Determination of extractable fluorine from residue of oil and gas industry by HR-CS MAS applying toxicity characteristic leaching procedure

Abstract Toxicity characteristic leaching procedure (TCLP) is a standard extraction procedure in acetic acid medium for toxicity assessment. Fluoride (F−) is one of the extracted forms of fluorine monitored that has a regulated value. In this study, the CaF molecule was used to determine the leached fluorine (F) (in acetic acid medium, at pH 2.88 and 4.93) of residues from the oil and gas industry. The thermal stability of the CaF molecule and the stoichiometric ratio Ca:F for the formation of the molecule were evaluated at the wavelength (λ) 606.4322 nm. The results demonstrated that the CaF is thermally stable, enabling the use of temperatures of 1000 and 2300 °C for pyrolysis and vaporization, respectively. The proposed method allows calibration against aqueous standards to determine the extracted F concentration in leachate extracts, low limit of detection (0.01 mg L−1) and good precision (RSD ≤ 5%). Evaluation of the stability of extracted F in the leachate extracts found that, under the evaluated conditions, the analyte remained stable for up to 21 days after the TCLP procedure. The extracted F concentration obtained in the leachate extracts ranged from 0.520 ± 0.002 to 1.18 ± 0.04 mg L−1 for pH 2.88 and from 0.149 ± 0.001 to 0.574 ± 0.004 mg L−1 at pH 4.93. Hence, all samples analyzed showed an extracted F concentration below 150.0 mg L−1 and were not classified as toxic considering this parameter.