钙乙酸分离-三氯化铝浸取-电感耦合等离子体原子发射光谱法测定地质样品中氟化钙

采用传统EDTA滴定法测定地质样品中氟化钙(CaF₂),操作过程复杂,涉及强碱、强酸等试剂用量大,滴定终点不易判断,严重影响了CaF₂的准确测定。采用钙乙酸分离碳酸钙(CaCO₃)、氧化钙(CaO)等杂质相钙,过滤后的滤渣用AlCl₃·6H₂O溶液浸取CaF₂,再使用电感耦合等离子体原子发射光谱法(ICP-AES)测定Ca,换算成CaF₂,最终实现了地质样品中CaF₂的测定。在选定的仪器条件下,试验探讨了乙酸(1+9)和钙乙酸分离杂质相钙的效果,以及样品粒度、钙乙酸浓度、水浴温度和AlCl₃·6H₂O溶液用量等关键因素对测定结果的影响。结果表明:使用乙酸(1+9)分离杂质相钙会使CaF₂溶失导致测定结果偏低,而使用钙乙酸分离杂质相钙可有效降低CaF₂的溶失;实验确定了样品粒度为0.106～0.074 mm,钙乙酸溶液(以Ca计)质量浓度为0.8 g/L,水浴温度为95 ℃,AlCl₃·6H₂O溶液用量为25 mL。校准曲线中Ca的线性范围为5.00～50.00 μg/mL,线性回归方程为I=462.13ρ+16.863,线性相关系数r为0.999 9; CaF₂检出限为5.1 mg/kg,定量限为16.8 mg/kg。按照实验方法测定具有代表性的典型实际地质样品中CaF₂,结果的相对标准偏差(RSD,n=7)为0.22%～0.44%。经实际地质样品分析和标准物质验证,CaF₂测定值与参考值/认定值相符。方法有效解决了地质样品前处理物相分离损失CaF₂、测定结果误差大、不宜批量生产等影响CaF₂快速准确测定的问题。

Determination of calcium fluoride in geological sample by inductively coupled plasma atomic emission spectrometry with calcium acetate separation-aluminum trichloride leaching

During the determination of calcium fluoride (CaF₂) in geological samples by traditional EDTA titration, the operation process is complicated. The consumption of involved reagents such as strong alkali and strong acid is large. The end point of titration is difficult to judge, which seriously affects the accurate determination of CaF₂. In experiments, calcium acetate was used to separate the calcium in impurity phases such as calcium carbonate (CaCO₃) and calcium oxide (CaO). After filtration, the CaF₂ in residue was leached with AlCl₃·6H₂O solution. The content of Ca was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES), which was then converted to CaF₂. Finally, the determination of CaF₂ in geological samples was realized. Under the selected instrument conditions, the separation effect of calcium impurities by acetic acid (1+9) and calcium acetate was investigated and discussed. The influence of key factors such as sample particle size, calcium acetate concentration, water bath temperature and dosage of AlCl₃·6H₂O solution on the determination results was studied. The results showed that the separation of calcium in impurity phases by acetic acid (1+9) would cause lower determination results due to the dissolution loss of CaF₂, while the use of calcium acetate could effectively reduce the dissolution loss of CaF₂. The experimental conditions were obtained as follows: the sample particle size was 0.106-0.074 mm, the calcium acetate mass concentration (in Ca) was 0.8 g/L, the water bath temperature was 95 ℃, and dosage of AlCl₃·6H₂O solution was 25 mL. The linear range of calibration curve for Ca was 5.00-50.00 μg/mL. The equation of linear regression was I=462.13ρ+16.863 with linear correlation coefficient of r=0.999 9. The limit of detection of CaF₂ was 5.1 mg/kg, and the limit of quantification was 16.8 mg/kg. The content of CaF₂ in representative typical geological samples was determined according to the experimental method. The relative standard deviations (RSD, n=7) of determination results were between 0.22% and 0.44%. Through the analysis of geological samples and verification of certified reference materials, the measured value of CaF₂ were consistent with the reference/certified values. The proposed method effectively solved the problems that affect the rapid and accurate determination of CaF₂, such as the loss of CaF₂ in the pretreatment of geological samples, large error of the determination results, and unsuitable for mass production.