Accoording to Eq. 1, the precipitation of struvite results in the release of protons, and therefore the evolution of pH can serve as a chemical proxy for the reaction kinetics (Fig. , Supplementary Material: Fig. ). Within the time resolution constraints of our experiment, it is evident that nucleation and crystallisation of struvite was occurring within ~60 s after mixing i.e. until a plateau at pH ~5.8 was reached, down from the initial ~7.9. Fig. shows the evolution of the most intense diffraction peak of struvite (at q = 14.74 nm -1 ;