Determination of calcium fluoride in geological sample by inductively coupled plasma atomic emission spectrometry with calcium acetate separation-aluminum trichloride leaching
A Lili1,2, WU Peiyuan1,2, MAO Meng1,2, HE Panhong1,2, MA Lin1,2, SUN Yinsheng1,2
1. Henan Province Nuclear Geology, Zhengzhou 450044, China; 2. Henan Radionuclide Detection of Nuclear Industry, Zhengzhou 450044, China
Abstract：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.
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