Carbon capture, utilization, and storage (CCUS) is among the selected strategies to restrain the effects of climate change in the near future. However, the amount of CO2 that is captured currently is much lower than the levels required for successful climate action. One key to unlock CCUS deployment is reducing the cost of captured CO2. The assessment of new technologies or different operating scenarios through process simulation rely on thermodynamic models that can reproduce the system’s properties. These models are fine-tuned based on accurate phase and chemical equilibrium measurements, especially vapor-equilibrium data. However, the measurement of such properties is often cumbersome and expensive. In this context, the goal of this work is to provide a reliable basis for thermodynamic modelling and process simulation of a CO2 absorption unit using a mixed salt solution. The work entails the commissioning and measurement of equilibrium data, which will be followed by the correlation of such properties using the extended UNIQUAC model. The developed model will be suitable for process simulations and should provide insights on energy consumption and cost of captured CO2.