三元体系Na_(2)CO_(3)-NaF-H_(2)O 298.15 K和318.15 K相平衡研究

Study on phase equilibrium of ternary system of Na_(2)CO_(3)-NaF-H_(2)O at 298.15 K and 318.15 K

在稀土提取工艺和氟化钠制备过程中会产生含碳酸钠和氟化钠的废水。研究了三元体系Na_(2)CO_(3)-NaF-H_(2)O的相平衡,为回收氟化钠和碳酸钠提供理论指导。采用等温溶解平衡法研究了三元体系Na_(2)CO_(3)-NaF-H_(2)O在298.15 K和318.15 K的相平衡关系,测定了该体系各物质组分的溶解度以及平衡液相的密度和pH,并根据溶解度数据绘制相图以及物化参数-组分含量的关系图,利用X射线衍射(XRD)对固相进行分析表征。实验研究表明:该体系无复盐和固溶体生成,属于水合物I型相图。相图包含1个全液相区、2个单盐结晶区、1个混合结晶区、1个全固相区以及3条单变量溶解度曲线、1个共饱点。碳酸钠对氟化钠具有较强的盐析作用。温度不变时,碳酸钠质量分数越高溶液密度越大、pH越大;碳酸钠质量分数不变时,温度越高溶液密度越大、pH越小。

Wastewater containing sodium carbonate and sodium fluoride will be generated in the rare earth extraction process and the preparation process of sodium fluoride.The phase equilibrium of the ternary system of Na_(2)CO_(3)-NaF-H_(2)O was studied to provide theoretical guidance for the preparation of practical production and recovery of sodium fluoride and sodium carbon-ate.The isothermal dissolution equilibrium method was used to study the phase equilibrium relationship of the ternary system of Na_(2)CO_(3)-NaF-H_(2)O at 298.15 K and 318.15 K.The solubility of each component of the system and the density and pH of the equilibrium liquid phase were measured.The phase diagram and the relationship between physicochemical parameters and content of component were drawn according to the solubility data.The solid phase was analyzed and characterized by X-ray diffraction(XRD).The experimental study showed that the system had no double salt and solid solution,and belonged to the I-type phase diagram of hydrate.The phase diagram included 1 all-liquid region,2 single-salt crystallization regions,1 mixed crystallization region,1 all-solid region,3 univariate solubility curves,and 1 co-saturation point.Na_(2)CO_(3)had a strong salting-out rate for NaF.When the temperature was constant,the mass fraction of Na_(2)CO_(3)was higher,the density was greater,and the pH of the solution was greater.When the mass fraction of Na_(2)CO_(3)was constant,the temperature was higher,the density was greater,and the pH of the solution was lower.