Cheers community, I have been studying the Struvite formation from respective ions. Being the general formula for Struvite MgNH4PO4.6H2O I intuitively tought the reaction would be Mg2+ + NH4+ + PO43- + 6H2O↔ MgNH4PO4.6H2O. However from literature and from practice, not only the optimal pH seems to be around the range from 7 to 10/11 where HPO42- is predominant as when Struvite forms tends to slightly decrease the pH of solutuon, which gives an hint for the release of a proton(H+), what suggests the real formula for struvite is Mg2+ + NH4+ + HPO42- + 6H2O↔ MgNH4PO4.6H2O + H+. My question is wouldn't it be more favorable for the system to generate Struvite directly from PO43- instead of HPO42-? doesn't it create a further energy consuming step for the deprotonation of the Hydrogen Phosphate? From what I checked being pKa = 12.346 for reaction HPO42- = H+ + PO43-, the Free energy Gibbs Variation is ≅30,6 kJ mol-1, implying from what I know that this deprotonation step is not a spontaneous reaction. Might there be a reason I'm negleting or forgetting that might explain why this reaction is driven by HPO42- instead of PO43-? Thanks in advance for any insight you might have.