Determination of Oxalate and Other Anions in Bayer Liquor Using Ion Chromatography

Significance of the Topic

The Bayer process is the primary industrial route for extracting alumina from bauxite ore. Monitoring oxalate and other anions in Bayer liquor is critical because oxalate complexes with aluminum, inhibiting the growth of large Al(OH)3 crystals and reducing process efficiency. Accurate quantification of these anions enables process optimization and improved yield in aluminum production.

Objectives and Study Overview

This application note describes the development of a robust, reagent-free ion chromatography (RFIC) method coupled with inline sample cleanup to determine oxalate, chloride, malonate, and sulfate in Bayer liquor. The goal was to overcome challenges posed by high ionic strength and elevated metal concentrations, particularly aluminum, through automated matrix elimination and direct injection.

Methodology and Instrumentation

The method employs a Reagent-Free IC system with an electrolytic anion purifier (CIRA 11AXCS) for automated removal of metals and matrix ions, followed by injection onto an IonPac AS17 analytical column. A gradient elution using KOH generated by an EluGen II KOH cartridge separates target anions within 18 minutes. A small co-injection of 0.1% sodium fluoride promotes ligand exchange to release aluminum-bound oxalate. Suppressed conductivity detection ensures high sensitivity and reproducibility.

Used Instrumentation

• Dionex ICS-2000 or ICS-3000 RFIC system with Chromeleon 6.8 software
• CIRA 11AXCS electrolytic anion purifier and installation kit
• IonPac AG17 guard column and AS17 analytical column
• UTAC LP1 trap column for concentrator function
• EGC II KOH eluent generator with CR-ATC
• ASRS 300 suppressor in external water mode
• AS40 or AS autosampler and PC-100 Pump Controller

Main Results and Discussion

Calibration over the range 1–30 mg/L for each analyte produced linear responses with R2 values ≥ 99.93%. Twelve real Bayer liquor samples were analyzed, yielding precise quantification of chloride, malonate, sulfate, and oxalate. Replicate injections of one sample showed RSDs below 1% for retention time and peak area, demonstrating excellent precision. Inline matrix elimination prevented column and suppressor fouling, allowing over six months of continuous operation without component replacement.

Benefits and Practical Applications

The method provides rapid, reproducible measurements of key anions in challenging matrices without manual pretreatment. Automated metal removal and direct injection reduce labor and sample handling errors. Process engineers can use the data to predict aluminum hydroxide crystal size distribution and optimize calcination feed, enhancing overall plant productivity.

Future Trends and Opportunities

Advances in column technology and high-pressure electrolyte generators may shorten analysis times further. Integration with process control systems and real-time data analytics could enable dynamic process adjustments. Expanding the approach to additional organic acids and anions may provide deeper insights into Bayer liquor chemistry.

Conclusion

A robust RFIC method with inline sample cleanup has been developed for the accurate determination of oxalate and other anions in Bayer liquor. The automated approach ensures high precision and long-term system stability, supporting improved process control in alumina production.

References

1. Xiao, J. B. Journal of the Chilean Chemical Society, 2006, 51(3), 964–967.