# Wastewater Treatment Using Alkali-Activated-Based Sorbents Produced from Blast Furnace Slag
###### Abstract  
Currently, slags from secondary steel production, foundries, and blast furnaces represent a major environmental problem since they end up mainly in landfills, and their valorization would bring undeniable advantages both to environment and economy. Moreover, the removal of heavy metal ions from mines wastewater is one of the challenges of the last decades, and adsorption has been proposed as one of the most promising techniques for this purpose. In this context, the use of alkali-activated slags as sorbent can be a good opportunity to develop low cost, environmentally friendly, and sustainable materials. Accordingly, wastewater decontamination by adsorption over a porous monolithic bed made of alkali-activated hydraulic binders is proposed. Alkali-activated materials were prepared using slags from the metallurgical industry and reacted with an alkaline component (high alumina calcium aluminate cement, CAC 80) at ambient conditions. The obtained monolithic foams were tested to evaluate the uptake efficiency towards metal capture. Solutions containing Cu(II), Fe(III), Ni(II), Mn(II), and simulating the metal concentrations of a real mine effluent were tested, both in single- and multi-ion solutions. Promising capture efficiency, values of 80-100% and of 98-100% in the case of the single ion and of the multi-ion solutions were obtained, respectively. alxi-activated binders; blast furnaces slags; water treatment; waste valorization +
Footnote †: journal: _Sci. 2021_, 11, 2985. [[https://doi.org/10.3390/app11072985](https://doi.org/10.3390/app11072985)]([https://doi.org/10.3390/app11072985](https://doi.org/10.3390/app11072985))  
Footnote †: journal: _Sci. 2021_, 11, 2985. [[https://doi.org/10.3390/app111072985](https://doi.org/10.3390/app111072985)]([https://doi.org/10.3390/app111072985](https://doi.org/10.3390/app111072985))  
vation has seriously contributed to the release of toxic pollutants in water streams. Unlike organic wastes, heavy metals are not biodegradable, but they can be adsorbed and accumulated in the environment and living organisms, causing various disorders and health problems. In the last years, awareness has grown of the fact that emissions prevention, rather than remediation of damage, is more economic and efficient for mitigating impacts on the environment [3]. There are a number of anthropogenic contributors to heavy metals release in the aquatic environment, and uncontrolled mining operations are certainly among them. Indeed, mining wastewater can contain a large amount of heavy metal ions, such as Cu, Zn, Fe, Mn, Ni, Cr, Cd, and Pb, and they must be treated before water reintroduction into the environment [3; 4; 5]. Therefore, various methods for heavy metal removal from wastewater have been extensively studied and proposed [6; 7]. Proposed technologies include chemical precipitation, ion-exchange, adsorption, membrane filtration, coagulation-flocculation, flotation, and electrochemical methods. However, ion-exchange, adsorption, and membrane filtration are the most frequently proposed solutions for this purpose. Adsorption, in particular, can be very effective, thanks to the wide variety of available sorbents, the high recovery efficiency, the fast extraction time, the low cost, and the low consumption of organic solvents. Common examples of sorbents are activated carbon, clay minerals, inorganic oxides, porous organic polymers, or organic-inorganic hybrid materials. In particular, our research group proposed the use of hybrid organic-inorganic mineral clays [8; 9; 10], carbon [11], and reduced graphene oxide [12] based materials both for heavy metals and rare earths capture, and demonstrated their effectiveness in metal removal, also when present at high concentration. Moreover, considering the new circular and greener economy paradigm, the development of sorbents, not only low cost, but also environmentally friendly and sustainable, is a key point of study [13; 14].