Determination of caustic, soda, carbonate and alumina in a spent Bayer Process liquor

Significance of the topic

Monitoring the composition of spent Bayer process liquors is critical for optimizing alumina extraction and recycling reagents in the aluminum industry. Precise quantification of caustic soda, carbonate, and residual alumina ensures process control, reduces waste, and maintains product purity.

Objectives and Study Overview

This work adopts and refines established titrimetric protocols by Watts-Utley and VanDalen-Ward to simultaneously determine caustic, soda, carbonate, and alumina in spent process liquors. The aim is to develop a reliable thermometric titration method that delivers accurate, reproducible results under industrially relevant conditions.

Methodology and Used Instrumentation

Sample preparation involves pipetting 25 mL of spent liquor into a 500 mL volumetric flask and diluting to volume with deionized water. A series of aliquots (15–30 mL) are used for blank calibration and sample analysis.
Instrumentation:

• 859 Titrotherm with Thermoprobe
• 804 Titration stand
• 802 Rod stirrer
• 800 Dosino units (1×10 mL, 3×10 mL, 50 mL)

Reagents:

• HCl titrant (1.5 mol/L)
• Complexing solution 1: potassium sodium tartrate (~614 g/L)
• Complexing solution 2: potassium fluoride (~620 g/L)

Titration is performed in two sequential exothermic endpoints: first after addition of tartrate, then after fluoride, using defined stirring rates, dosing rates, and endpoint criteria.

Key Results and Discussion

The method yielded the following average concentrations (n=10):

• Caustic soda: 340.2 g/L (RSD 0.06%)
• Soda: 353.0 g/L (RSD 0.10%)
• Carbonate: 12.6 g/L (RSD 2.80%)
• Alumina: 97.8 g/L (RSD 0.16%)

High precision for caustic, soda, and alumina demonstrates method robustness. Slightly higher variability in carbonate determination is attributed to CO2 absorption and lower endpoint temperature changes.

Benefits and Practical Applications

This thermometric titration approach offers:

• Rapid, simultaneous multi-analyte determination
• Minimal sample preparation and reagent consumption
• High repeatability suitable for routine QC
• Compatibility with industrial process conditions

It supports plant monitoring, reagent recovery optimization, and compliance with environmental regulations.

Future Trends and Potential Applications

Advancements may include further automation, integration with process analytical technology (PAT), miniaturization of titration cells, and application of chemometric data analysis or machine learning to enhance endpoint detection and reduce analysis time.

Conclusion

The described thermometric titration method provides a reliable, precise, and efficient solution for analyzing key components in spent Bayer liquors. Its implementation can drive improved process control and resource utilization in alumina refining.

References

Watts-Utley and VanDalen-Ward procedures adapted for thermometric titration (original literature not specified).