Thermodynamic Principles of Dittmarite Precipitation

Abstract

Dittmarite is a naturally occurring mineral which is also produced by municipal wastewater treatment processes. It contains ammonium:magnesium:phosphate in molar ratios of 1:1.25:1, respectively. Dittmarite (MgNH 4 PO 4 •H 2 O) has a very stable crystalline structure, its solubility constant (K so) is a product of the activity coefficient (ɣ) and the activity of the individual species that make up the compound. The conditional solubility product, P S = C T, Mg C T ,NH 4 C T ,PO 4 = K so /αMg αNH 4 αPO 4 ɣMg ɣNH 4 ɣPO 4. A theoretical plot of-log Ps vs. pH gives a pH of 10.7 for maximum dittmarite precipitation, albeit precipitation may begin at lower pH values. The pK so for dittmarite at 25 °C is determined to be 13.359 from the final equilibrium pH values taking all relevant magnesium, phosphate and ammonium species into account. The geochemical speciation model, MINTEQA2 was used to verify the optimum conditions for the precipitation of dittmarite. Such theoretical predictions allow the control of phosphorus and nitrogen discharges from animal and municipal wastewaters and serve as key factors in preventing surface water eutrophication and groundwater pollution.

A Comprehensive Review of Defects Genealogy in Olivines: From the Mineral World to Modern Electrode Materials

“…Since the crystal structure defects influence the material properties significantly, the mineral genesis and formation conditions could be applied to the synthesis process of functional materials and could serve as additional ways of tuning the material properties. As a reference, the natural genesis processes of dittmarite (NH 4 Fe(Mn)PO 4 •H 2 O) and struvite (NH 4 MgPO 4 •H 2 O) minerals were studied from the thermodynamic point of view; as the result, the optimal conditions of precipitation were found [105]. Dittmarites are applied as precursors for triphylite LiMPO 4 cathode synthesis [11,106].…”