Removal of A Cadmium from Wastewater Using Hydrochar-Supported Nanoscale Zero-Valent Iron (nZVI) on Composite Materials
Authors: Ngobeh Jusu M , Nan Xu , Sorathiya Vishal 
Published: February 2024

Abstract
Among the most hazardous heavy metals, cadmium can be found in various environmental compartments. Cadmium pollutants are ubiquitous in soil, surface water, groundwater, plants, vegetables, and the atmosphere. The focus of this research was specifically on cadmium pollution in wastewater. When present at high concentrations, cadmium can lead to a range of intricate health problems, including but not limited to cancer, kidney failure, high blood pressure, etc. Suppose industrial wastewater effluent is not treated to meet the World Health Organization (WHO) standards. In that case, cadmium can be released into the environment due to increased industrialization, originating from both point and nonpoint sources. Many new technologies have emerged in recent years to help solve the world's environmental concerns regarding heavy metal pollution. However, some of these technologies are challenging and expensive, while others have proven to exacerbate the problem of cleaning up our environment. Among the various available technologies, nanoscale zero-valent iron nZVI has gained significant attention for removing heavy metals from polluted soils and wastewater and even employing in situ remediation methods.
Nevertheless, nZVIs encounter easy oxidation and poor suspension stability, severely limiting their application in groundwater and industrial wastewater treatment. To increase the removal efficiency of nZVI for the heavy metal cadmium removal and improve its suspension stability in solution, this study focused on hydrochar-modified nZVI or hydrochar- nano-zero valence iron (H-nZVI). This study aimed to investigate this treatment's impact on wastewater by explicitly examining cadmium removal and suspension stability in different solutions. In the experiment as mentioned above, H-nZVI was characterized using techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The characterization results indicated that nZVI was effectively loaded onto the hydrochar substrate, enhancing its absorption capacity. Adsorption experiments demonstrated that H-nZVI exhibited a high cadmium removal capacity and strong adsorption capability, with a maximum removal percentage of 97.56%.
Furthermore, the sedimentation kinetics experiment revealed that H-nZVI displayed superior suspension stability to nZVI. The sedimentation percentage of H-nZVI varied with the solution's ionic strength due to agglomeration changes, which depended on factors such as zeta potential and fluid dynamic radius. This research was a state-of-the-art contribution, especially for new researchers in environmental real-time research, whether at the undergraduate or graduate level. The experimental setups, steps, analysis, and explanations were so explicit that any researcher could easily follow them and replicate the same or related work. This research follows the paradigm of modern research work, explicitly explaining the ramifications of cadmium in our environment and its removal method using nZVI technology.