Thermodynamic Properties Of Lithium Borates Aqueous Solution

Products of lithium borates were widely used in inorganic industry,glasses production,battery manufacturing,medicine and agriculture for their excellent characteristics.The salt-lake brines in Qinghai-Tibet Plateau with abundant lithium and boron resources are well known around the world,and the mainly existed forms for lithium borates in salt-lake brines are LiBO2·8H2O,Li2B4O7·3H2O and LiB5O8·5H2O.However,the basically thermodynamic data for lithium borates aqueous solution were extremely absent.Therefore,the synthesis,identification and thermodynamic properties of lithium borates aqueous solution were studied in this thesis,and the conclusions were shown as bellow.In this thesis,Li2B4O7·3H2O was obtained by the recrystallization method,and LiB5O8·5H2O was synthesized by the hydrothermal method using H3BO3 and LiOH·H2O.Then,the high purity lithium borates products were characterized by X-ray powder diffraction,TG-DSC and chemical analysis.Densities of lithium pentaborate aqueous solution at different molalities and at 5 K intervals from 283.15 to 363.15 K which is not reported in the literatures were measured using a digital vibrating-tube densimeter.On the basis of the measured results,the thermal expansion coefficients,apparent molar volumes and partial molar volumes were calculated by the corresponding equations.According to the Pitzer ion-interaction model of apparent molar volumes,the Pitzer single-salt parameters and the coefficients of temperature-dependence formula were fitted by the least square method.Isopiestic equilibrium molalities of the ternary systems(LiBO2+ Li2B4O7+ H2O),(Li2B4O7+ LiB5O8+H2O)and their subsystems at 288.15 K were measured by an improved isopiestic apparatus.On the basis of the measured results,the water activities and osmotic coefficients were calculated.Eventually,the Pitzer single-salt and mixing parameters of Pitzer model were obtained.