Babić-Ivancić Vesna, Kontrec Jasminka, Brecević Ljerka, Kralj Damir
Laboratory for Precipitation Processes, Division of Materials Chemistry, Ruder Bosković Institute, P.O. Box 180, HR-10002 Zagreb, Croatia.
Water Res. 2006 Oct;40(18):3447-55. doi: 10.1016/j.watres.2006.07.026. Epub 2006 Sep 15.
The influence of the initial reactant concentrations on the composition of the solid phases formed in the precipitation system MgCl(2)-NH(4)H(2)PO(4)-NaOH-H(2)O was investigated. The precipitation diagram constructed shows the approximate concentration regions within which struvite, newberyite, and their mixtures exist at 25 degrees C and an aging time of 60 min. It was found that immediately after mixing the reactant solutions, struvite (MgNH(4)PO(4).6H(2)O) precipitated in nearly the whole concentration area, while newberyite (MgHPO(4).3H(2)O) appeared mostly within the region of the excess of magnesium concentration. It was also found that after aging time of 60 min the precipitation domain of struvite alone is much broader than that of newberyite or the domain of their coexistence, and shows that struvite is more abundant in the systems in which the initial concentration of ammonium phosphate is higher than that of magnesium. The kinetics of struvite to newberyite transformation (conversion) was systematically studied under the conditions of different initial reactant concentrations and different initial pH in the systems in which a mixture of both phases precipitated spontaneously. The struvite to newberyite conversion period was found to be strongly related to the ratio of initial supersaturations, S(N)/S(S), rather than to the any particular physical quantity that can describe and predict the behavior of the precipitation system. Experimental data suggest a solution-mediated process as a most possible transformation mechanism. Along with a continuous monitoring of the changes in the liquid phase, the content of struvite in the solid phase was estimated by means of a Fourier transform infrared (FT-IR) method, developed for this particular precipitation system.
研究了初始反应物浓度对沉淀体系MgCl₂-NH₄H₂PO₄-NaOH-H₂O中形成的固相组成的影响。构建的沉淀图显示了在25℃和60分钟老化时间下鸟粪石、磷酸镁石及其混合物存在的近似浓度区域。研究发现，反应物溶液混合后立即在几乎整个浓度区域内沉淀出鸟粪石（MgNH₄PO₄·6H₂O），而磷酸镁石（MgHPO₄·3H₂O）大多出现在镁浓度过量的区域内。还发现，在60分钟的老化时间后，单独鸟粪石的沉淀区域比磷酸镁石或它们共存的区域要宽得多，这表明在磷酸铵初始浓度高于镁的体系中鸟粪石更为丰富。在两种相的混合物自发沉淀的体系中，在不同初始反应物浓度和不同初始pH条件下，系统地研究了鸟粪石向磷酸镁石转化（转变）的动力学。发现鸟粪石向磷酸镁石的转化期与初始过饱和度之比S(N)/S(S)密切相关，而不是与任何能够描述和预测沉淀体系行为的特定物理量相关。实验数据表明溶液介导过程是最可能的转化机制。在持续监测液相变化的同时，通过为该特定沉淀体系开发的傅里叶变换红外（FT-IR）方法估算了固相中鸟粪石的含量。
