Speciation programs

Parker, D.R., W. A. Norvell and R. L. Chaney, 1995, GEOCHEM-PC, a chemical speciation program for IBM and compatible personal computers. In R. H. Loep-pert, A. P. Schwab and S. Goldberg (eds.), Chemical Equilibrium and Reaction Models. Soil Science Society of America Special Publication 42,253-269. 

With these experimental surface reaction parameters and the speciation program MICROQL the species distribution in the river using metal and particle concentrations, pH and alkalinity measured in the river at the concerned sampling data was calculated. Various assumptions for the complexation in solution may be used, which affect ai and thus Kd-... 

Illustration of the distribution of chemical species in an example output of the MINTEQ speciation program... 

Speciation programs fail by attempts of simultaneous fitting of too many adjustable parameters. Therefore, it is expedient to model the primary surface charging first in a possibly simple system (only ions and ions of inert... 

Triple layer model TLM is very popular and it is build into many commercial speciation programs. It combines the 2-pK model, i.e. reactions (5.32) and (5.33) with binding of inert electrolyte ... 

The CD concept can be also combined with the Stern or TLM model without introduction of the additional electrostatic plane. This offers a possibility of formulation of problem in terms of the CD model within standard features offered by commercial speciation programs. Recent study of Gd and Ni adsorption on alumina in the framework of TLM model produced significantly better fit for the charge of the specifically adsorbed cations distributed 50-50 between the surface and the / -plane than for inner- or outer-sphere complexation [99]. 

EQ3/6 (Wolery, 1992). EQ3 is a speciation program, which can be used alone or to prepare input for eq6, a reaction path program. A kinetics option is also available. The program has a comprehensive database, primarily through the effort of Dr James Johnson. Unlike many other databases, the sources of thermodynamic data are documented in this database. 

Part of almost all homogeneous kinetic calculations will be some method to decouple the reactive species, which are often redox species. In kinetic calculations, the species are obviously not at equilibrium with each other, at least at the start of the calculation they approach equilibrium during the calculation. But speciation programs such as phreeqc and react assume all species to be at equilibrium unless told otherwise. In this case we want CH4 to not react with other species, partly to see what it is doing during the reaction, and partly because in nature it is extremely unreactive. We also want acetate to be decoupled because it is metastable and will not even exist in the solution at equilibrium. At the time of writing, this is not necessary in phreeqc, because the... 

Apart from trivial examples, calculation of species concentrations requires use of computers using a speciation program, discussed in Chapter 16. Most such programs have a selection of 30-80 or more basis species, plus a collection of minerals and gases, from which the modeler chooses those required to... 

J Coves, G Sposito. MICROQL-UCR A Surface Chemical Adaptation of the Speciation Program MICROQL. Riverside, CA University of California Press, 1989. 

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