Due to their remarkable adsorptive qualities, low cost, and wide availability, iron oxides and hydroxides have attracted a lot of interest as efficient materials for the removal of heavy metals from wastewater. The mechanisms by which iron-based minerals, such as ferrihydrite, magnetite, haematite and goethite interact with heavy metals through ion exchange, co-precipitation, and adsorption are covered in detail in this chapter. In order to maximise metal uptake efficiency, the importance of surface chemistry, particle size and mineral crystallinity is emphasised. This study critically examines developments in iron oxide functionalisation and modification to improve their capacity and selectivity for particular metals, including cadmium, lead and arsenic. While there are naturally occurring iron oxides/hydroxides, it is possible to synthesise them, coupling the synthesis with surface modifications, and these are usually monitored or verified using easily accessible instruments such as X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). This integration of the iron oxides/hydroxides with materials in nanotechnology and polymers has been beneficial for the removal of both heavy metals and other pollutants, such as organic ones, which highlights the versatility of the materials. The ability of the materials to be regenerated for further use makes them attractive in the wastewater treatment industry and in terms of environmental beneficiation. This chapter, therefore, provides a comprehensive analysis of iron oxides and hydroxides, highlighting their crucial role in developing sustainable wastewater treatment systems and reducing heavy metal pollution.

The increasing use of nanomaterials in modern industries and consumer products has led to the release of various contaminants into wastewater streams and the surrounding environment. However, nanoparticle detection and characterisation in wastewater remain analytically challenging due to the presence of dissolved metals, suspended solids, natural colloids, and heterogeneous particulate matter. In this study, we demonstrate an integrated analytical workflow combining single-particle inductively coupled plasma mass spectrometry (SP-ICP-MS) with transmission electron microscopy (TEM) and ImageJ version 1.54g image analysis for the comprehensive characterisation of engineered nanoparticles (ENPs) in industrial wastewater. In contrast to earlier research on well-defined manufactured nanoparticles in controlled laboratory suspensions, this work uses complementary analytical techniques to analyse real industrial wastewater, allowing for quantitative elemental analysis, particle sizing, and morphological confirmation in South Africa. Additionally, a supporting bibliometric analysis serves as supporting evidence to identify research trends and knowledge gaps, revealing limited application of integrated analytical workflows to complex industrial wastewater matrices. Analytical conditions were optimised according to the recommendations of previous publications, with a dwell period of 3 μs to limit particle coincidence and enable reliable single-particle detection. The combined approach was effectively applied to characterise silver (AgENPs) and gold (AuENPs) nanoparticles with median particle sizes of 14 nm and 8 nm, respectively. The particle number concentrations ranged from 3.00 × 10⁷ to 3.60 × 10⁸ particles L⁻¹ for AgENPs and 3.80 × 10⁸ particles L⁻¹ for AuENPs. Comparing dissolved metal concentrations with particle mass concentrations gave some insight into the partitioning of metals between the dissolved and nanoparticulate fractions. Moreover, bibliometric analysis has shown that despite the exponential growth of research on SP-ICP-MS, very few studies have simultaneously employed analytical techniques to describe nanoparticles in complicated industrial wastewater matrices. These results show the utility of integrating complementary analytical approaches for the reliable characterisation of particulate pollutants in environmentally relevant samples and promote improved environmental monitoring and risk assessment of manufactured nanoparticles.