(硬)石膏矿物中硼的提取分离及硼同位素测定

Extraction and Separation of Boron in Anhydrite and Gypsum Minerals and Its Isotopic Measurement by Thermal Ionization Mass Spectrometry

(硬)石膏作为海湖水蒸发过程中常见的硫酸盐矿物,能很好反映原始母液的组成及相关水文地质信息。硼属于易溶元素,常赋存于各种蒸发岩矿物中,目前硼同位素在矿床学,地球化学,古环境等地球科学中已得到广泛应用。由于(硬)石膏硼含量较低且难溶于水和盐酸,所以其硼含量及硼同位素组成特征研究较少。本研究通过物相转化与树脂交换法提取纯化(硬)石膏中的硼:首先使用碳酸氢铵与石膏混合,将微溶硫酸钙转化为难溶碳酸钙,随后使用盐酸溶解,一次转化率为85%,两次转化与分解可以保证石膏的完全溶解;之后经过硼特效树脂(Amberlite IRA 743)完成硼富集及阴阳离子混合树脂(Ion ExchangeⅡ和Dowex50W×8)对硼的纯化;最终通过He改进的正热电离质谱法测定硼同位素。测得试剂石膏中的硼含量为(3.501±0.128)μg/g(n=12,RSD=3.6%),平均加标回收率为100.5%;同时加标试剂石膏的δ^(11)B值为17.98‰±0.21‰(n=3,RSD=1.2%),说明整个流程的重复性良好,可以满足(硬)石膏中硼含量及其硼同位素组成的准确测定。

The anhydrite and gypsum are the main sulfate minerals during evaporation of seawater or lake.They record the information about relative hydrogeology and the composition of mother liquor.Boron is diffluent element,and often occurs in all kinds of evaporites.Presently,the boron isotope has been applied widely in mineral deposits forming,geochemistry and palaeoenvironment.However,there is little research about characteristic of boron isotope in anhydrite and gypsum minerals,because of the low content of boron and micro-solubility in water and hydrochloric acid.This study developed a method of extracting and purifying boron in anhydrite and gypsum by phase transformation and ion-exchange.Firstly,the samples were mixed with ammonium hydrogen carbonate to transform the calcium sulfate to calcium carbonate.And diluted hydrochloric acid(1mol/L)was added to resolve calcium carbonate.The percent conversion was about85%in the first stage,and up to complete resolution by repeating this process.Secondly,boron specific ion-exchange resin(Amberlite IRA743)was used to gather the boron ions fully and further refined the samples with more than1ug of boron by anionic and cationic resin mixed by Ion Exchange II and Dowex50W*8.Finally,according to the modified method by He,the values of boron isotope were determined by TIMS.The boron content is analytically pure gypsum was3.501+-0.128ug/g(n=12,RSD=3.6%)and the average recovery was100.47%.Besides,the啄11B value of analytically pure gypsum added with NIST SRM951was17.98‰+-0.21‰(n=3,RSD=1.2%).This method has good repeatability and can meet the requirements of boron isotopic measurement of anhydrite and gypsum.