Determination of Free Acid in Copper Refining Solutions

Importance of the Topic

Accurate measurement of free sulfuric acid in copper refining solutions is essential for process control, corrosion prevention, and product quality. A robust analytical method supports efficient operations and rapid decision making in industrial and quality assurance laboratories.

Objectives and Study Overview

The objective of this work is to develop and validate a thermometric titration procedure for determining free acid concentration in copper leach and refining solutions. The method addresses potential interference by iron(III) through complexation and covers a wide range of acid levels.

Methodology and Instrumentation

Thermometric titration detects the heat released during neutralization of sulfuric acid with sodium hydroxide. Prior to titration, iron(III) is complexed with oxalate to prevent endpoint distortion. Key experimental parameters include:

• Data acquisition rate: 10 readings per second
• Titrant delivery rate: 2 mL per minute
• Single exothermic endpoint detection
• Data smoothing factor: 50

Sample preparation involves dispensing 1–10 mL of test solution, adding 15 mL of saturated potassium oxalate solution, and diluting to 25 mL with deionized water. The solution is titrated to the first exothermic endpoint using standard 1 molar sodium hydroxide solution.

Main Results and Discussion

Application of the method to synthetic solutions with varying iron content yielded consistent free acid values near the expected 10 g per liter. Even in the absence of iron, results remained accurate. Analysis of a high concentration electrolyte containing 0.2 g per liter iron returned approximately 203 g per liter free acid. Real leach solutions showed free acid values between 1.65 and 2.20 g per liter, while a refined product solution measured approximately 6.36 g per liter. The procedure demonstrated high precision, typically within ±0.05 g per liter. Titration curves revealed clear and reproducible exothermic peaks, confirming method reliability.

Benefits and Practical Applications

• Eliminates the need for visual indicators or glass electrodes
• Suitable for colored or turbid samples
• Rapid analysis with minimal sample preparation
• High precision and reproducibility
• Adaptable for routine process monitoring and quality control

Future Trends and Applications

Integration of thermometric titration into automated process control systems will enable continuous monitoring of acid levels in industrial streams. Advances in sensor miniaturization and data analytics may expand applications to other acid-base determinations and improve real-time decision support.

Conclusion

The thermometric titration method offers a fast, accurate, and interference-resistant approach for determining free sulfuric acid in copper refining solutions. Its robustness and simplicity make it an attractive alternative to conventional titration techniques in industrial and laboratory settings.

Used Instrumentation

• Thermometric titrator with temperature sensor and data acquisition module
• Automated burette or dosing pump for titrant delivery
• Analytical balance, pipettes, and volumetric glassware