盐湖卤水中硼同位素分馏因子的第一性原理计算

Ab initio evaluation of boron isotope fractionation factors in Salt Lake Brine

硼同位素已在物源示踪、古环境研究等方面得到广泛应用.对于盐湖硼同位素研究而言,获得盐湖卤水中不同硼物种(包括B(OH)_(3)、B(OH)_(4)^(–)和多聚硼酸盐阴离子B_(3)O_(3)(OH)_(4)^(–)、B_(3)O_(3)(OH)_(5)^(2–)、B_(4)O_(5)(OH)_(4)^(2–)、B_(5)O_(6)(OH)_(4)^(–))之间准确的硼同位素平衡分馏因子,是开展盐湖硼同位素地球化学研究的基础.本研究利用量子化学计算法精确计算了卤水中B(OH)_(3)和B(OH)_(4)^(–)与多聚硼酸盐阴离子之间的硼同位素平衡分馏因子,并就非谐效应和溶剂化效应对计算结果的贡献进行了校正.结果显示,B(OH)_(3)和B(OH)_(4)^(-)与多聚硼酸盐阴离子之间的平衡硼同位素分馏因子分别为:α_(3-4)=1.0286;α_(3-334)=1.0389;α_(3-335)=1.0717;α_(3-45)=1.0889;α_(3-56)=1.1180;α_(4-334)=0.9545;α_(4-335)=0.9849;α_(4-45)=0.9728;α_(4-56)=0.9711.这些分馏因子的确定,为研究盐湖卤水硼迁移过程的硼同位素分馏行为提供了基础数据和理论指导.

Boron isotopes have found extensive applications in fields such as source tracing and paleoenvironmental research.It is important to obtain accurate boron isotope equilibrium fractionation factors between different boron species in brine to study boron isotope geochemistry in salt lakes.These boron species include boric acid (B(OH)_(3)),borate ion (B(OH)_(4)^(-)) and polyborate ion B_(3)O_(3)(OH)_(4)^(-),B_(3)O_(3)(OH)_5^(2-),B_4O_5(OH)_4^(2-)and B_5O_6(OH)_4^(-).In this study,the boron isotope equilibrium fractionation factors between B(OH)_(3) and B(OH)_4^(-) and polyborate ions in brine were accurately calculated by quantum chemical calculation method,and the effects of anharmonic effect and solvation effect on the calculation results were corrected.According to the results,the equilibrium boron isotope fractionation factors between B(OH)_(3) and B(OH)_(4)^(–) and polyborate ions are as follows:α_(3-4)=1.0286,α_(3-334)=1.0389,α_(3-335)=1.0717,α_(3-45)=1.0889,α_(3-56)=1.1180,α_(4-334)=0.9545,α_(4-335)=0.9849,α_(4-45)=0.9728,α_(4-56)=0.9711.The identification of these fractionation factors provides foundational data and theoretical insights into the boron isotope fractionation occurring during the transport of boron in salt lakes brine.