Fluorine and chlorine in iron ore by Combustion Ion Chromatography

Significance of the topic

Iron ore serves as the primary raw material for steel production. The presence of halogens, notably fluorine and chlorine, affects both the processing and durability of steel due to the corrosive properties of their halides. Accurate quantification of these elements is therefore crucial for quality control in mining and metallurgical industries.

Study objectives and overview

This application note describes the use of combustion ion chromatography (combustion IC) with sacrificial vial technology to determine fluorine and chlorine levels in iron ore samples. A key focus is evaluating the effect of tungsten trioxide (WO₃) addition on recovery rates, alongside optimizing combustion and detection parameters to achieve reliable and reproducible results.

Methodology and instrumentation

Sample preparation involves weighing 5–15 mg of finely homogenized iron ore and mixing it with an equal mass of WO₃ in a quartz tube packed with quartz wool. The tube is then sealed within a sacrificial quartz vial.

The combustion IC analysis is performed using a high-temperature furnace (1100 °C) under a continuous flow of argon (100 mL/min) and oxygen (300 mL/min). Post-combustion gases are absorbed in a solution containing hydrogen peroxide (100 mg/L) before separation by ion chromatography. Key operating parameters:

• Absorber feed rate: 0.2 mL/min
• Water inlet: 0.2 mL/min
• Post-combustion rinsing volume: 1.0 mL
• Injection volume: 200 µL (intelligent partial loop)
• Flow rate: 0.8 mL/min
• Column temperature: 45 °C
• Analysis time: 18 min

The separation employs a Metrosep A Supp 16 column with guard, supplemented by Metrosep A PCC and trap columns for matrix elimination. Detection is achieved via suppressed conductivity. The system setup is based on the Metrohm 930 Compact IC Flex platform, including absorber, autosampler MMS 5000, and solid sampling kit.

Key results and discussion

Results demonstrate that adding WO₃ significantly enhances fluoride recovery from 80.0% to 92.7%, while chlorine recovery improves from 94.7% to 97.8%. The relative standard deviations (RSDs) remain below 2% for both analytes, indicating high precision. Concentration values measured in replicate analyses (N=3) were approximately 84.0% for fluorine and 70.2% for chlorine. Unquantified peaks corresponding to bromine and sulfur were observed, highlighting the method’s capability to detect multiple halogens and chalcogen elements.

Benefits and practical applications of the method

Combustion IC with sacrificial vial technology offers:

• High sensitivity and reproducibility for fluorine and chlorine analysis
• Minimal sample preparation and reduced matrix interference
• Improved recovery rates through WO₃ addition
• Rapid throughput suitable for routine QA/QC in mining and steel industries

Future trends and potential applications

Further developments may include automation of sampling, expansion to other halides and sulfur species, integration with mass spectrometry for speciation studies, and the use of machine learning for data interpretation and method optimization. Miniaturized combustion modules and inline sample pretreatment could enhance field deployability.

Conclusion

This study confirms that combustion ion chromatography combined with sacrificial vial technology is a robust and precise approach for determining fluorine and chlorine in iron ore. The addition of WO₃ significantly improves analyte recovery, making the method highly suitable for industrial quality control and research applications.

References

Application Note CIC–028, Metrohm AG, Version 1, September 2018