## 2 Synthetic Protocols for Hydrometallurgy
MV heat not only decreases energy consumption, but also enables precise and more volumetric heating, which leads to the significant reduction of time for reactions to be completed [21; 22; 23; 24; 25]. The latter one is essential for avoiding hydrolysis of the VBC. The procedure of MV-assisted synthesis of VBC-co-DVB copolymer, which based on the standard procedure, involving suspension copolymerization of VBC and DVB monomers in the presence of toluene and in water phase, consisted of poly(vinyl alcohol) and NaCl [26]. The difference was that the duration of the polymerization process was reduced to 4 h, as compared to the conventional method carried out within 25 h [27]. The outcome of the approach exceeded expectations. As displayed in Table 1, despite significantly shortened time of polymerization, MV heating allowed us to achieve 20% greater conversion of monomers (VBC and DVB). Moreover, based on the recorded FT-IR spectra, it was stated that the VBC copolymerized in the MV heat did not hydrolyze. All of that resulted in the fabrication of VBC-co-DVB copolymer with significantly increased concentration of -CH2 Cl groups (based on Cl concentration) [27], which in further steps improved characteristics of IX resins. Because MV heat allowed for receiving polymeric matrices with improved characteristics, the undertaken approach was pushed further by carrying out MV-assisted modification of VBC-co-DVB copolymer. Based on the obtained results, it can be stated that utilization of MV heat allows us to reduce energy consumption over 800-times, as compared to the most efficient conventional techniques [28]. Further optimizations allowed for defining optimal reaction environments that modification is carried out in. It was found that, among different organic solvents revealing favorable dielectric constants (defying MV-conductivity), dimethyl formamide (DMF) should not be applied, as the MV field promotes its building-into the VBC-co-DVB copolymer, making the characteristics of IX resins worse. \begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Copolymer.**} & **Method of Synthesis** & **Synthesis** & **Conversion of** & **Hydrolysis of** & **Cl 1** \\ \cline{2-6}  & **Synthesis** & **Time** & **Monomers** & **VBC** & **Cl 1** \\ \hline \multirow{2}{*}{VBC-co-DVB} & Conventional & 25 h & 70\% & + & 4.63 \(\pm\) 0.04 \\ \cline{2-6}  & MV-assisted & 4 h & 90\% & – & 5.24 \(\pm\) 0.04 \\ \hline \end{tabular} \({}^{1}\) Concentration of Cl derived from –CH2 Cl groups (mmol g\({}^{-1}\)).  
\end{table} 
Table 1: Comparison of VBC-co-DVB matrices obtained conventionally and with the aid of the microwave (MV) heat [27]. Thus, the reactions should be carried out in dimethyl sulfoxide (DMSO) or N-methyl pyrrolidone (NMP) [29]. Finally, it was possible to link relationships between different reagents, organic solvents, and applied density of MV field [30]. Based on the research carried out, it was possible to conclude that the energy consumption may be even more reduced, as there is no need to apply high input powers and prolonged time of exposure to MVs to receive an IX resin characterized by greatest possible capacity. Even more, when synthesizing anion exchange resins applying amines possessing bis-amino functionality, the power density of MVs should be as low as possible, to avoid additional crosslinking [30]. Based on these experiences, the \"enhanced\" VBC-co-DVB copolymer obtained in the MV field [27] was subjected to MV-assisted modification using 1-(3-aminopropyl)imidazole, small power of MV (20 W), and short time (10 min). As displayed in Figure 2, the so-prepared anion exchange resin was then tested toward its adsorption of Re(VII) ions from solutions simulating copper-molybdenum ones.