四元体系Li~+,K~+//CO_3~(2-),B_4O_7~(2-)-H_2O273K介稳相平衡研究

针对西藏扎布耶盐湖卤水组成,用等温蒸发平衡法研究了四元体系Li+,K+//CO23-,B4O27--H2O 273 K的相平衡,测定了平衡时各组分的溶解度及平衡液相的密度。四元体系Li+,K+//CO32-,B4O72--H2O273 K时的相图由5条溶解度单变量线、4个结晶区及2个共饱点组成。4个结晶区分别为对应于盐Li2CO3,K2CO3.1.5H2O,K2B4O7.4H2O及Li2B2O4.16H2O。2个共饱点中,一个为Li2CO3,K2CO3.1.5H2O及K2B4O7.4H2O三盐相称共饱点,另一个为Li2CO3,K2B4O7.4H2O和Li2B2O4.16H2O的三盐不相称共饱点。体系属四元水合物相图Ⅰ型,4种原始组分间未形成复盐或固溶体。对于该四元体系273 K和288 K下的介稳相图发现,碳酸锂盐的溶解度呈现较明显的负温度效应,它在273 K下的结晶相区比在288 K下的要小,且析出固相为偏硼酸锂;而碳酸钾、硼酸钾及硼酸锂结晶区则比288 K下的大。

Study on metastable phase equilibrium of quaternary system Li+ ,K+//CO32- ,B4O72- - H2O at 273 K

To aim at the composition characteristics of the brines of Zabuye Saline Lake in Tibet,the metastable equilibrium of the quaternary system Li+,K+ // CO2-3,B4O2-7-H2O at 273 K was studied with the isothermal evaporation method.According to the determined values the phase diagram of the quaternary system was plotted.The phase diagram of the system consists of 2 invariant points E and F,5 invariant curves,and 4 crystallization fields which are corresponding to the salt Li2CO3,K2CO3·1.5H2O,K2B4O7·4H2O and Li2B2O4·16H2O.Of 2 invariant points one is three-salt proportional invariant point of Li2CO3,K2CO3·1.5H2O and K2B4O7·4H2O,and another one is three-salt disproportional invariant point of Li2CO3,K2B4O7·4H2O and Li2B2O4·16H2O.The system is quaternary hydrate phase diagram Type I.Four compositions do not form double salt or solid solution.The metastable phase diagrams of the system at 273 K and 288 K show that the solubility of the lithium carbonate has a negative temperature effect;the crystallization field for lithium carbonate at 273 K is smaller than that at 288 K;and the crystallization form is lithium metaborate at 273 K,while the crystallization fields for potassium carbonate,potassium borate,and lithium borate at 273 K are larger than those at 288 K.