Transformations of neat and heated struvite (MgNH4PO4⋅6H2O)

Struvite (MgNH4PO4⋅6H2O) is the mineral phase of one of the urinary tract stones of humans and animals, besides being an important phase seen in waste water treatment and purification plants. Single-phase and highly crystalline struvite powders were synthesized in this study at room temperature in aqueous solutions containing dissolved salts of MgCl2⋅6H2O and (NH4)2HPO4 at the Mg/P molar ratio of 1.00. As-synthesized, crystalline struvite powders (neat powders) completely transformed into cryptocrystalline apatitic calcium phosphate (Ap-CaP), in less than 72 h, when soaked in Ca-containing saline solutions at 37 °C. Moreover, crystalline struvite powders heated at temperatures from 90° to 200 °C became x-ray amorphous. Amorphous powders stirred for 4 h at room temperature in water containing dissolved diammonium hydrogen phosphate recrystallized back into struvite.

Research highlights
► Struvite powders were synthesized via MgCl2⋅6H2O-(NH4)2HPO4 route at RT.
► No pH control was necessary during the synthesis process.
► Heated (90 to 200 °C) struvite powders became x-ray amorphous.
► Struvite powders soaked in Ca-ctg saline solutions (37 °C) transformed to apatitic CaP.
► Amorphous struvite is useful for removing ammonium ions from contaminated water.