Impact of Additives on the Physiochemical Properties of Copper Electrowinning Solutions for Acid Mist Suppression

Abstract

During copper electrowinning (EW), oxygen evolution at the anode generates gas bubbles that rupture at the electrolyte–air interface, releasing a hazardous sulfuric acid mist. This dissertation systematically investigates the physiochemical mechanisms governing acid mist formation and demonstrates how targeted manipulation of electrolyte properties—through surfactant and polymer additives—can significantly suppress mist generation.The research began with a detailed characterization of the baseline electrolyte (density, viscosity, and surface tension) over industrial operating temperatures (20–50 °C). High-precision measurements revealed that commonly cited literature values are unrepresentative of true industrial electrolytes, underscoring the necessity of direct characterization under realistic conditions. Methodologically, this study identified critical limitations in traditional surface-tension techniques; specifically, cationic and zwitterionic surfactants were found to adsorb onto platinum Wilhelmy plates, violating zero-contact-angle assumptions. Consequently, pendant drop tensiometry was established as the essential method for accurate characterization in high-acidity, high-salt environments. Furthermore, the study identified a kinetic limitation at low surfactant concentrations (ppm range), where slow adsorption necessitated improved experimental protocols to ensure interfacial equilibration and reproducible data. A central finding is the profound "salt effect" exerted by the extreme ionic strength of EW solutions. A comprehensive study of five surfactants (two anionic, two cationic, and one zwitterionic) demonstrated that high sulfate content shifts Critical Micelle Concentrations (CMC) significantly toward lower concentrations, fundamentally altering adsorption behavior. This effect was most pronounced for anionic surfactants and explains the discrepancies often observed when extrapolating laboratory data to industrial systems. By incorporating these updated temperature-dependent expressions into classical jet-drop and film-drop models, this work demonstrates that acid mist generation is highly sensitive to the minimum bubble diameter. Surfactants and polymers influence this through complementary, synergistic mechanisms: surfactants reduce surface tension to shift interfacial detachment, while polymers (such as guar) increase viscosity to dampen bubble growth and collapse. These mechanistic predictions were validated using a custom-engineered laboratory-scale mist-generation column. By isolating physical bubble dynamics from electrochemical variables, the column served as a high-sensitivity screening tool, confirming that additives act synergistically to narrow the range of mist-producing bubble diameters. Finally, the study addresses the practical constraints of polymeric additives. Degradation studies of naturally derived polymers like guar revealed rapid acid hydrolysis, with rates accelerating at elevated temperatures. These findings indicate that while polymers are highly effective, their limited chemical lifetime must be incorporated into industrial dosing and economic models. Ultimately, this research provides a robust physicochemical framework for the development of next-generation, environmentally compatible mist suppression strategies in the hydrometallurgical industry.