The Physical一Chemical Characteristics of Ulexite of Qinghai一Tibetan Plateall

Abstract: Ulexite is a kind of mineral containing Na, Ca and crystalline water borate. It has been obtained from the borate deposits of Da一Chaidan and Xiao一Chaidan salt lakes in Qinghai and Z.azangzaka salt lake in TI- betan. After purification of the two samples,the contents of Na⁺,Ca⁺⁺,B₂O₂ and H₂O of ulexites were determined. They are in line with the chemical fromulae (2Ca0 2Na₂O.5B₂0₂,.16H₂0). The results show that the samples are better than the ulexite reported by China. American and Russia in references. The physleal-chemical characteristics of ulexite have been, studied by X一ray powder differaction,IRspectrasopy. thermoanalysis methods,photomicro一graph and conventional chemical analysis. The results are comparatively systematical and satisfactory. The structure characteristics of ulexite in two regoin determined by X一ray powder differation are all completely agreed with standard card of JCPDS of ulexite. In the IR一spectra of the ulexite,there are four absorption peaks at 3220. 3320. 3420 and 3520 cm^-1.They may be due to the bonding vibration of OH in crystalline water. In the 1500-400 cm^-1region absorplion peaks are those of polyanion of borate. The asymmetric vibration of BO₃^-3. the bending vibration In the area of M一OH。the asymmetric vibration of BO₄^-1, the symmetric vibration of BO₃^-3. BO₄^-1. the bending vibration of BO₃^-3 and BO₄^-1. Those spectra show that the ulexite has two different type stracture of triganle BO₃^-3tetrahedra BO₄^-1. The crystal structure of ulexite is tricline, we also gave reflective index Ng=1. 517. Nm=1. 505. Np=1. 498 The two samples of Qlnghai and Tibetan are completely the same. The photoicrograph shows that they are needle一like crystals. Thermal behavior of the ulexites has been studied by DSC and DTA. Three endothermic peaks on the curve, they are dehydration crystall water. The endothermic peak at 800℃ is the rearrangement of polyborate molecule. The self-melt peak appears at 900℃. The first suggested solubilities of ulexite in the water at different temperature 3. 45. 3. 91,4. 25. 5. 00.5. 44 and 5. 95 g/1 at 10. 15. 20. 25, 30 and 35 respectively. The calculated values of enthapy of solution and entropy of solution.