NH_4^+-Mg^(2+)-PO_4^(3-)-H^+-H_2O体系的优势区相图(英文)

Predominance Diagrams for NH_4^+-Mg^(2+)-PO_4^(3-)—H^+-H_2O System

通过优势区相图的构建对NH4+-Mg2+-PO43--H+-H2O体系的热力学平衡关系进行了研究。在不同镁、磷物质的量比和离子强度的条件下绘制了lgCT,Mg-lgCT,P和lgCT,P-pH相图,确定了MgNH4PO4.6H2O、Mg3(PO4)2.8H2O、MgHPO4.3H2O和Mg(OH)2的热力学稳定区。结果表明,在相当广的pH范围内,MgNH4PO4.6H2O和Mg3(PO4)2.8H2O都是主要存在的固相;在较低pH和较高磷浓度的条件下,MgNH4PO4.6H2O和MgHPO4.3H2O可以共存;而MgNH4PO4.6H2O和Mg(OH)2在碱性条件下更为稳定。当MgNH4PO4.6H2O、Mg3(PO4)2.8H2O与液相共存、pH=9.08~9.52时,溶液总氮浓度达到最低值。lgCT,Mg-lgCT,P和lgCT,P-pH相图可以用于指导磷酸铵镁的沉淀-溶解平衡过程,有利于废水中氨氮的脱除和回收。

The thermodynamics of NH44^＋-Mg^2＋-PO4^3--H^＋-H2O system was investigated based on the construction of predominance diagrams. The lglgCTMg-lgCTP and lgCTs-pH diagrams were constructed at an arbitrary Mg/P molar ratio with consideration of the ion strength influence（CTMg： total concentration of magnesium; CTy： total concentration of phosphorus; CTN： total concentration of nitrogen）. The thermodynamic stable zones of struvite （MgNH4PO4· 6H20）, bobierrite （Mg3（PO4）2· 8H20）, newberyite （MgHPO4· 3H20）, and magnesium hydroxide （Mg（OH）2） were determined. The results show that struvite and bobierrite are the dominating phases in a wide range of pH value. Struvite and newberyite coexist with solute phase at low pH value and high total concentration of phosphorus while struvite and magnesium hydroxide are more stable at the alkaline condition. The minimum total concentration of nitrogen appears at pH value of 9.08-9.52 while struvite and bobierrite coexist with the solute phase. The predominance diagrams could be used to predict the precipitation-dissolution equilibrium of struvite for ammonia nitrogen removal and recovery from wastewater.