Determination of organic soda in Bayer aluminate liquors

Importance of the topic

Organic soda, defined as extractable acidic organic compounds expressed as Na2CO3 or Na2O, can impact the efficiency and corrosion control in alumina refining. Reliable quantification ensures stable process performance, product quality, and reduced maintenance costs in Bayer process operations.

Study objectives and overview

This application note introduces a thermometric titration procedure to measure total basicity of extractable organic acids in spent Bayer liquors. The method streamlines sample preparation and endpoint detection to deliver rapid and precise results suitable for refinery laboratories.

Methodology and instrumentation

The procedure encompasses:

• Sample dilution: 25 mL spent liquor with 125 mL deionized water.
• Neutralization and acidification: Titrate with concentrated HCl until clear.
• Liquid–liquid extraction: Five 25 mL cyclohexanol extractions, followed by four 100 mL water washes.
• Drying: Overnight over anhydrous Na2SO4 with stirring.
• Dilution: 25 mL dried extract to 200 mL with propan-2-ol.
• Titration: 30 mL aliquot with 0.1 mol/L KOH in propan-2-ol to a catalyzed thermometric endpoint using paraformaldehyde.

Key instrument settings include a titrant rate of 2 mL/min, one exothermic endpoint detection, data smoothing factor 75, stirring speed setting 5, and a 3 s pre-titration delay. A thermometric titrator with magnetic stirring enables precise thermal endpoint recognition.

Main results and discussion

Six replicate analyses yielded an average organic soda concentration of 9.92 ± 0.01 g/L as Na2CO3. The narrow standard deviation highlights the method’s high repeatability. The thermometric endpoint provided clear, reproducible detection even in viscous, complex matrices, minimizing subjective judgment in endpoint determination.

Benefits and practical applications

This approach offers:

• High precision and accuracy for routine quality control of Bayer liquors.
• Reduced solvent consumption through efficient extraction and washing steps.
• Rapid analysis turnaround, supporting timely process adjustments.
• Minimal interference from color or turbidity due to thermal endpoint detection.

Future trends and opportunities

Emerging directions include inline process titration integration, automation of liquid–liquid extraction, adoption of microextraction techniques to reduce reagent use, and coupling with digital data analytics for real-time monitoring and predictive process control.

Conclusion

The thermometric titration method detailed here provides a robust, precise, and efficient means to quantify extractable organic soda in Bayer process liquors. Implementation in refinery laboratories can enhance process control, reduce downtime, and improve overall productivity.

Reference

• Carneiro M.J.D., Feres Júnior M.A., Godinho O.E.S. Determination of the acidity of oils using paraformaldehyde as a thermometric end‐point indicator. J. Braz. Chem. Soc. 13(5):692-694 (2002)
• Thermo. Titr. Application Note H-028. Standardization of 0.1 mol/L KOH in propan-2-ol.