Ionic liquid promoted extraction of gold(III) from electronic waste: a modeling study

ABSTRACT

Being an expensive metal, the large-scale requirement of gold in the ever-growing market of electronics increases the overall cost of manufacturing. Hence, recycling gold from electronic waste mitigates the demand and subsequently bounds the price of electronic goods. However, the extraction of gold from electronic waste poses a severe hazard to the environment. Because of tuneable and fascinating properties, ionic liquids (ILs) have emerged as state-of-the-art solvents to extract gold from electronic waste. Herein, the modeling of IL-assisted liquid-liquid-extraction incorporating UNIQUAC extended Pitzer–Debye–Hückel* (PDH*) thermodynamic model has been used for the extraction process of gold from an aqueous acidic solution. The long-range, weak electrostatic interactions present in ionic liquids are adequately represented by the extended PDH* model. The model parameters are obtained from the polarizable continuum medium (PCM) calculation, conductor-like screening model for real solvent (COSMO-RS), and genetic algorithm formulation. Altogether, 11 hydrophobic ILs consisting of 9 imidazolium, 1 pyrrolidinium, and 1 ammonium class with 51 tie line data points are considered for the modeling. The estimated root mean square deviation of 0.002–0.99% over 51 tie lines reveals the goodness of the fitting. The projected percentage extraction efficiency lies in the range of 98.5% to 99.3%.

KEYWORDS:

• Gold
• ionic liquid
• solvent extraction
• Pitzer–Debye–Hückel theory
• UNIQUAC model

Acknowledgments

The corresponding author, i.e. Dr. Debashis Kundu, had optimized the molecular structures and PCM calculations and generated the COSMO files while pursuing his doctoral studies at the Department of Chemical Engineering, Indian Institute of Technology Guwahati under the guidance of Prof. Tamal Banerjee. Hence, the authors gracefully acknowledge the contribution of Prof. Tamal Banerjee (Department of Chemical Engineering, Indian Institute of Technology Guwahati) for mentoring Dr. Debashis Kundu to accomplish the geometry optimized structures (Gaussian 09) and COSMO files (Gaussian 03) of the respective compounds.

Disclosure statement

No potential conflict of interest was reported by the authors.

Statement of novelty

The manuscript formulates a modeling framework of extraction of gold(III) using liquid–liquid equillibria. The UNIQUAC extended Pitzer–Debye–Hückel* (PDH*) thermodynamic model has been incorporated to model the systems. A combination of quantum chemical calculation and global optimization algorithm has been deployed to estimate the parameters of the systems, which further facilitate the estimation of adequate phase equilibrium properties. This is the first such theoretical approach for the extraction of gold using ionic liquid. Further, it includes extended Pitzer–Debye–Hückel* (PDH*) thermodynamic model to accommodate the electrolyte behavior of the system.