Ironmaking and Steelmaking Slags as Sustainable Adsorbents for Industrial Effluents and Wastewater Treatment: A Critical Review of Properties, Performance, Challenges and Opportunities

Abstract

This paper critically discusses the structure, properties and applications of ironmaking and steelmaking slags and their silicate-based variants as low-cost adsorbents for removing cations and anions from industrial effluents and wastewater. Undoubtedly, the performance of slag-based adsorbents depends on their physical, chemical and phase chemical properties. The presence of crystalline phases, for example, has a significant effect on the adsorption capacity. However, despite their low cost and ubiquity, their chemical and geometric heterogeneity significantly affects the performance and applications of slag-based adsorbents. These challenges notwithstanding, the efficacy of slag-based adsorbents can be significantly enhanced through purposeful activation to increase the specific surface area and density of adsorption sites on the surfaces of adsorbent particles. The synthesis of functionalised adsorbents such as geopolymers, zeolites and layered double hydroxides from silicate and aluminosilicate precursors can also significantly increase the performance of slag-based adsorbents. In addition, the ability to stabilise the dissolved and/or entrained toxic metal species in stable phases in slags, either through controlled post-process fluxing or crystallisation, can significantly enhance the environmental performance of slag-based adsorbents. Most critical in the design of future slag-based adsorbents is the integration of the engineered properties of molten and solidified slags to the recovery and stabilisation of dissolved and/or entrained metals.

High-capacity adsorbents from stainless steel slag for the control of dye pollutants in water

“…Steel manufacturing produces a significant amount of different slags (10–15% by weight of the produced steel) (Proctor et al 2000 ). It can be categorized as carbon steel slag and stainless steel slag (SSS) according to the type of steel, and as pretreatment slag, basic oxygen furnace slag (BOFS), electrical arc furnace slag (EAFS), ladle refining slag (LFS), and casting residue according to the steelmaking process (Manchisi et al 2020 ; Yi et al 2012 ). The steel slag mainly consists of SiO 2, CaO, Fe 2 O 3 , FeO, Al 2 O 3 , MgO, MnO, and P 2 O 5 .…”

A Review of Circular Economy Prospects for Stainless Steelmaking Slags

“…Slag's "journey" from the process conditions ≥ 1600 ºC to outdoors temperature is, thus, extremely crucial, and it is strongly connected to utilization of slags in different applications. For different controlled cooling rates, several methods are available from slower to faster cooling: free air cooling in slag pot or bed < the same with water spraying < air granulation < water quenching < pouring thin layer on metal substrate or corresponding rapid cooling technique [43][44][45][46][47][48][49][50]. Rapid cooling can prevent crystallization in accordance with the phase diagram resulting in an amorphous glassy structure, encapsulating eventual metal particulates and solid oxides, and thereby lowering the solubility of heavy metals.…”

“…By enhancing the fraction of amorphous material in a slag, the potential hydrating properties are improved, and the slag can be used in cement and concrete products for high-quality construction applications. Controlled cooling conditions can be a means to affect minerals formation and transformation and, consequently, the solubility of elements such as Cr, Mo, and V. Their leachability depends on the distribution between glassy and crystalline phases which is influenced by the whole cooling curve including the hightemperature liquid and liquid-solid stages too [48][49][50].…”

Geopolymers and Alkali-Activated Materials for Wastewater Treatment Applications and Valorization of Industrial Side Streams

“…These materials are sub-categorized, depending on the process of their formation. Both basic oxygen furnace slag (BOFS) and electric arc furnace slag (EAFS) are formed during the steelmaking process [36,37]. These types of slags are similar in composition to BFS, except for their iron, manganese, chromium and sulfur contents, which are higher in BOFS and EAFS.…”