Removal of \(\hbox {Al}^{3+}\), \(\hbox {Fe}^{2+}\), and \(\hbox {Mn}^{2+}\) from quarry water by electrocoagulation process: nature of electrodes, electrodes arrangement, and electrical conductivity influence

At a quarry site, the extraction of construction materials leads to heavy metal pollution in the water. A year-long study of quarry water quality located in Brittany region allowed to develop a synthetic quarry water with the characteristics: \(\hbox {pH} = 3.5\) $\text{pH}=3.5$ and \(\sigma = 2.0\,\hbox {mS}\,\hbox {cm}^{-1}, [\hbox {Al}^{3+}] = 34\,\hbox {mg}\,\hbox {L}^{-1}; [\hbox {Fe}^{2+}] = 9.4\,\hbox {mg}\,\hbox {L}^{-1}; [\hbox {Mn}^{2+}] =6.0\,\hbox {mg}\,\hbox {L}^{-1}\) $\sigma =2.0\text{mS}{\text{cm}}^{-1},[{\text{Al}}^{3+}]=34\text{mg}{\text{L}}^{-1};[{\text{Fe}}^{2+}]=9.4\text{mg}{\text{L}}^{-1};[{\text{Mn}}^{2+}]=6.0\text{mg}{\text{L}}^{-1}$ . To treat this contaminated water, an investigation of the electrocoagulation process has been made using different electrode materials (Al or Fe), at different current densities (1.3 to \(13\,\hbox {mA}\,\hbox {cm}^{-1}\) $13\text{mA}{\text{cm}}^{-1}$ for Al and 1.2 to \(12\,\hbox {mA}\,\hbox {cm}^{-1}\) $12\text{mA}{\text{cm}}^{-1}$ for \(\hbox {Fe}\) $\text{Fe}$ ) and for different electrode arrangements (monopolar or bipolar). With aluminum electrodes in monopolar configuration at \(13\,\hbox {mA}\,\hbox {cm}^{-2}\) $13\text{mA}{\text{cm}}^{-2}$ , removal yields of 99.9, 91.5, and 85.0% were obtained for \(\hbox {Al}^{3+}\) ${\text{Al}}^{3+}$ , \(\hbox {Fe}^{2+}\) ${\text{Fe}}^{2+}$ , and \(\hbox {Mn}^{2+}\) ${\text{Mn}}^{2+}$ , respectively. Although aluminum electrodes demonstrated similar treatment results in both monopolar and bipolar arrangements, the bipolar required more energy and electrode dissolution to remove the same amount of pollutants. For example, power consumption for \(\hbox {Mn}^{2+}\) ${\text{Mn}}^{2+}$ removal on Al electrode varied from 20.5 to \(759\,\hbox {kWh}\,\hbox {g}_{{\textrm{Mn}}^{2+}}^{-1}\) $759\text{kWh}{\text{g}}_{{\text{Mn}}^{2+}}^{-1}$ and from 59.3 to \(2597\,\hbox {kWh}\,\hbox {g}_{{\textrm{Mn}}^{2+}}^{-1}\) $2597\text{kWh}{\text{g}}_{{\text{Mn}}^{2+}}^{-1}$ , respectively, for monopolar and bipolar arrangement. Conductivity varied in solution during electrolysis with the bipolar arrangement ( \(\sigma = 2\,\hbox {to}\,8\,\hbox {mS}\,\hbox {cm}^{-1}\) $\sigma =2\text{to}8\text{mS}{\text{cm}}^{-1}$ ). It indicated that sacrificial electrode dissolution is localized within a specific region of the reactor rather than being uniformly distributed. This study showed that aluminum electrodes outperformed iron electrodes for quarry water treatment. While monopolar and bipolar configurations achieved similar treatment outcomes, the bipolar configuration proved to be significantly more costly. In addition, the conductivity of the solution during electrolysis in a bipolar configuration can affect the dissolution of the electrode.