In this work, we determined the full set of thermodynamic properties for the ferric orthoarsenate, FeAsO4 . 0.75H2O. This phase could be expected in metallurgical waste forms from pressure oxidation of arsenopyrite-rich ores and its solubility is therefore of interest for the understanding of arsenic mobility in such waste forms.
Using a combination of solubility experiments at low pH (200 °C). One could, however, attempt to tweak the pressure oxidation technology such that the formation of ferric orthoarsenate would be enhanced, hence producing a waste form with relatively low arsenic solubility.