Synthesis and characterization of kaolinite-supported zero-valent iron nanoparticles and their application for the removal of aqueous Cu2+ and Co2+ ions

This study reports the synthesis and characterization of nano-scale zero-valent iron in the presence of kaolinite clay (nZVI-kaol). The adsorbent, nZVI-kaol, was produced at initial Fe:kaolinite mass ratios of 1:1, 0.5:1, and 0.2:1. The presence of kaolinite resulted in decreased aggregation of iron nanoparticles, yielding composites with iso-electric points (IEPs) around 6.7–7.0. The reduction in Fe2+ precursor concentration appeared to decrease further the extent of aggregation and the size of individual nZVI particles. The synthesized nZVI-kaol materials were then tested for the removal of aqueous Cu2+ and Co2+ ions. The investigated parameters in the uptake experiments included volume/mass (V/M) ratio, initial concentrations of Cu2+ and Co2+ ions, contact time, pH, and repetitive application of the adsorbent. The adsorbents demonstrated high removal abilities towards both cations under the investigated conditions. Repetitive loading tests showed that significant removal could still be achieved at small concentrations by samples reused several times. X-ray photoelectron spectroscopy (XPS) analysis showed that while Co2+ was mainly fixed by the oxyhydroxyl groups of iron nanoparticles, Cu2+ ions were fixed by a redox mechanism, leading to the formation of Cu2O and Cu0.