General implications of aluminium speciation-dependent kinetic dissolution rate law in water–rock modelling

Recent experimental and theoretical work has demonstrated that the dissolution rates of many aluminosilicate minerals are inversely proportional to the activity of aqueous Al3+. The consequences of these observations on the rates of natural geochemical processes have been calculated by the KIRMAT hydrochemical code. Comparisons are performed at the steady state limit of the pure advective transport through a homogeneous semi-infinite isothermal porous media at 25 and 150°C. K-feldspar, albite, and muscovite dissolution kinetics are studied over a broad range of initial pH (2–10) and aluminium concentration (from 1×10−9 to 1×10−3 molal) matching most the natural conditions. Regardless of the mineral, the characteristic distance requires to reach equilibrium (leq) is two and three orders of magnitude larger and lower than predicted using the standard Transition State Theory (TST) law, respectively. The maximum decrease in muscovite and alkali-feldspar dissolution rates due to aqueous aluminium at 25°C is found at near to neutral pH, and at 150°C it is found at basic pH. The maximum dissolution rate increase at 25°C at acid pH, but at 150°C it is found at basic pH. These results demonstrate that consideration of the effect of the aluminium speciation on aluminosilicate dissolution rates is required to improve the accuracy in water–rock interaction modelling.