# Wastewater Treatment Using Alkali-Activated-Based Sorbents Produced from Blast Furnace Slag
## 2 Materials and Methods  
### Alkali-Activated Materials and Monoliths Preparation  
The alkali-activated monoliths (PGM, in the following) were prepared according to a recipe developed by Opigco SrI, Padova, Italy. Blast furnace slag (aluminosilicate source) was blended with high alumina calcium aluminate cement CAC-80 and Li\({}_{2}\)CO\({}_{3}\) as a setting accelerator. Blast furnace slag was obtained from Ecocem, Aix-en-Provence, France, while CAC-80 was obtained from Istra Cement DOO, Pula, Croatia. The elemental chemical composition of the blast furnace slag and of the high alumina calcium aluminate cement is reported in Table 1. The alkali-activated binder was formulated with 20% by weight of CAC-80 and 80% by weight of blast furnace slag, and with the addition of 0.004% by weight of Li\({}_{2}\)CO\({}_{3}\) (0.02% over CAC-80). The binder was mixed with water at the water-to-solid ratio of 0.4 by weight. The mixture was foamed, to reach the desired porosity, with the addition of an aqueous solution of hydrogen peroxide (foaming agent). Hydrogen peroxide 130 Vol. was used, and the weight ratio H\({}_{2}\)O\({}_{2}\)/H\({}_{2}\)O was 0.02. The bubbles, generated during H\({}_{2}\)O\({}_{2}\) decomposition, were stabilized with the addition of two surfactants, in particular cocamidopropyl betaine (Sigma Aldrich, Milan, Italy, 99%) and mymistic acid (BASF, 30-40%) in the ratio 85:15. Coamidopropyl betaine was used at a concentration of 1/3 its critical micellar concentration, i.e., at 0.084 g/100 mL, while mymistic acid was used at 0.015 g/100 mL. The formulation of the alkali-activated sorbent is reported in Table 2. \begin{table}
\begin{tabular}{c c c} \hline
**Oxide Type** & **Oxide Content in Blast** & **Oxide Content in Calcium** \\  & **Furnace slag (\% _w/w_)** & **Aluminate Cement (\% _w/w_)** \\ \hline SiO\({}_{2}\) & 36.23 & 0.35 \\ Al\({}_{2}\)O\({}_{3}\) & 10.70 & 80.73 \\ CaO & 40.92 & 16.97 \\ MgO & 7.41 & 0.46 \\ Fe\({}_{2}\)O\({}_{3}\) & 0.72 & 0.20 \\ TiO\({}_{2}\) & 0.68 & 0.23 \\ MnO & 0.27 & – \\ K\({}_{2}\)O & 0.45 & 0.37 \\ Na\({}_{2}\)O & 0.22 & 0.31 \\ P\({}_{2}\)O\({}_{5}\) & 0.01 & – \\ others & 2.39 & 0.38 \\ \hline \end{tabular}
\end{table} 
Table 1: Elemental composition of blast furnace slag and high alumina cement. \begin{table}
\begin{tabular}{c c} \hline
**Component** & **Effect** & **Content** \\ \hline Blust Furnace slag & Aluminosilicates source & 80\% (_w/w_) \\ Cement CAC-80 & Aluminosilicates source, weak alkali, binder & 20\% (_w/w_) \\ Li\({}_{2}\)CO\({}_{3}\) & setting accelerator & 0.02\% (_w/w_) \\ H\({}_{2}\)O\({}_{2}\) & Bubbles generator & 2\% (_r/v_) \\ H\({}_{2}\)O/total solids & & 0.004\% (_w/w_) \\ \hline H\({}_{2}\)O\({}_{2}\)/H\({}_{2}\)O & Bubbles generator & 0.02 (_v_/_v_) \\  & & 0.0125 g \\ Cocamidopropyl betaine (COCA) & Surfactant & 0.084\% \\  & & (g/100 mL liquid) \\  & & 0.0022 (g) \\ Myristic acid (MYRAC) & Surfactant & 0.015\% \\  & & (g/100 mL liquid) \\ COCA/MYRAC & Surfactant, bubbles stabilizer & 15/85 (_w/w_) \\ Liquid/Solid & & 0.4 \\ \hline \end{tabular}
\end{table} 
Table 2: Formulation used in the porous monolith synthesis. In a typical experiment, the solution of the surfactants, distilled water, and hydrogen peroxide were quickly poured onto the solid components, and vigorously stirred until a dense, homogeneous, and creamy mixture was obtained. The mixing step had to be performed as quickly as possible to control the tendency to harden unevenly. In a few minutes, the H\({}_{2}\)O\({}_{2}\) decomposition started, and the bubbles form. The geopolymeric monoliths are thus obtained by spreading the paste (a few minutes after the synthesis reaction) on the plane surface of a Buchner filter (Figure 1), in order to get a homogeneous layer. The Buchner is then covered with Parafilm and the monolith is let to dry overnight, and subsequently characterized by XRD, SEM-EDX, EPR, and porosity measurements. The density of the hardened porous monolith is around 1.1 g/mL.