Accuracy and application of quantitative X-ray diffraction on the precipitation of struvite product

Struvite (MgNH4PO4·6H2O) crystallization from wastewater can gain a great advantage for phosphorus recovery and recycling. Although the recovery process and reaction modeling have been investigated, few studies have been conducted to quantify the different phases in recovered phosphorus products. The quantitative X-ray diffraction (QXRD) technique was employed in the present study to quantitatively determine the crystal phases and amorphous content of recovered struvite-containing products. Substantial mixed phase samples (i.e. struvite, newberyite and amorphous phase) were prepared to perform quantitative analysis to calibrate against known phase composition information by Rietveld refinement on powder X-ray diffraction data. The results showed a high level of accuracy (mean error = ∼3%) in our quantification model and validated the use of the Rietveld method to quantify the amorphous and crystal phases in the struvite-containing products. In addition, the influence of N:P molar ratio on struvite crystallization suggested that the weight percentage of struvite increased from 52% to 93%, when the N:P molar ratio was elevated from 0.2:1 to 1.2:1. This finding suggested the effectiveness of QXRD in facilitating the recovery of quality struvite products from waste streams.