Direct recovery of copper nanoparticles from leach pad drainage by surfactant-assisted cementation with iron powder

Copper nanoparticles were directly recovered from a leach pad drainage by surfactant-assisted cementation with iron powder. Factorial experimental designs were implemented to assess the influence of polyvinylpyrrolidone (PVP), sodium dodecyl sulfate (SDS) and temperature on cementation kinetics and copper particle size. Analysis of variance (ANOVA) was performed to quantify the effect of the investigated factors. Copper(II) was selectively reduced to metal copper by Fe powder, while Mn, Fe, Cd and Zn ions were left in solution. The cementation proceeded under enthalpic driving force and could be described by a pseudo-second-order kinetic model. Without the surfactants, the activation energy of cementation was 22.7 kJ/mol and the cemented product aggregated into micro-clusters ranging from 1 to 15 μm in size, depending on the temperature. The cementation with PVP at above 311 K was controlled by physical adsorption of PVP on Fe powder and exhibited an activation energy of about 10 kJ/mol. The average size of copper particles obtained using 4 mM PVP at 348 K was 280 nm. Adding SDS was associated with a dramatic increase in the activation energy to about 45 kJ/mol, and with the formation of nanoparticles. Using 0.2 M SDS at 348 K enabled the recovery of Cu of about 99% purity with an average particle size less than 100 nm. All results suggested that capping by SDS and PVP inhibited the cementation kinetics but provided the templating ability required to form nanoparticles.