Mechanistic insight into biopolymer induced iron oxide mineralization through quantification of molecular bonding

Microbial production of iron (oxyhydr)oxides on polysaccharide rich biopolymers occurs on such a vast scale that it impacts the global iron cycle and has been responsible for major biogeochemical events. Yet the physiochemical controls these biopolymers exert on iron (oxyhydr)oxide formation are poorly understood. Here we used dynamic force spectroscopy to directly probe binding between complex, model and natural microbial polysaccharides and common iron (oxyhydr)oxides. Applying nucleation theory to our results demonstrates that if there is a strong attractive interaction between biopolymers and iron (oxyhydr)oxides, the biopolymers decrease the nucleation barriers, thus promoting mineral nucleation. These results are also supported by nucleation studies and density functional theory. Spectroscopic and thermogravimetric data provide insight into the subsequent growth dynamics and show that the degree and strength of water association with the polymers can explain the influence on iron (oxyhydr)oxide transformation rates. Combined, our results provide a mechanistic basis for understanding how polymer-mineral-water interactions alter iron (oxyhydr)oxides nucleation and growth dynamics and pave the way for an improved understanding of the consequences of polymer induced mineralization in natural systems

Comparison of atomic force microscopy and zeta potential derived surface charge density

Surface charge density can be derived from atomic force microscopy (AFM) by using Derjaguin, Landau, Vervey and Overbeek (DLVO) theory. The sub-micrometer data allows observation of local differences in charge density and changes with time or solution composition, which has interesting applications in crystal growth and inhibition, bone formation and colloid behavior. To calibrate this type of AFM data and verify DLVO assumptions, it has to be correlated with an established technique. We successfully matched AFM derived surface charge densities with zeta potential measurements on a mica surface within one order of magnitude. A reproducible difference between surface charge of the mica substrate exposed to solutions cations with monovalent and divalent charge was also observed. The results provide confidence that the AFM method is valid for obtaining local surface charge information

Numerical simulations of NMR relaxation in chalk using local Robin boundary conditions

The interpretation of nuclear magnetic resonance (NMR) data is of interest in a number of fields. In \"{O}gren [Eur. Phys. J. B (2014) 87: 255] local boundary conditions for random walk simulations of NMR relaxation in digital domains were presented. Here, we have applied those boundary conditions to large, three-dimensional (3D) porous media samples. We compared the random walk results with known solutions and then applied them to highly structured 3D domains, from images derived using synchrotron radiation CT scanning of North Sea chalk samples. As expected, there were systematic errors caused by digitalization of the pore surfaces so we quantified those errors, and by using linear local boundary conditions, we were able to significantly improve the output. We also present a technique for treating numerical data prior to input into the ESPRIT algorithm for retrieving Laplace components of time series from NMR data (commonly called $T$-inversion)

Calcite Growth Kinetics: Dependence on Saturation Index, Ca2+:CO32- Activity Ratio, and Surface Atomic Structure

It is becoming increasingly clear that the rate of crystal growth, even at constant saturation, varies with pH, ionic strength, and solution stoichiometry. Here, we contribute to the limited data set on experimentally obtained calcite step velocities from solutions with strictly controlled parameters. We measured growth on obtuse and acute edges in solutions with five Ca2+:CO32– activity ratios (r): 0.1, 1.0, 10, 25, and 50, at three saturation indices: SI = 0.6, 0.8, and 1.0. The curve describing rate as a function of r is not centered at r = 1, and the maximum velocity is different for each step. Obtuse steps generally grow faster in Ca2+-rich solutions, i.e., r > 1, whereas the acute rates dominate when CO32– is in excess, i.e., r < 1. We show that the local arrangement of every second carbonate at the acute steps can help explain these rate differences. To further analyze the differences in growth rates, we fitted four currently used growth models to our data set, to derive growth parameters for each type of step. Some of the models worked for some of the conditions, but none could describe the results over the full range of our experiments

Mechanistic insight into biopolymer induced iron oxide mineralization through quantification of molecular bonding.

Microbial production of iron (oxyhydr)oxides on polysaccharide rich biopolymers occurs on such a vast scale that it impacts the global iron cycle and has been responsible for major biogeochemical events. Yet the physiochemical controls these biopolymers exert on iron (oxyhydr)oxide formation are poorly understood. Here we used dynamic force spectroscopy to directly probe binding between complex, model and natural microbial polysaccharides and common iron (oxyhydr)oxides. Applying nucleation theory to our results demonstrates that if there is a strong attractive interaction between biopolymers and iron (oxyhydr)oxides, the biopolymers decrease the nucleation barriers, thus promoting mineral nucleation. These results are also supported by nucleation studies and density functional theory. Spectroscopic and thermogravimetric data provide insight into the subsequent growth dynamics and show that the degree and strength of water association with the polymers can explain the influence on iron (oxyhydr)oxide transformation rates. Combined, our results provide a mechanistic basis for understanding how polymer-mineral-water interactions alter iron (oxyhydr)oxides nucleation and growth dynamics and pave the way for an improved understanding of the consequences of polymer induced mineralization in natural systems

Calcite Growth Kinetics: Dependence on Saturation Index, Ca2+:CO32- Activity Ratio, and Surface Atomic Structure

It is becoming increasingly clear that the rate of crystal growth, even at constant saturation, varies with pH, ionic strength, and solution stoichiometry. Here, we contribute to the limited data set on experimentally obtained calcite step velocities from solutions with strictly controlled parameters. We measured growth on obtuse and acute edges in solutions with five Ca2+:CO32– activity ratios (r): 0.1, 1.0, 10, 25, and 50, at three saturation indices: SI = 0.6, 0.8, and 1.0. The curve describing rate as a function of r is not centered at r = 1, and the maximum velocity is different for each step. Obtuse steps generally grow faster in Ca2+-rich solutions, i.e., r > 1, whereas the acute rates dominate when CO32– is in excess, i.e., r < 1. We show that the local arrangement of every second carbonate at the acute steps can help explain these rate differences. To further analyze the differences in growth rates, we fitted four currently used growth models to our data set, to derive growth parameters for each type of step. Some of the models worked for some of the conditions, but none could describe the results over the full range of our experiments

Calcite Growth Kinetics: Dependence on Saturation Index, Ca2+:CO32- Activity Ratio, and Surface Atomic Structure

It is becoming increasingly clear that the rate of crystal growth, even at constant saturation, varies with pH, ionic strength, and solution stoichiometry. Here, we contribute to the limited data set on experimentally obtained calcite step velocities from solutions with strictly controlled parameters. We measured growth on obtuse and acute edges in solutions with five Ca2+:CO32– activity ratios (r): 0.1, 1.0, 10, 25, and 50, at three saturation indices: SI = 0.6, 0.8, and 1.0. The curve describing rate as a function of r is not centered at r = 1, and the maximum velocity is different for each step. Obtuse steps generally grow faster in Ca2+-rich solutions, i.e., r > 1, whereas the acute rates dominate when CO32– is in excess, i.e., r < 1. We show that the local arrangement of every second carbonate at the acute steps can help explain these rate differences. To further analyze the differences in growth rates, we fitted four currently used growth models to our data set, to derive growth parameters for each type of step. Some of the models worked for some of the conditions, but none could describe the results over the full range of our experiments

Calcite Growth Kinetics: Dependence on Saturation Index, Ca2+:CO32- Activity Ratio, and Surface Atomic Structure

It is becoming increasingly clear that the rate of crystal growth, even at constant saturation, varies with pH, ionic strength, and solution stoichiometry. Here, we contribute to the limited data set on experimentally obtained calcite step velocities from solutions with strictly controlled parameters. We measured growth on obtuse and acute edges in solutions with five Ca2+:CO32– activity ratios (r): 0.1, 1.0, 10, 25, and 50, at three saturation indices: SI = 0.6, 0.8, and 1.0. The curve describing rate as a function of r is not centered at r = 1, and the maximum velocity is different for each step. Obtuse steps generally grow faster in Ca2+-rich solutions, i.e., r > 1, whereas the acute rates dominate when CO32– is in excess, i.e., r < 1. We show that the local arrangement of every second carbonate at the acute steps can help explain these rate differences. To further analyze the differences in growth rates, we fitted four currently used growth models to our data set, to derive growth parameters for each type of step. Some of the models worked for some of the conditions, but none could describe the results over the full range of our experiments