Improved templating of the net-rate of mineral batch-dissolutions

Extensive investigations with silica gel, gypsum, sucrose and calcium carbonate has revealed that depictions of the kinetics of batch-dissolution tend to cluster into those from studies of either sedimentary minerals, e.g., calcite, or silicate and alumino-silicate minerals. The sedimentary-mineral cluster relies upon plots of concentration versus time, or more rarely, rate versus c/csat, the fractional concentration at any time. The silicate cluster relies mainly upon plots of rate versus ΔGr, the free energy of reaction, with ΔGr estimated from the Reaction Quotient, Q/KP, where Q is the ionic product and KP is the Solubility Product. This clustering arises from accumulated operational choices, rather than anything geochemically advantageous. The sedimentary-mineral cluster follows Empirical Kinetics (EK) which prescribes three distinct stages of: experimental observations (phenomenology); rate equation, and mechanism. Thus, the rate equation is discovered by comparing the experimental curves against a bank of theoretically constructed, template curves. Meanwhile, the silicate cluster represents the approach taken after 1982 when Transition State Theory (TST) was adopted as the mechanism for silicate mineral dissolution. This would have been simple if the templating process within EK had been carried forward, alongside the TST. However, it was not, and the depictions of mineral dissolution kinetics within TST have become largely detached from any diagnostic facility. This has led to a major problem in silicate mineral investigation. To re-establish this facility, a combined spreadsheet and algebraic analysis demonstrates the comparability and inter-changeability of the plots used in both clusters. It has also identified a new plot for use with TST. Evidence of past confusion over the precise shape of the plot of Rate versus ΔGr is provided, and improved templating offered for the future, especially to define ideal and non-ideal dissolutions. For best effect, ΔGr should be rationalised to the prevailing stoichiometry, to give ΔGr′, as this reduces the Reaction Quotient to the fractional solubility used in the sedimentary-mineral cluster. This also explains away much of the confusion evident in the literature over stoichiometric numbers, e.g., the Temkin number. It is also shown that both the stoichiometry (ν) and the temperature of dissolution affect the range over which ΔGr′ needs to be studied in a dissolution experiment, and this can improve experimental design.