Fig. 7. Dissolved Fe(II) as a function of acid added to maintain pH 6.0 in selected reduction reactor experiments. Suspensions contained 0.5 g ferrihydrite kg^–1, 750 mmol P kg^–1 ferrihydrite, and boehmite additions of 0, 0.002, 0.008, or 0.3 g kg^–1 suspension.