The acid neutralisation capacity of the olivine flour is illustrated in Fig. 2, which shows the pH of the suspension as a function of reaction time for three different solid/solution ratios. Following an initial rapid increase of the pH, all the isotherms reach a peak value before a significant decrease of the pH can be observed. As indicated by an observed change in suspension colour from grey to reddish brown and directly supported by previous initial experiments, this behaviour can be explained by the oxidation and subsequent precipitation of iron. The combined effect of these mechanisms, illustrated by Eqs. (2) and (3), is the release of two moles of protons per mole of ferrous iron oxidised (Eq. (2)) and precipitated (Eq. (3)):
Consequently, the pH of the system is effectively buffered by the precipitation of ferric iron hydroxide. The observed pH of the suspension represents a kinetic compromise’ between olivine dissolution (Eq. (1)) and iron oxidation and precipitation