Me-NaHCO_3-NH_3-H_2O体系和Me-NaOH-NaHCO_3-H_2O体系的热力学分析

Thermodynamic Analysis on the Me-NaHCO_3-NH_3-H_2O and Me-NaOH-NaHCO_3-H_2O Systems

通过对Me(Fe2+,Ni2+,Cu2+,Zn2+)-NaHCO3-NH3-H2O体系以及Me-NaOH-NaHCO3-H2O体系的热力学分析,得到各金属离子总浓度cMe与pH值的关系,确定了2种体系的完全共沉淀区域。热力学分析结果表明:在Me-NaHCO3-NH3-H2O体系中,Ni2+,Cu2+,Zn2+这3种离子和氨的配位能力很强。当总碳的浓度cC=1mol.L-1且总氮的浓度cN=0.01mol.L-1时,在pH=7.5～11范围内可实现完全共沉淀;当cN=0.05mol.L-1且cC=3mol.L-1时,在pH=70.5时可实现完全沉淀,但共沉淀范围较窄,不利于铁氧体组分的精确控制。在Me-NaOH-NaHCO3-H2O体系中,共沉淀区域由cC决定,当cC=1mol.L-1,pH=7.5～11时可实现完全共沉淀。

Through thermodynamic analysis for different Me^2＋ ions （Me refers to Fe, Ni, Cu, Zn） in NaHCO3-NH3-H2O and NaOH-NaHCO3-H2O systems, the total Me^2＋ concentration cMe as a function of pH was obtained, and hence the pH window of complete co-precipitation for several of Me^2＋ ions is determined. The results show that Ni^2＋, Cu^2＋ and Zn^2＋ ions are difficult to completely co-precipitate in the system containing NH3 because of their strong complexing ability with NH3,When the total carbon concentration cc is 1mol·L^-1 and the total nitrogen concentration cN is smaller than 0.01mol·L^-1, the four kinds of metal ions can be completely co-precipitated in the pH range from 7.5 to 11. Though they can also be co-precipitated entirely at pH of 6.5-7.5, while keeping CN 0.05mol·L^-1 and Cc greater than 3mol·L^-1, the pH window of complete co-precipitation is so narrow that it is disadvantage for ensuring the desired composition. In the system of Me-NaHCO3-NaOH-H2O, the pH window of complete co-precipitation is determined by the total carbon concentration co. When Cc is 1mol·L^-1, they can complete co-precipitate at the pH of 7.5-11.