Transformations of neat and heated struvite (MgNH_4P0_4-6H_2O)

摘要

Struvite (MgNH_4P0_4-6H_2O) 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 MgCI_2-6H_2O and (NH_4)_2HPO_4 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.