A comprehensive and consistent mineral dissolution rate database: Part II: Secondary silicate minerals

Abstract

This paper describes the creation of a consistent database of the far-from-equilibrium dissolution rates of secondary silicate minerals including clays, zeolites, serpentines, chlorites, prehnite, wollastonite, epidotes, garnets, kyanite, staurolite, cordierite, tourmaline, and feldspathoids. This work, based on the regression of available dissolution rate data normalized to their BET surface area as a function of pH and temperature, was performed using equations described in Heřmanská et al. (2022a) using a least-squares algorithm. The average difference between calculated and measured rates ranged from 0.18 to 0.66 log units depending on the mineral. Where relevant data were lacking, rate parameters are proposed based upon the rate behaviors of minerals with similar structures. All obtained rate equations and parameters have been incorporated into the KINEC.v1.dat database for direct use in geochemical fluid reactive transport software.The far-from-equilibrium dissolution rates of most naturally forming silicate minerals are notably similar to one another at neutral conditions. More than 65% of the silicate minerals considered in this study and that of Heřmanská et al. (2022a) range in value from 10-11.8 to 10-12.5 mol m-2 s-2 at 25 oC and pH 7; this range is within the uncertainties associated with these rates. This similarity in rates is attributed to the likelyhood that breaking Si-O bonds is the rate limiting step of the dissolution of each of these minerals. Faster rates are observed for minerals that can be dissolved without breaking Si-O bonds. Retrieved apparent activation energies for the silicate minerals are found to be similar over all pH conditions and average ∼55 kJ mol-1. This apparent activation energy suggests that rates at 100, 200 and 300 °C will be approximately 86, 3,600 and 42,000 times higher, respectively, than corresponding rates at 25 oC.