Thermochemical Properties Of Aqueous System Containing Alkalis Borates

As one kinds of crucial chemicals,alkalis borates are widely used in the field of glass fibre,ceramic,fire retardant,nonlinear optical material,agriculture and so on.The salt lakes distributed in the Qinghai-Tibet Plateau are famous for their high concentration of lithium,sodium,potassium,boron and so on.For this case,studies on the synthesis and thermochemical properties of different alkalis borates are essential to promote the comprehensive utilization of the salt lake resources.In this paper,the three hydrated 0031 alkalis borates with high purity i.e.LiB₅O₈·5H₂O,NaB₅O₈·5H₂O and KB₅O₈·4H₂O were synthesized under each optimium synthesizing conditions obtained after a series of studies.And then,the re-crystallization high purity products were characterized by chemical analysis,X-ray diffraction as well as TG-DSC.In this paper,the capacities of aqueous systems（NaB₅O₈-H₂O）at 298.15 K and（Li₂B₄O₇-H₂O）at（298.15,308.15 and 323.15）K were systematically measured by Micro-calorimeter with the type of Setaram BT 2.15 for the purpose of calculating apparent molar capacity.The relational expressions between apparent molar capacity and the concentration of alkalis borates were deduced.Moreover,the Pitzer single salt parameters of NaB₅O₈·5H₂O and Li₂B₄O₇·3H₂O at various temperatures were fitted on the basis of the Pitzer ion-interaction theory of the electrolytes,and the experimental results of capacity data or the systems（NaB₅O₈-H₂O）and（Li₂B₄O₇-H₂O）at different temperatures agree well with the calaulated values.