Determination of ion association in dilute aqueous lithium chloride and lithium hydroxide solutions to 600°C and 300 MPa by electrical conductance measurements

The limiting molar conductances (Lambda(0)) and ion association constants of dilute aqueous lithium chloride and lithium hydroxide solutions (<0.01 mol.kg(-1)) were determined by electrical conductance measurements at temperatures from 100 to 600 degrees C and pressures up to 300 MPa. The values of Lambda(0)(LiCl) and Lambda(0)(LiOH) obtained from with Shedlovsky (at densities greater than or equal to 0.6 g.cm(-3)) and Fuoss-Hsia-Fernandez-Prini (FHFP) equations (at densities <0.6 g.cm(-8)) increase with increasing temperature up to 300 degrees C and decreasing density. Above 300 degrees C and densities between 0.8 and 0.5 g.cm(-3) for LiCl(aq) and 0.8 to 0.6 g.cm(-3) for LiOH(aq), Lambda(0) is nearly temperature-independent but does increase linearly with decreasing density. The molal association constants, K-A(m) for both electrolytes were computed exclusively from the data greater than or equal to 400 degrees C (at densities 0.8-0.3 for LiCl and 0.8-0.5 g.cm(-3) for LiOH) by the Shedlovsky equation and can be represented as functions of temperature (Kelvin) and the logarithm of water density (rho(w)) as follows: log K-A(m)(LiCl) = 0.724 - 8.980/(T/X) - (12.796 - 5431.2/(T/K)) log rho(w)/g.cm(-3)) and log K-A(m)(LiOH) = 0.856 + 135.60/(T/K) - (11.998 - 4226.3/(T/K)) log rho(w)/(g.cm(-3)). At corresponding conditions and within experimental error, the degree of ion association of LiCl(aq) is comparable with NaCl(aq) and KCl(aq), whereas ion association for LiOH(aq), is significantly stronger than for NaOH(aq) and KOH(aq). Moreover, the same values of K-A(m) were obtained for each electrolyte irrespective of the whether the Shedlovsky or FHFP equations were employed. This point is exemplified by a comparison of the K-A(m) value for LiCl obtained from the present study with those of a recent investigation that utilized an advanced design for moderately high temperature conductance measurements.