Investigations of aluminum hydroxyphosphates and activated sludge by ²⁷Al and ³¹P MAS NMR

Abstract

High-resolution solid-state 2 7~1 and 3 1~ MAS NMR has been used to investigate the nature of aluminum-and phosphorus-containing solids formed during wastewater treatment. Although difficult to characterize by conventional techniques, these amorphous solids can be characterized by MAS NMR, providing information about their short-range ordering. In the present study, most of the solids were precipitated under conditions of high alkalinity, similar to those encountered during wastewater treatment. The ageing time of the aluminum hydroxide prior to the addition of phosphate (t,), the ageing time of the aluminum hydroxyphosphates after the addition of phosphate (t2), and the phosphorus to aluminum molar ratio were controlled while the effects of changing the parameters were examined. It was found that the aluminum MAS NMR chemical shift was related to the amount of phosphate present in the solid, which in turn was related to t,, t2, and the P:AI molar ratio. The results also lend support to the hypothesis that phosphate removal occurs through an adsorption process onto amorphous aluminum hydroxide, rather than through direct precipitation of aluminum phosphate. The increased understanding of aluminum and phosphate chemistry and the species formed during wastewater treatment will be useful in optimizing wastewater treatment processes.Key words: aluminum, phosphate, NMR, activated sludge, wastewater treatment.Resume : On a utilisC la RMN MAS du 2 7~1 et du "P pour Ctudier la nature de solides, contenant du phosphore et de I'aluminium, formCs au cours du traitement des eaux usCes. M&me s'ils sont difficiles caractkriser par les techniques conventionnelles, ces solides amorphes peuvent facilement &tre caractCrisCs par la RMN MAS et on obtient ainsi des informations sur leur arrangement B courte distance. Dans la presente ttude, la plupart des solides ont CtC prCcipitCs dans des conditions d'alcalinitk ClevCe semblables B celles utiliskes durant le traitement des eaux usCes. Le temps de vieillissement de l'hydroxyde d'aluminium avant I'addition du phosphate (t,), le temps de vieillissement des hydroxyphosphates d'aluminium aprks l'addition du phosphate (t,) et les rapports molaires du phosphore l'aluminium ont CtC contr81Cs alors que les effets d'un changement de ces parametres ont CtC examinks. On a trouvC que le dCplacement chimique de l'aluminium dans la RMN MAS est reliC a la quantitC de phosphate prCsente dans le solide qui, a son tour, est relie B t , , a t, et au rapport molaire P : Al. Les rCsultats supportent aussi l'hypothkse selon laquelle l'enlkvement du phosphate se produit par un processus de surface sur I'hydroxyde d'aluminium plut6t que par une prkcipitation directe du phosphate d'aluminium. La meilleure comprkhension de la chimie de I'aluminium et des phosphates ainsi que des espkces qui se forment au cours du traitement des eaux usCes sera utile pour l'optimisation dc ces procCdCs de traitement.Mots elks : aluminium, phosphate, RMN, boues activCes, traitement des eaux usCes.[Traduit par la rCd...

Analysis of Aluminum Hydroxyphosphate Vaccine Adjuvants by 27Al MAS NMR

“…There is a suggestion that the proportion of aluminum that is tetrahedrally coordinated increased with increasing phosphate content, a trend reported previously by Duffey et al in their study of wastewater precipitates. 7 However, the trend was not consistently observed in the other experiments reported here.…”

“…Goldschmid and Rubin proposed that above pH 6, the precipitate that forms from a solution containing aluminum and phosphate is aluminum hydroxide with surface adsorbed phosphate 3 and Duffy et al have supported this assertion. 7 Goldschmid and Rubin based their prediction on an observation that the concentration of soluble phosphate was dependent on the amount of precipitate present. However, this need not exclude the fact that phosphate is also incorporated into the bulk solid.…”

Five-Coordinate Aluminum in Allophane

“…The presence of 27A1 NMR signals within, or close to, the chemical-shift range 31 to 41 ppm has been used as evidence for 5-coordinate A1 in a number of less-well-characterized solids, such as zeolites (Gilson et al 1987;Kellberg et al 1991;Rocha and Klinowski 1991;Coster et al 1994), aluminosilicate glasses (Risbud et al 1987;Kohn et al 1991;Sato et al 1991), pyrophyllite dehydroxylate (Fitzgerald et al 1989), A1 hydroxyphosphates (Duffy and vanLoon 1995), amorphous and crystalline A1 borates (Simon et al 1995), amorphous aluminosilicates (De Witte et al 1995) and partly dehydrated gibbsite (Kunath-Fandrei et al 1995). Five-coordinate A1 has not been reported in allophanes previously, but most of the relevant literature has been confined to descriptions of NMR spectra obtained with a medium magnetic field strength (Childs et al 1990;MacKenzie et al 1991), for which the signals from tetrahedral and octahedral sites are so broad that they overlap, or with MAS at 3 to 4 kHz (Goodman et al 1985), which is too slow for a clear distinction between centerband and spinning-sideband signals.…”

Role of montmorillonite for enhancing fire retardancy of intumescent PLA

“…Indeed, it was already observed interactions between APP and C30B [24]. The room temperature PLAMel5APP25C30B spectrum had one band centered at 8 ppm, which can be assigned to Al in octahedral coordination [25,26]. Another signal from the OMMT should be observed at 68 ppm corresponding to Al in tetrahedral coordination [25][26][27] but since the amount of OMMT is very low, that one is not observed.…”

“…The room temperature PLAMel5APP25C30B spectrum had one band centered at 8 ppm, which can be assigned to Al in octahedral coordination [25,26]. Another signal from the OMMT should be observed at 68 ppm corresponding to Al in tetrahedral coordination [25][26][27] but since the amount of OMMT is very low, that one is not observed. At 120 s the spectrum presents two peaks, a broad one at14ppm and second one which is low intense and broad at 8 ppm.…”