NH4+-Mg2+-PO43--H+-H2O体系的固液平衡热力学

对NH4+-Mg2+-PO43--H+-H2O体系中固相MgNH4PO4,Mg3(PO4)2,MgHPO4及Mg(OH)2与液相间的热力学平衡关系进行计算,绘制溶液总镁与总磷摩尔比为1-1时该体系的lgcMg-pH图、lgcN-lgcMg图和lgcN-pH图,确定体系中各种固相稳定存在的pH值范围.结果表明,溶液中的氨氮浓度和pH值是影响固相稳定存在的重要因素,MgNH4PO4的稳定区随氨氮浓度的降低而变小并最终消失,当pH=8.5且MgNH4PO4与Mg3(PO4)2共存时,溶液中的氨氮平衡浓度最低.

Thermodynamics of solid-liquid equilibrium in NH4+-Mg2+-PO43--H+-H2O system

The thermodynamics of equilibrium was calculated between solid phases MgNH_4PO_4, Mg_3(PO_4)_2, MgHPO_4, Mg(OH)_2 and liquid phase in NH_4~+-Mg~(2+)-PO_4~(3-)-H~+-H_2O system. The lgcMg-PH, lgCN-igcMg and lgcN-PH diagrams when the molar ratio N(Mg)/n(P) was equal to 1:1 in liquid phases were drawn, and the pH range when solid phases existed stably in the system was determined. The results show that the ammonia-nitrogen concentration and pH are very important factors which influence the stable zone of solid phases. The stable zone of MgNH_4PO_4 reduces and finally disappears with the decrease of ammonia-nitrogen concentration. The lowest ammonia-nitrogen concentration in equilibrium is found at pH=8.5 when MgNH_4PO_4 and Mg_3(PO_4)_2 coexist with liquid phase.