Inline analysis of borate and sulfate solutions with Raman spectroscopy

Significance of the Topic

Efficient and sustainable production of boric acid from borax is critical for industries ranging from glass manufacturing to electronics and detergents. Traditional gravimetric methods are labor-intensive, slow, and lack real-time feedback, leading to suboptimal control of sodium sulfate by-products and increased costs. Inline spectroscopic monitoring offers a reagent-free, rapid alternative that enhances process understanding and environmental compliance.

Objectives and Study Overview

This study evaluates the performance of the Metrohm PTRam Process Analyzer for inline measurement of boric acid (H₃BO₃) and sodium sulfate (Na₂SO₄) concentrations at low levels (<100 mg/L) during boric acid crystallization. Key aims include:

• Developing a simple calibration model with minimal reference data.
• Assessing detection limits and quantification accuracy for each component.
• Comparing inline Raman results with traditional methods.

Methodology and Instrumentation

Inline Raman spectroscopy was performed using a 785 nm laser integrated in the PTRam Analyzer. Single-channel measurements were collected for pure and mixed salt solutions under process-mimicking conditions. Calibration required only a small set of reference titrations to build quantitative chemometric models. Spectra were recorded in the region of characteristic vibrational bands.

Main Results and Discussion

Boric acid exhibited a strong Raman band at 880 cm⁻¹, while sulfate appeared at 993 cm⁻¹. Calibration models yielded limits of detection around 15 mg/L for H₃BO₃ and 10 mg/L for Na₂SO₄. Mixed-matrix tests confirmed accurate quantification without significant interference. The inline approach provided continuous, reagent-free monitoring, enabling immediate detection of concentration deviations and supporting tighter process control.

Benefits and Practical Applications

Inline Raman analysis introduces multiple advantages:

• Real-time concentration data for process optimization.
• Reduced reagent consumption and waste generation.
• Enhanced throughput and reproducibility in boric acid crystallization.
• Improved safety by minimizing acid handling and manual sampling.

Future Trends and Opportunities

Advances in chemometric algorithms and hardware miniaturization will expand inline Raman’s applicability. Potential developments include:

• Integration with automated feedback loops for closed-loop control.
• Multicomponent analysis across broader chemical processes.
• Cloud-based analytics and remote monitoring capabilities.
• Combination with complementary spectroscopy (e.g., NIR) for enhanced selectivity.

Conclusion

The PTRam Process Analyzer demonstrates that inline Raman spectroscopy is a robust, accurate, and eco-friendly solution for monitoring borate and sulfate concentrations during boric acid production. Its implementation can drive efficiency gains, lower costs, and support sustainable manufacturing practices.

Reference

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5. Britannica. Gravimetric Analysis: Definition, Steps, Types & Facts.
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7. ISO. Sodium Sulphate for Industrial Use — Determination of Sulphates Content — Calculation Method and Barium Sulphate Gravimetric Method, 1975.