Water activity and freezing points in aqueous solutions of manganese nitrate: experimental and modeling

The water activities of manganese nitrate solutions were measured using a humidity sensor instrument up to almost the saturation molality at 298.15 K; the thermodynamic properties of the system were described by the Pitzer model and specific interaction theory (SIT). The evaluation of the ion interaction parameters for the Pitzer model and SIT were carried out using experimental freezing points and osmotic coefficients of manganese nitrate aqueous solutions, collected from the open literature, and the water activity data measured in this work. A set of Pitzer and SIT parameters were estimated using a temperature dependency, that enables us to cover wider temperature ranges, and consequently calculate system properties to higher molalities. Both approaches represent very satisfactorily, and with similar accuracy, the experimental data and the calculated manganese nitrate molal activity coefficients are comparable to those already published for analogous systems. Additionally, the Pitzer model was also able to calculate the ice curve and the solubility branch of manganese nitrate hexahydrate up to a salt solution 6.5 mol-kg-1.This work was developed in the scope of the projects POCI-01-0145-FEDER- 006984—Associate Laboratory LSRE-LCM both funded by European Regional Development Fund (ERDF) through COMPETE2020—Programa Operacional Competitividade e Internacionalização (POCI)—and by national funds through FCT—Fundação para a Ciência e a Tecnologia. This work is also a result of project ‘‘AIProcMat@N2020—Advanced Industrial Processes and Materials for a Sustainable Northern Region of Portugal 2020’’, with the reference NORTE-01-0145-FEDER-000006, supported by Norte Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through ERDF.info:eu-repo/semantics/publishedVersio