TOC and IC Measurements for Lithium Refining Processes

Importance of the Topic

Lithium-ion battery demand is driving increased production and refining of lithium from both traditional and emerging sources. Organic and inorganic carbon species in lithium extraction solutions can impair refining efficiency and final product quality. Accurate measurement of total organic carbon (TOC) and inorganic carbon (IC) is therefore crucial for process control and quality assurance.

Objectives and Study Overview

This study aimed to evaluate the performance of a Shimadzu TOC-L analyzer for TOC and IC determination in lithium salt solutions obtained via direct lithium extraction (DLE). Three sample types were compared:

• S1: Lithium hydroxide reagent solution
• S2: Lithium extraction solution with carbon reduction treatment
• S3: Lithium extraction solution without carbon reduction treatment

Methodology and Instrumentation

The NPOC method was employed for TOC analysis, involving automatic acidification with 4.5 M sulfuric acid (2 % addition rate), purging (80 mL/min, 90 s), and high-temperature combustion at 680 °C. An optional high-salt combustion tube kit, featuring a larger diameter and TOC catalyst designed for salt-rich samples, was used to minimize clogging and extend maintenance intervals. IC was measured by acidifying samples in an IC reactor containing 25 wt% phosphoric acid and bubbling carrier gas to extract CO₂. Calibration curves for both NPOC and IC were established over four concentration points, each exhibiting excellent linearity (r = 1.000).

Main Results and Discussion

TOC measurements revealed low organic carbon levels in S1 (0.615 mgC/L) and S2 (0.630 mgC/L), and a significantly higher level in S3 (9.174 mgC/L), confirming the efficacy of carbon reduction treatment. IC analysis showed 5.821 mgC/L for S1, 11.34 mgC/L for S2, and 119.8 mgC/L for S3, demonstrating the impact of treatment on carbonate content. The use of sulfuric acid prevented salt melting in the combustion tube, while the NPOC approach maintained sensitivity and reproducibility for high-alkalinity samples.

Benefits and Practical Applications

• Reliable TOC and IC determination in high-salt lithium samples
• Reduced maintenance frequency through high-salt combustion tube kit
• Automated dilution and sample handling enhance throughput
• Quantitative assessment of carbon reduction treatments supports process optimization

Future Trends and Possibilities

Advancements may include inline TOC/IC monitoring integrated into lithium refining lines, development of robust catalysts for even higher salt matrices, and application of machine learning for predictive analytics. Expanding this methodology to new battery chemistries and recycling streams can further support sustainable energy technologies.

Conclusion

The Shimadzu TOC-L analyzer, equipped with dedicated high-salt components and using the NPOC and IC methods, provides precise and reproducible carbon analysis in lithium extraction solutions. This tool is instrumental for refining process control, ensuring high product purity, and reducing operational costs.