A new biogenic, struvite-related phosphate, the ammonium-analog of hazenite, (NH_4)NaMg_2(PO_4)_2·14H_2O

摘要

A new biogenic, struvite-related phosphate, the ammonium analog of hazenite (AAH), ideally (NH_4)NaMg_2(PO_4)_2·14H_2O, has been found in cultures containing the bacterial strain Virgibacillus sp.NOT1 (GenBank Accession Number: JX417495.1) isolated from an XVII Century document made of parchment. The chemical composition of AAH, determined from the combination of electron microprobe and X?ray structural analyses, is [(NH_4)_(0.78)K_(0.22)]NaMg_2(PO_4)_2·14H_2O. Single-crystal X?ray diffraction shows that AAH is orthorhombic with space group Pmnb and unit-cell parameters a = 6.9661(6), b = 25.236(3), c = 11.292(1) ?, and V = 1985.0(3) ?~3. Compared with hazenite, the substitution of NH_4~+ for K~+ results in a noticeable increase of the average A-O (A = NH_4~++K~+) bond length and the unit-cell volume for AAH, as also observed for struvite vs. struvite-K. Both infrared and Raman spectra of AAH resemble those of hazenite, as well as struvite. Our study reveals that AAH forms only in cultures with Na-bearing solutions and pH below 10.0. No AAH or hazenite was found in experiments with the K-bearing solutions, suggesting the necessity of a Na-bearing solution for AAH formation.