Interaction with mineral surfaces

Diagenesis increases with depth and time of burial [34]. Maturation (also termed catagenesis) is the result of elevated heat and pressure acting on OM, and interactions with mineral surfaces and complexed metals may also be involved... 

In the present paper the chemistry of plutonium is reviewed, with particular reference to the ambient conditions likely to be encountered in natural waters. In addition, experimental work is presented concerning the effects of such variables as pH, plutonium concentration, ionic strength, and the presence of complexing agents on the particle size distributions of aqueous plutonium. In subsequent papers it will be shown that these variables, as they influence the particle size distribution of the aqueous plutonium, greatly affect its interaction with mineral surfaces. The orientation of these studies is the understanding of the likely behavior and fate of plutonium in environmental waters, particularly as related to its interaction with suspended and bottom sediments. 

There is some spectroscopic evidence that y-APS interacts with mineral surfaces by forming metallosiloxane bonds. Naviroj et al. [10] investigated the... 

Ultrastructural patterns that arise when amino acids or small peptides interact with mineral surfaces have been studied in some detail99,100). A poly-L-alanine solution evaporated at 40 °C on a rhombohedral plane of R-quartz deposits the peptide principally in a-conformation. Chain-folded helices are aligned in the form of lamellae which exhibit a sharp phase boundary at the organic-mineral contact zone (Fig. 9). Frequently the lamellae are split along the direction of their fold axis ("zipper effect ). Insertion of 0-pleated sheets running perpendicular to the long axis of the lamellae act as dispersion forces and cause the formation of cross-0-... 

III. BIOGEOCHEMICAL PROCESSES INTERACTIONS WITH MINERAL SURFACES... 

In terms of improving our ability to predict soil C turnover, we identify five priorities for research (1) The interactive effects of temperature and moisture on microbial decomposition rates, because soils will experience novel and transient conditions (2) the mechanisms governing protection of OM through interactions with mineral surfaces and due to spatial structure (3) the mechanisms leading to slower OM turnover times with depth (4) the potential for nonlinear responses of decomposition to C availability—for example, the role of labile C inputs in stimulating decomposition of less labile OM (i.e., priming) and density-dependent microbial behavior and (5) how the chemical characteristics of organic compounds, as inputs from different plant species, charred (black) carbon, or microbial cell walls and by-products, influence mechanisms of stabilization and turnover. 

The acid-base properties of DOM are of intrinsic interest because acidic functional groups contribute to the acid-base balance of natural waters, affect complexation and transport of dissolved metals, and interact with mineral surfaces. The concentrations of carboxyl and phenolic functional groups are among the most widely measured and reported properties of DOM. Methodologically, there are two basic approaches for measuring acidic group content—indirect titrations and direct titrations (Perdue et al., 1980 Perdue, 1985 Ritchie and Perdue, 2003). 

This partially oxidized material contains 4.2-5.4 mmol g of carboxylic acid functional groups, which account in part for its generally acidic character, its charge distribution as a function of pH, its complexation of metal ions, and its interaction with mineral surfaces in the environment. Phenolic hydroxyl groups are present at concentration of —1.5-1.8 mmol g in FAs, HAs, and NOM. The ratio of carboxyl-to-phenolic groups is thus —3 1, which is significantly greater than the ratio of 2 1 that is commonly used in some mathematical models of the acidity of these materials. 

TOF-SIMS studies on impregnating mixtures suggest enrichment of the more reactive component in the uppermost polysiloxane layer. Furthermore, the results obtained from combination of TOF-SIMS and DRIFT indicate stronger interaction between stone surface and the polycondensate formed from the silane mixture as compared to the siloxane system. In order to confirm the trends, surface analysis will be extended to larger numbers of samples. In general, combination of different analytical techniques for systematic studies on the structure of polysiloxane coating and its interaction with mineral surfaces will be a main subject of future investigation. 

Laboratory experiments with model systems under static conditions have been aimed at the determination of the retention mechanisms of colloids and pseudocolloids (association of a heavy element with a colloid) onto mineral surfaces. This will give a better understanding of the fate of radioelements associated with colloids upon interaction with mineral surfaces as it will occur in the water fiow across fissures and fractures around a radwaste repository. In these studies, polished cm-sized monoliths are used to simulate macroscopic surfaces of fine particles or as mineral surfaces. Rutherford Backscattering Spectrometry BS) is the technique chosen to determine accurately the amount of elements fixed on the monolith. 

Although sorption of TCB by the silica surfaces can increase values of KDi over those predicted from /oc and K()C alone, the effect is only weakly apparent until very large quantities of mineral surface and very low/oc values are obtained. Some caution must be exercised in extrapolating these comparisons between the reactions of organic contaminants with organic and mineral surfaces to solutes less hydrophobic than TCB. As noted earlier, specific interactions with mineral surfaces may be more important determinants of sorption for less hydrophobic contaminants. 

Teppen, B.J., R.R. Arands, and J. Farrell. 1998a. TCE interactions with mineral surfaces Correlating molecular simulations with experimental data. p. 197. In Agronomy abstracts. ASA, Madison, WI. 

One research area that is certain to benefit from use of these facilities is the study of molecular-scale mechanisms of bioremediation and phytoremediation, where knowledge of the spatial distribution of contaminant species at the cellular level is critical for understanding reaction mechanisms and locations within or external to cells. Microfluorescence tomography is already beginning to yield this information in three dimensions at spatial scales of a few microns. Another growth area that will exploit X-ray microscopes is the characterization of natural organic matter and its interaction with mineral surfaces under in situ conditions. An X-ray microscopy study of fulvic acid in aqueous solutions at the ALS has already provided the first direct images of the macromolecular conformation of fulvic acid under in situ conditions (Myneni et al. 

Fig. 18 Concept of DHBCs, their interaction with mineral surfaces and possibilities for particle stabilization or self-assembly, a Nanoparticle stabilization, b unordered particle aggregation, c oriented attachment, d ordered aggregation/mesocrystal formation, e arrangement of nanoparticles around a template. Reproduced from [151] with permission of the Materials Research Society...

Payne, T.E. 1999. Uranium (VI) interactions with mineral surfaces Controlling factors and surface complexation modeling. Ph.D. Diss. Univ. of New South Wales, Australia. 

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