Leaching of a copper-nickel flotation concentrate in choline-chloride based deep eutectic solvents

Abstract

The quest for sustainable and environmentally friendly metal extraction has driven the exploration of reagents such as deep eutectic solvents (DESs) as alternatives to conventional leaching reagents. This study investigated the leaching of nickel (Ni), copper (Cu), and cobalt (Co) from copper-nickel sulphide ore concentrates using three choline chloride-based DESs: ethaline, reline, and maline. Ethaline demonstrated the highest nickel recovery (56.34%) in factor screening experiments, while copper recoveries varied, with maline achieving the highest copper recovery of 19.61%. Cobalt recoveries were relatively low, peaking at 16% and showing minimal variation across the solvents. All solvents selectively recovered nickel, highlighting the potential of DESs as lixiviants for targeted metal dissolution. Pulp density was identified as the most critical factor influencing nickel recovery in ethaline, with lower densities improving nickel extraction. Although the stirring rate was not independently significant, its interaction with temperature and leaching time was statistically significant. Optimal leaching conditions, of 0.5% pulp density, 600 rpm stirring rate, 25°C, and 1-hour leaching time, resulted in a nickel recovery of 59.06%, closely matching the response surface methodology (RSM) predicted maximum recovery of 58.12%. The process's rapid kinetics (1 hour) at near-ambient temperatures underscores its potential efficiency and scalability for sustainable metal extraction. Kinetic studies revealed that the nickel dissolution is primarily controlled by mass transport, as indicated by a low activation energy of 12.24 kJ/mol. Activation energy calculations further showed copper dissolution was governed by mixed control mechanism. The nickel and cobalt kinetic data were fitted by a hybrid shrinking core model coupled with pseudo-second-order kinetics (R² > 80%), capturing the dynamic interactions of mass transfer and surface reactions. The study further found that adding ethylene glycol as a diluent to reduce solvent viscosity did not enhance metal recoveries, with neat solvents showing superior performance. This study highlights the potential of DESs, particularly ethaline, for selective and efficient nickel recovery from sulphide ores, providing sustainable insights into key operational parameters.