*3.4. Solution pH*

The pH of the investigated hydroxides and the reaction solutions was adjusted to 6 prior to the experiments. After a 2 h desorption time, the pH of the sample solutions increased for nearly all treatments and hydroxides (Table 7). Only goethite, ferrihydrite, 5 Fe: 1 Al, and 1 Fe: 1 Al had a decreasing or constant pH during desorption using 50 mM KCl. The same was observed for goethite and ferrihydrite during desorption using 50 mM His. No correlation was detected for the change of solution pH and the amount of desorbed P (not shown).


**Table 7.** Change of H+ concentrations in the sample solutions after 2 h desorption time.
