『Abstract
Struvite (MgNH4PO4・6H2O) was dissolved and precipitated in closed-system
reactors at 25℃ and 7.76<pH<10.65. Reactive fluid Mg and P concentrations
attained a stationary-state after 〜10 h in all experiments. The
temporal variation of these concentrations was evaluated to retrieve
struvite solubilities, and dissolution and precipitation rates.
Resulting struvite solubilities are consistent with an equilibrium
constant for the reaction:
MgNH4PO4・6H2O⇔Mg2+
+ NH4- + PO43-
+ 6H2O
of 10-13.24±0.5, which is similar to values previously
reported in the literature. Measured struvite dissolution and
precipitation rates (r) are found to be consistent with
r = r+ (1 - exp(A/2RT))
where r+ symbolizes the forward dissolution
rate, A refers to the chemical affinity of the dissolution reaction,
R designates the gas constant, and T represents absolute temperature.
Values of r+ are found top be independent
of pH and equal to 10-12.85±0.15 mol/cm2/s
in initially NH4-free reactive fluids. The
presence of 0.06 mol/kg NH4 in the initial
reactive fluid led to non-stoichiometric element release interpreted
to stem from the precipitation of a NH4-rich
phosphate phase. Use of measured rates in geochemical modeling
calculations indicate that both undersaturated and supersaturated
aqueous fluids will rapidly equilibrate with struvite, supporting
its potential use as a renewable fertilizer.』
1. Introduction
2. Theoretical background
3. Materials and methods
3.1. Preparation and characterization of solids
3.2. Closed-system experiments
3.3. Calculation of rates
4. Results
5. Discussion
6. Conclusions
Acknowledgements
Appendix A. Supplementary data
References