THE SYSTEM NACL-CACL2-H2O - PART 3 - HEATS OF DILUTION AND MIXING AT 373 TO 573 K AND 21.5 MPA USING A NEW HIGH-TEMPERATURE, FLOW-THROUGH CALORIMETER

New heat of mixing and heat of dilution data are presented for the sys tem {NaCl + CaCl2} (aq) at 373, 423, 473, 523, and 573 K and 21.5 MPa. At each temperature heat of mixing measurements were made over an ion ic strength range between 0.5 and 4.0 mol.kg(-1) H2O and a constant io nic strength fraction of 0.5. Heats of dilution of CaCl2(aq) were meas ured at each temperature over the ionic strength range of 0.3-18 mol/k g H2O. All measurements were made using heats of dilution of NaCl(aq) to calibrate the device. CaCl2 dilution enthalpies compare favorably w ith the available published data to 523 K. Mixing enthalpies at these temperatures have not been previously measured. While dilution enthalp ies for the aqueous salt binaries in this system are exothermic, mixin g enthalpies are endothermic. At fixed ionic strength and pressure, mi xing 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 Fitter ion-interaction formalism, incorporating pu blished ion-interaction parameters for the aqueous salt binaries. In o rder to reproduce the data within their accuracy, the model must inclu de the mixing parameters Phi(NaCa)(L) and Psi(NaCaCl)(L). Copyright (C ) 1998 Elsevier Science Ltd.