Recovery of nitric acid from waste etching solution using solvent extraction

Area of Science:

• Chemical Engineering
• Environmental Chemistry
• Industrial Chemistry

Background:

• Semiconductor manufacturing generates waste streams containing valuable acids like nitric acid (HNO(3)) and hazardous components such as hydrofluoric acid (HF) and silicon (Si).
• Effective recovery of HNO(3) is crucial for economic viability and environmental sustainability in the wafer industry.
• Traditional methods may struggle with complex waste compositions and high concentrations of impurities.

Purpose of the Study:

• To develop and optimize a solvent extraction process for recovering high-purity nitric acid from a complex industrial waste stream generated during wafer manufacturing.
• To evaluate the effectiveness of tributyl phosphate (TBP) as an extractant for HNO(3) in the presence of acetic acid (HAc), HF, and Si.
• To demonstrate the feasibility of the developed process through continuous operation.

Main Methods:

• Solvent extraction using tributyl phosphate (TBP) as the extractant.
• Pre-treatment of the waste stream to remove silicon and hydrofluoric acid as sodium hexafluorosilicate (Na(2)SiF(6)).
• Optimization of extraction, scrubbing, and stripping stages using batch tests, followed by continuous operation in a multistage mixer-settler.

Main Results:

• Pre-treatment successfully removed over 99% of silicon and hydrofluoric acid.
• Optimized conditions involved four extraction stages (O:A ratio 3), four scrubbing stages (O:A ratio 5), and five stripping stages (O:A ratio 1.5).
• Continuous operation for 200 hours yielded pure nitric acid at a concentration of 235 g/L with 99.8% purity, despite the presence of acetic acid.

Conclusions:

• Solvent extraction with TBP is a highly effective method for recovering pure nitric acid from complex semiconductor industry waste streams.
• The developed pre-treatment and optimized extraction process significantly reduces hazardous waste and recovers a valuable chemical product.
• The process demonstrates technical and economic feasibility for industrial application in acid recovery and waste minimization.