Atomistic Simulation of Surface Selectivity on Carbonate Formation at Calcium and Magnesium Oxide Surfaces

2012 ◽  
Vol 116 (24) ◽  
pp. 13240-13251 ◽  
Author(s):  
Jeremy P. Allen ◽  
Arnaud Marmier ◽  
Stephen C. Parker
Keyword(s):  
Magnesium Oxide ◽  
Atomistic Simulation ◽  
Oxide Surfaces ◽  
Carbonate Formation ◽  
Calcium And Magnesium

Atomistic Simulation of the Surface Carbonation of Calcium and Magnesium Oxide Surfaces

2009 ◽  
Vol 113 (19) ◽  
pp. 8320-8328 ◽  
Author(s):  
Jeremy P. Allen ◽  
Stephen C. Parker ◽  
David W. Price
Keyword(s):  
Magnesium Oxide ◽  
Atomistic Simulation ◽  
Oxide Surfaces ◽  
Calcium And Magnesium

scholarly journals Weathering by tree-root-associating fungi diminishes under simulated Cenozoic atmospheric CO<sub>2</sub> decline

2014 ◽  
Vol 11 (2) ◽  
pp. 321-331 ◽  
Author(s):  
J. Quirk ◽  
J. R. Leake ◽  
S. A. Banwart ◽  
L. L. Taylor ◽  
D. J. Beerling
Keyword(s):  
Mycorrhizal Fungi ◽  
Biological Activities ◽  
Arbuscular Mycorrhizal ◽  
Tree Roots ◽  
Carbonate Formation ◽  
Low Co2 ◽  
Surface Alteration ◽  
Calcium And Magnesium ◽  
Atmospheric Co2 Concentrations ◽  
Vertical Scanning Interferometry

Abstract. Trees dominate terrestrial biotic weathering of silicate minerals by converting solar energy into chemical energy that fuels roots and their ubiquitous nutrient-mobilising fungal symbionts. These biological activities regulate atmospheric CO2 concentrations ([CO2]a) over geologic timescales by driving calcium and magnesium fluvial ion export and marine carbonate formation. However, the important stabilising feedbacks between [CO2]a and biotic weathering anticipated by geochemical carbon cycle models remain untested. We report experimental evidence for a negative feedback across a declining Cenozoic [CO2]a range from 1500 to 200 ppm, whereby low [CO2]a curtails mineral surface alteration via trenching and etch pitting by arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) fungal partners of tree roots. Optical profile imaging using vertical scanning interferometry reveals changes in nanoscale surface topography consistent with a dual mode of attack involving delamination and trenching by AM and EM fungal hyphae on phyllosilicate mineral flakes. This is consistent with field observations of micropores in feldspar, hornblende and basalt, purportedly caused by EM fungi, but with little confirmatory evidence. Integrating these findings into a process-based biotic weathering model revealed that low [CO2]a effectively acts as a "carbon starvation" brake, causing a three-fold drop in tree-driven fungal weathering fluxes of calcium and magnesium from silicate rock grains as [CO2]a falls from 1500 to 200 ppm. The feedback is regulated through the action of low [CO2]a on host tree productivity and provides empirical evidence for the role of [CO2]a starvation in diminishing the contribution of trees and mycorrhizal fungi to rates of biological weathering. More broadly, diminished tree-driven weathering under declining [CO2]a may provide an important contributory mechanism stabilising Earth's [CO2]a minimum over the past 24 million years.

Study of One Sort of Romanian Diatomite as Precursor in the Synthesis of Some Metallic Silicates

2008 ◽  
Vol 59 (6) ◽  
Author(s):  
Dan Macarovici ◽  
Viorel Paraschiv ◽  
Elisabeth-Jeanne Popovici
Keyword(s):  
Calcium Carbonate ◽  
Magnesium Oxide ◽  
Alkaline Earth ◽  
Thermal Reaction ◽  
Calcium Silicates ◽  
Magnesium Silicates ◽  
Calcium And Magnesium ◽  
Alkaline Earth Silicates

The behaviour of one sort of Romanian diatomite as precursor in the synthesis of calcium and magnesium silicates was studied. The calcination of this diatomite, 3 h at 10000C in air, does not produce major modifications in structure and composition. In the same conditions, the thermal reaction between diatomite and calcium carbonate leads to a mixture of calcium silicates (CaSiO3, Ca2SiO4, Ca3SiO5) whereas the reaction product with magnesium oxide is orthomagnesium silicate (Mg2SiO4 - forsterite). This sort of Romanian diatomite can play the same role as other silica sources in the synthesis of alkaline-earth silicates.

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