The primary peak of Fe 0 that is normally observed around 2 u of 44.8 cannot be clearly distinguished in the XRD pattern, although its presence was verified from XPS results and SEM images, as discussed next. As seen in Fig. 2, SEM images of clinoptilolite (A and B) show tabular and coffin like morphologies typical for clinoptilolite. The edge sizes appear to range from 1 to 5 m m. The presence of some irregular globular shaped species along with the clinoptilolite crystals can also be seen in the SEM images indicating the presence of some mineralogical impurities. The SEM images of nZVI (Fig. 2C and D) show its characteristic chain like morphology. The particle size of individual nanoparticles ranges between 40 and 60 nm. SEM images of the composite Cl-nZVI material are displayed in Fig. 2E and F. The images show that nZVI morphology in the composite resembles that of pure nZVI. Most of iron nanoparticle chains appear to grow in between the clinoptilolite crystals while others seem to cover the surface of these crystals. The chain-like morphology, characteristic for nZVI, is also revealed by TEM and STEM images of a Cl-nZVI sample (Fig. 3). EDX maps of Fe and O obtained from a Cl-nZVI domain rich in nZVI are shown in Fig. 4. The sharper Fe signals compared with O are indicative that Fe is more dominant in the structure of the nanoparticles, which is a typical consequence of the core-shell structure of nZVI, as the core contains Fe 0 solely, while the shell is composed of iron (hydr)oxides [31]. The EDX spectrum of clinoptilolite (Fig. 5A) reveals its elemental composition. The mineral is composed mainly of Si, Al and O. The EDX spectrum of Cl-nZVI composite (Fig. 5B) clearly shows a distinct Fe peak. Moreover, EDX analysis for various Cl- nZVI composites