Industrial wastes with a high iron or aluminium oxide content are produced in huge quantities as by-products of water treatment (water treatment residuals), bauxite processing (red mud) and hard and brown coal burning in power plants (fly ash). Although they vary in their composition, the wastes have one thing in common – a high content of amorphous iron and/or aluminium oxides with a large specific surface area, whereby this group of wastes shows very good adsorbability towards heavy metals, arsenates, selenates, etc. But their physical form makes their utilisation quite difficult, since it is not easy to separate the spent sorbent from the solution and high bed hydraulic resistances occur in dynamic regime processes. Nevertheless, because of the potential benefits of utilising the wastes in industrial effluent treatment, this issue attracts much attention today. This study describes in detail the waste generation processes, the chemical structure of the wastes, their physicochemical properties, and the mechanisms of fixing heavy metals and semimetals on the surface of iron and aluminium oxides. Typical compositions of wastes generated in selected industrial plants are given. A detailed survey of the literature on the adsorption applications of the wastes, including methods of their thermal and chemical activation, as well as regeneration of the spent sorbents, is presented. The existing and potential ways of modifying the physical form of the discussed group of wastes, making it possible to overcome the basic limitation on their practical use, are discussed.

The aim of the present study was to investigate As(III) oxidation and adsorption on the surface of hybrid anion exchangers containing Cu(II)-Fe(III) binary oxide deposited in their porous structure with the same Cu:Fe ratio of 1:2 but with different amounts and distribution of inorganic deposit within polymeric beads. The equilibrium studies confirmed high adsorption capacity of the best hybrid polymer: 94.4 mg As/g. Moreover, the adsorption was effective over a wide pH range, selective in the presence of interfering ions, and the material was effectively regenerated. The performance of the hybrid polymer was also confirmed in the column process which enabled both As(III) and As(V) concentrations to be lowered from 500 μg/L to below 10.0 μg/L in a solution with a composition similar to natural groundwater. The breakthrough point of the bed was reached after the solution amounting to 1833 bed volumes passed through the column. Desorbed As speciation, FTIR and XPS studies showed that As(III) was mainly adsorbed on the surface of Cu-Fe oxides followed by its oxidation to As(V). In the oxidation reaction metal oxides acted as catalysts and adsorbents, while the oxidant was probably oxygen dissolved in solution.

The purpose of the presented study was to explore the photocatalytic activity of Cu₂O-supported anion exchangers and to explain the mechanism of their action in water purification processes. The functionality of this type of material was studied in the process of As(III) removal from water. As a result of the reactivity of cuprous oxide and functional groups of the polymer, the obtained composite exhibited complex activity towards arsenic(III) species. The adsorption studies were conducted under various conditions: dark, UV-VIS irradiation, VIS irradiation, under aerobic and anoxic conditions. The results from chemical analyses were supported by instrumental analyses - X-ray photoelectron spectroscopy, and FTIR and Raman spectroscopy. These studies showed that the mechanism of As(III) oxidative adsorption is based on the coupling of several reaction pathways: 1) photocatalytic oxidation involving Cu₂O as a photocatalyst, and photogenerated holes and ROS as oxidative agents, 2) chemical oxidation on the surface of CuO (being a result of the ageing process) with a re-oxidation of the produced Cu₂O to CuO by ROS and oxygen present in water, and 3) photochemical oxidation of As(III) in solution under UV light irradiation and subsequent adsorption of arsenates in the functional groups of the polymer.