X-ray Diffraction Analysis of the Effect of the NH4+: PO43- Molar Ratio on the Formation of Crystallized Struvite and Recovery Rate of Phosphorus

摘要

Phosphorus and nitrogen are directly responsible for the eutrophication of water bodies, and thus their removal from wastewater is obligatory, although this is not performed in many cases. However, when it is considered that global phosphorus resources will be exhausted in the near future, phosphorus recovery from wastewater will become a more viable process. Crystallization of phosphorus and nitrogen in the form of struvite (MgNH4PO4·6H2O), a slow-releasing and valuable fertilizer, is one feasible technique for this purpose. In this study, the effect of different NH4+:PO43-molar ratios on the formation of crystallized struvite and recovery rate of phosphorus was estimated by X-ray diffraction (XRD). By maintaining the same conditions (PO43--P concentration 60 mgL-1, molar ratio Mg2+:PO43-of 1:1, and reaction pH 10.0), the results showed the precipitate was mainly composed of Mg3(PO4)2·22H2O when the NH4 +:PO4 3-molar ratios were 1:1, 1.2:1 or 1.6:1.However, the precipitate became a mixture of Mg3(PO4)2·22H2O and MgNH4PO4·6H2O when the NH4 +:PO4 3-molar ratio was 2:1.Finally, the precipitate was mainly MgNH4PO4·6H2O when the NH4 +:PO4 3-molar ratios were 3:1 and 6:1.Overall, the recovery rate of phosphorus increases from 51.6% to 84.6% with an increase of the NH4 +:PO4 3-molar ratio from 1:1 to 6:1.