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通过对Me2+–CO32––NH3–H2O(Me2+=Fe2+,Mg2+,Mn2+,Zn2+)体系的热力学分析,得到各金属离子浓度与pH值的关系,绘制不同[C]t和[N]t条件下各金属离子的浓度对数–pH曲线。热力学分析表明:在固定[N]t、改变[C]t的条件下,提高[C]t有利于金属离子的沉淀,并且随着溶液pH值的升高,金属离子浓度不断下降;但在固定[C]t而改变[N]t的条件下,如果[N]t过高,将会导致溶液中残留金属离子浓度增大。分析结果还表明:将溶液中[C]t和[N]t分别控制在1.0mol/L和0.2mol/L,Fe2+、Mg2+、Mn2+和Zn2+共沉淀的最佳pH值范围为8～9,当pH=8.65时,各金属离子浓度均可达到最低值,此时溶液中残留的各金属离子总浓度可控制在10–5mol/L以下。
Through the thermodynamic analysis of the system of Me2 + -CO32 - NH3-H2O (Me2 + = Fe2 +, Mg2 +, Mn2 +, Zn2 +), the relationship between the concentration of each metal ion and the pH value was obtained. Under different [C] t and [N] t conditions Concentration of each metal ion log-pH curve. The thermodynamic analysis shows that the increase of [C] t is beneficial to the precipitation of metal ions with [N] t and [C] t change, and the concentration of metal ions decreases with the increase of solution pH. Fixing [C] t and changing [N] t, if [N] t is too high, it will lead to the increase of residual metal ion concentration in the solution. The results also showed that the optimal pH values of [C] t and [N] t were 1.0mol / L and 0.2mol / L respectively, and the optimal pH values for the coprecipitation of Fe2 +, Mg2 +, Mn2 + and Zn2 + When the pH = 8.65, the metal ion concentration can reach the lowest value, then the total concentration of residual metal ions in the solution can be controlled below 10-5mol / L.