环境中磷回收的磷酸盐矿物结晶热力学计算模拟.doc

环境中磷回收的磷酸盐矿物结晶热力学计算模拟 【中文摘要】从污水中往除和回收磷对于防治水体富营养化和磷资源的回收利用具有重要意义。为了解溶液条件对污水磷回收的影响,必须开展系统的磷酸盐结晶化学研究,而运用地球化学水质模型程序研究磷酸盐结晶化学,对磷回收的科研和工程实践具有重要指导。本文选择美国地质调查局研制的PHREEQC水质模型程序,根据磷回收可能的溶液条件设计了开展模拟计算的体系,对磷酸钙和磷酸镁盐结晶的热力学参数溶液饱和度指数进行了大量计算模拟,并将数据模型化处理,熟悉了磷酸盐结晶影响因素的效应。研究表明,磷酸钙的饱和度指数值SI是其构成离子浓度钙离子和磷酸根离子的对数函数,随着构成离子浓度的升高而增大;SI值是溶液pH值的多项式函数,HAP和TCP的饱和度指数随着溶液pH值的升高而增大,OCP和DCPD的饱和度指数值分别在pH值9.0～9.5和7.0～7.5范围内达到最大值;SI值是溶液碱度的线性函数,随着溶液的碱度增大而降低;SI值是溶液离子强度的对数函数,随着溶液的离子强度度增大而降低;磷酸钙HAP的SI值与温度呈正相关关系,而其他磷酸钙盐的SI值与温度的关系较复杂;碳酸钙的饱和度指数值与钙离子浓度、碱度值呈对数函数关系,也是溶液pH值的多项式函数,随着溶液温度离子强度的增大而减小,与温度基本呈正相关关系;碳酸钙反应会与磷酸钙结晶反应形成竞争。磷酸铵镁的饱和度指数值SI是其构成离子浓度镁离子、铵离子和磷酸根离子的对数函数,而磷酸镁的SI值是镁离子和磷酸根离子的对数函数,SI值随着构成离子浓度的升高而增大;磷酸盐的SI值是溶液pH值的多项式函数,MAP结晶的最佳pH值是9.0左右,磷酸镁结晶的最佳pH值在9.5～10.5之间;磷酸镁盐的饱和度指数值随着溶液的碱度和离子强度增大而降低;磷酸镁盐的饱和度指数值是温度的多项式函数,温度效应与反应条件有关。对于模拟养猪废水的工况条件变化的热力学计算模拟研究表明,进步溶液pH值会使磷酸钙和磷酸镁的饱和度指数值明显增大,但同时碳酸钙的饱和度指数值也增大;投加钙盐使促进磷酸钙的结晶但抑制镁盐的结晶,反之亦然;但无论投加钙盐还是镁盐,都会使碳酸钙镁的饱和度指数增大;调高溶液的pH值,同时投加钙镁盐,将大大进步磷酸盐结晶的饱和度指数,但同时碳酸钙的饱和度指数值也增大;综合而言,调节溶液pH值是调控磷酸盐结晶最有效的手段之一。; 【Abstract】 It is very important to remove and recover phosphorus P from wastewater so as to prevent eutrophication of waters and to recover and reuse P resource. To understand the effect of solution condition on P recovery from wastewater it is necessary to carry out systematic study on phosphate crystallization, and to study phosphate crystallization chemistry by using geochemical water quality model program is of significance for research and engineering practice of P recovery.PHREEQC Program from the U. S. Geology Survey was chosen, and the probable solution condition systems for P recovery were designed. A great deal of calculations on the thermodynamic parameters of phosphate calcium and phosphate magnesium salts have been carried out and modeled; the effects on phosphate crystallization have been understood.It shows that the saturation index SI of calcium phosphate is the logarithmic functions of Ca and phosphate concentrations, and increases with the increasing of their concentrations. SI is the polynomial function of pH value; the SI values of hydroxyapatite HAP and tricalcium phosphate TCP increase with the increase of pH value; while the SI of octacalcium phosphate OCP and dicalcium phosphate dehydrate DCPD have highest values at pH 9.0～9.5 and 7.0～7.5, respectively. SI is the linear function of alkalinity and decreases with its increase. SI value is the logarithmic function of ionic strength and deceases with its increase. .The SI of HAP is positively correlated to temperature, but other calcium phosphates show their complex temperature effect. The SI of carbonate is the logarithmic function of Ca and carbonate concentrations, respectively; and it is also the polynomial function of pH value, decreasing with the increase of ionic strength and being positively correlated to temperature. Carbonate and phosphate may compete in crystallization.The SI of magnesium ammonium phosphate MAP is the logarithmic function of the concentrations of its constitutional Mg ion, ammonium ion and phosphate ion, and the SI of magnesium phosphate MP is the logarithmic function of the concentrations of its constitutional Mg ion and phosphate ion. The SI values of MAP and MP are the polynomial functions of pH value; and the optimum pH for MAP crystallization is around 9.0, while it is at 9.5～10.5 for MP. The SI values of MAP and MP decrease with the increases of alkalinity and ionic strength, and being the polynomial functions of temperature correlating to reaction conditions.The thermodynamic simulation on the process conditions of synthetic swine wastewater treatment shows that the SI of calcium phosphate and magnesium phosphate can be increased by increasing pH, but the SI value of carbonate also increases. The crystallization of calcium phosphate can be promoted by dosing Ca but this may inhibit the crystallization of magnesium phosphate, and vice versa. However, both dosing Ca and Mg may increase the SI of calcium and magnesium carbonate. The SI values of phosphate salts can be greatly improved by increasing pH and dosing Ca and Mg, but meanwhile the SI of calcium carbonate also increases. With a comprehensive thinking, to adjust solution pH is one of the most effective measures for phosphate crystallization adjustment.