Effect of pH and temperature on olivine dissolution anisotropy

Le résumé fourni par la source

Olivine is a ubiquitous mineral in mafic and ultramafic environments, whose reactivity has recently received a renewed interest for the study of extraterrestrial environments and the development of carbon capture and storage technologies. While olivine dissolution has long been qualitatively described as occurring preferentially following specific crystallographic orientations, determination of kinetic parameters capturing the anisotropy of olivine dissolution and the underlying mechanistic controls is still lacking. In the present study, the dissolution rate of four major faces ( r ( h k l ) ) of olivine was monitored as a function of pH and temperature using nanoscale measurements of surface microtopography before and after dissolution. At temperatures ranging between 30 °C and 90 °C, the reactivity of olivine faces was found to observe the following trend: r ( 010 ) > r ( 130 ) > r ( 111 ) > r ( 110 ) . At 90 °C and pH range between 1 and 6, the reaction order with respect to a H + was found to be face-specific and vary between n = 0.65 for the (010) face and n = 1.07 for the (110) face. Furthermore, n for (010) was the same within uncertainty at 30 °C ( n = 0.66). The results are also consistent with an activation energy that neither depends on surface orientation, nor on pH for the (010) face, and which is on the order of 60–70 kJ/mol. Finally, the relative reactivity of the investigated faces was found to be dictated by their surface energy determined by ab initio calculations, as predicted by the stepwave model. Overall, this study paves the way to the development of physically more robust models of crystal reactivity, of prime importance to predict the reactivity of olivine in a broad range of contexts.

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