Thermodynamic Analysis on the Coprecipitation of Ni-Co-Mn Hydroxide

Abstract

The thermodynamic data of various species in Ni-H₂O, Co-H₂O, Mn-H₂O, and Ni-Co-Mn-H₂O systems were obtained by thermodynamic calculation. The potential-pH diagrams for Ni-H₂O, Co-H₂O, and Mn-H₂O systems at different ion activities at 323 K (50 °C), as well as Ni-Co-Mn-H₂O complex systems at activity 1.00 at 298 K, 323 K, and 373 K (25 °C, 50 °C, and 100 °C) were constructed, respectively. The costable regions of Ni(OH)₂, Co(OH)₂, and Mn(OH)₂ are verified to be thermodynamically stable in aqueous solution, which indicates the thermodynamic possibility of Ni-Co-Mn hydroxide coprecipitation. The potential-pH diagrams show that the temperature and ion activity have significant effects on the coprecipitation process. As the temperature increases or the ion activity decreases, the coprecipitation region of the Ni-Co-Mn hydroxide narrows. Moreover, the metal oxides, rather than the metal hydroxide, are more easily formed when the temperature increases. Experimental confirmation was performed to further verify the constructed potential-pH diagrams. The Ni-Co-Mn hydroxide with typical hexagonal CdI₂ structure and quasi-spherical morphology was successfully obtained, and the SEM results show the uniform distribution of the elements Ni, Co, and Mn. The experimental results confirm the reliability of the prediction of thermodynamics analysis.

Appendices

Appendix A

See Table AI.

Table AI $\Delta_{r} G_{298.15}^{\varTheta }$ and $\Delta_{r} \text{S}_{298.15}^{\varTheta }$ of Various Species Considered in the Me-H₂O System at 298.15 K (25 °C)

Appendix B

See Table BI.

Table BI $\varphi_{T}^{\varTheta }$ of Reactions in the Me-H₂O Systems at 298 K, 323 K, and 373 K (25 °C, 50 °C, and 100 °C)

Appendix C

See Table CI.

Table CI $\text{pH}_{T}^{\varTheta }$ of Reactions in the Me-H₂O Systems at 298 K, 323 K, and 373 K (25 °C, 50 °C, and 100 °C)