Metallurgical Wastes Employed as Catalysts and Photocatalysts for Water Treatment: A Review

Abstract

Metallurgical slags are a mass-produced industrial solid waste, often destined to landfills; the volumes disposed represent an environmental burden. Over the last three decades, applications have been found for these wastes, mainly as a low-cost additive in building materials. More recently, their unique chemical properties have attracted attention to produce high-added-value materials for environmental applications, to be used as adsorbents, catalysts, or a source of reactive species in environmental engineering. Such uses can be classified as a function of the added value generated, technological complexity, and environmental impact. This review will focus specifically on the modification and use of slags for catalysis, photocatalysis, and photocatalytic production of hydrogen, which have received relatively little attention in literature. A summary will be presented about the general requirements for using unmodified slags as well as slag processed under alkaline or acidic conditions for advanced oxidation processes. Then, an overview will be given of the use of slags as photocatalysts in water treatment, organized according to the origin of the product (steel, copper, magnesium, ferromanganese), as well as emerging reports on the photocatalytic production of hydrogen, in contrast to the use of highly specific titania-based products developed for the same purpose.

Photocatalytic Degradation of Diclofenac in Tap Water on TiO2 Nanotubes Assisted with Ozone Generated from Boron-Doped Diamond Electrode

“…The synergetic TiO 2 /O 3 /UV method is an ideal AOP method for waste degradation in air or water. Under UV irradiation, the photo-generated electrons (in the conduction band, CB) and holes (in the valence band, VB) are separated in TiO 2 (4), which are captured by H 2 O and O 3 molecules on the TiO 2 surface to form more active radicals such as OH• to attack the organics in water ( 5)-(8) (Figure 5a). Besides the decomposition of organics via the reactions ( 9)- (11) by O 3 individually, O 3 on the TiO 2 surface can trap the photo-generated electrons, thus effectively suppressing the recombination of the charge carrier pairs.…”

“…TiO 2 photocatalyst, owing to its chemically inert, environmentally friendly, and low cost, has been extensively studied for the decomposition of varieties of pharmaceuticals in water [1,2]. In recent years, the degradation of diclofenac in municipal drinking water has been investigated by TiO 2 photocatalysis [3,4]. Diclofenac is a popular anti-inflammatory pharmaceutical drug, and its trace has been widely used around the world.…”

Prewetting Induced Hydrophilicity to Augment Photocatalytic Activity of Nanocalcite @ Polyester Fabric

“…The trapped holes are liable to form a weak bond between the lattice oxygen and a metal atom results in producing oxygen vacancies (OV) in the crystal by liberation of oxygen. The oxygen vacancies and hydroxyl group functionalities on its surface promote both hydrophilicity and photocatalytic activity [28]. Photo-reactivity enhanced by OV-induced localized states, which can extend the response to visible irradiation and efficiently trap charge carriers [29].…”

Combined Action of Adsorption and Catalytic Oxidation in Aluminum Dye Removal by Groundwater Treatment Waste

“…These iron-rich solids may be suitable for activating hydrogen peroxide. Using steel-making or goldmine waste as catalysts instead of iron salts can reduce the cost of treating wastewater contaminated with methyl orange and other dyes without compromising process efficiency (Ali et al, 2013;Montoya-Bautista et al, 2019;Huang et al, 2011). FeO-containing iron slag wastes were employed to degrade Reactive Red 24 dye in an aqueous solution (Van et al, 2019).…”