Struvite

The reaction between MgO and ammonium dihydrogen phosphate (ADP) in aqueous solution yields struvite, MgNH4P04. bHjO, and schertelite, Mg(NH4)2(HP04)2.4H2O, as the main reaction products. Both may be regarded as cementing species. Only minor amounts of MgO are consumed during these reactions as it is present in excess. The reaction is exothermic. Sodium tripolyphosphate (STPP) or borax may be added to retard the reaction. The main course of the reactions may be represented thus ... 

On mixing, an exothermic reaction takes place with some loss of ammonia. As the reaction proceeds crystalline phases are formed. All workers are in agreement that these are the tetrahydrate schertelite, or the hexahydrate struvite, or a mixture of both. They also agree that schertelite is first formed, which is then hydrated further, if water is available, to form struvite. The relative amounts thus depend on the water available for hydration. Sometimes dittmarite, MgNH4P04. HjO, and stercorite, NaNH4HP04.4H20, are found in minor amounts. 

Abdelrazig, Sharp El-Jazairi (1988, 1989) prepared a series of mortars based on a powder blend of MgO and ADP with a quartz sand filler. They were hydrated by mixing with water. A mortar I (MgO ADP silica water = 17T 12-9 70-0 12-5), with a water/solid ratio of 1 8, formed a workable paste which set in 7 minutes with evolution of ammonia. The main hydration product, struvite, was formed in appreciable amounts within 5 minutes and continued to increase. Schertelite also appeared, but only in minor amounts, within the first 5 minutes and persisted only during the first hour of the reaction. Dittmarite appeared in minor amounts after 15 minutes, and persisted. 

The addition of STPP (1-7%) acted as a retarder and increased compressive strength (mortar II). Less heat and ammonia were evolved and the cement set more slowly in 10 minutes. The paste hardened in 30 to 60 minutes. Traces of ADP persisted for 30 minutes but no STPP was detected in the reaction products. Struvite, the main hydration product, schertelite and dittmarite all appeared within 5 minutes. Struvite continued to increase in amount as the cement aged schertelite disappeared after 3 hours and dittmarite after a week. Stercorite was found only during the first 7 hours. 

Handschuh and Orgel (1973) studied the mineral struvite. It can be precipitated from ocean water in the presence of phosphate if the concentration of NH ions in the water is greater than 0.01 M. If struvite is heated with urea, magnesium pyrophosphate is obtained in a yield of about 20% after 10 days at 338 K if nucleosides are added to the reaction mixture described above, nucleoside diphosphates such as uridine-5 -diphosphate and diuridine-5 -diphosphate are formed in good yields. 

Schuiling, R.D. and Anderade, A. Recovery of struvite from calf manure, Environmental Technol., 20, 1999 p. 756-768. 

In renal stones, apatite (Ca5(P04)3 OH, 1/2 C03) with a hexagonal shape has been observed however, this mineral is difficult to identify because of its cryptocrystalline appearance. Struvite (MgNH4P04 6 H20) orthorhombic, newberyte (MgHP04 3 H20) orthorhombic, whit-ockite (Ca3(P04)2) hexagonal, and also brushite have been reported to occur in renal stones82. ... 

INFRARED AND RAMAN SPECTRA OF MAGNESIUM AMMONIUM PHOSPHATE HEXAHYDRATE (STRUVITE) AND ITS ISOMORPHOUS ANALOGUES... 

It should perhaps be noted that the crystal structure of struvite has been determined or refined on the basis of X-ray diffraction data by Whitaker and Jeffery [4] and by Abbona, Calleri and Ivaldi [5],... 

Figure 1. Part of the structure of struvite according to Ferraris, Fuess and Joswig [6]. Only the water molecules and the atoms to which they are bound are shown the numbers refer to the O O distances measured in picometers...

The infrared spectra of ammonium magnesium phosphate hexahydrate and its potassium analogue recorded at room temperature have already been studied [8] and the RT Raman spectrum of struvite has also been reported [9], In addition to that, our results of the study of the spectra of KMgP04-6H20 will be published shortly [10], To the best of our knowledge, the vibrational spectra of arsenstruvite and its deuterated analogues and also the vibrational spectra of the whole series of deuterated analogues of either of the three compounds have not been reported yet. 

Since, as mentioned, the detailed analysis of the spectra of KMgP04-6H20 [10] is about to be published and that of struvite and arsenstruvite will follow, the present paper will deal mainly with the spectra in the O H/N H region of the protiated compounds and in the O-D/N-D region of compounds with a low deuterium content ( 3 5 % D). Needless to say, no N-H or N-D modes are present in the case of KMgP04-6H20 and its deuterated analogues. 

The RT and LNT infrared spectra of synthetic struvite are shown in Fig. 2. As seen, the lowering of the temperature does not produce dramatic changes in the spectral picture, although some of the bands become sharper and the substructure of the high-frequency feature is more apparent. In addition to that, the bands originating from water librations (hindered rotations) become more intense and shift towards higher frequencies. 

In principle, the bands originating from the vibrations of the H20 molecules and NH4+ ions the Raman spectra are weaker than those arising from the vibrations localized in the E043 ions (of these, the strongest band is due to the totally symmetric E04 stretch). This is clearly seen in the case of the Raman spectrum of synthetic arsenstruvite (Fig. 4). On the other hand, the X-H stretching bands are rather prominent in the Raman spectra of struvite itself (Fig. 5). 

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