0.5 à 5. Les sauts de sorption ainsi obtenus montrent une nette augmentation du pourcentage de sorption avec l'augmentation de la température, traduisant un phénomène globalement endothermique. Deux sites de sorption différents ont été identifiés à la surface du solide par SLRTIF. Ils sont associés aux temps de vie de fluorescence de l'uranyle sorbé de 12 $\pm$ 2 et 60 $\pm$ 5 $\mu$s. Les sauts de sorption ont été modélisés à l'aide du code FITEQL en utilisant le modèle à capacitance constante. Cette simulation des sauts de sorption a été réalisée en tenant compte des résultats de l'étude structurale (deux sites de surface $\equiv Sr - OH$ et $\equiv Ti – OH$ et formation de complexe surfacique de sphère interne bidendate, mononucléaire) et des données obtenues dans la modélisation des titrages potentiométriques. Les équilibres de sorption modélisés ont confirmé la formation de deux complexes de surface de caractère bidendate : [($\equiv SrOH)($\equivTiOH)UO_2]^{2+}$ et [($\equiv TiOH)($\equivTiO)UO_2]^{2+}$. Suite à l'obtention des constantes thermodynamiques obtenues par cette simulation, la relation van't Hoff a été appliquée pour déterminer les variations d'enthalpie et d'entropie associés au processus de sorption. Finalement, une étude sur les transferts d'énergie a été présentée entre deux ions sorbés sur le solide SrTiO$_3$. Ainsi, le transfert d'énergie non-radiatif des ions Tb$^{3+}$ vers les ions EU$^{3+}$ a été étudié. L'application du modèle de Inokuti-Hirayama et Dexter a conduit à l'évaluation du rayon de la sphère d'interaction (2,7-3,4 Å) entre les deux ions (Tb$^{3+}$ et EU$^{3+}$)

Surface complexation models (SCMs) have proven to be a useful tool in predicting ion adsorption at the mineral – water interface. In particular, previous research has shown that the Diffuse Layer Model (DLM), Constant Capacitance Model (CCM), and Triple Layer Model (TLM), are all capable of predicting ion adsorption in relatively simple single solute systems. To better simulate the environmental conditions experienced by groundwater sources present in the Earth’s subsurface, experimental adsorption studies have been conducted for more complex multi-solute systems. Under these conditions, SCMs have not proven to be reliable in consistently predicting ion adsorption behavior for the adsorbates of interest. This inability of these SCMs to predict ion adsorption for more complex, multi-solute systems is thought to stem from the variable site density (NS) values utilized in these models. In this research, a methodology was developed for characterizing mineral surface heterogeneity that allows for the different site density values predicted from crystallography, microscopic imaging, tritium exchange, surface saturation data, and surface charging data to all be explained using a single unified theory. This methodology was applied to a goethite mineral sample used in performing batch adsorption studies in single and bi-solute systems with Cd(II), Pb(II), and Se(IV). The adsorption behavior of these adsorbates onto the goethite sample was successfully predicted using the Charge Distribution Multi-Site Complexation (CD-MUSIC) Model and surface complexes consistent with spectroscopic data and computational molecular modeling simulations. A second, separate modeling study was performed using CD-MUSIC to predict Hg(II) adsorption onto different goethite samples of varying size and crystal morphology in single and multi-solute systems. In this study, site density values were predicted for the mineral samples studied utilizing a linear relationship observed for goethite between specific surface area and proton reactive site density. The CD-MUSIC model proved successful in predicting Hg(II) adsorption over all conditions studied while employing only surface complexes consistent with molecular scale analyses. In addition, a novel method for quantifying carbonate’s presence in experimental systems was developed. / text

The long-lived fission product 126Sn (105 years) (Weast (1972)) is of substantial interest in the context of nuclear waste disposal in deep underground repositories. However, the prevalent redox state, the aqueous speciation as well as the reactions at the mineral-water interface under the expected anoxic conditions are a matter of debate. Therefore, in this PhD thesis I present work on the reactions of SnII with three Fe-bearing minerals as a function of pH, time, and SnII loading under anoxic condition with O2 level < 2 ppmv. The first mineral, goethite, contains only trivalent Fe (FeIIIOOH), the second, magnetite, contains both FeII and FeIII (FeIIFeIII2O4), and the third, mackinawite (FeIIS), contains only divalent Fe. The uptake behavior of the three mineral surfaces was investigated by batch sorption studies. Tin redox state was investigated by Sn-K X-ray absorption near-edge structure (XANES) spectroscopy, and the local, molecular structure of the expected Sn surface complexes and precipitates was studied by extended X-ray absorption fine-structure (EXAFS) spectroscopy. Selected samples were also investigated by transmission electron microscopy (TEM) to elucidate the existence and nature of secondary, Fe- and /or Sn containing solids, and by Mössbauer spectroscopy to study FeII and FeIII in the minerals. Based on the such-obtained molecular-level information, surface complexation models (SCM) were fitted to the batch sorption data to derive surface complexation constants. In the presence of the FeIII-bearing minerals magnetite and goethite, I observed a rapid uptake and oxidation of SnII to SnIV. The local structure determined by EXAFS showed two Sn-Fe distances of about 3.15 and 3.60 Å in line with edge and corner sharing arrangements between octahedrally coordinated SnIV and the Fe(O,OH)6 octahedra at the magnetite and goethite surfaces. While the respective coordination numbers suggested formation of tetradentate inner-sphere complexes between pH 3 and 9 for magnetite, bidentate inner-sphere complexes (single edge-sharing (1E) and corner-sharing (2C)) prevail at the goethite surface at pH > 3, with the relative amount of 2C increasing with Sn loading. The interfacial electron transfer between sorbed SnII and structural FeIII potentially leads to dissolution of FeII and transformation to secondary FeII/FeIII oxide minerals. There is no clear evidence to confirm the reductive dissolution in the Sn/ magnetite system, Rietveld refinement of XRD patterns, however, indicates an increase of FeII/FeIII ratio in the magnetite structure. For the Sn/goethite system, dissolved FeII increased with SnII loading at the lowest pH investigated, indicative of reductive dissolution. At pH >5, spherical and cubic particles of magnetite were observed by TEM, and their number increased with SnII loading. Based on previous finding, this secondary mineral transformation of goethite should proceed via dissolution and recrystallization. The molecular structure and oxidation state of sorbed Sn were then used to fit the batch sorption data of magnetite and goethite with SCM. The sorption data on magnetite were fit with the diffuse double layer model (DLM) employing two different complexes, the first ( = -14.97±0.35) prevailing from pH 2 to 9, and the second ( = -17.72±0.50), which forms at pH > 9 by co-adsorption of FeII, thereby increasing sorption at this high pH. The sorption data on goethite were fitted with the charge distribution–multisite complexation model (CD-MUSIC). Based on the EXAFS-derived presence of two different bidentate inner-sphere complexes ((≡FeOH)(≡Fe3O)Sn(OH)3 (1E) and (≡FeOH)2Sn(OH)3) (2C)), sorption affinity constants of 15.5 ±1.4 for the 1E complex and of 19.2 ±0.6 for the 2C complex were obtained. The model is not only able to predict sorption across the observed pH range, but also the transition from a roughly 50/50 distribution of the two complexes at 12.5 µmol/g Sn loading, to the prevalence of the 2C complex at higher loading, in line with the EXAFS data. The retention mechanism of SnII by mackinawite is significantly dependent on the solution pH, reflecting the transient changes of the mackinawite surface in the sorption process. At pH <7, SnII is retained in its original oxidation state. It forms a surface complex, which is characterized by two short (2.38 Å) Sn-S bonds, which can be interpreted as the bonds towards the S-terminated surface of mackinawite, and two longer Sn-S bonds (2.59 Å), which point most likely towards the solution phase, completing the tetragonal SnS4 innersphere sorption complex. Precipitation of SnS or formation of a solid solution with mackinawite could be excluded. At pH > 9, SnII is completely oxidized by an FeII/FeIII (hydr)oxide, most likely green rust, forming on the surface of mackinawite. Six O atoms at 2.04 Å and 6 Fe atoms at 3.29 Å demonstrate a structural incorporation by green rust, where SnIV substitutes for Fe in the crystal structure. The transition between SnII and SnIV and between sulfur and oxygen coordination takes place between pH 7 and 8, in accordance with the transition from the mackinawite stability field to more oxidized Fe-bearing minerals. The uptake processes of SnII by mackinawite are largely in line with the uptake processes of divalent cations of other soft Lewis-acid metals like Cd, Hg and Pb. Very different Sn retention mechanisms were hence active, including oxidation to SnIV and formation of tetradentate and bidentate surface complexes of the SnIV hydroxo moieties on goethite and magnetite, and in the case of mackinawite a SnII sulfide species forming a bidentate surface complex at low pH, and structural incorporation of SnIV by an oxidation product, green rust, at high pH. In all three mineral systems and largely independent on the retention mechanisms, inorganic SnII was strongly retained, with Rd values always exceeding 5, across the relatively wide pH range relevant for the near and far-field of nuclear waste respositories. For the goethite and magnetite systems, the retention could be well modeled with surface complexation models based on the molecular structural data. This is an important contribution to the safety case for future nuclear waste repositories, since such SCMs provide reliable means for predicting the radioactive dose released by 126Sn from nuclear waste into the biosphere across a wide range of physicochemical conditions typical for the engineered as well as natural barriers.

Copper based interconnects with low dielectric constant layers are currently used to increase interconnect densities and reduce interconnect time delays in integrated circuits. The technology used to develop copper interconnects involves Chemical Mechanical Planarization (CMP) of copper films deposited on low-k layers (silica or silica based films), which is carried out using slurries containing abrasive particles. One issue using such a structure is copper contamination over dielectric layers (SiO2 film), if not reduced, this contamination will cause current leakage. In this study, the conditions conducive to copper contamination onto SiO2 films during Cu-CMP process were studied, and a post-CMP cleaning technique was discussed based on experimental results. It was found that the adsorption of copper onto a silica surface is kinetically fast (< 0.5 minute). The amount of copper absorbed is pH and concentration dependent and affected by presence of H2O2, complexing agents, and copper corrosion inhibitor Benzotrazole. Based on de-sorption results, DI water alone was unable to reduce adsorbed copper to an acceptable level, especially for adsorption that takes place at a higher pH condition. The addition of complex agent, citric acid, proved effective in suppressing copper adsorption onto oxide silica during polishing or post-CMP cleaning by forming stable copper-CA complexes. Surface Complexation Modeling was used to simulate copper adsorption isotherms and predict the copper contamination levels on SiO2 surfaces.Another issue with the application of copper CMP is its environmental impact. CMP is a costly process due to its huge consumption of pure water and slurry. Additionally, Cu-CMP processing generates a waste stream containing certain amounts of copper and abrasive slurry particles. In this study, the separation technique electrocoagulation was investigated to remove both copper and abrasive slurry particles simultaneously. For effluent containing ~40 ppm dissolved copper, it was found that ~90% dissolved copper was removed from the waste streams through electroplating and in-situ chemical precipitation. The amount of copper removed through plating is impacted by membrane surface charge, type/amount of complexing agents, and solid content in the slurry suspension. The slurry particles can be removed ~90% within 2 hours of EC through multiple mechanisms.

It is important to understand the processes that regulate phosphorus (P) fluxes to coastal environments, because P is an important nutrient in coastal ecosystems. Phosphorus adsorbs to the surface of minerals in sediment and bedrock, and an influx of seawater can cause some of that P to desorb, raising the P concentration of ambient water. Although seawater-induced P desorption is thought to be an important source of P to coastal environments, the chemical reactions that underlie it have not been established. Previous work provides some relevant surface reactions and associated affinity constants between various aqueous P species and the surface of calcite and in dilute calcium carbonate-P solutions. However, these reactions with their respective affinity constants from the literature fail to predict the behavior of P with calcite in seawater. In this study, we conducted a series of batch experiments involving both adsorption and desorption of P in seawater, freshwater, dilute seawater, and mixtures of seawater and freshwater. We used these results in the geochemical model PHREEQC and the parameter estimation model PEST to optimize the affinity constants for the existing surface reactions. We found that after making minor adjustments to the affinity constants, the existing surface complexation models of calcite surface reactions from the published literature are sufficient to explain seawater-induced P desorption. Specifically, our results suggest that CaPO4- and either CaHPO40 or HPO42- may be important species in the P adsorption/desorption reactions in freshwater-seawater mixing.

Several recent studies that have proposed MUSIC models for gibbsite surfaces have purported to achieve a very good fit with potentiometric titration data. However, in order to achieve such results, several significant parameters, such as the number of surface sites, site densities, and pKa values were sometimes re-introduced in the model as fitted parameters, and physically unrealistic modeling assumptions were sometimes used. In addition, recent evidence supports the idea that some of the gibbsite potentiometric titration data from these studies may be unreliable. In order to re-interpret the potentiometric titration data, we used several recently published methods. In order to detect possible problems with estimates of gibbsite basal and edge surface area, we synthesized two gibbsite samples with different aspect ratios and characterized their surface areas using BET, AFM, and computerized image analysis routines. We also estimated pKa values for acid/base reactions at gibbsite surfaces by applying a new bond-valence method to gibbsite (001)-type and (100)-type surface structures based on ab initio calculations. The resulting pKa estimates are not to be taken as precise values due to difficulties and assumptions associated with calculating reasonable ab initio surface structures. Instead, we believe they represent a more reasonable range than has been previously estimated. Using these estimates, we propose an improved MUSIC model for gibbsite, which seems to predict surface adsorption, not perfectly, but within a reasonable range for a number of titration data sets without re-introducing any of our estimated parameters as adjustable parameters. Discrepancies that exist between model predictions and various potentiometric titration data sets are likely due to error associated with potentiometric titrations and pKa predictions.

Canada is in the process of implementing a Deep Geologic Repository (DGR) to dispose of used nuclear waste. Adsorption behaviour of both Se(-II) and Tc(IV) onto granite, shale, limestone, illite, and MX-80 bentonite has been elucidated. Se(-II) adsorption onto granite and MX-80 bentonite displays a decrease in Rd with an increase in solution pH. Se(-II) adsorption onto granite decreases with an increase in solution ionic strength. Se(-II) adsorption onto MX-80 bentonite does not return evidence which supports an apparent effect due to the ionic strength. Tc(IV) adsorption onto shale, limestone, illite, and MX-80 bentonite remains constant as the solution pH increases. Ionic strength does not affect the magnitude of Tc(IV) adsorption across the adsorbents, however an increase in ionic strength accelerates Tc(IV) adsorption. Se(-II) surface complexation models are best simulated with the following surface complexes: ≡Feldspar_sSe-, ≡Biotite_sOH2HSe, ≡Albite_sSe-, ≡Montmorillonite_sSe-, and ≡Montmorillonite_sOH2HSe. Tc(IV) adsorption is best simulated with: ≡Biotite_sOTcO(OH), ≡Quartz_sOTcO(OH), (≡Feldspar_sOH)2TcO(OH)-, ≡Montmorillonite_sOTcO(OH), (≡Albite_sOH)2TcO(OH)-, ≡Illite_sOTcO(OH), and ≡Chlorite_sOTcO(OH). Se(-II) adsorption onto granite and MX-80 bentonite in CR-10 solution returns Rd values of (1.80 ± 0.10) m3∙kg-1 and (0.47 ± 0.38) m3∙kg-1, respectively. Tc(IV) adsorption onto granite and MX-80 bentonite in CR-10 solution returned Rd values of (1.47 ± 0.25) m3∙kg-1 and (2.19 ± 0.33) m3∙kg-1, respectively. Tc(IV) adsorption onto shale, limestone, illite, and MX-80 bentonite in SR-270-PW solution returned Rd values of (0.16 ± 0.10) m3∙kg-1, (0.44 ± 0.21) m3∙kg-1, (1.86 ± 0.44) m3∙kg-1, and (0.23 ± 0.10) m3∙kg-1, respectively. This thesis will further deepen the understanding of Se(-II) and Tc(IV) adsorption. / Thesis / Doctor of Philosophy (PhD) / Determining the adsorption of Se(-II) and Tc(IV) onto granite, shale, limestone, illite, and MX-80 bentonite is beneficial to choosing a location within Canada to locate a used nuclear fuel repository. This thesis aims to quantify the adsorption behaviour of Se(-II) and Tc(IV) in Ca-Na-Cl and Na-Ca-Cl solutions with respect to a varying solution ionic strength and pH. Quantification of the adsorption was accomplished with adsorption experiments used in conjunction with geochemical simulations. New simulated surfaces specific to granite, shale, and MX-80 bentonite have been developed to complete these simulations. A final achievement was quantifying the adsorption of Se(-II) and Tc(IV) in groundwater representative solutions specific to locations considered for the used nuclear fuel repository.

Pu (III) is one of the key elements in the safety assessments of Canadian deep geological repository program (DGR). Sorption is a potential mechanism for retarding radionuclide transport from a DGR to the environment. In the current scenario, Pu (III) is considered to be a dominant radioactive element in the deep geological groundwater. Eu, considered to be a chemical analogue of Pu (III), its sorption behavior is now the target of our research. This thesis investigates the sorption properties of Eu on MX-80 under saline reducing conditions, and highly saline reducing conditions. The thermodynamic sorption modelling of Eu is also need to be applied. A surface sorption model is also developed by applying computer program for Eu (III) on MX-80 to investigate the sorption mechanisms of Eu (III) sorption. / Thesis / Master of Applied Science (MASc)

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