Phosphorus‐31 magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy was used to examine the forms of P in two municipal sludges and a sludge‐amended soil. The signal‐to‐noise ratio and the resolution of the spectra improved considerably when paramagnetics in the sludge and sludge‐treated soil samples were removed by a reducing treatment involving citrate‐bicarbonate‐dithionite (CBD). The spectra suggested that the P solid phases in the anaerobically digested sludge from Los Angeles County, California were calcium phosphates. The strong paramagnetic effects, however, precluded more precise identification of the calcium phosphate phase. In the anaerobically digested alum‐treated sludge from Riverside, three P solid phases are detected, carbonated apatite, a pyrophosphate, and aluminium phosphate. In the Domino soil (fine‐loamy, mixed, thermic Xerollic Calciorthid), amended with sludge from Los Angeles County, 31 P MAS NMR indicated the presence of carbonated apatite and pyrophosphate solid phases.
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Hinedi et al. (1989) studied this question.