Relations Among Equilibrium and Nonequilibrium Aqueous Species of Aluminum Hydroxy Complexes

1971 ◽  
pp. 250-279 ◽  
Author(s):  
ROSS W. SMITH
Keyword(s):  
Aqueous Species

Changing the Basis

1996 ◽  
Author(s):  
Craig M. Bethke
Keyword(s):  
Numerical Technique ◽  
Current System ◽  
Equilibrium Constants ◽  
Bulk Composition ◽  
Reaction Model ◽  
Chemical Components ◽  
New Mineral ◽  
Equilibrium System ◽  
Modeling Software ◽  
Aqueous Species

To this point we have assumed the existence of a basis of chemical components that corresponds to the system to be modeled. The basis, as discussed in the previous chapter, includes water, each mineral in the equilibrium system, each gas at known fugacity, and certain aqueous species. The basis serves two purposes: each chemical reaction considered in the model is written in terms of the members of the basis set, and the system’s bulk composition is expressed in terms of the components in the basis. Since we could not possibly store each possible variation on the basis, it is important for us to be able at any point in the calculation to adapt the basis to match the current system. It may be necessary to change the basis (make a basis swap, in modeling vernacular) for several reasons. This chapter describes how basis swaps can be accomplished in a computer model, and Chapter 9 shows how this technique can be applied to automatically balance chemical reactions and calculate equilibrium constants. The modeler first encounters basis swapping in setting up a model, when it may be necessary to swap the basis to constrain the calculation. The thermodynamic dataset contains reactions written in terms of a preset basis that includes water and certain aqueous species (Na+, Ca++, K+, Cl-, HCO-3, SO4- -, H+, and so on) normally encountered in a chemical analysis. Some of the members of the original basis are likely to be appropriate for a calculation. When a mineral appears at equilibrium or a gas at known fugacity appears as a constraint, however, the modeler needs to swap the mineral or gas in question into the basis in place of one of these species. Over the course of a reaction model, a mineral may dissolve away completely or become supersaturated and precipitate. In either case, the modeling software must alter the basis to match the new mineral assemblage before continuing the calculation. Finally, the basis sometimes must be changed in response to numerical considerations (e.g., Coudrain-Ribstein and Jamet, 1989). Depending on the numerical technique employed, the model may have trouble converging to a solution for the governing equations when one of the basis species occurs at small concentration.

GaN Nanowire Microfluidic Sensor for Detection of Dissolved Aqueous Species

2006 ◽  
Author(s):  
Avijit Basu ◽  
Postdoctoral Fellow ◽  
Kathleen N. Weigandt ◽  
Barbara C. Williams ◽  
Jamie M. F. Jabal ◽  
...  
Keyword(s):  
Gan Nanowire ◽  
Aqueous Species

Summary of the Apparent Standard Partial Molal Gibbs Free Energies of Formation of Aqueous Species, Minerals, and Gases at Pressures 1 to 5000 Bars and Temperatures 25 to 1000 °C

1995 ◽  
Vol 24 (4) ◽  
pp. 1401-1560 ◽  
Author(s):  
Eric H. Oelkers ◽  
Harold C. Helgeson ◽  
Everett L. Shock ◽  
Dimitri A. Sverjensky ◽  
James W. Johnson ◽  
...  
Keyword(s):  
Free Energies ◽  
Aqueous Species

Oxidative alteration of Ce-rich pyrochlore: HRTEM/EELS investigation

1999 ◽  
Vol 556 ◽  
Author(s):  
Huifang Xu ◽  
Yifeng Wang
Keyword(s):  
Inner Mongolia ◽  
Diffusion Processes ◽  
Northern China ◽  
Alpha Decay ◽  
Daughter Product ◽  
Ore Deposit ◽  
Transmission Electron ◽  
Abundant Element ◽  
Electron Energy Loss ◽  
Aqueous Species

AbstractTransmission electron microscopy (TEM) and associated electron energy-loss spectroscopy (EELS) study show intergrowth of Ce4+-rich pyrochlore (metamict) and Ce3+-rich pyrochlore (partially metamict) in a Ce-rich pyrochlore from a rare earth element (REE) ore deposit of Inner Mongolia, Northern China. The partially metamict material is Ba-free and dominated by Ce3+. However, the metamict material is Ba-bearing and dominated by Ce3+,. The Ce4+-rich pyrochlore may result from radiation damage by alpha decay that also causes oxidation of Fe 2+ in titanite, and the interaction with a Ba-bearing oxidizing fluid. The oxidation of Ce3+ in the primary pyrochlore is accompanied by in the loss of REE, Ca, and Pb, a daughter product of U via alpha decay, during the alteration. However, most REE were incorporated in the alteration product, the Ce4+-rich pyrochlore. Based on EDS and EELS analyses, the chemical formulae of the partially metamict Ce3+-rich pyrochlore and metamict Ce4+-rich pyroeblore can be written as: (Ca, Ce3+, U, Pb) 2(Ti, Nb)2O7−x(OH)x, and (Ba, Ca, Ce4+, U)2 (Ti, Nb)2O7−y(OH)y, respectively. Ce is the most abundant element among all REE. It is proposed that the alteration takes place in solid-state with oxidizing fluid as a catalyst. The alteration kinetics is controlled by diffusion processes of aqueous species in metamict pyrochlore.

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