The system NaCl-CaCl_2-H_2O: Part 3. Heats of dilution and mixing at 373 to 573 K and 21.5 MPa using a new high-temperature, flow-through calorimeter

摘要

New heat of mixing and heat of dilution data are presented for the system {NaCl + CaCl_2}(aq) at 373, 423, 473, 523, and 573 K and 21.5 MPa. At each temperature heat of mixing measurements were made over an ionic strength range between 0. 5 and 4.0 mol·kg~(-1) H_2O and a constant ionic strength fraction of 0.5. Heats of dilution of CaCl_2(aq) were measured at each temperature over the ionic strength range of 0.3-18 mol/kg H_2O. All measurements were made using heats of dilution of NaCl(aq) to calibrate the device. CaCl_2 dilution enthalpies compare favorably with the available published data to 523 K. Mixing enthalpies at these temperatures have not been previously measured. While dilution enthalpies for the aqueous salt binaries in this system are exothermic, mixing enthalpies are endothermic. At fixed ionic strength and pressure, mixing enthalpies in this system have a roughly quadratic dependence on temperature with a broad minimum between 373 and 473 K. The data have been fit within the Pitzer ion-interaction formalism, incorporating published ion-interaction parameters for the aqueous salt binaries. In order to reproduce the data within their accuracy, the model must include the mixing parameters Φ_(NaCa)~L and Ψ_(NaCaCl)~L.